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Why is Table Mountain flat?

Table Mountain walks, Table Mountain hikingNo, it wasn’t bulldozed. And even though a daredevil WW2 pilot landed his plane on the summit, and members of a WW2 Army regiment used it as a football field, Table Mountain’s iconic profile is the product of nature alone – except for the pimple on the north-western corner, the upper cable station, completed in 1929.

Let’s first deal with a pertinent technicality: Table Mountain is much more than just the “Table” – the flat-topped, square-cut facade as seen from the city center – but comprises four parts: (1) the actual Table, known as the Summit, the Upper Plateau, the Tabletop and sometimes the Summit Plateau; (2) the Lower Plateau, also known as the Back Table, located behind the Table and about 300 meters lower down; (3) the Suburban side, or Eastern side, both uninspiring names for the impressive chain of buttresses extending south of the Table on the eastern side; (4) the Twelve Apostles, the eighteen-odd buttresses extending south of the “Table” on the western side. It’s the Summit Plateau that inspired the name ‘Table Mountain’, because of its flat and featureless terrain.

So what forces and events conspired to produce such a singular mountaintop? Table Mountain is a sedimentary rock-formation (formed by or from deposits of sediment) that was laid down in layers over a period of about 200 million years. A collision between Africa and an unknown oceanic continent about 250 million years ago upheaved the earth’s crust around the southwest corner of Africa, scrunching together multiple layers of solidified sediment about 5 km thick in a concertina-like effect. The result: a massive chain of mountains known today as the Cape Fold Belt, stretching 150 km north and 700 km east of Cape Town.

Back then, Table Mountain soared 3 to 4 times higher than what it is today. Then erosion got to work on it – millions of years’ rain and wind – gnawing away its tilted outer layers one grain at a time, reducing it to its inner core, where the layers had remained horizontal. These layers eroded along the vertical planes formed during deposition and voila, you have a flat-topped mountain. But that’s only part of the story: what contributed to the formation of the Table is the random absence of major faults in the chunk of rock that ended up being Table Mountain. Faults, or cracks, are lines of weakness that erodes more rapidly (water run-off) than the surrounding rock, forming ravines, gorges and gullies. Although several ravines slice up the slopes below the summit plateau, none are so deep that it breaks the summit’s flat appearance. One ravine, though, leaves a distinct notch in the Table: Platteklip Gorge; but though expansive, it cuts only about 30 meters into the summit. Also, it runs diagonally up the mountain, reducing the visibility of the notch.

Another type of tabletop mountain – called tepuis – is found in southern Venezuela. Sheer-sided and detached from any range or foothills, they seem to float on the flat jungle landscape like islands. Their formation differs somewhat to that of Table Mountain: they are leftovers of an ancient plateau of continental size. Most of the plateau eroded away over millions of years, leaving these monoliths breaking the monotony of an otherwise featureless landscape. Like Table Mountain, they are made up of sandstone and ranks as some of the oldest mountains on the planet.

Join Hike Table Mountain on a journey of discovery up some of the impressive ravines dissecting Table Mountain. Traverse the entire summit plateau to the highest point on the mountain at Maclear’s Beacon. Venture further along the summit to the remote eastern rim, where stupendous views to the east await.

(c) www.hiketablemountain.co.za

June 18, 2012 / Posted by riaan / COMMENTS (0)