This website is the digital version of the 2014 National Climate Assessment, produced in collaboration with the U.S. Global Change Research Program. For the official version, please refer to the PDF in the downloads section.
Lahars move rapidly down valleys like rivers of concrete. If you are on the floor of a valley that leads from a volcano and become aware of an oncoming lahar, seek high ground. Lahar is an Indonesian term that describes a hot or cold mixture of water and rock fragments that flows down the slopes of a volcano and typically enters a river valley.
Back to our lunch discussion: How fast, we wondered over our kebabs, would a geostationary satellite have to be moving to stay stationary in the sky? The space shuttle orbiter, we know, orbits at around 8,000 meters per second (18,000 miles per hour) but it does a complete orbit in about 90 minutes. Would a geostationary satellite be going faster or slower? To find out, I did a little math.