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The sediments on Mount St. Helens were unconsolidated volcanic ash , which is easily eroded . Lahars almost always occur on or near stratovolcanoes because of their tendency to erupt explosively and their tall , steep cones are either snow covered , topped with a crater lake , constructed of weakly consolidated rock debris that is easily eroded , or internally weakened by hot hyrothermal fluids . If the signal or response from the limit is delayed and if the environment is irreversibly eroded when overstressed , then the growing economy will overshoot its carrying capacity , degrade its resource base , and collapse . Soft rocks and sediment , which are easily eroded by flowing water , allow rivers to have more latitude as to where they can move . Rock that is easily eroded is one of the essential ingredients of arroyo formation . The soft , red Triassic sandstones are easily eroded and have formed deep , coarse soils . It is so soft and crumbly that it is easily eroded , and as it erodes it washes away back under the harder and stronger layers of Muav and Redwall above it . When trees are cut down , and other vegetation cleared , the soil is easily eroded . Generally , the soils are poorly developed , stony , shallow , have low moisture-holding capacities , and are easily eroded , so that in many places little or no topsoil is present . The Po River plume is particularly easy to see because it has a large amount of carbonate rocks in its watershed , which are easily eroded to produce light-colored , reflective sediments . In urban areas the health and nutrition of the poor is constantly eroded by rising prices of basic necessities . On the Earth , small craters are easily eroded by the effects of the atmosphere ( wind , rain , etc. ) over time . University staffing is constantly eroded by promotions to Parliament or the public service .