Heaps of sand in a desert are called sand dunes.

Sand dunes are a common feature found in deserts all around the world. They are formed by the wind and are made up of heaps of sand that accumulate over time. Sand dunes can vary in shape, size, and formation, depending on various factors such as wind speed, direction, and the availability of sand particles.

Formation of Sand Dunes:
Sand dunes are formed through a process known as aeolian processes, which involve the transportation and deposition of sand grains by wind. The formation of sand dunes requires three essential elements: a source of sand, a strong wind, and a place for the sand to accumulate.

1. Source of Sand: The sand needed to form dunes comes from various sources such as riverbeds, coastal areas, and eroded rocks. These sources provide the necessary sand particles that can be transported by the wind.

2. Wind: Strong winds are crucial for the formation of sand dunes. The wind lifts and carries loose sand particles, transporting them across the desert landscape. As the wind encounters an obstacle, such as a rock or vegetation, it slows down, causing the sand to settle and accumulate.

3. Accumulation: When the wind slows down, it loses its ability to carry the sand particles, resulting in their deposition. This deposition occurs on the windward side of an obstacle, such as a rock or vegetation, forming a mound or heap of sand. Over time, these mounds grow larger and develop into sand dunes.

Characteristics of Sand Dunes:
Sand dunes exhibit various characteristics depending on the prevailing wind patterns and local conditions. Some key features of sand dunes include:

1. Shape: Sand dunes can take on different shapes, such as crescent-shaped (barchans), linear (seif), star-shaped (star), or dome-shaped (dome). The shape of a sand dune is influenced by the wind direction and the availability of sand particles.

2. Size: Sand dunes can vary in size, ranging from a few meters to several hundred meters in height. Some of the largest sand dunes in the world can reach heights of over 200 meters.

3. Movement: Sand dunes are not static structures but can move and change shape over time. This movement is caused by the continuous action of wind, which pushes and reshapes the sand dunes.

4. Vegetation: Sand dunes can support a unique ecosystem of plants and animals that are adapted to the harsh desert environment. Some plants, known as xerophytes, have specialized adaptations to survive in the sandy and arid conditions of sand dunes.

In conclusion, sand dunes are formed by the accumulation of heaps of sand in deserts. They are shaped by wind patterns and can vary in size and shape. Sand dunes are an important feature of desert landscapes and support specialized plant and animal life.

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