Environmental Problems, Their Causes, and Sustainability 1

cant (less than 4.0 on the Richter scale), minor (4.0–4.9),damaging (5.0–5.9), destructive (6.0–6.9), major (7.0–7.9),and great (over 8.0).Earthquakes often have aftershocks that graduallydecrease in frequency over a period of up to severalmonths, and some have foreshocks from seconds toweeks before the main shock.The primary effects of earthquakes include shakingand sometimes a permanent vertical or horizontal displacementof the ground. These effects may have seriousconsequences for people and for buildings,bridges, freeway overpasses, dams, and pipelines. Anearthquake is a very large rock-and-roll event.Secondary effects of earthquakes include rockslides,urban fires, and flooding caused by subsidence(sinking) of land. Coastal areas can be severely damagedby earthquakes at sea that can generate hugewater waves, called tsunamis (also called tidal waves,although they have nothing to do with tides) thattravel as fast as 950 kilometers (590 miles) per hour.You cannot outrun one of these waves.One way to reduce loss of life and property fromearthquakes is to examine historical records and makegeologic measurements to locate active fault zones. Wecan also map high-risk areas (Figure 16-7), establishbuilding codes that regulate the placement and designof buildings in areas of high risk, and increase researchon projecting when and where earthquakes will occur.Then people can decide how high the risk might beand whether they want to accept the risk and live inareas subject to earthquakes.Engineers know how to make homes, large buildings,bridges, and freeways more earthquake resistant.But this can be expensive, especially the reinforcementof existing structures.Liquefaction ofrecent sedimentscauses buildingsto sinkLandslides mayoccur onhilly groundShockwavesEpicenterFocusTwo adjoining platesmove laterally alongthe fault lineEarth movementscause flooding inlow-lying areasFigure 16-6 Major features and effects of an earthquake.CanadaUnited StatesNo damage expectedMinimal damageModerate damageSevere damageFigure 16-7 Expected damage from earthquakes in Canadaand the contiguous United States. This map is based on earthquakerecords. (U.S. Geological Survey)What Are Volcanoes? Popping an EarthCorkSome volcanoes erupt quietly and release flowsof molten rock but others erupt explosively andspew large chunks of lava rock, ash, and harmfulgases into the atmosphere.An active volcano occurs where magma (molten rock)reaches the earth’s surface through a central vent or along crack (fissure; Figure 16-8, p. 338). Volcanic activitycan release ejecta (debris ranging from large chunksof lava rock to ash that may be glowing hot), liquidlava, and gases (such as water vapor, carbon dioxide,and sulfur dioxide) into the environment.Volcanic activity is concentrated for the most partin the same areas as seismic activity. Some volcanoeserupt explosively and eject large quantities of gases andparticulate matter (soot and mineral ash) high into thetroposphere. Most of the particles of soot and ash soonfall back to the earth’s surface. But gases such as sulfurdioxide remain in the atmosphere and are converted totiny droplets of sulfuric acid, many of which stay abovethe clouds and may not be washed out by rain for up to3 years. These tiny droplets reflect some of the sun’s energyand can cool the atmosphere for 1–4 years.http://biology.brookscole.com/miller14337