Table Mountain, towering over Cape Town, South Africa, is a world-renowned landmark and a designated UNESCO World Heritage Site. This iconic, flat-topped mountain is recognized globally for its dramatic silhouette. Its distinctive form is a direct result of geological processes spanning hundreds of millions of years, involving deep-sea deposition, continental collisions, and relentless erosion. Understanding its structure requires tracing the formation of the ancient rock layers that make up its foundation.
The Deep Time Foundation of Rock Layers
The mountain’s structure rests on a base of two older rock formations. The oldest layer is the Malmesbury Group, a dark grey metamorphic rock composed of ancient mudstones and sandstones, formed roughly 540 million years ago from sediments deposited on a seafloor. Magma then intruded into this layer, cooling slowly beneath the surface to form the Cape Granite, an extremely hard, coarse-grained igneous rock of a similar age.
These foundational rocks were subjected to millions of years of erosion, creating a flat plain where new sediments began to accumulate. Between approximately 520 and 400 million years ago, this area became a vast inland sea, depositing thick layers of sand and silt. This material compressed and cemented into the Table Mountain Group, a sequence of sedimentary rocks up to 7,000 meters thick.
The bulk of the mountain, including the sheer cliff faces and the flat summit, is composed of the Peninsula Formation, a highly resistant, quartzitic sandstone layer within the Table Mountain Group. This durable rock, formed from ancient sea and river sediments, sits atop the softer, reddish-brown sandstones of the underlying Graafwater Formation. The difference in hardness between these stacked layers proved instrumental in shaping the mountain’s final form.
The Massive Uplift of the Cape Fold Belt
The horizontal layers of sediment were disturbed by a powerful tectonic event. Beginning around 280 million years ago, the landmass that would become South Africa was part of the Gondwana supercontinent. Intense pressure from a continental collision, specifically the Falkland Plateau moving into the African Plate, initiated the Gondwana Orogeny.
This compressional force crumpled the sedimentary layers, lifting them and forming the extensive Cape Fold Belt mountain chain, which stretches for over a thousand kilometers across the Western and Southern Cape. Table Mountain is a remnant of this folding event, pushed up as the entire region was elevated. While other parts of the fold belt experienced intense folding, the rock layers forming Table Mountain were uplifted as a less severely deformed block.
The mountain represents a broad syncline, a downward-facing fold in the rock layers. Counterintuitively, the flat top of Table Mountain was once the bottom of a synclinal valley, preserving the harder sandstone. The surrounding anticlinal ridges (the upward folds) were subsequently eroded away. This tectonic tilting explains why the sandstone layers across the mountain are not perfectly horizontal but dip slightly towards the south, a consequence of the continental collision.
Shaping the Mountain Through Differential Erosion
The final stage of the mountain’s formation was sculpted by millions of years of weathering and erosion. The distinctive flat top and steep sides are a textbook example of differential erosion, where rocks erode at different rates. The hard, pure quartzitic Table Mountain Sandstone, which forms the upper 600 meters, proved highly resistant to the forces of nature.
In contrast, the underlying Malmesbury Group and the softer layers of the Graafwater Formation eroded more quickly. As wind, rain, and ice wore away the softer material from the sides and base, the resistant sandstone cap was undercut. This process left the durable, flat slab of sandstone perched high above the surrounding landscape, creating the mountain’s signature sheer cliffs.
Past glacial periods, including a major ice age approximately 300 million years ago, played a role in flattening the mountain’s summit and carving out valleys and gorges on its sides. The resistance of the cap rock allowed it to persist, while the softer rock that once surrounded it was stripped away. The mountain’s current shape is a testament to the durability of its quartzitic cap, which resisted the forces that reduced the surrounding landscape.