6.14.2. Playas

Plains are by far the most prominent landforms in the deserts. In basins with mountains and hills around and along, the drainage is towards the centre of the basin and due to gradual deposition of sediment from basin margins, a nearly level plain forms at the centre of the basin.

In desert environments, the most widespread landforms are plains known as playas. These playas form in basins that are surrounded by mountains and hills. The water from rainfall or melting snow drains into these central basins. Over time, sediment from the surrounding areas is deposited, creating a flat landscape that can collect water.

Think of a bowl. When it rains, water collects at the bottom of the bowl, and if the sides are steep, the water cannot escape quickly. Similarly, playas are like the bottom of that bowl where water gathers temporarily.

In times of sufficient water, this plain is covered up by a shallow water body. Such types of shallow lakes are called as playas where water is retained only for short duration due to evaporation and quite often the playas contain good deposition of salts. The playa plain covered up by salts is called alkali flats.

When there is enough rain or melting snow, the flat area of the playa can become a shallow lake. However, because deserts are hot and dry, this water does not last long and evaporates quickly. As the water evaporates, it leaves behind salts and minerals, which accumulate on the surface. When playas have a significant salt layer, they are specifically referred to as alkali flats.

Consider what happens when you spill saltwater on a countertop. As the water evaporates, you can see white salt left behind. Playas work the same way; they are the desert's way of showing how water can gather only to disappear, leaving behind minerals.

Weathered mantle from over the rocks or bare soil, gets blown out by persistent movement of wind currents in one direction. This process may create shallow depressions called deflation hollows. Deflation also creates numerous small pits or cavities over rock surfaces.

Deflation is the process where strong winds remove loose soil and rock material, leading to the formation of shallow depressions, known as deflation hollows. Over time, these hollows can develop into small pits or caves as wind continues to erode and wear down the rocks.

Imagine how a vacuum cleaner pulls up dirt from your carpet, creating empty spots where the dirt used to be. In the desert, strong winds act like a vacuum, removing loose material and leaving behind hollows where the soil used to be.

Many rock-outcrops in the deserts easily susceptible to wind deflation and abrasion are worn out quickly, leaving some remnants of resistant rocks polished beautifully in the shape of mushroom with a slender stalk and a broad and rounded pear-shaped cap above.

In deserts, certain types of rocks are more resistant to wind erosion than others. Over time, as softer surrounding material erodes away, the remaining rock can take on unique shapes, like mushrooms or tables. Mushroom rocks have a narrow base with a wider top, while table rocks are flat on top and can appear as broad plates above the eroded landscape.

Think of a sandcastle that you built at the beach. As waves wash against it, the parts that are sticking out first are worn away faster, while the middle part that remains sturdy takes on a unique shape. Mushroom rocks are like those sturdy parts of a sandcastle that withstand the erosional forces.

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