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. DUST STORM
Particles are
transported by saltation
and suspension,
causing soil erosion
from one place and
deposition in another.
4. SANDSTORM
The term sandstorm is used most often
in the context of desert sandstorms,
especially in the Sahara.
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. 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. 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. 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. 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. Gallery
Dust plume off the Sahara desert
over the northeast Atlantic Ocean.
A Dust Bowl storm approaches
Stratford, Texas in 1935
11. Gallery
Animation showing the global movement
of dust from an Asian dust storm
Dust from the Sahara moves into the
North Atlantic
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!
