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hazards, for which American taxpayers pay billions of dollars each year.
Many other geological hazards are driven by energy from the sun and reflect the interaction of the hydrosphere, lithosphere, atmosphere, and biosphere. Heavy or prolonged rains can cause river systems to overflow, flooding low-lying areas and destroying towns, farmlands, and changing the course of major rivers. There are several types of floods, ranging from flash floods in mountainous areas to regional floods in large river valleys such as the great floods of the mississippi and missouri Rivers in 1993. Coastal regions may also experience floods, sometimes the result of typhoons, hurricanes, or coastal storms that bring high tides, storm surges, heavy rains, and deadly winds. Coastal storms can cause large amounts of coastal erosion, including cliff retreat, beach and dune migration, and opening of new tidal inlets and closing of old inlets. All these normal beach processes have become hazardous since so many people have migrated into beachfront homes. Hurricane Andrew caused more than $19 billion of damage to the southern united states in 1992.
Deserts and dry regions are associated with their own natural geologic hazards. Blowing winds and shifting sands hinder agricultural efforts, and deserts have a limited capacity to support large populations. some of the greatest disasters in human history have been caused by droughts, some associated with the expansion of desert regions into areas that previously received significant rainfall and supported large populations dependent on agriculture. In this century the sub-saharan sahel region of Africa has been hit with drought disasters several times, affecting millions of people and animals. This appears to be part of a natural climate cycle of alternating wet and dry periods in the sahara. Contraction and expansion of the desert fringes has severe consequences for those who try to live in such changing conditions.
Desertification is but one possible manifestation of global climate change. The Earth has fluctuated in climate extremes, from hot and dry to cold and dry or cold and wet, and has experienced several periods when much of the land's surface was covered by glaciers. Glaciers have their own set of local-scale hazards that affect those living or traveling on or near their ice crevasses, which can be deadly if fallen into. Glacial meltwater streams can change in discharge so quickly that encampments on their banks can be washed away without a trace, and icebergs present hazards to shipping lanes. more important, glaciers reflect subtle changes in global climate—when gla ciers are retreating, climate may be warming and becoming drier. When glaciers advance, the global climate may be getting colder and wetter. Glaciers have advanced and retreated over northern North America several times in the past 100,000 years. The Earth is currently experiencing an interglacial episode and may see the start of the return of the continental glaciers over the next few hundred or thousand years.
Geologic materials themselves can be hazardous. Asbestos, a common mineral, is being removed from thousands of buildings in the united states because of the threat that certain types of airborne asbestos fibers present to human health. In some cases (for certain types of asbestos fibers), this threat is real and removal of the fibers is necessary. in other cases leaving the asbestos alone is safer than disturbing it and releasing airborne particles. Natural radioactive decay releases harmful gases, including radon, that creep into homes, schools, and offices, and causes numerous cases of cancer every year. Mitigating this hazard is often easy—simple monitoring and ventilation can prevent many health problems associated with radon exposure. other materials can be hazardous even though they seem inert. For instance, some clay minerals expand by hundredsfolds when wetted. These expansive clays rest under many foundations, bridges, and highways, and cause billions of dollars of damage every year in the united states.
sinkholes, including the one in Winter Park, Florida, have swallowed homes and businesses in Florida and in other locations in recent years. sinkhole collapse and other subsidence hazards are more important than many realize. Large parts of southern California near Los Angeles have sunk tens of feet (about 10 meters) in response to pumping of groundwater and oil out of underground reservoirs. other developments above former mining areas have begun sinking into collapsed mine tunnels. Coastline areas experiencing subsidence face the added risk of having the ocean rise into former living space. Coastal subsidence coupled with gradual sea-level rise is rapidly becoming one of the major global hazards that humans must deal with in the next century, since most of the world's population lives near the coast in the reach of the rising waters. Cities may become submerged and farmlands covered by shallow salty seas. New orleans and much of the Gulf coast have been sinking at rates of up to one inch per year (2.5 cm per year) in response to natural and human-induced processes, placing some urban areas at high risk for storm surge and hurricane damage. These risks were shown dramatically by Hurricanes Katrina and Rita in 2005. An enormous amount of planning is needed, as soon as possible, to deal with this growing threat.
occasionally in the Earth's history the planet has been hit with asteroids and meteorites from outer space, and these have completely devastated the biosphere and climate system. Many of the mass extinctions in the geologic record are now thought to have been triggered, at least in part, by large impacts from outer space. For instance, the extinction of the dinosaurs and a huge percent of other species on Earth 66 million years ago is thought to have been caused by a combination of massive volcanism from a flood basalt province preserved in India, coupled with an impact with a six-mile (10-km) wide meteorite that hit the Yucatán Peninsula of mexico. When the impact occurred, a 1,000-mile (1,610-km) wide fireball erupted into the upper atmosphere, a tsunami hundreds or thousands of feet (hundreds of meters) high washed across the Caribbean, southern North America, and much of the Atlantic, and huge earthquakes accompanied the explosion. The dust blown into the atmosphere immediately initiated a dark global winter, and as the dust settled months or years later, the extra carbon dioxide in the atmosphere warmed the Earth for many years, forming a greenhouse condition. many forms of life could not tolerate these rapid changes and perished. similar impacts at several times in the Earth's history have had a profound influence on the extinction and development of life.
The human population is growing at an alarming rate and currently doubling every 50 years. At this rate, there will be only a three-foot by one-foot space (1 square meter) for every person on Earth in 800 years. The unprecedented population growth has put such a stress on other species that we are driving a new mass extinction on the planet. Because details of the relationships between different species are unknown, many fear that destroying so many other life-forms may contribute to our own demise. In response to the population explosion, people are moving into hazardous locations including shorelines, riverbanks, along steep-sloped mountains, and along the flanks of volcanoes. Populations that grow too large to be supported by the environment usually suffer some catastrophe, disease, famine, or other mechanism that limits growth, and society needs to find ways to limit human population growth to sustainable rates. survival of the planet depends on our ability to maintain these limits.
Advances in science and engineering in recent decades have dramatically changed perceptions of natural hazards. In the past people viewed destructive natural phenomena (including earthquakes, volcanic eruptions, floods, landslides, and tsunamis) as unavoidable and unpredictable. society's attention to basic scientific research has changed that view dramatically, and the resulting ability to make general predictions regarding the timing, location, and
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Disasters: Why No ones Really 100 Safe. This is common knowledgethat disaster is everywhere. Its in the streets, its inside your campuses, and it can even be found inside your home. The question is not whether we are safe because no one is really THAT secure anymore but whether we can do something to lessen the odds of ever becoming a victim.