The Origin of Deserts

By Waheed Ali Laghari

The Earth's environment is over 3 billion years old, and its atmosphere is shaped by various natural processes. The movement of air, influenced by temperature and pressure, plays a significant role in determining the Earth's weather patterns. In the field of geography, Desert Morphology focuses on the study of deserts' formation and their characteristics. Experts in this field are known as Desert Morphologists.

According to Desert Morphology, a desert is defined as an area receiving less than 10 inches of annual rainfall. The creation of deserts can be attributed to several factors:

1. Hot and Dry Climates

Deserts typically form in areas with extremely low rainfall and dry climates.

2. Mountain Barriers

Large mountain ranges often prevent rain clouds from passing, leading to the formation of deserts on the opposite side of the range, such as the Andes, which created the Atacama Desert.

3. Air Movement

In many deserts, air movement is minimal. Winds usually move from west to east, and as the wind loses its moisture while traveling, western areas often turn into deserts. An example is the Thar Desert, located in western India.

4. Erosion and Weathering

Wind, water, and ice contribute to shaping deserts by gradually breaking down rocks and soil, forming the distinctive desert landscapes.

5. Tectonic Plate Movement

The Earth's surface consists of plates that are constantly moving, altering the landscape. This movement can cause seas to recede, creating new deserts.

Types of Deserts

Desert experts classify deserts into different types, including:

• Hot Deserts: Characterized by extremely high temperatures, such as the Sahara.
• Cold Deserts: These have very low nighttime temperatures, like the Gobi and the Mungo Deserts.

Sand Dunes (Bhitt)

Deserts are often covered in sand dunes, locally known as Bhitt. There are four main types of dunes:

1. Transverse Dunes

These are small in size, with large particles and low wind speeds. The surface often has hollows that align with the wind direction, with an average height of a few hundred meters. Found in Sindh’s Thar Desert.

2. Longitudinal Dunes

Formed due to high wind speeds, these dunes run parallel to the wind direction and can reach heights of up to 100 meters. Also found in Tharparkar, Sindh.

3. Barchan Dunes

Known as crescent-shaped dunes, they resemble the crescent moon. The side facing the wind is more elevated, while the opposite side slopes downward. These dunes are common in Asia and Africa.

4. Complex Dunes

These are formed when various types of dunes combine. They have no specific shape and result from the interaction of wind and sand particles.

The formation of dunes depends on factors such as particle size, wind speed, wind direction, and the height of the land. Wind carries and deposits sand particles in deserts, rivers, and seas, contributing to the ever-changing desert landscape.