Dust Storms and Sandstorms

Factors involved: Geological forces, human activity, plants, rain, weather conditions, wind

Regions affected: Deserts, plains, valleys

Definition

Dust storms and sandstorms are composed of airborne and windblown clouds of soil particles, mineral flakes, and vegetative residue that impact climate, air temperature, air quality, rainfall, desertification, agricultural productivity, human health, and human habitation of the land.

Science

Dust storms result from wind erosion, desertification, and physical deterioration of the soil caused by persistent or temporary lack of rainfall and wind gusts. Dust storms develop when wind velocity at 1 foot above soil level increases beyond 13 miles per hour, causing saltation and surface creep. In saltation, small particles are lifted off the surface, travel 10 to 15 times the height to which they are lifted, then spin downward with sufficient force to dislodge other soil particles and break down earth clods. In surface creep, larger particles creep along the surface in a rolling motion. The larger the affected area, the greater the cumulative effect of saltation and surface creep, leading to an avalanche of soil particles across the land, even during moderate wind gusts. The resulting soil displacement erodes the structure and texture of the remaining soils, reduces the moisture content of the soil, exposes bedrock, and limits the type of vegetation sustainable on the remaining soil.

Dust storms remove smaller and lighter soil particles, leaving behind the larger and denser particles and granular minerals associated with deserts, and erode rock surfaces, creating dust and granular particles. As soils become drier and more dense, and as ground cover is reduced, the number and intensity of subsequent dust storms increases. Arid or semiarid soil eventually becomes desert. Atmospheric dust increases soil and air temperature by trapping heat in the lower atmosphere. Dust may also reduce soil and air temperature by reflecting the sun’s heating radiation back into space. Changes in air temperature, coupled with dust in the atmosphere and drier land surfaces, reduce local rainfall, encouraging desertification.

Dust storms result from the dislodging of small, light soil particles, mineral flecks, and decomposing vegetation matter. Dust storms rise miles into the atmosphere and have both local and global impacts. Sandstorms result from dislodging larger, heavier particles of soil and rock. They tend to occur in conjunction with desert cyclones. Sandstorms remain close to ground level and have primarily local impacts. Dust and sandstorms may occur simultaneously.

There are many types of dust storms. Haze reduces visibility to three-fourths of a mile or less and results from persistent wind gusts across arid soils or across temporarily dry or disturbed semi-arid soils. Dust devils lift silt and clay particles several hundred yards into the air. Tornadoes generate local vortices that lift silt, clay, mineral flecks, and vegetation residue more than a mile high and transport it hundreds of square miles. Cyclones form at the leading edge of thunderstorm cells, extending across a front of several hundred miles, generating winds up to 150 miles per hour, and lifting particles and debris several miles into the upper atmosphere and jet stream for distribution around the globe.

Geography

Dust storms and sandstorms of global significance originate in the arid deserts and semiarid lands covering 36 percent of the earth’s land surface. Major deserts are located in northern Africa, northeast Sudan, southwest Africa, the Arabian Peninsula, southwest Asia, the Middle East, northern and western China, central Australia, southwest North America, parts of southern and western South America, the Caucasus of Russia, central Spain, and the southern coast of the Mediterranean Sea. In addition, dust storms arise when normally semiarid lands periodically become arid, undergo abnormally strong windy periods, or have their vegetation removed by humans or nature. These areas include sub-Saharan Africa, the U.S. Midwest, the northern coast of the Mediterranean, the steppe of central Asia, and all lands immediately adjacent to deserts.

Globally significant storms cover areas of several hundred to several thousand square miles and transport dust from one continent to another. Locally significant dust storms originate in overly cultivated agricultural fields, residential or commercial developments denuded of ground cover, major road construction sites, and any lands experiencing a temporary drought. Local storms are often confined to only a few square miles in area.

Locales with the highest frequency of dust storms are Mexico City and Kazakhstan in central Asia, with about 60 storms per year; western and northern China, with 30 storms each year; West Africa, with 20 storms; and Egypt, with 10 storms. Storms of the longest known duration occurred in the southwestern United States, with a storm of twenty-eight days in Amarillo, Texas, in April, 1935, and a storm of twenty-two days in the Texas Panhandle in March of 1936.

Prevention and Preparations

The number and intensity of dust storms and sandstorms are reduced through soil conservation practices, such as covering the soil with vegetation, reducing soil exposure on tilled land, creating wind barriers, installing buffer strips around exposed soils, and limiting the number and intensity of soil disturbing activities on vulnerable arid and semiarid soils. Vegetative cover slows the wind at ground level, protects soil particles from detachment, and traps blowing or floating soil particles, chemicals, and nutrients. Because the greatest wind erosion damage often occurs during seasons when no crops are growing or when natural vegetation is dormant, dead residues and standing stubble of the previous crop often remain in place until the next planting season. Planting grass or legume cover crops until the next planting season, or as part of a crop rotation cycle or no-till planting system, also reduces dust.

No-till and mulch-till planting systems reduce soil exposure to wind erosion. No-till systems leave the soil cover undisturbed before inserting crop seeds into the ground through a narrow slot in the soil. Mulch-till planting keeps a high percentage of the dead residues of previous crops on the surface when the new crop is planted. Row crops are planted at right angles to the prevailing winds to absorb wind energy and trap moving soil particles. Crops are planted in small fields to prevent avalanching caused by an increase in the amount of soil in particles transported by wind as the distance across bare soil increases.

Because wind breaks slow wind speeds at the surface of the soil, good wind barriers include tree plantings, cross-wind strips of perennial shrubs, and high grasses. The protected area is ten times the height of the barrier. Alley cropping is used in areas of sustained high wind; crops are planted between rows of larger, mature trees.

Strip farming reduces field width, thereby reducing wind erosion. Large fields are subdivided into narrow cultivated strips. Planting crops along the contour lines around hills is called contour strip cropping. Planting crops in strips across the top of predominant slopes is called field stripping. Crops are arranged so that a strip of hay or sod, such as grass, clover, alfalfa, or a close-growing small grain, such as wheat or oats, is alternated with a strip of cultivated row crop, such as tobacco, cotton, or corn. In areas of high wind, the greater the average wind velocity, the narrower the strips. Blown dust from the row-crop strip is trapped as it passes through the subsequent strip of hay or grain, thereby reducing dust. Contour strip cropping or field stripping can reduce soil erosion by 65 to 75 percent.

Limiting land-disturbing activities by humans on highly vulnerable arid and semiarid soils reduces the number and intensity of both dust storms and sandstorms. Deserts are especially vulnerable to impacts of animal herds and motor-vehicle traffic. Many fragile desert plants, shrubs, and trees are easily destroyed by animal or human activity, especially foraging and vehicle traffic. The surface of the desert consists of a thin layer of small and microscopic plants, microorganisms, and insects, whose combined activities produce a thin crust that limits the impact of wind on the surface of the desert. When this crust is broken by surface traffic, the underlying sands and minerals are vulnerable to wind erosion. Natural repair to the broken crust and natural revegetation processes may take decades or centuries.

Rescue and Relief Efforts

Little can be done to protect humans, buildings, or crops from the impact of dry wind tornadoes or cyclones producing major dust storms or sandstorms, but soil conservation measures reduce the number and intensity of these storms. The effects of these storms on humans is partly ameliorated by remaining indoors, by wearing heavy clothing or remaining inside vehicles when outdoors, and by covering the nose and mouth to prevent the ingestion of dust, spores, and pollens.

Impact

Sandstorms and dust storms have moved sufficient soil particles over the centuries to reshape continents; alter the distribution of plant and animal life; alternately heat and cool the earth; and silt rivers, lakes, and oceans. The volume of annual wind-blown dust is approximately equal to the volume of soil transported each year through water erosion. Approximately half a billion tons of dust is borne aloft each year, with more than half that dust deposited in the world’s oceans.

The desertification processes associated with sandstorms and dust storms impacted the historic rise and fall of many civilizations, including the early Pueblo Indians of the American Southwest, the Harappan civilization of southwest Asia, the city-states of Arabia, and the caravan empires of sub-Saharan Africa. Dust storms on agricultural lands cause soil nutrient loss, reduce the moisture-retaining capacity of the soil, and concentrate salts and fertilizer acids in the soil, thereby reducing agricultural production. Efforts to replace lost topsoil with fertilizers have proven futile. Crop yields are reduced by up to 80 percent.

Sandstorms kill people and animals and damage, destroy, or bury roads, buildings, machinery, and agricultural fields. Many people and animals are killed each year by the force of the storms or by ingestion of wind-borne particles. In 1895, more than 20 percent of the cattle in eastern Colorado died of suffocation in a particularly intense dust storm.

Dust storms are a major source of air pollution and a major distribution vehicle for mold spores, pollens, and other harmful airborne particles. One pathogen causing “valley fever” or “desert rheumatism” kills approximately 120 people each year in the United States alone. Sandstorms and intense dust storms contribute to traffic accidents and disrupt mass-transportation systems. In many southwestern American states, dust storms are responsible for up to 20 percent of all traffic accident fatalities.

On May 2 and 3, 2018, dust storms and lightning strikes in India left more than 125 people dead and more than 200 injured. The storms destroyed homes and businesses, downed trees and electrical lines, and killed livestock. The northern states of Uttar Pradesh, Rajasthan, and Punjab were particularly hard hit by the storms.

Bibliography

Bever, Lindsey. “‘It Was a Nightmare’: Killer Dust Storm Blasts India, Leaving at Least 125 Dead.” The Washington Post, 3 May 2018, www.washingtonpost.com/news/capital-weather-gang/wp/2018/05/03/india-dust-storm-uttar-pradesh-rajasthan-officials-say-at-least-100-dead/. Accessed 31 Jan. 2019.

Morales, Christer, ed. Saharan Dust: Mobilization, Transport, Deposition. Chichester, England: John Wiley & Sons, 1979. The editor presents numerous scientific papers and recommendations from a workshop held in Sweden sponsored by the Scientific Committee on Problems in the Environment.

Pewe, Troy L., ed. Desert Dust: Origin, Characteristics, and Effect on Man. Boulder, Colo.: Geological Society of America, 1981. This collection of scientific papers provides detail on the causes and effects of sandstorms and dust storms.

Stallings, Frank L. Black Sunday: The Great Dust Storm of April 14, 1935. Austin, Tex.: Eakin Press, 2001. A collection of newspaper reports and the eyewitness accounts of more than 100 people about this devastating dust storm.

Sundar, Christopher A., Donna V. Vulcan, and Ronald M. Welch. Radiative Effects of Aerosols Generated from Biomass Burning, Dust Storms, and Forest Fires. Washington, D.C.: National Aeronautics and Space Administration, 1996. This book discusses global heating and cooling from dust storms.

Tannehill, Ivan R. Drought: Its Causes and Effects. Princeton, N.J.: Princeton University Press, 1947. Discusses the effects of drought on dust storms.

U.S. Department of Agriculture. Crop Residue Management to Reduce Erosion and Improve Soil Quality. Conservation Research Reports 37-39. Washington, D.C.: Author, 1994-1995.

‗‗‗‗‗‗‗. Soil Erosion by Wind. Agriculture Information Bulletin Number 555. Washington, D.C.: Author, 1989. These public information booklets, as well as a variety of Conservation Practice Job Sheets, describe appropriate soil conservation measures to limit dust storms.

Worster, Donald. Dust Bowl: The Southern Plains in the 1930’s. 25th anniversary ed. New York: Oxford University Press, 2004. Describes the dust storms of the southwestern United States.