1.9: Vegetation and Fire
The first chapters of these notes have largely covered generic subjects in passive optical remote sensing – issues of general importance and image processing techniques that are not specific to one field of application or another. In this chapter we will look at some techniques developed and widely used specifically for remote sensing of two things: vegetation, and fire. Similar chapters could be written on many other specific applications of remote sensing – vegetation and fire are used here because the use of satellite imagery to map and monitor them is well-developed and used operationally at both national and global scales.
Vegetation
Given how much of Earth is covered by some form of green vegetation, it is not surprising that much research effort has gone into using remote sensing to map and assess various aspects of vegetation. This is important for basic industries that support human livelihoods across the globe, such as forestry and agriculture, as well as for almost any environmental assessment of terrestrial areas. In fact, so much research has been done that entire books have been written just on remote sensing of vegetation .
In the simplest terms, the ability to detect vegetation in passive optical remote sensing is based on its spectral signature (Figure 67), which is quite different from other surface types.
Visible wavelength region
Healthy green vegetation absorbs most of the visible light incident on it, using it to grow through the process of photosynthesis. Photosynthesis is a relatively complex biochemical process that begins with the absorption of a photon by a pigment molecule, which sets off an electronic transition (the movement of an electron from one energy level to a higher one) that starts a chain-reaction leading to production of plant material from the basic chemical components of CO 2 and water. A form of chlorophyll is the dominant pigment in almost all vegetation, and chlorophyll is very good at absorbing visible light, which is why vegetation has low reflectances across the visible wavelengths. Chlorophyll is a little better at absorbing blue and red wavelengths than it is at absorbing green wavelengths, so relatively more of the green radiation is reflected, giving vegetation its green appearance.
Infrared wavelength region
Incoming photons at wavelengths in the near-infrared region individually contain less energy (recall that the energy in a photon is proportional to its frequency, and hence inversely proportional to its wavelength). These photons are therefore unable to cause an electronic transition so pigments used for photosynthesis cannot use them, and in general do not absorb them. Other parts of plants, especially liquid water found in the leaves, do absorb these photons, which rotate and stretch chemical bonds in the water or in plant cells, effectively heating up the absorbing material. In general, plants have no need for heating up, and except for wavelengths around 1.4 μm and 1.9 μm where water is a strong absorber, plants reflect much of the incoming near-infrared radiation.
The combination of low reflectance in the visible and high reflectance in the near-infrared wavelengths is the most characteristic signature of vegetation used in remote sensing, and is used for quick-and-dirty mapping of vegetation on Earth. Consider that most land areas contain a mix of vegetated and unvegetated areas. Sometimes this ‘mix’ is very one-sided, as in the Amazon, the Sahara desert, or the Canadian Arctic, and sometimes it is truly more mixed, as on the African savanna (Figure 68).
Vegetation indices
Using the reflectance in the visible wavelengths alone does not tell us how much vegetation is in an area, because water also has low reflectance in this wavelength region. And using the reflectance in the near-infrared region alone also does not tell us much about vegetation, because other surface types, such as the bright sand and bright snow depicted in Figure 68 also have higher near-infrared reflectance. However, the ratio of the visible and near-infrared reflectances is a useful indicator for the amount of vegetation present in an area because no other surface type has both as high near-infrared and as low visible reflectance as vegetation. This observation led initially to the development of what is called the Simple Ratio (SR):
where NIR is the surface reflectance in the near-infrared wavelength region (typically around 700-1000 nm), and RED is the same for the red wavelength region (600-700 nm).
68: Four areas with rather different vegetation characteristics. Top left: The African savanna contain a mix of trees and grass cover. Trees On The African Savanna by Lynn Greyling, PublicDomainPictures.net, CC0 1.0 . Top right: The Sahara desert is in most places void of vegetation. Sahara Desert by Azer Koçulu, Wikimedia Commons, CC0 1.0 . Bottom left: The Amazon rainforest is covered in dense vegetation. Amazon Rainforest by CIFOR (Neil Palmer/CIAT), Flickr, CC BY-NC-ND 2.0 . Bottom right: The Canadian Arctic has large areas with no vegetation. Patterned ground in Canadian tundra by Raymond M. Coveney, Wikimedia Commons, CC BY-SA 3.0 .
While surface reflectance values should in principle always be used to calculate this and any other vegetation index, in practice these calculations are often done instead based on TOA reflectance or even TOA radiance (or even DN values!). The Simple Ratio has one drawback that means it is rarely used – its values approach infinity when red reflectance approaches zero, which makes differences between large values difficult to interpret. A simple improvement called the Normalized Difference Vegetation Index (NDVI), based on the same two measurements, is therefore more commonly used:
NDVI values range from a minimum of -1 to a maximum of +1. Typical values for bare soil are around 0, for water around -0.2, and for vegetation in the range 0.1-0.7 depending on vegetation health and density. Because NDVI relies only on two measurements, in the near-infrared and red wavelength regions, it can be calculated with data from the earliest multispectral sensors in orbit, including the Landsat series (since 1972) and the AVHRR series (since 1978). This allows easy visualizations of vegetation cover, on small or large scales, such as the one shown in Figure 69.
69: NDVI composite of Earth, showing relative differences in vegetation cover. Globalndvi tmo 200711 lrg by Reto Stockli and Jesse Allen (NASA), Wikimedia Commons, public domain.
Vegetation indices can be used for more than producing pretty pictures of global vegetation distribution. As a result of global warming, which is especially pronounced in the Arctic region, the northern parts of Canada are undergoing rapid changes in vegetation distribution and growth patterns. Monitoring such changes over this large and very sparsely populated region is based on long-term NDVI trends in the summer months, which among other things demonstrates that region undergoing faster warming also experience more rapid growth in vegetation density. Another important use of vegetation indices is in crop yield forecasting: by tracking NDVI through an agricultural growing season, the development of the crops can be quantified and their eventual yields predicted statistically. Probably the most important use of such crop prediction models is to forecast droughts, crop failures and famines in parts of the world where people depend on local agriculture for their food supply. This is done systematically for countries that are prone to famine by the Famine Early Warning Systems Network (FEWS) , a US-based organization, and it is also done by many national governments and regional/global organizations. Vegetation indices thus literally have the potential to save lives – if the global community responds to the predictions generated by them .
Many refinements have been introduced since the development of NDVI, to create vegetation indices that perform better under a range of conditions. These include the Soil-Adjusted Vegetation Index , the Enhanced Vegetation Index used with MODIS data, and the Global Vegetation Index used with MERIS data. These newer vegetation indices were specifically designed to be more robust to varying environmental conditions, such as variations in soil brightness and atmospheric conditions. Despite such refinements, all vegetation indices suffer from a fundamental drawback: while their interpretation is quite clear in relative terms (higher values indicate more green vegetation), their relationship to real measureable vegetation characteristics used by people outside the field of remote sensing is not clear.
A vegetation index not intended to portray vegetation density, but rather to portray relative differences in vegetation water content, has been developed specifically to take advantage of the water absorption feature around 1.4 μm shown in Figure 67. It is called the Normalized Difference Water Index (NDWI), and its generic equation is:
where SWIR denotes a measurement in the short-wave infrared region (1.4 μm). Dry vegetation contains less water, and therefore absorbs less of the SWIR radiation, reducing the value of NDWI.
For any vegetation index, the specific bands that are used as the ‘RED’, ‘NIR’ and ‘SWIR’ bands depends on the sensor in question, and not all sensors have bands appropriate for calculating one or another index.
Mapping real vegetation attributes
Vegetation attributes that are more used by non-remote sensing people include among other things above-ground biomass, absorbed photosynthetically active radiation (APAR), and the Leaf Area Index (LAI). Above-ground biomass can be measured (by cutting and weighing it) in kg/ha, and is of fundamental interest in monitoring vegetation trends. APAR is the amount of radiation that is absorbed by vegetation (per areal unit), and is strongly linked to vegetation growth and crop yield. LAI is the (one-sided) area of leaves divided by the area of ground, so it is a unitless measure of leaf density. Because (water and) gas exchange between vegetation and the atmosphere happens through the leaves, LAI can be used as a proxy for this exchange, which is important for vegetation’s function as a carbon sink, among other things. All of these vegetation attributes are thus more directly linked to the function of vegetation in the environment, and certainly more directly interpretable, than is a vegetation index. But they are also much more difficult to map with remote sensing data.
Empirical approach
A simple approach to mapping LAI is illustrated in Figure 70, in which NDVI values have been regressed against field-measured LAI. As is obvious from Figure 70, what we measure in remote sensing data is related, but not very closely, and certainly not linearly, to actual LAI measured on the ground. Nevertheless the regression lines can be used to produce a first approximation of LAI from these remote sensing data. A similar approach can be taken to map other vegetation attributes.
Radiative transfer approach
More sophisticated approaches to mapping vegetation attributes rely on radiative transfer models. Radiative transfer models build up a simple 3D world consisting of a) the ground, b) some vegetation on the ground, c) the atmosphere, and d) the Sun. Each of these elements have specific attributes that define how they interact with radiation: The Sun emits a certain amount of radiation at each modeled wavelength, the atmosphere absorbs and scatters this radiation to some degree, and the vegetation and the ground absorb and reflect the radiation. Once specified, the model can then be ‘run’ to determine what the TOA radiance (or other measureable radiation parameter) would be for a given combination on element definition. These elements can then be changed and the model ‘run’ again to see how the change affects the TOA radiance. For example, different densities of vegetation can be included, representing different values of LAI, each producing a unique combination of TOA radiances in different wavelengths. To produce a robust picture of how LAI influences TOA radiance, the other elements must also be varied, so the influence of soil colour and atmospheric constituents also get captured in the process. Even more importantly, non-LAI variation in vegetation must also be considered. Individual leaves may have different spectral signatures depending on their pigment composition, leaves of different shapes and orientation interact with the Sun’s radiation differently, and the structure of the canopy also exerts its own influence (e.g. are the leaves distributed randomly, evenly, or in a clumped manner?). Varying all of these parameters, each time running the radiative transfer model to determine what their specific combination would look like at the top of the atmosphere, allows you to build up a look-up table with a) environmental conditions including the parameter of interest (e.g. LAI) and b) the resulting TOA (spectral) radiance. When mapping LAI with a satellite image, the observed TOA radiance of each pixel can then be matched to the entry in the table it matches most closely to determine the probably value of LAI in that pixel.
Fire
Another sub-field of remote sensing concerns mapping of fire. Active fire is relatively easily detected because it is hot, and heat can be detected with thermal sensors, and because it creates smoke, and smoke is visible in satellite imagery. Detecting active fire with satellite data is so well-developed that a near-instantaneous ‘ active fire product ’ is made each time a MODIS or VIIRS sensor passes over an area.
72: Example of active fire detection from space during the Australian wildfires of 2019. Satellite image of bushfire smoke over Eastern Australia by the European Space Agency, Flickr, CC BY-SA 2.0 .
Once a fire is over, it may be important to assess how much area was burned, and how intensely it was burned. This has important implications for the recovery of the vegetation and associated biota in the area, and it can also help us answer important questions related to climate change, like how the frequency, duration, size, and intensity of wildfires are changing as the climate warms. While there are different ways to assess these parameters, the most commonly used approach involves quantifying something called the Normalized Burn Ratio (NBR). The NBR is calculated as:
which, you might say, is the same as the definition of NDWI! And it is close, but the term SWIR covers a fairly wide range of wavelengths, and while for NDWI the original definition of ‘SWIR’ referred to wavelengths around 1.24 μm, for NBR ‘SWIR’ was specifically designed for band 7 on Landsat 4 and 5, which is centered around 2.2 μm. Nevertheless, NBR is really just a vegetation index, and while it is not the only index one can use for mapping fire impacts, and not even necessarily the best one , it is the most commonly used. To use it for quantification of fire severity, one needs to compare NBR values in two images, one from before and one from after the fire, which leads to the calculation of δNBR:
To minimize the effects of other environmental factors on this calculation, it is ideal to use ‘anniversary dates’ to calculate δNBR, although this is not necessary if two images are available from a small period covering just before and just after the fire (Figure 73).
73: Example of a pre-fire image (top left), a post-fire image (top middle), pre-fire NBR (top right), post-fire NBR (bottom left), and δNBR (bottom middle). While the impact of the fire is evident in the original imagery, the use of δNBR helps highlight the difference between the two images. Example of normalized burn ratio from a fire at Camp Gurnsey , Wyoming in 2006 by Jason Karl, The Landscape Toolbox, CC0 1.0 .
Because NBR is calculated as a normalized difference, its values range between -1 and +1, so δNBR ranges, in theory, from -2 to +2, with higher values indicating greater fire severity. As with other vegetation indices, extreme values are rare though, so even values of 0.2-0.3 indicate relatively severe fire impacts.
74: An example of both vegetation and fire, both of which can be mapped well with remote sensing. Forest Fire , by YIvers, Pixabay, Pixabay License .


16.13: Risk Tradeoffs in Global Business
- Differentiate among the risk tradeoffs for exporting, licensing, alliances, wholly owned affiliates, and global ventures.
Improved transportation, low-cost communication technologies, and a growing mass of educated people in countries around the world are contributing to business globalization. This section will focus on some different ways businesses can enter these new global markets. We will look at the benefits and examine the risks of these enterprises.
Franchising, Licensing, and Export/Import Businesses
Export/Import Business
Exporting is the shipping of goods from the domestic country to a foreign country. Importing, the flip side, is bringing in goods from another country. Both types of businesses create local jobs and so are generally favored by governments. Both types of businesses are scrutinized by custom authorities and reported in various categories as part of a country’s gross domestic product. The main advantage of an export business is a wider market for the products, as importers can frequently sell goods below the price charged for domestic items. You also retain control over how the product is designed and produced. But as with any international business, there are risks involved with interruptions in the supply chain and fluctuating foreign currencies. There are also increased transportation and tariff costs.
Licensing
Licensing is a strategic alliance made by a licensor that allows a licensee to provide products or services under the licensor’s brand name. Let’s say that a food snack manufacturer is prevented by a foreign government from competing against local sellers of food snacks. The company can license its formula to a local producer, thus avoiding the regulations. The licensee makes the product and returns a percentage of the overall revenues to the outside company, usually in the form of royalties. There are subtle but key differences between franchising and licensing. An important one is that the owner of the license retains complete control over the product. For example, Microsoft licenses its software to users; it does not “sell” the product outright. The software is licensed to customers subject to strict terms and conditions. Licensing has many of the same advantages and disadvantages of franchising. Advantages include avoiding barriers to entering a foreign market, such as tariff and production costs. The major risk is that the licensor trusts their brand to an outside partner, and that partner may eventually become a competitor.
Franchising
Franchising lets businesses enter into foreign markets at a low cost while at the same time offering local entrepreneurs the chance to operate an established business. When McDonald’s or Subway wants to expand into a new foreign market, it often arranges for a company or individual to pay for the use of its trademarked or protected resources, such as the plans for buildings, product ingredients, recipes, and management systems. The buyer, or franchisee , agrees to follow product and operating procedures to safeguard the franchiser’s brand name and reputation. The franchiser receives a percentage of the revenue from the local operator. The benefits include relative low risk and easy market penetration for the franchiser. Franchising requires very little capital investment or effort on the corporation’s side. A locally run franchise can avoid many of the cultural pitfalls facing a foreign-run investment. Risks, or downsides, include a loss of quality control and a lower rate of return than a wholly owned and operated business. The franchiser must also make sure the local manager can implement the required training and quality control measures to safeguard the corporate brand.
Strategic Alliances
Some types of businesses are strategic alliances in which international partners cooperate for mutual gains. Companies agree to combine key resources, costs, risks, technology, and personnel. Each organization sees an opportunity to get something they couldn’t get on its own. Examples include joint ventures, affiliates, and subsidiaries. There are two types of strategic alliances: joint ventures and wholly owned affiliates.
Joint Venture
In an international joint venture , two or more companies (usually one foreign and one local) agree to work together on a new project. Each company contributes to the partnership in time, equity, or effort for the development of the project. Sometimes one company buys into an already established firm. Each partner benefits from the arrangement. One partner may hope to widen their market with the help of local experts; the other partner may want access to technology and training in advanced skills. The advantage is that each partner carries part of the burden of costs to start and run the joint company. The disadvantages may include leadership/management power struggles and the fact that profits must be shared. In 2014, Sony of Japan set up joint ventures in China to produce its popular PlayStation. One company produced the software; the other company produced the hardware.
Wholly Owned Foreign Affiliates
A business may decide that instead of partnering with a company in a foreign country to expand its market, it is more efficient to acquire an existing firm. The acquiring company takes full ownership of the acquired company. The advantage is that the company saves on transportation, distribution, and storage costs while gaining local business knowledge through the affiliate’s (or subsidiary’s) employees. For example, Kraft Foods bought Cadbury, an English confectionary (candy) company. Home Depot bought Home Mart, a popular home-improvement retailer in Mexico. Finally, in 2010 Wal-Mart Stores Inc. spent $2.4 billion to acquire Massmart, a South African retail store much like Wal-Mart with stores throughout Africa.
Greenfield Venture
A different type of foreign investment is called a greenfield venture , where a company builds a subsidiary from scratch in a foreign country instead of acquiring an established firm. This is the riskiest type of direct investment but also, if successful, can be extremely profitable because the profits do not have to be shared. The parent company can dictate from the beginning how the company should be managed and developed. But the company must be committed to a long-term association with the market and country it is entering. Large, multinational companies are most likely to use a greenfield strategy to enter a market because of the high start-up costs and the long-term commitment, as well as their experience in negotiating trade barriers. In July 2017, Foxconn, a large electronics manufacturer in Taiwan, announced plans to invest more than $10 billion in a greenfield venture in Wisconsin. The obvious risk with this business structure is that a great difference in the laws between the parent and subsidiary countries can lead to misunderstandings and false assumptions. This is especially true in the handling of intellectual property such as patents, trademarks, and copyrights.
Watch the following video to see some other recent greenfield ventures taking place in the United States.
Contributors and Attributions
- Risk Tradeoffs in Global Business. Authored by : John/Lynn Bruton and Lumen Learning. License : CC BY: Attribution
- Image: Bdg McDonalds 07-2013. Authored by : Pit1233. Located at : https://commons.wikimedia.org/wiki/File:Bdg_McDonalds_07-2013.jpg . License : CC0: No Rights Reserved
- Video: Chinese Greenfield investors seek larger market in the US . Authored by : CGTN America. Located at : https://www.youtube.com/watch?v=JhrBrvC35gA . License : All Rights Reserved . License Terms : Standard YouTube License


6.2: Earth's Crust
Learning Objectives
By the end of this section, you will be able to:
- Denote the primary types of rock that constitute Earth’s crust
- Explain the theory of plate tectonics
- Describe the difference between rift and subduction zones
- Describe the relationship between fault zones and mountain building
- Explain the various types of volcanic activity occurring on Earth
Let us now examine our planet’s outer layers in more detail. Earth’s crust is a dynamic place. Volcanic eruptions, erosion, and large-scale movements of the continents rework the surface of our planet constantly. Geologically, ours is the most active planet. Many of the geological processes described in this section have taken place on other planets as well, but usually in their distant pasts. Some of the moons of the giant planets also have impressive activity levels. For example, Jupiter’s moon Io has a remarkable number of active volcanoes.
Composition of the Crust
Earth’s crust is largely made up of oceanic basalt and continental granite. These are both igneous rock, the term used for any rock that has cooled from a molten state. All volcanically produced rock is igneous (Figure \(\PageIndex{1}\)).
Two other kinds of rock are familiar to us on Earth, although it turns out that neither is common on other planets. Sedimentary rocks are made of fragments of igneous rock or the shells of living organisms deposited by wind or water and cemented together without melting. On Earth, these rocks include the common sandstones, shales, and limestones. Metamorphic rocks are produced when high temperature or pressure alters igneous or sedimentary rock physically or chemically (the word metamorphic means “changed in form”). Metamorphic rocks are produced on Earth because geological activity carries surface rocks down to considerable depths and then brings them back up to the surface. Without such activity, these changed rocks would not exist at the surface.
There is a fourth very important category of rock that can tell us much about the early history of the planetary system: primitive rock , which has largely escaped chemical modification by heating. Primitive rock represents the original material out of which the planetary system was made. No primitive material is left on Earth because the entire planet was heated early in its history. To find primitive rock, we must look to smaller objects such as comets, asteroids, and small planetary moons. We can sometimes see primitive rock in samples that fall to Earth from these smaller objects.
A block of quartzite on Earth is composed of materials that have gone through all four of these states. Beginning as primitive material before Earth was born, it was heated in the early Earth to form igneous rock, transformed chemically and redeposited (perhaps many times) to form sedimentary rock, and finally changed several kilometers below Earth’s surface into the hard, white metamorphic stone we see today.
Plate Tectonics
Geology is the study of Earth’s crust and the processes that have shaped its surface throughout history. (Although geo - means “related to Earth,” astronomers and planetary scientists also talk about the geology of other planets.) Heat escaping from the interior provides energy for the formation of our planet’s mountains, valleys, volcanoes, and even the continents and ocean basins themselves. But not until the middle of the twentieth century did geologists succeed in understanding just how these landforms are created.
Plate tectonics is a theory that explains how slow motions within the mantle of Earth move large segments of the crust, resulting in a gradual “drifting” of the continents as well as the formation of mountains and other large-scale geological features. Plate tectonics is a concept as basic to geology as evolution by natural selection is to biology or gravity is to understanding the orbits of planets. Looking at it from a different perspective, plate tectonics is a mechanism for Earth to transport heat efficiently from the interior, where it has accumulated, out to space. It is a cooling system for the planet. All planets develop a heat transfer process as they evolve; mechanisms may differ from that on Earth as a result of chemical makeup and other constraints.
Earth’s crust and upper mantle (to a depth of about 60 kilometers) are divided into about a dozen tectonic plates that fit together like the pieces of a jigsaw puzzle (Figure \(\PageIndex{2}\)). In some places, such as the Atlantic Ocean, the plates are moving apart; in others, such as off the western coast of South America, they are being forced together. The power to move the plates is provided by slow convection of the mantle, a process by which heat escapes from the interior through the upward flow of warmer material and the slow sinking of cooler material. (Convection, in which energy is transported from a warm region, such as the interior of Earth, to a cooler region, such as the upper mantle, is a process we encounter often in astronomy—in stars as well as planets. It is also important in boiling water for coffee while studying for astronomy exams.)
The US Geological Survey provides a map of recent earthquakes and shows the boundaries of the tectonic plates and where earthquakes occur in relation to these boundaries. You can look close-up at the United States or zoom out for a global view.
As the plates slowly move, they bump into each other and cause dramatic changes in Earth’s crust over time. Four basic kinds of interactions between crustal plates are possible at their boundaries: (1) they can pull apart, (2) one plate can burrow under another, (3) they can slide alongside each other, or (4) they can jam together. Each of these activities is important in determining the geology of Earth.
Alfred Wegener: catching the drift of plate tectonics
When studying maps or globes of Earth, many students notice that the coast of North and South America, with only minor adjustments, could fit pretty well against the coast of Europe and Africa. It seems as if these great landmasses could once have been together and then were somehow torn apart. The same idea had occurred to others (including Francis Bacon as early as 1620), but not until the twentieth century could such a proposal be more than speculation. The scientist who made the case for continental drift in 1920 was a German meteorologist and astronomer named Alfred Wegener (Figure \(\PageIndex{3}\)).
Born in Berlin in 1880, Wegener was, from an early age, fascinated by Greenland, the world’s largest island, which he dreamed of exploring. He studied at the universities in Heidelberg, Innsbruck, and Berlin, receiving a doctorate in astronomy by reexamining thirteenth-century astronomical tables. But, his interests turned more and more toward Earth, particularly its weather. He carried out experiments using kites and balloons, becoming so accomplished that he and his brother set a world record in 1906 by flying for 52 hours in a balloon.
Wegener first conceived of continental drift in 1910 while examining a world map in an atlas, but it took 2 years for him to assemble sufficient data to propose the idea in public. He published the results in book form in 1915. Wegener’s evidence went far beyond the congruence in the shapes of the continents. He proposed that the similarities between fossils found only in South America and Africa indicated that these two continents were joined at one time. He also showed that resemblances among living animal species on different continents could best be explained by assuming that the continents were once connected in a supercontinent he called Pangaea (from Greek elements meaning “all land”).
Wegener’s suggestion was met with a hostile reaction from most scientists. Although he had marshaled an impressive list of arguments for his hypothesis, he was missing a mechanism . No one could explain how solid continents could drift over thousands of miles. A few scientists were sufficiently impressed by Wegener’s work to continue searching for additional evidence, but many found the notion of moving continents too revolutionary to take seriously. Developing an understanding of the mechanism (plate tectonics) would take decades of further progress in geology, oceanography, and geophysics.
Wegener was disappointed in the reception of his suggestion, but he continued his research and, in 1924, he was appointed to a special meteorology and geophysics professorship created especially for him at the University of Graz (where he was, however, ostracized by most of the geology faculty). Four years later, on his fourth expedition to his beloved Greenland, he celebrated his fiftieth birthday with colleagues and then set off on foot toward a different camp on the island. He never made it; he was found a few days later, dead of an apparent heart attack.
Critics of science often point to the resistance to the continental drift hypothesis as an example of the flawed way that scientists regard new ideas. (Many people who have advanced crackpot theories have claimed that they are being ridiculed unjustly, just as Wegener was.) But we think there is a more positive light in which to view the story of Wegener’s suggestion. Scientists in his day maintained a skeptical attitude because they needed more evidence and a clear mechanism that would fit what they understood about nature. Once the evidence and the mechanism were clear, Wegener’s hypothesis quickly became the centerpiece of our view of a dynamic Earth.
See how the drift of the continents has changed the appearance of our planet’s crust.
Rift and Subduction Zones
Plates pull apart from each other along rift zones, such as the Mid-Atlantic ridge, driven by upwelling currents in the mantle (Figure \(\PageIndex{4}\)). A few rift zones are found on land. The best known is the central African rift—an area where the African continent is slowly breaking apart. Most rift zones, however, are in the oceans. Molten rock rises from below to fill the space between the receding plates; this rock is basaltic lava, the kind of igneous rock that forms most of the ocean basins.
From a knowledge of how the seafloor is spreading, we can calculate the average age of the oceanic crust. About 60,000 kilometers of active rifts have been identified, with average separation rates of about 5 centimeters per year. The new area added to Earth each year is about 2 square kilometers, enough to renew the entire oceanic crust in a little more than 100 million years. This is a very short interval in geological time—less than 3% of the age of Earth. The present ocean basins thus turn out to be among the youngest features on our planet.
As new crust is added to Earth, the old crust must go somewhere. When two plates come together, one plate is often forced beneath another in what is called a subduction zone (Figure \(\PageIndex{4}\)). In general, the thick continental masses cannot be subducted, but the thinner oceanic plates can be rather readily thrust down into the upper mantle. Often a subduction zone is marked by an ocean trench; a fine example of this type of feature is the deep Japan trench along the coast of Asia. The subducted plate is forced down into regions of high pressure and temperature, eventually melting several hundred kilometers below the surface. Its material is recycled into a downward-flowing convection current, ultimately balancing the flow of material that rises along rift zones. The amount of crust destroyed at subduction zones is approximately equal to the amount formed at rift zones.
All along the subduction zone, earthquakes and volcanoes mark the death throes of the plate. Some of the most destructive earthquakes in history have taken place along subduction zones, including the 1923 Yokohama earthquake and fire that killed 100,000 people, the 2004 Sumatra earthquake and tsunami that killed more than 200,000 people, and the 2011 Tohoku earthquake that resulted in the meltdown of three nuclear power reactors in Japan.
Fault Zones and Mountain Building
Along much of their length, the crustal plates slide parallel to each other. These plate boundaries are marked by cracks or faults . Along active fault zones, the motion of one plate with respect to the other is several centimeters per year, about the same as the spreading rates along rifts.
One of the most famous faults is the San Andreas Fault in California, which lies at the boundary between the Pacific plate and the North American plate (Figure \(\PageIndex{5}\)). This fault runs from the Gulf of California to the Pacific Ocean northwest of San Francisco. The Pacific plate, to the west, is moving northward, carrying Los Angeles, San Diego, and parts of the southern California coast with it. In several million years, Los Angeles may be an island off the coast of San Francisco.
Unfortunately for us, the motion along fault zones does not take place smoothly. The creeping motion of the plates against each other builds up stresses in the crust that are released in sudden, violent slippages that generate earthquakes. Because the average motion of the plates is constant, the longer the interval between earthquakes, the greater the stress and the more energy released when the surface finally moves.
For example, the part of the San Andreas Fault near the central California town of Parkfield has slipped every 25 years or so during the past century, moving an average of about 1 meter each time. In contrast, the average interval between major earthquakes in the Los Angeles region is about 150 years, and the average motion is about 7 meters. The last time the San Andreas fault slipped in this area was in 1857; tension has been building ever since, and sometime soon it is bound to be released. Sensitive instruments placed within the Los Angeles basin show that the basin is distorting and contracting in size as these tremendous pressures build up beneath the surface.
Example \(\PageIndex{1}\): Fault Zones and Plate Motion
After scientists mapped the boundaries between tectonic plates in Earth’s crust and measured the annual rate at which the plates move (which is about 5 cm/year), we could estimate quite a lot about the rate at which the geology of Earth is changing. As an example, let’s suppose that the next slippage along the San Andreas Fault in southern California takes place in the year 2017 and that it completely relieves the accumulated strain in this region. How much slippage is required for this to occur?
- Answer
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The speed of motion of the Pacific plate relative to the North American plate is 5 cm/y. That’s 500 cm (or 5 m) per century. The last southern California earthquake was in 1857. The time from 1857 to 2017 is 160 y, or 1.6 centuries, so the slippage to relieve the strain completely would be 5 m/century × 1.6 centuries = 8.0 m.
Exercise \(\PageIndex{1}\)
If the next major southern California earthquake occurs in 2047 and only relieves one-half of the accumulated strain, how much slippage will occur?
- Answer
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The difference in time from 1857 to 2047 is 190 y, or 1.9 centuries. Because only half the strain is released, this is equivalent to half the annual rate of motion. The total slippage comes to 0.5 × 5 m/century × 1.9 centuries = 4.75 m.
When two continental masses are moving on a collision course, they push against each other under great pressure. Earth buckles and folds, dragging some rock deep below the surface and raising other folds to heights of many kilometers. This is the way many, but not all, of the mountain ranges on Earth were formed. The Alps, for example, are a result of the African plate bumping into the Eurasian plate. As we will see, however, quite different processes produced the mountains on other planets.
Once a mountain range is formed by upthrusting of the crust, its rocks are subject to erosion by water and ice. The sharp peaks and serrated edges have little to do with the forces that make the mountains initially. Instead, they result from the processes that tear down mountains. Ice is an especially effective sculptor of rock (Figure \(\PageIndex{6}\)). In a world without moving ice or running water (such as the Moon or Mercury), mountains remain smooth and dull.
Volcanoes
Volcanoes mark locations where lava rises to the surface. One example is mid ocean ridges, which are long undersea mountain ranges formed by lava rising from Earth’s mantle at plate boundaries. A second major kind of volcanic activity is associated with subduction zones, and volcanoes sometimes also appear in regions where continental plates are colliding. In each case, the volcanic activity gives us a way to sample some of the material from deeper within our planet.
Other volcanic activity occurs above mantle “hot spots”—areas far from plate boundaries where heat is nevertheless rising from the interior of Earth. One of the best-known hot spot is under the island of Hawaii, where it currently supplies the heat to maintain three active volcanoes, two on land and one under the ocean. The Hawaii hot spot has been active for at least 100 million years. As Earth’s plates have moved during that time, the hot spot has generated a 3500-kilometer-long chain of volcanic islands. The tallest Hawaiian volcanoes are among the largest individual mountains on Earth, more than 100 kilometers in diameter and rising 9 kilometers above the ocean floor. One of the Hawaiian volcanic mountains, the now-dormant Mauna Kea, has become one of the world’s great sites for doing astronomy.
The US Geological Service provides an interactive map of the famous “ring of fire,” which is the chain of volcanoes surrounding the Pacific Ocean, and shows the Hawaiian “hot spot” enclosed within.
Not all volcanic eruptions produce mountains. If lava flows rapidly from long cracks, it can spread out to form lava plains. The largest known terrestrial eruptions, such as those that produced the Snake River basalts in the northwestern United States or the Deccan plains in India, are of this type. Similar lava plains are found on the Moon and the other terrestrial planets.
Key Concepts and Summary
Terrestrial rocks can be classified as igneous, sedimentary, or metamorphic. A fourth type, primitive rock, is not found on Earth. Our planet’s geology is dominated by plate tectonics, in which crustal plates move slowly in response to mantle convection. The surface expression of plate tectonics includes continental drift, recycling of the ocean floor, mountain building, rift zones, subduction zones, faults, earthquakes, and volcanic eruptions of lava from the interior.
Glossary
- convection
- movement caused within a gas or liquid by the tendency of hotter, and therefore less dense material, to rise and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat
- fault
- in geology, a crack or break in the crust of a planet along which slippage or movement can take place, accompanied by seismic activity
- igneous rock
- rock produced by cooling from a molten state
- metamorphic rock
- rock produced by physical and chemical alteration (without melting) under high temperature and pressure
- plate tectonics
- the motion of segments or plates of the outer layer of a planet over the underlying mantle
- primitive rock
- rock that has not experienced great heat or pressure and therefore remains representative of the original condensed materials from the solar nebula
- rift zone
- in geology, a place where the crust is being torn apart by internal forces generally associated with the injection of new material from the mantle and with the slow separation of tectonic plates
- sedimentary rock
- rock formed by the deposition and cementing of fine grains of material, such as pieces of igneous rock or the shells of living things
- subduction
- the sideways and downward movement of the edge of a plate of Earth’s crust into the mantle beneath another plate
- volcano
- a place where material from a planet’s mantle erupts on its surface
Contributors and Attributions
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Andrew Fraknoi (Foothill College), David Morrison (NASA Ames Research Center), Sidney C. Wolff (National Optical Astronomy Observatory) with many contributing authors. Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at https://openstax.org/details/books/astronomy ).


15.18E: Fungal Skin and Nail Diseases
- Describe how fungal skin and nail diseases arise, their characteristic symptoms and the treatment options available
A cutaneous condition is any medical condition that affects the integumentary system — the organ system that comprises the entire surface of the body and includes skin, hair, nails, and related muscle and glands. Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). Common fungal skin and nail diseases include athlete’s foot, jock itch, and ringworm.
Athlete’s foot (also known as ringworm of the foot and tinea pedis; ) is an infection of the skin that is caused by a fungi in the genus Trichophyton. While it is typically transmitted in moist communal areas where people walk barefoot, the disease requires a warm moist environment, such as the inside of a shoe, in order to incubate. Athlete’s foot causes scaling, flaking, and itching of the affected skin. Blisters and cracked skin may also occur, leading to exposed raw tissue, pain, swelling, and inflammation. Secondary bacterial infection can accompany the fungal infection, sometimes requiring a course of oral antibiotics. Athlete’s foot can usually be diagnosed by visual inspection of the skin, but where the diagnosis is in doubt direct microscopy of a potassium hydroxide preparation (known as a KOH test) may help rule out other possible causes, such as eczema or psoriasis. Without medication athlete’s foot resolves in 30–40% of cases and topical antifungal medication consistently produce much higher percentages of a cure. Conventional treatment typically involves daily or twice daily application of a topical medication in conjunction with hygiene measures outlined in the above section on prevention. Keeping feet dry and practicing good hygiene is crucial to preventing reinfection. Severe or prolonged fungal skin infections may require treatment with oral antifungal medication.
Tinea cruris, also known as crotch itch, crotch rot, Dhobie itch, eczema marginatum, gym itch, jock itch, jock rot, and ringworm of the groin is a dermatophyte fungal infection of the groin region in any sex, though more often seen in males. As the common name for this condition implies, it causes itching or a burning sensation in the groin area, thigh skin folds, or anus. It may involve the inner thighs and genital areas, as well as extending back to the perineum and perianal areas. Affected areas may appear red, tan, or brown, with flaking, rippling, peeling, or cracking skin. Opportunistic infections (infections that are caused by a diminished immune system) are frequent. Fungus from other parts of the body (commonly tinea pedis or ‘athlete’s foot’) can contribute to this itch. A warm, damp environment allowing the fungus to cultivate greatly contributes; especially with tight, sweaty, or rubbing clothing such as a jockstrap. Medical professionals suggest keeping the groin area clean and dry by drying off thoroughly after bathing and putting on dry clothing right away after swimming or perspiring. Other recommendations to prevent this infection are: not sharing clothing or towels with others, showering immediately after athletic activities, wearing loose cotton underwear, avoiding tight-fitting clothes, and using antifungal powders. Tinea cruris is best treated with topical antifungal medications of the allylamine or azole type.
Dermatophytosis or ringworm is a clinical condition caused by fungal infection of the skin in humans, pets such as cats, and domesticated animals such as sheep and cattle. The term “ringworm” is a misnomer, since the condition is caused by fungi of several different species and not by parasitic worms. The fungi that cause parasitic infection (dermatophytes) feed on keratin, the material found in the outer layer of skin, hair, and nails. These fungi thrive on skin that is warm and moist, but may also survive directly on the outsides of hair shafts or in their interiors. In pets, the fungus responsible for the disease survives in skin and on the outer surface of hairs. Advice often given to prevent this infection includes: avoiding sharing clothing, sports equipment, towels, or sheets and washing clothes in hot water with fungicidal soap after suspected exposure to ringworm. After being exposed to places where the potential of being infected is high, one should wash with an antibacterial and anti-fungal soap or one that contains tea tree oil, which contains terpinen-4-ol. Antifungal treatments include topical agents such as miconazole, terbinafine, clotrimazole, ketoconazole, or tolnaftate applied twice daily until symptoms resolve — usually within one or two weeks
Key Points
- Athlete’s foot (also known as ringworm of the foot and tinea pedis) is an infection of the skin that causes scaling, flaking, and itching of affected areas and is caused by a fungi in the genus Trichophyton.
- Tinea cruris, also known as jock itch, is a dermatophyte fungal infection of the groin region in any sex, though more often seen in males.
- Dermatophytosis or ringworm is a clinical condition caused by fungal infection of the skin in humans, pets such as cats, and domesticated animals such as sheep and cattle.
Key Terms
- jock itch : a fungal infection, tinea cruris, of the groin region, due to the fungus Trichophyton rubrum and others.
- ringworm : a contagious fungal affliction of the skin, characterized by ring-shaped discoloured patches, covered by vesicles or scales.
- athlete’s foot : a fungal infection of the skin of the foot, usually between the toes, caused by the pathogen fungi. Scientific name: tinea pedis.


6.1.6: Distinguishing between Two Types of Situations
Lesson
Let's think about equations with and without parentheses and the kinds of situations they describe.
Exercise \(\PageIndex{1}\): Which One Doesn't Belong: Seeing Structure
Which equation doesn't belong?
\(4(x+3)=9\)
\(4\cdot x+12=9\)
\(4+3x=9\)
\(9=12+4x\)
Exercise \(\PageIndex{2}\): Card Sort: Categories of Equations
Your teacher will give you a set of cards that show equations. Sort the cards into 2 categories of your choosing. Be prepared to explain the meaning of your categories. Then, sort the cards into 2 categories in a different way. Be prepared to explain the meaning of your new categories.
Exercise \(\PageIndex{3}\): Even More Situations, Diagrams, and Equations
Story 1: Lin had 90 flyers to hang up around the school. She gave 12 flyers to each of three volunteers. Then she took the remaining flyers and divided them up equally between the three volunteers.
Story 2: Lin had 90 flyers to hang up around the school. After giving the same number of flyers to each of three volunteers, she had 12 left to hang up by herself.
- Which diagram goes with which story? Be prepared to explain your reasoning.
- In each diagram, what part of the story does the variable represent?
- Write an equation corresponding to each story. If you get stuck, use the diagram.
- Find the value of the variable in the story.
Are you ready for more?
A tutor is starting a business. In the first year, they start with 5 clients and charge $10 per week for an hour of tutoring with each client. For each year following, they double the number of clients and the number of hours each week. Each new client will be charged 150% of the charges of the clients from the previous year.
- Organize the weekly earnings for each year in a table.
- Assuming a full-time week is 40 hours per week, how many years will it take to reach full time and how many new clients will be taken on that year?
- After reaching full time, what is the tutor’s annual salary if they take 2 weeks of vacation?
- Is there another business model you’d recommend for the tutor? Explain your reasoning.
Summary
In this unit, we encounter two main types of situations that can be represented with an equation. Here is an example of each type:
- After adding 8 students to each of 6 same-sized teams, there were 72 students altogether.
- After adding an 8-pound box of tennis rackets to a crate with 6 identical boxes of ping pong paddles, the crate weighed 72 pounds.
The first situation has all equal parts, since additions are made to each team. An equation that represents this situation is \(6(x+8)=72\), where \(x\) represents the original number of students on each team. Eight students were added to each group, there are 6 groups, and there are a total of 72 students.
In the second situation, there are 6 equal parts added to one other part. An equation that represents this situation is \(6x+8=72\), where \(x\) represents the weight of a box of ping pong paddles, there are 6 boxes of ping pong paddles, there is an additional box that weighs 8 pounds, and the crate weighs 72 pounds altogether.
In the first situation, there were 6 equal groups, and 8 students added to each group. \(6(x+8)=72\).
In the second situation, there were 6 equal groups, but 8 more pounds in addition to that. \(6x+8=72\).
Glossary Entries
Definition: Equivalent Expressions
Equivalent expressions are always equal to each other. If the expressions have variables, they are equal whenever the same value is used for the variable in each expression.
For example, \(3x+4x\) is equivalent to \(5x+2x\). No matter what value we use for \(x\), these expressions are always equal. When \(x\) is 3, both expressions equal 21. When \(x\) is 10, both expressions equal 70.
Practice
Exercise \(\PageIndex{4}\)
A school ordered 3 large boxes of board markers. After giving 15 markers to each of 3 teachers, there were 90 markers left. The diagram represents the situation. How many markers were originally in each box?
(From Unit 6.1.2)
Exercise \(\PageIndex{5}\)
The diagram can be represented by the equation \(25=2+6x\). Explain where you can see the 6 in the diagram.
(From Unit 6.1.3)
Exercise \(\PageIndex{6}\)
Match each equation to a story. (Two of the stories match the same equation.)
- \(3(x+5)=17\)
- \(3x+5=17\)
- \(5(x+3)=17\)
- \(5x+3=17\)
- Jada's teacher fills a travel bag with 5 copies of a textbook. The weight of the bag and books is 17 pounds. The empty travel bag weighs 3 pounds. How much does each book weigh?
- A piece of scenery for the school play is in the shape of a 5-foot-long rectangle. The designer decides to increase the length. There will be 3 identical rectangles with a total length of 17 feet. By how much did the designer increase the length of each rectangle?
- Elena spends $17 and buys a $3 book and a bookmark for each of her 5 cousins. How much does each bookmark cost?
- Noah packs up bags at the food pantry to deliver to families. He packs 5 bags that weigh a total of 17 pounds. Each bag contains 3 pounds of groceries and a packet of papers with health-related information. How much does each packet of papers weigh?
- Andre has 3 times as many pencils as Noah and 5 pens. He has 17 pens and pencils all together. How many pencils does Noah have?
Exercise \(\PageIndex{7}\)
Elena walked 20 minutes more than Lin. Jada walked twice as long as Elena. Jada walked for 90 minutes. The equation \(2(x+20)=90\) describes this situation. Match each expression with the statement in the story with the expression it represents.
- \(x\)
- \(x+20\)
- \(2(x+20)\)
- \(90\)
- The number of minutes that Jada walked
- The number of minutes that Elena walked
- The number of minutes that Lin walked


14.11: Essay Questions
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43 .
Explain what the challenge of generativity means in middle adulthood and give two examples of such challenges. What are opportunities and obstacles to healthy generativity?
44 .
As individuals approach middle adulthood, they often face new challenges and opportunities that require them to adapt their sense of identity. How might changes in work, family dynamics, or health influence one’s identity during this stage? Discuss how identity adaptation can lead to personal growth and fulfillment.
45 .
Analyze how attachment styles from early life influence relationships in middle adulthood. Discuss how these attachment patterns may affect marital satisfaction, caregiving responsibilities, and stress levels. Provide examples from the text to illustrate how secure, avoidant, and anxious attachment styles manifest during this stage.
46 .
Assess the role of communication styles and conflict resolution in marital satisfaction during middle adulthood. Referencing Gottman’s research, discuss the impact of positive and negative communication patterns on relationship stability. How can couples in middle adulthood use these strategies to maintain a healthy, fulfilling relationship?
47 .
Multigenerational households are increasingly common in middle adulthood. Analyze the factors that contribute to the rise of multigenerational living, such as financial considerations, cultural values, or the need for caregiving support. How do these households impact the family dynamic, and what are some strategies for managing the complexities that arise in these living situations?
48 .
Middle adulthood often involves managing multiple roles—caregiver, professional, parent, and more. Discuss how role enhancement (the positive impact of fulfilling multiple roles) and role strain (the negative impact) can affect well-being during this life stage. Reflect on strategies that individuals can use to maintain balance, prevent burnout, and sustain their sense of purpose across these varied responsibilities.
49 .
Life satisfaction is influenced by both short-term factors, such as enjoyable activities, and long-term factors, such as financial stability and social support. Reflect on these influences and discuss how life satisfaction might change during middle adulthood. What role do factors like career stability, family relationships, and health play in contributing to or detracting from overall satisfaction during this stage of life.
50 .
Life satisfaction is evaluated differently across cultures. In some cultures, individual achievements and personal success are key factors, while in others, family well-being and social harmony are prioritized. Analyze how cultural values might influence life satisfaction during middle adulthood. Provide examples of how different cultures emphasize unique aspects of well-being and how these perspectives shape individual goals and priorities.


4.2: Water Storage
Student Learning Outcomes
After reading this chapter, you should be able to:
- Explain the uses and requirements of water storage
- List the various types of water storage facilities
- List water storage facility equipment
- Describe the operations and maintenance of water storage facilities
Water storage is an important component of a distribution system. The main purpose is to provide sufficient amounts of water to average or equalize the daily demands on the system. Storage provides increased operating conveniences by providing sources of supply throughout the day and at night when utility employees are not typically at work. It levels out pumping requirements, can decrease power costs from pumping, provides a supply of water during power outages, fire storage, and other benefits. This chapter of the text will examine water storage systems, the various types of water storage, how water storage affects water quality, and a general overview of the operation and maintenance of water storage structures.
Why Water Storage Is Needed
Water demand is highest in the early more and evening hours of the day. In the morning, customers are showering, using toilets, and preparing meals, which require water. In addition, most irrigation systems are in use in the early morning hours before temperatures get too hot. In the evening hours, people are returning from work and school and water demand typically increases during these times. There is low use midday and during overnight hours. Without storage, the pumping capacity would be approximately two times the average requirement. Adequate storage allows for uniform pumping. Storage also allows minimal operator involvement during non-working hours. Without storage, workers would need to be available to operate the system if unexpected increases in demand occur. A utility would require various different size pumps to match changes in demand. Frequent on-off cycling of pumps causes increased wear on pumps and motors and higher costs for electricity.
Another benefit of water storage is the ability to store and supply water during emergencies and power outages. If a water utility solely relied on pumps to meet demands, anytime there is a power outage, water service would be interrupted. Having water stored in tanks allows for uninterrupted service during these times. Some distribution systems have long transmission water mains bringing the water supply into the community being served. Under these circumstances, any repairs made to these pipes requiring the water main to be isolated, would disrupt water supply to customers.
Fire fighting is another critical need of community water systems. Water utilities not only need to meet operational demands, they must also meet the demands to extinguish fires. Fire fighting may account for as much as fifty (50) percent of total storage. In addition, fire-fighting demands must be met during main line breaks, power outages, and maximum customer demands. Adequate pressure must also be maintained during fire flows.
Water Storage and Water Quality
Water storage can help with water quality and it can also contribute to water quality problems. As part of the Safe Drinking Water Act, a set of regulations called Surface Water Treatment Rule (SWTR), requires specific times that chlorine must be in contact with the water before the water reaches the first customer. Water storage tanks can provide detention time to allow the chlorine to remain in contact with the water long enough provide the required time. Water storage can also be an area where blending multiple sources of supply can take place. If an impaired source of supply is pumped into a storage tank, unimpaired sources can also be pumped into the tank providing adequate blending of the impaired source.
Water quality can also degrade in water storage tanks. While water storage tanks provide various benefits, storing too much water can lead to water quality degradation. Chlorine residuals can diminish and water can become stagnant if the water within storage tanks is not changed. Cycling tanks (allowing the level in a tank to rise and fall) can help avoid stagnation and water quality degradation.
What Type and Size of Storage Is Needed?
Water storage tanks come in various sizes and styles. Some of the factors to determine the type and capacity of storage in a distribution system depend on the size of the system, the topography of the distribution system, and how the distribution system is laid out (is the system spread out or concentrated in a small area). These and other criteria are used to design the water storage needs.
Several terms related to water storage should be understood.
- Average Day Demand (ADD)—This is the total demand for water during a period of time divided by the number of days in that time period. This is also called the average daily demand.
- Maximum Day Demand (MDD)—This is the highest total demand over a 24 hour period within a given year
- Peak Hour Demand (PHD)—This is the maximum demand over a one hour period within a given year
- Float on the System—This is a method of operating a storage facility. Daily flow into the system is approximately equal to the average day demand. When customer demands are low, the storage facility will be filling and when demands are high the storage facility will be emptying.
System hydraulics are directly related to the location of water storage facilities within a distribution system. If a water storage tank is located in close proximity to a pumping station, the head loss (pressure) to the farthest portion of the distribution system may be excessive through normal size piping. Additional transmission mains can help alleviate this type of pressure loss. If a storage tank is placed at the farthest end of a service area adequate pressure is typically received at the far ends and near the pumping stations. This type of set up avoids the need for increased main sizes. However, there must be enough capacity to the remote location to refill the tank during off-peak periods. In addition, if there is a great separation between the pumping facility and storage, lower pressures might occur in the middle of the distribution system. If possible, locating storage structures adjacent to the area with the lowest pressure is ideal. This typically provides enough available pressure to the entire service area and smaller diameter water mains can be used because flow from the tank is split into two directions.
For hydraulic purposes, it is more ideal to have multiple smaller tanks instead of one larger tank. This allows for more stabilized and equal pressures throughout the distribution system. Head losses also increase whenever pumping is required over long distances and during peak demand conditions. Locating storage tanks near the center of a distribution system allows pumping stations to operate at or near average day demand conditions most of the time.
Types of Water Storage Structures
There are various types of water storage facilities. They are made of different types of materials and are designed in different shapes to serve various needs. While there are various storage structures storing raw water and within a treatment plant, this section only discusses storage structures found in distribution systems. The following are some of the more common water storage facilities within a distribution system:
- Elevated Storage Tanks—In regions with relatively flat topography, elevated storage tanks are commonly used. They are above ground tanks supported by a steel or concrete tower or pedestal. Most are made of steel and designed to float on the system. If they are not constructed tall enough, they can overflow and provide inadequate pressures.
- Hydroneumatic Storage Tanks—These tanks are used in very small systems with in adequate pressure. They are kept partially full with compressed air to provide water in excess of the pump capacity when required. These types of systems will also provide water for a limited time if a pump fails.
- Standpipes—These tanks are constructed directly on the ground and have a height greater than the diameter. They are commonly used to equalize storage near a source of supply like a well field. They can also be used to provide additional fire protection.
- Above Ground Storage Tanks—These are the most commonly used forms of storage tanks along the west coast of the United States. They can store large quantities of water and are located where the topography is such that they can be constructed on hillsides. The main downside is that they require a fairly large area of land.
Components of Elevated and Above Ground Storage Tanks
These tanks have very similar components. This section will review the major components and address any differences between the two styles of storage structures.
Inlet and Outlet Pipes
Elevated storage tanks generally have a common inlet and outlet pipe, while above ground storage tanks can have either common or separate inlet and outlet pipes. The purpose of these pipes is to bring water in and allow water to exit the tank. The purpose of having a separate inlet and outlet-piping configuration is to help water circulate inside the tank. The common pipe (called a riser) for an elevated storage tank typically runs up the middle of the support structure holding the tank. The inlet and outlet piping of an above-ground storage tank typically enters the tank along the bottom portion of the tank. In the separate inlet/outlet configuration, the location of the inlet and outlet connection is typically at opposite ends of the tank.
Overflow Pipe
Each type of tank is equipped with an overflow pipe. It is designed to allow water to exit the tank to the atmosphere in the event the water-level controls fail. They are commonly constructed to discharge into a catch basin and should never be directly connected to a sewer or storm drain. They should have a proper air gap separation from the area they are discharging into and should be screened or have a weighted flap to prevent animals from entering the pipe.
Drain Connection
All tanks need to be inspected periodically. While some inspections can occur with water in the tank, it is common to drain a tank for inspection, cleaning, and repairs. Water in a tank can be lowered by preventing pumps from turning on to fill the tank. However, they can only be lowered to a level the height of the outlet pipe and at no time should a tank be drained completely while in service. Once the water is brought down as far as in can while in service, a separate drain pipe can be opened to drain the rest of the water.
Monitoring Devices
Water storage tanks, just like other water distribution facilities are commonly equipped with monitoring devices. Details about these monitoring devices are covered in another chapter. However, the will also be discussed here briefly. One of the most important things to monitor on storage tanks is the water level. Therefore, most are equipped with either a physical site gauge mounted on the outside of the tank and/or level sensors which can transmit tank levels to remote locations. These devices are commonly furnished with high and low water level alarms.
Valves
In order to isolate a tank from the distribution system, a valve must be furnished along the inlet/outlet piping coming in to the tank. This valve can then be closed to take the tank out of service for maintenance and repairs. Sometimes a tank will be furnished with a valve referred to as an altitude valve. This valve is designed to close preventing the tank from overflowing.
Vents
Air ventilation is usually provided at the tops of tanks to allow air to escape as the tank is filling and air to enter and the level in the tank drops. These air vents must be large enough to prevent the tank from collapsing and they must be properly screened with a minimum mesh size of ¼”.
Access Hatches
Access inside a tank also needs to be provided. There are at least and sometimes multiple access hatches on the top of storage tanks. These allow works to enter the tank for inspection and maintenance. These hatches must be properly constructed with rims under the cover to prevent surface water runoff from getting into the tank. There are also manways at the bottom of the tank for access when a tank has been drained and taken out of service for maintenance and inspection.
Ladders
Access needs to be provided to the tops of tanks and inside tanks. Ladders usually provide this access. Some above ground water storage tanks use spiral staircases as opposed to ladders. Elevated storage tanks are usually equipped with three (3) different ladders. The first one runs up the leg of the tower from the ground to the balcony around the tank. The second ladder runs from the balcony to the top of the tank roof. The third ladder runs along the inside of the tank for inside access. Outside ladders should be installed six (6) to eight (8) feet off the ground or have a locked metal shield around the bottom to prevent unauthorized access.
Cathodic Protection
Interior tank walls are subject to corrosion, especially in the upper portions, which are not constantly submerged in water. Cathodic protection can reduce this interior corrosion in coated steel tanks. Cathodic protection reverse the flow of current that tends to dissolve iron from the tank surface causing rust and corrosion. Electrodes with a direct current (DC) are used and will corrode instead of the tank walls. In warm climates, the electrodes can be suspended from the tank roof. In cold climates, the electrodes must be submerged. The anodes can last up to ten (10) years, but should also be inspected annually.
Tank Coatings
Since steel can oxidize and deteriorate and since water is considered the “universal solvent”, it is important to properly coat the interior and exterior of tanks. Interior coatings must be able to withstand constant emersion in water, varying water temperatures, alternate wetting and drying periods, ice abrasion, high humidity, heat, chlorine, and mineral content in the water. Exterior coatings must endure similar conditions and maintain a good appearance. All interior coatings must be NSF approved.
Operation and Maintenance
The American Water Works Association recommends that all water storage structures be completely inspected every three (3) to five (5) years. Elevated and above ground storage tanks should be periodically drained, cleaned, inspected, repaired, and painted. The interior surfaces should be cleaned thoroughly with a high-pressure water jet or by sweeping and scrubbing. All dirt and debris should be removed from the tank and a complete or spot re-coating should also occur.
All tanks need to be disinfected before being placed in service. This includes new construction and tanks taken out of service for maintenance. There are three (3) basic methods for disinfecting storage tanks:
- The first method involves filling the entire tank with water and held at a disinfectant residual level of 10 mg/L. If the water is disinfected before entering the tank the detention time is six (6) hours and is the tank is filled and then disinfected, the detention time is twenty-four (24) hours.
- The second method involves spraying the interior walls with a disinfectant solution concentration of 200 mg/L
- The third method requires six (6) percent of the tank to be filled and disinfected to a residual of 50 mg/L. The tank is then completely filled and held for twenty-four (24) hours.
The tank must then be sampled and analyzed for total coliform bacteria. If the results come back positive, additional disinfection is required until two (2) consecutive samples are negative. New and recoated tanks must also be sampled and analyzed for volatile organic compounds.
Routine inspections should also be conducted at water storage tanks. The overflow piping, vents, hatches, ladders, and locks should be monitored frequently for damage and vandalism. Ladders should be in good condition and replaced if deemed unsafe. The roof and access points should also be checked for cracks and holes to prevent surface water leaking into the tank.
Sample Questions
1. An altitude valve is used to ___________.
- Prevent storage tanks from filling too fast
- Prevent storage tanks from overflowing
- Separate the inlet and out let flows
- None of the above
2. Water storage reservoirs should be completely inspected?
- Every year
- Every other year
- Every 3 to 5 years
- Every 5 to 10 years
3. Without storage, pumping capacity would be approximately ___________.
- Twice the average requirement
- Three times the average requirement
- Less than the average requirement
- None of the above
4. Fire demand may account for as much as ___________.
- 10% of storage
- 25% of storage
- 50% of storage
- 100% of storage
5. It is recommended that storage tanks have ___________.
- Separate inlet and outlet piping
- Common inlet and outlet piping
- Outlets twice as large as inlet piping
- There are no recommendations


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exoplanet
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a planet orbiting a star other than our Sun
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giant molecular clouds
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large, cold interstellar clouds with diameters of dozens of light-years and typical masses of 10
5
solar masses; found in the spiral arms of galaxies, these clouds are where stars form
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Herbig-Haro (HH) object
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luminous knots of gas in an area of star formation that are set to glow by jets of material from a protostar
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mini-Neptune
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a planet that is intermediate between the largest terrestrial planet in our solar system (Earth) and the smallest jovian planet (Neptune); generally, mini-Neptunes have sizes between 2.8 and 4 times Earth’s size
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protostar
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a very young star still in the process of formation, before nuclear fusion begins
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stellar wind
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the outflow of gas, sometimes at speeds as high as hundreds of kilometers per second, from a star
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super-Earth
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a planet larger than Earth, generally between 1.4 and 2.8 times the size of our planet
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transit
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when one astronomical object moves in front of another


4.9: Cognitive Differences
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Sometimes children’s brains work differently. One form of this neurodiversity is Autism spectrum disorder .
Autism: Defining Spectrum Disorder
Autism spectrum disorder (ASD) describes a range of conditions classified as neuro-developmental disorders in the fifth revision of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-5). The DSM-5, published in 2013, redefined the autism spectrum to encompass the previous (DSM-IV-TR) diagnoses of autism, Asperger syndrome, pervasive developmental disorder not otherwise specified (PDD-NOS), and childhood disintegrative disorder. These disorders are characterized by social deficits and communication difficulties, repetitive behaviors and interests, sensory issues, and in some cases, cognitive delays.
Asperger syndrome was distinguished from autism in the earlier DSM-IV by the lack of delay or deviance in early language development. Additionally, individuals diagnosed with Asperger syndrome did not have significant cognitive delays. PDD-NOS was considered "subthreshold autism" and "atypical autism" because it was often characterized by milder symptoms of autism or symptoms in only one domain (such as social difficulties). In the DSM-5, both of these diagnoses have been subsumed into autism spectrum disorder.
Autism spectrum disorders are considered to be on a spectrum because each individual with ASD expresses the disorder uniquely and has varying degrees of functionality. Many have above-average intellectual abilities and excel in visual skills, music, math, and the arts, while others have significant disabilities and are unable to live independently. About 25 percent of individuals with ASD are nonverbal; however, they may learn to communicate using other means.
Social Communication Symptoms
Social impairments in children with autism can be characterized by a distinctive lack of intuition about others. Unusual social development becomes apparent early in childhood. Infants with ASD show less attention to social stimuli, smile and look at others less often, and respond less to their own name. Toddlers with ASD differ more strikingly from social norms; for example, they may show less eye contact and turn-taking and may not have the ability to use simple movements to express themselves. Individuals with severe forms of ASD do not develop enough natural speech to meet their daily communication needs.
Restricted and Repetitive Behaviors
Children with ASD may exhibit repetitive or restricted behavior, including:
- Stereotypy—repetitive movement, such as hand flapping, head rolling, or body rocking.
- Compulsive behavior—exhibiting intention to follow rules, such as arranging objects in stacks or lines.
- Sameness—resistance to change; for example, insisting that the furniture not be moved or sticking to an unvarying pattern of daily activities.
- Restricted behavior—limits in focus, interest, or activity, such as preoccupation with a single television program, toy, or game.
- Self-injury—movements that injure or can injure the person, such as eye poking, skin picking, hand biting, and head banging.
Etiology
While specific causes of ASD have yet to be found, many risk factors have been identified in the research literature that may contribute to its development. These risk factors include genetics, prenatal and perinatal factors, neuroanatomical abnormalities, and environmental factors. It is possible to identify general risk factors, but much more difficult to pinpoint specific factors.
Genetics
ASD affects information processing in the brain by altering how nerve cells and their synapses connect and organize; thus, it is categorized as a neuro-developmental disorder. The results of family and twin studies suggest that genetic factors play a role in the etiology of ASD and other pervasive developmental disorders. Studies have consistently found that the prevalence of ASD in siblings of children with ASD is approximately 15 to 30 times greater than the rate in the general population. In addition, research suggests that there is a much higher concordance rate among monozygotic (identical) twins compared to dizygotic (fraternal) twins. It appears that there is no single gene that can account for ASD; instead, there seem to be multiple genes involved, each of which is a risk factor for part of the autism syndrome through various groups. It is unclear whether ASD is explained more by rare mutations or by combinations of common genetic variants.
The Diversity of the Autism Spectrum
The rainbow-colored infinity symbol represents the diversity of the autism spectrum as well as the greater neurodiversity movement. The neurodiversity movement suggests that diverse neurological conditions appear as a result of normal variations in the human genome. It challenges the idea that such neurological differences are inherently pathological, instead asserting that differences should be recognized and respected as a social category on a par with gender, ethnicity, sexual orientation, or disability status.
Prenatal and Perinatal Factors
A number of prenatal and perinatal complications have been reported as possible risk factors for ASD. These risk factors include maternal gestational diabetes, maternal and paternal age over 30, bleeding after first trimester, use of prescription medication (such as valproate) during pregnancy, and meconium (the earliest stool of an infant) in the amniotic fluid. While research is not conclusive on the relation of these factors to ASD, each of these factors has been identified more frequently in children with ASD than in developing youth without ASD.
Environmental Factors
Evidence for environmental causes is anecdotal and has not been confirmed by reliable studies. In the last few decades, controversy surrounded the idea that vaccinations may be the cause for many cases of autism; however, these theories lack scientific evidence and are biologically implausible. Even still, parental concern about a potential vaccine link with autism has led to lower rates of childhood immunizations, outbreaks of previously controlled childhood diseases in some countries, and the preventable deaths of several children.
Treatment
There is no known cure for ASD, and treatment tends to focus on management of symptoms. The main goals when treating children with ASD are to lessen associated deficits and family distress and to increase quality of life and functional independence. 32 Treatment for ASD should begin as soon as possible after diagnosis. Early treatment for ASD is important as proper care can reduce individuals’ difficulties while helping them learn new skills and make the most of their strengths.
The wide range of issues facing people with ASD means that there is no single best treatment for ASD.33 So treatment is typically tailored to the individual person's needs. Intensive, sustained special-education programs and behavior therapy yearly in life can help children acquire self-care, social, and job skills. The most widely used therapy is applied behavior analysis (ABA); other available approaches include developmental models, structured teaching, speech and language therapy, social skills therapy, and occupational therapy. 34
There has been increasing attention to the development of evidenced-based interventions for young children with ASD. Although evidence-based interventions for children with ASD vary in their methods, many adopt a psychoeducational approach to enhancing cognitive, communication, and social skills while minimizing behaviors that are thought to be problematic. 36
Contributors and Attributions
32. Children’s Development by Ana R. Leon is licensed under CC BY 4.0
33. Autism Spectrum Disorder by the National Institute of Mental Health is in the public domain
34. Children’s Development by Ana R. Leon is licensed under CC BY 4.0
36. Children’s Development by Ana R. Leon is licensed under CC BY 4.0


6.8: Transitions
As the speaker continues to fill in the outline with main points and supporting material, the information should begin to “flow” together. However, before going much further, consider the elements of speech composition that help tie each of these various points together seamlessly. Those are called transitions . Ideally, transitions should sound conversational, so as to make the speech feel effortless as the audience listens. At the same time, transitions must guide and direct listeners toward where the information is headed. A speaker could do this by explicitly announcing that transition to a new point: “For my second main point, I would like to cover…” However, avoid using such obvious transitions. They sound mechanical and stiff while adding a proverbial speed bump to the flow of information. They should sound effective and clear while at the same time appear seamless and conversational.
One helpful technique for transitioning between points involves creating a single sentence that links prior information with a preview of upcoming information, often called a bridge . To do this, create a sentence with two parts, or clauses, where the first half of the sentence provides a summary of the previous topic, and the second half of the sentence gives a brief preview of the next talking point. For example:
Main Point I : Public speaking provides us with a way to learn about how to communicate in front of groups .
- Most of us suffer from varying degrees of public speaking anxiety, requiring us to learn how to overcome this anxiety so that we might effectively communicate our ideas with others.
- Many of the lessons we learn in public speaking impact our ability to write, as well as interact with people on a daily basis.
Transition : Speaking in front of groups can truly be nerve-wracking, but there are times when speaking to just one person can be equally daunting.
Main Point II : Interpersonal communication gives students the opportunity to learn about one-on-one communication in a variety of contexts.
In this example, the first half of the sentence “Speaking in front of groups can truly be nerve-wracking…” summarizes the supporting point the speaker just made, while the second half of the sentence “…but there are times when speaking to just one person can be equally daunting” previews the next point regarding interpersonal communication studies. With practice, these types of transitions can easily become second nature to speakers, and some may even become clever enough to compose and use them on the spot!
Transitions can also come in the form of a signpost , and just as with an actual signpost on a road, these phrases signal listeners, in a literal or explicit sense, to the direction of the speech. For example, if a preview of points states that a speech will inform the audience about: “First, public speaking, second, interpersonal communication, and third, intercultural communication,” then between each of those main points, speakers could signal where they are headed by inserting a signpost such as, “Moving on to our second topic of the day…”
Finally, the last transitional device is the spotlight , which shares similarity to the eye-catching headlines broadcast on a viral social media article: “What this public speaking class taught me was more important than anything I had ever learned before.” Note that this sentence builds curiosity through suspense, but at the same time, spotlights the upcoming information will concern public speaking.