Mushroom rocks
From Wikipedia, the free encyclopedia
Mushroom rocks, also called Rock pedestals, are one of the most striking manifestations of the processes of erosion and weathering. Usually found in desert areas, they are formed over thousands of years when erosion of an isolated rocky outcrop progresses at a different rate at its bottom to that at its top. Abrasion by wind-borne grains of sand is most prevalent within the first three feet of the ground, causing the bases of outcrops to erode more rapidly than their tops. Running water can have the same effect. Occasionally the chemical composition of the rocks can be an important factor; if the upper part of the rock is more resistant to erosion and weathering, it will erode more slowly than the base. Its formation has also been attributed to chemical weathering at the base of the rock due to the collection of dew near the surface.
