An ancient seabed in the Sahara
The rock that forms these surreal sculptures is not stone, but chalk. This entire region of Egypt's Western Desert was once the floor of the Tethys Sea. During the Late Cretaceous period, 70 to 100 million years ago, the skeletons of countless marine microorganisms accumulated on the seabed. This sediment, composed primarily of calcium carbonate (CaCO3), compacted over millions of years to form the massive chalk and limestone layers of the Khoman Formation.
Around 30 million years ago, tectonic forces lifted this ancient seabed, causing the sea to retreat and exposing the soft chalk to the elements. The Farafra Depression, where the park is located, formed as the exposed plateau collapsed, revealing the thick sedimentary layers. Today, the chalk formations are direct evidence of the area's deep aquatic past. Embedded within the layers are numerous fossils of ammonites, sea urchins, and even the teeth of prehistoric sharks, confirming the region's marine origins.
The mechanics of wind abrasion
The mushroom shapes are the product of millions of years of wind erosion, a process known as aeolian abrasion. These formations are a specific type of wind-sculpted rock feature called a yardang. The desert winds carry sand grains, which bounce along the ground in a process called saltation. This sandblasting effect is most intense within a meter of the desert floor.
The bases of the chalk formations, being softer and more exposed to this low-lying sandblasting, erode more quickly than the tops. Scientists estimate the current erosion rate under present climatic conditions is about 1 millimeter per year. The "caps" of the mushrooms are often composed of a harder, more resistant layer of limestone or have a protective crust, which slows their erosion. This difference in erosion rates—fast at the bottom, slow at the top—carves the narrow stems and wide caps characteristic of the mushroom rocks. The tallest of these formations can reach heights of 3 to 4.5 meters. The prevailing northerly winds also align the yardangs into long, streamlined ridges that follow the wind's direction.