Dust Storm

From the mighty sandstorms which are the regular weather of such desert regions as the Sahara and the Arabian peninsula, to the dust clouds raised from parched cropland in the temperature zones, dust storms are a regular feature of the Earth's weather. They have appeared in countless movies about the arid regions, generally as a deadly menace, and they play a considerable role in shaping the landscape conditions of the world's surface. They can also affect human life in many ways.

Some areas of the planet witness dust storms annually, even when they are not true desert. A thunderstorm in the dry steppes of Kazakhstan, for example, can send opaque rivers of airborne dust streaming along just a few inches above the ground, with finer clouds of dust filling the air to a height of four or five stories above that, while the local pigeons rise in clouds and remain airborne, circling above the dust until the worst has passed. Other places only undergo dust storms when extraordinary droughts occur -- such as the "black rollers" of the infamous United States Dust Bowl in the 1930s.

Dust storms can range in size from a relatively modest cloud that only rises a few dozen feet into the air, to massive walls of airborne particles that can loom two miles into the sky and cover thousands of square miles. The size and vigor of a dust storm depends on how it is created, where it is happening, and what the general weather conditions over that area of the Earth's surface.

Where dust storms occur

Dust storms can only occur when the ground's surface is dry and there are loose particles available for the wind to pick up. If the ground has been wet by recent rain, or if there is a dense covering of moist vegetation, then a dust storm cannot be created in that area, although it could possibly blow in from elsewhere. Arid regions like deserts are the most prone to dust storms -- indeed, in these areas, dust storms and sandstorms are the main type of weather other than clear and sunny.

Semi-arid regions like some parts of the American southwest, sections of Russia, Mongolia, Africa, and the Middle East have other kinds of weather besides dust storms, but can still experience them as part of the normal weather cycle. These areas may have hot, dry summers -- not dry enough to produce desert conditions, but not moist enough to securely anchor the dust at the surface, so that a strong wind or a thunderstorm can lift this dust in clouds and drive it across the landscape.

Any area that is subject to a prolonged drought can also experience dust storms, even when they are not a normal feature of the local climate. The Dust Bowl, cited above, is an example of a huge drought in normally relatively temperate regions, which parched the central part of the American continent in the early half of the 20th century and turned the topsoil into loose, powdery dust. This dust was easily swept up by the strong winds of the Plains and became enormous dust storms, vividly but starkly depicted as dark, churning walls of opaque dust in the black and white photographs of the time. The areas where these dust storms occurred generally do not experience such weather, but the parching effects of the drought made dust storms possible there anyway.

Dust storms can therefore occur anywhere that dry, loose soil or dust is available and a strong enough wind blows over this surface. They can travel for hundreds or potentially thousands of miles if they are strong enough and there are no obstacles. Dust from Saharan storms sometimes reaches Florida, for example, and Asian dust storms have raised dust that has traveled around the globe.

How dust storms form

Besides dust, a dust storm needs strong winds to form. Dry cold fronts -- cold fronts which move through an area where the air is too lacking in moisture to form rain clouds, or clouds at all -- are a very common source of these winds. Desert sandstorms may result from the conditions of the desert itself. Because the ground is heated intensely by the sun in these cloudless regions, massive convection occurs, and this results in strong flows of wind that can create a powerful sandstorm covering a very large region and lasting a long time.

The dust itself helps to form the dust storm, as the wind causes it to saltate or "leap" across the ground before becoming airborne. This saltation raises more dust with each impact, so the kinetic impact of the windblown dust is added to the lifting effect of the wind, multiplying the results. If an area has been stripped of vegetation by overgrazing or poorly managed farming, the ground will be prone to generating dust storms as well.

The effects of dust storms

The effects of dust storms are varied and depend on how large and how long-lasting they are. A brief, temperate-region dust storm caused by a short-lived drought in an ordinarily moist region will have few effects beyond making driving conditions temporarily hazardous and dirtying the houses of those who are unfortunate enough to be in its path.

Larger dust storms have much more impact on both the landscape and humanity, however. A large-scale dust storm in a non-arid region can strip considerable amounts of fertile topsoil away, reducing the agricultural potential of the land. If the drought is persistent and dry cold front produce a long series of dust storms, as in the Dust Bowl, the landscape can become permanently less fertile thanks to the loss of topsoil. These dust storms also impact the health of people who undergo them and cause.

On the other hand, dust storms can also improve the agricultural value of a region if they deposit dust there rather than taking it away. The rich topsoil blown off some areas must end up somewhere, and although a lot of it is blown into the ocean, much is also dropped in regions where the dust storms finally blow themselves out. One region's loss may be another's gain when it comes to dust storm transportation of topsoil.

Sandstorms and dust storms from the desert regions have several different effects. The fine particles of a dust storm, when breathed many times over a human lifespan, can lessen that lifespan by a noticeable amount. If the dust blows over the ocean, it can have a slight but measurable cooling effect on the waters and thus make the hurricane season weaker than ordinary.

One barely-explored aspect of dust storms is the ability of dust to carry harmful bacteria and viruses over a huge distance. The smallest particles can travel the farthest, since they are the lightest, and it is these which have been shown to be frequent carriers of meningococcal meningitis, pneumonia, and bacteremia. Nobody has yet made a direct link between dust and disease outbreaks, but the disease organisms are present in the dust, and may well be spread from one place to another on the wings of a persistent dust storm.