Desert terrain, demanding and difficult to traverse, often provides very few landmarks. Furthermore, with cover and concealment highly limited, the threat of exposure to the enemy is constant. Most arid areas have several types of terrain.
4-1. The five basic desert types are
- Mountainous (high altitude).
- Rocky plateaus.
- Sand dunes.
- Salt marshes.
- Broken, dissected terrain (gebels or wadis).
4-2. Scattered ranges or areas of barren hills or mountains separated by dry, flat basins characterize mountainous deserts. High ground may rise gradually or abruptly from flat areas to several thousand meters above sea level. Most of the infrequent rainfall occurs on high ground and runs off rapidly in the form of flash floods. These floodwaters erode deep gullies and ravines, and deposit sand and gravel around the edges of the basins. Water rapidly evaporates, leaving the land as barren as before, although there may be short-lived vegetation. If enough water enters the basin to compensate for the rate of evaporation, shallow lakes may develop, such as the Great Salt Lake in Utah or the Dead Sea. Most of these lakes have a high salt content.
ROCKY PLATEAU DESERTS
4-3. Rocky plateau deserts have relatively slight relief interspersed with extensive flat areas with quantities of solid or broken rock at or near the surface. There may be steep-walled, eroded valleys, known as wadis in the Middle East and arroyos or canyons in the US and Mexico. Although their flat bottoms may be superficially attractive as assembly areas, the narrower valleys can be extremely dangerous to men and material due to flash flooding after rains. The Golan Heights is an example rocky plateau desert.
4-4. Sand dune deserts are extensive flat areas covered with sand or gravel. “Flat” is a relative term, as some areas may contain sand dunes that are over 1,000 feet (300 meters) high and 10 to 15 miles (16 to 24 kilometers) long. Traffic ability in such terrain will depend on the windward or leeward slope of the dunes and the texture of the sand. However, other areas may be flat for 10,000 feet (3,000 meters) and more. Plant life may vary from none to scrub over 7 feet (2 meters) high. Examples of this type of desert include the edges of the Sahara, the empty quarter of the Arabian Desert, areas of California and New Mexico, and the Kalahari in South Africa.
4-5. Salt marshes are flat, desolate areas sometimes studded with clumps of grass, but devoid of other vegetation. They occur in arid areas where rainwater has collected, evaporated, and left large deposits of alkali salts and water with a high salt concentration. The water is so salty it is undrinkable. A crust that may be 1 to 12 inches (2.5 to 30 centimeters) thick forms over the saltwater. Arid areas may contain salt marshes as many as hundreds of kilometers square. These areas usually support many insects, most of which bite. Avoid salt marshes, as this type of terrain is highly corrosive to boots, clothing, and skin. A good example salt marsh is the Shatt al Arab waterway along the Iran-Iraq border.
BROKEN AND DISSECTED TERRAIN
4-6. All arid areas contain broken or highly dissected terrain. Rainstorms that erode soft sand and carve out canyons form this terrain. A wadi may range from 10 feet (3 meters) wide and 7 feet (2 meters) deep to several hundred meters wide and deep. The direction a wadi takes varies as much as its width and depth. It twists and turns in a maze-like pattern. A wadi will give you good cover and concealment, but be cautious when deciding to try to move through it, because it is very difficult terrain to negotiate.
4-7. Surviving in an arid area depends on what you know and how prepared you are for the environmental conditions.
4-8. In a desert area, you must consider–
- Low rainfall.
- Intense sunlight and heat.
- Wide temperature range.
- Sparse vegetation.
- High mineral content near ground surface.
4-9. Low rainfall is the most obvious environmental factor in an arid area. Some desert areas receive less than 4 inches (10 centimeters) of rain annually. When they do, it comes as brief torrents that quickly run off the ground surface.
Intense Sunlight And Heat
4-10. Intense sunlight and heat are present in all arid areas. Air temperature can rise as high as 140º F (60º C) during the day. Heat gain results from direct sunlight, hot blowing sand-laden winds, reflective heat (the sun’s rays bouncing off the sand), and conductive heat from direct contact with the desert sand and rock. The temperature of desert sand and rock typically range from 30 to 40º F (16 to 22º C) more than that of the air. For example, when the air temperature is 110º F (43º C), the sand temperature may be 140º F (60º C). Intense sunlight and heat increase the body’s need for water. Radios and sensitive equipment items exposed to direct intense sunlight can malfunction.
Wide Temperature Range
4-11. Temperatures in arid areas may get as high as 130º F (55º C) during the day, and as low as 50º F (10º C) at night. The drop in temperature at night occurs rapidly and will chill a person who lacks warm clothing and is unable to move about. The cool evenings and nights are the best times to work or travel.
4-12. Vegetation is sparse in arid areas; therefore, you will have trouble finding shelter and camouflaging your movements. During daylight hours, large areas of terrain are easily visible. If traveling in hostile territory, follow the principles of desert camouflage:
- Hide or seek shelter in dry washes (wadis) with thick vegetation and cover from oblique observation.
- Use the shadows cast from brush, rocks, or outcroppings. The temperature in shaded areas will be 52 to 63º F (11 to 17º C) cooler than the air temperature.
- Cover objects that will reflect the light from the sun.
4-13. Before moving, survey the area for sites that provide cover and concealment. Keep in mind that it will be difficult to estimate distance. The emptiness of desert terrain causes most people to underestimate distance by a factor of three: what appears to be 1/2 mile (1 kilometer) away is really 1.75 miles (3 kilometers) away.
4-14. Sandstorms (sand-laden winds) occur frequently in most deserts. The Seistan desert wind in Iran and Afghanistan blows constantly for up to 120 days. In Saudi Arabia, winds can reach 77 mph (128 kph) in early afternoon. Major sandstorms and dust storms occur at least once a week. The greatest danger is getting lost in a swirling wall of sand. Wear goggles and cover your mouth and nose with cloth. If natural shelter is unavailable, mark your direction of travel, lie down, and wait out the storm. Dust and wind-blown sand interfere with radio transmissions. Therefore, plan to use other means of signaling such as pyrotechnics, signal mirrors, or marker panels, whichever you have.
4-15. Mirages are optical phenomena caused by the refraction of light through heated air rising from a sandy or stony surface. Mirages occur in the desert’s interior about 6 miles (10 kilometers) from the coast. They make objects that are 1 mile (1.5 kilometers) or more away appear to move. This mirage effect makes it difficult for you to identify an object from a distance. It also blurs distant range contours so much that you feel surrounded by a sheet of water from which elevations stand out as “islands.” The mirage effect makes it hard for a person to identify targets, estimate range, and see objects clearly. However, if you can get to high ground 10 feet [3 meters] or more above the desert floor), you can get above the superheated air close to the ground and overcome the mirage effect. Mirages make land navigation difficult, because they obscure natural features. You can survey the area at dawn, dusk, or by moonlight when there is little likelihood of mirage. Light levels in desert areas are more intense than in other geographic areas. Moonlit nights are usually clear, with excellent visibility, because daytime winds die down and haze and glare disappear. You can see lights, red flashlights, and blackout lights at great distances. Sound carries very far as well. Conversely, during nights with little moonlight, visibility is extremely poor. Traveling is extremely hazardous. You must avoid getting lost, falling into ravines, or stumbling into enemy positions. Movement during such a night is practical only if you have a means to determine direction and have spent the day resting; observing and memorizing the terrain; and selecting your route.
NEED FOR WATER
4-16. Since the early days of World War II, when the US Army was preparing to fight in North Africa, the subject of Soldier and water in the desert has generated considerable interest and confusion. At one time, the US Army thought it could condition men to do with less water by progressively reducing their water supplies during training. This practice of water discipline has caused hundreds of heat casualties. A key factor in desert survival is understanding the relationship between physical activity, air temperature, and water consumption. The body requires a certain amount of water for a certain level of activity at a certain temperature. For example, a person performing hard work in the sun at 109º F (43º C) requires 19 liters (5 gallons) of water daily. Lack of the required amount of water causes a rapid decline in an individual’s ability to make decisions and to perform tasks efficiently. Your body’s normal temperature is 98.6º F (36.9º C). Your body gets rid of excess heat (cools off) by sweating. The warmer your body becomes-whether caused by work, exercises, or air temperature-the more you sweat. The more you sweat the more moisture you lose. Sweating is the principal cause of water loss. If you stop sweating during periods of high-air temperature, heavy work, or exercise, you will quickly develop heat stroke and require immediate medical attention. Understanding how the air temperature and your physical activity affect your water requirements allows you to take measures to get the most from your water supply. These measures are–
- Find shade and get out of the sun!
- Place something between you and the hot ground.
- Limit your movements!
- Conserve your sweat. Wear your complete uniform to include T-shirt. Roll the sleeves down, cover your head, and protect your neck with a scarf or similar item. These steps will protect your body from hot-blowing winds and the direct rays of the sun. Your clothing will absorb your sweat, keeping it against your skin so that you gain its full cooling effect.
4-17. Thirst is not a reliable guide for your need for water. A person who uses thirst as a guide will drink only two thirds of his daily water requirement. Drinking water at regular intervals helps your body remain cool and decreases sweating. Even when your water supply is low, sipping water constantly will keep your body cooler and reduce water loss through sweating. Conserve your fluids by reducing activity during the heat of day if possible. To prevent this voluntary dehydration, use the following guide:
- Below 100º F (38º C), drink 0.5 liter of water every hour.
- Above 100º F (38º C), drink 1 liter of water every hour.
4-18. Several hazards are unique to the desert environment. These include insects, snakes, thorny plants and cacti, contaminated water, sunburn, eye irritation, and climatic stress. Insects of almost every type abound in the desert. Man, as a source of water and food, attracts lice, mites, wasps, and flies. Insects are extremely unpleasant and may carry diseases. Old buildings, ruins, and caves are favorite habitats of spiders, scorpions, centipedes, lice, and mites. These areas provide protection from the elements and attract other wildlife. Therefore, take extra care when staying in these areas. Wear gloves at all times in the desert. Do not place your hands anywhere without first looking to see what is there. Visually inspect an area before sitting or lying down. When you get up, shake out and inspect your boots and clothing. All desert areas have snakes. They inhabit ruins, native villages, garbage dumps, caves, and natural rock outcroppings that offer shade. Never go barefoot or walk through these areas without carefully inspecting them for snakes. Pay attention to where you place your feet and hands. Most snakebites result from stepping on or handling snakes. Avoid them. Once you see a snake, give it a wide berth.