Natural disasters

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Natural disasters

  1. 1. Martín André Montes Zarria 4th Grade F. Kauffman D. Natural Disasters
  2. 2. DUST STORM  A dust storm or a sandstorm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front blows loose sand and dust from a dry surface.
  3. 3. DUST STORM  Particles are transported by saltation and suspension, causing soil erosion from one place and deposition in another.
  4. 4. SANDSTORM  The term sandstorm is used most often in the context of desert sandstorms, especially in the Sahara.
  5. 5. DUST STORM  The term dust storm is more likely to be used when finer particles are blown long distances, especially when the dust storm affects urban areas.
  6. 6. CAUSES  As the force of wind passing over loosely held particles increases, particles of sand first start to vibrate, then to saltate ("leap"). As they repeatedly strike the ground, they loosen smaller particles of dust which then begin to travel in suspension. At wind speeds above that which causes the smallest to suspend, there will be a population of dust grains moving by a range of mechanisms: suspension, saltation and creep.
  7. 7.  Drought and wind contribute to the emergence of dust storms, as do poor farming and grazing practices by exposing the dust and sand to the wind.  Dryland farming is also another cause of dust storms, since dryland farmers rely on rainfall to water their crops, they engage in practices to maintain moisture in the soil. Such practices include leaving a field fallow for a year after harvesting to allow the buildup of water to build in the soil and covering the field with dry earth in an attempt to seal in the underlying. These practices make dryland agriculture susceptible to dust storms.
  8. 8. PHYSICAL AND ENVIRONMENTAL IMPACTS  Saharan dust storms have increased approximately 10- fold during the half-century since the 1950s, causing topsoil loss in Niger, Chad, northern Nigeria, and Burkina Faso. In Mauritania there were just two dust storms a year in the early 1960s, but there are about 80 a year today, according to Andrew Goudie, a professor of geography at Oxford University. Levels of Saharan dust coming off the east coast of Africa in June (2007) were five times those observed in June 2006, and were the highest observed since at least 1999, which may cool Atlantic waters enough to slightly reduce hurricane activity in late 2007.  Dust storms have also been shown to increase the spread of disease across the globe. Virus spores in the ground are blown into the atmosphere by the storms with the minute particles then acting like urban smog or acid rain.
  9. 9. ECONOMIC IMPACT  Dust storms cause soil loss from the dry lands, and worse, they preferentially remove organic matter and the nutrient-rich lightest particles, thereby reducing agricultural productivity. Also the abrasive effect of the storm damages young crop plants. Other effects that may impact the economy are: reduced visibility affecting aircraft and road transportation; reduced sunlight reaching the surface; increased cloud formation increasing the heat blanket effect; high level dust sometimes obscures the sun over Florida; effects on human health of breathing dust.  Dust can also have beneficial effects where it deposits: Central and South American rain forests get most of their mineral nutrients from the Sahara; iron-poor ocean regions get iron; and dust in Hawaii increases plantain growth. In northern China as well as the mid-western U.S., ancient dust storm deposits known as loess are highly fertile soils, but they are also a significant source of contemporary dust storms when soil- securing vegetation is disturbed.
  10. 10. Gallery Dust plume off the Sahara desert over the northeast Atlantic Ocean. A Dust Bowl storm approaches Stratford, Texas in 1935
  11. 11. Gallery Animation showing the global movement of dust from an Asian dust storm Dust from the Sahara moves into the North Atlantic
  12. 12. Video
  13. 13.  If you want to see this presentation, you can go to:  HTTP: / / www.myspace.com  Source: Internet  Credits: Wikipedia  Martín André Montes Zarria ¡Thanks!

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