Bottoms up: The story of Table Mountain

December 3, 2015 Jodi Ettenberg

If you’ve searched for any photos of Cape Town in South Africa, no doubt you have stumbled upon many of Table Mountain, which looms over the city. On cloudy days it is not visible when you wander around town, covered in a “table cloth” of clouds, but as the view clears its flat features come into focus.

I only visited Cape Town briefly but my main question was: what gives the mountain its iconic flat shape?

Looking up at Table Mountain.

The mountain’s plateau is about 3km (1.8 mi) across, with Devil’s Peak on one side and Lion’s Head on the other, and contains quartzite (sandstone that is almost fully made from quartz) as well as granite. More specifically: a type of hardened sandstone called  “Table Mountain Sandstone,” as well as a second kind of rock called the Graafwater Formation. As a result of its durable rock types, Table Mountain currently has some of the slowest erosion rates on earth, leading Live Science (a science news website) to call it the “world’s strongest mountain.”

So why such a flat surface?

Around 300 million years ago, what is currently Africa was in the centre of a former continent called Pangea, a sprawling supercontinent surrounded by a vast ocean. Over millions of years, Pangea splintered off in fragments and by approximately 100 million years ago, Australia, Antarctica and India had moved away from the centre — Africa — which remained.

What we see as the summit of Table Mountain was actually once the bottom of a valley floor.

What we see as the summit of Table Mountain was actually once the bottom of a valley floor.

The mountain owes its relative flatness at the summit to the fact that it is a syncline mountain — that is, what we see as the summit of Table Mountain was actually once the bottom of a valley floor, likely worn away by the sea. The rest of the mountain, and its softer sandstone, has been weathered down over the years, leaving the tough, resilient quartzite at the top.

Wait a second, if the top was the bottom, how did it get so high?

Fair question.

The valley’s movement upwards can be attributed to a geological phenomenon called isotasy, or “equal standstill.” Going back to those supercontinents, their movement put a considerable amount of pressure on the earth’s crust, forcing rocks upward. Many new “folded” mountains were created in the region as a result, such as the Hottentot-Holland range in the Cape Winelands.   In the case of Table Mountain, its strong granite deflected some of the pressure downward. So instead of rolling hills or other geological formations, the earth’s mantle was displaced by a steady downward pressure, with mass added to the earth’s crust and the mantle pushed toward the centre of the earth. There was an “equal standstill” between the surface granite and the mantle underneath, so the mantle dented and moved out of the way under the pressure.

Clouds starting to roll in on the Table Mountain range.

Clouds starting to roll in on the Table Mountain range.

Geologists have noted that eventually with isotasy the mantle “bounced back” (and by “bounced” I mean “rebounded slowly over many thousands of years”). As the mantle returned to where it was pushed aside, the mass on top was pushed upward. What we know as Table Mountain rose slowly as it floated on the mantle of the earth.

Wait, are all table mountains created this way?

Actually, no. Gros Morne National Park, in Newfoundland, includes a huge slab of red periodite rock called the Tablelands, created via tectonic collisions about 500 million years ago. Studying these rocks helped scientists develop the theory of plate tectonics, and the geological formation led UNESCO to designate Gros Morne National Park a World Heritage Site in 1987.

The difference here is that the Tablelands are part of the earth’s mantle, which is a pretty trippy bit of mountain to walk on. It’s extremely rare that a part of the mantle is exposed in this way, and Gros Morne’s Tablelands are one of the few tourists can access. I went there a few years ago and it was just beautiful. They are barren because the rock is low in nutrients and has a toxic amount of heavy metals and iron.

For this we can blame Captain James Cook, who was sent to map what is now Newfoundland for the British Admiralty in the mid 1700s. He was right; it does look like a table. But several hundred years prior, Portuguese Admiral Antonio de Saldanha climbed Table Mountain and in 1503 named it tabua da caba, table of the cape. Both called it like they saw it, and similar names have stuck with each of these very different mountains ever since.

Well worth a visit

Whether you take the cable car or decide to hike up Table Mountain, it provides an incredible view of the city below. You can also camp at the top or even abseil down on one of the world’s tallest abseil experiences. No matter which route you take, it is well worth a visit to this former valley that now overlooks the sea.

Table Mountain provides an incredible view of the city below.

Table Mountain provides an incredible view of the city below.

Getting There

G Adventures runs a number of departures in South Africa encompassing a wide range of departure dates and activities to cater for different tastes. We’re thrilled at the prospect of showing you this big blue planet of ours — check out our small group trips here.

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