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Hazardous waste water can be disposed of by underground injection, incineration, evaporation from open pits, or export to other areas. The most common domestic method is under- ground injection, but because the underground geology is inadequately known, liquid hazardous waste injected deep underground has seeped into underground water supplies in about half the states. About 20% of hazardous waste is inciner- ated, but the Environmental Protection Agency (EPA) estimates that 60% could be disposed of by this safer method. Incinera- tion is more expensive than subsurface disposal, however. Disposal by evaporation from surface impoundments is very unsafe and has caused ground-water contamination in about three-quarters of the 50 states. Floods Floods are the most commonly experienced natural calami- ties and are the cause of about 60% of declared disasters. Flooding may be caused by hurricanes from the ocean or excessive water from landward areas. Hurricanes cannot be controlled, and the value of property destroyed by them has increased considerably over time because of people's desire to live near the seashore. Loss of life has decreased, however, because of improved forecasting and early warning. Flood- ing resulting from excessive rain on the land surface has been exacerbated by the human desire to live near river channels, to pave land surfaces and increase the rate of runoff, and to de- nude hill slopes by excessive logging. Without vegetation and porous soil, the rate of runoff of rainwater is increased and river channels cannot hold all the water they receive. The massive flooding in central China in 1998 was attributed to the stripping of vegetation over large areas. Atmosphere Concerns about air quality revolve around increases in the amount of carbon dioxide, decreases in the amount of ozone 15 – 30 km (9 – 18 miles) above the surface, and pollution of the air that sustains life in the lower atmosphere. Increasing carbon dioxide levels result largely from the burning of coal and oil, the main sources of energy in industrial societies. The amount of carbon dioxide in the air has increased to unprecedented levels during the past 150 years. Carbon dioxide absorbs radiation from the Earth's surface and has caused a measurable increase in global temperatures (greenhouse effect); this global warm- ing is raising sea levels (from melting glaciers and thermal expansion), endangering coastal communities. Ozone in the stratosphere absorbs most of the Sun's ultravio- let (UV) radiation, thus protecting people from excessive skin cancers, damaged immune systems, and other maladies. The thickness of the ozone layer decreased significantly because of the release to the atmosphere of chlorofluorocarbons (CFCs) which destroy ozone molecules. Production of CFCs has now has stopped worldwide, but the ozone layer will not restore itself completely for years. Noxious gases and particulates in the air result largely from combustion of coal and oil in automobiles and factories. It is the cause of many lung problems and premature deaths in industrial countries. Earthquakes and Volcanoes Earthquakes and volcanoes tend to be associated geographi- cally and are prominent around the Pacific rim. Japan and the American west coast are particularly vulnerable, and both have suffered major quakes. In the United States, California is the most seriously affected by earthquakes, with major property damage and loss of life (see illustration). Attempts to predict the timing and location of earthquakes have not yet been suc- cessful despite very large research efforts in many countries over several decades. Dangers from volcanic eruptions include mud and rock flows, lavas, and acid gases. Most dangerous to people are the debris flows, which can move down-slope at speeds as high as 50 miles/hour for distances of tens of miles. Entire towns have been buried by such flow with much loss of life. Lava flows move slowly and hence cause few deaths, but their power is irresistible and property damage is extensive. Eruptions can sometimes be predicted, but surprises are common. Environmental Geology (continued) + ward ' s science 5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com + ward ' s science 5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com This article was originally published by McGraw Hill's AccessScience. Click here to view and find more articles like this.