The term “Great Escarpment” describes a major geological feature: a distinct boundary separating elevated inland plateaus from lower coastal plains. An escarpment is a specific type of landform, not merely a mountain range, created by immense geological processes. These features significantly shape a continent’s geography, climate, and biological diversity. While several global features bear this name, the Great Escarpment of Southern Africa is the most prominent example, defining the topography of an entire subcontinent.
Defining a Great Escarpment
An escarpment is a steep slope or cliff face separating two areas of differing elevation. Geologically, it is defined by its asymmetry, featuring a steep front (the scarp face) and a more gradual slope in the opposite direction. Escarpments primarily form through two mechanisms: differential erosion of rock layers or tectonic movement along a geologic fault. Differential erosion occurs when softer rock layers beneath a resistant caprock are worn away more quickly, causing the overlying rock to collapse and retreat. This process distinguishes an escarpment from a simple fault scarp, which is a cliff created by the vertical displacement of the Earth’s crust. Escarpments represent a retreating edge of a plateau, constantly reshaped by weathering and erosion.
Global Geography and Localization
Features called a “Great Escarpment” exist on several continents, including the eastern coast of Australia and parts of the Brazilian Highlands. However, the term is most frequently associated with the structure that encircles the central plateau of Southern Africa. This continuous feature spans thousands of kilometers, stretching from Angola in the northwest, across South Africa, and up to Mozambique. Its height varies, but the most dramatic section is the Drakensberg, which forms the border between Lesotho and KwaZulu-Natal. Here, the escarpment rises to its greatest elevation, with peaks soaring over 3,000 meters, separating the high interior from the narrow coastal strip.
Formation and Structure of the South African Escarpment
The formation of the Southern African Great Escarpment is linked to the breakup of the supercontinent Gondwana, which began approximately 180 million years ago. As the continental crust bulged due to a mantle plume, rift valleys formed along what would become the coastline. These rifts separated the landmass of Southern Africa from other fragments of Gondwana, forming the initial, steep walls of the continental edge. Following the rifting, the continental plateau experienced passive margin uplift, maintaining its high elevation relative to the newly formed ocean basins.
Since its formation, the escarpment has been subject to erosion, causing its steep face to slowly retreat inland, approximately 150 kilometers from the original fault lines. This erosion created the present structure, with the steep slope facing the high plateau. The structure is characterized by the rock layers of the Karoo Supergroup, a vast sequence of sedimentary rocks. In the Drakensberg, the escarpment is capped by hard, erosion-resistant basaltic lavas, known as the Drakensberg Group. These lavas overlie softer sandstones and shales, and the differential resistance of these rock types maintains the stark, clifflike appearance of the scarp face as it retreats.
Climatic and Environmental Impact
The Great Escarpment influences the climate and hydrology of Southern Africa, acting as a major weather barrier. The structure forces moist air masses moving inland from the Indian Ocean to rise abruptly, a phenomenon known as the orographic effect. This rising and cooling air sheds its moisture as rain and snow on the seaward side and the upper slopes of the escarpment. The result is a sharp climatic divide, with the coastal plain and eastern slopes being relatively wet and supporting diverse ecosystems.
Conversely, the air that descends onto the interior plateau, having lost much of its moisture, is drier. This creates the arid and semi-arid conditions characteristic of the central plateau, including the Great Karoo region. The escarpment also functions as a continental watershed divide, determining the flow of major river systems. Rivers originating on the interior plateau and flowing toward the coast have cut deep gorges into the escarpment’s face, shaping the regional landscape and water availability.