Page 23 - KBHA BULLETIN 3

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through the rock could vary greatly from centimetres to kilometres. As the water travels

through the cracks and crevices it dissolves a little of the rock and takes the dissolved rock
with it. Over many, many years of dissolving the rock bit by bit, the water enlarges the cracks

into tubes, then the tubes into tunnels, and the tunnels into large passages and chambers, and

it eventually forms voids in the rocks that we know as caves. So, to form a cave, we need a
rock that will dissolve in water, the water to dissolve the rock, cracks and capillaries to allow

the water into and out of the rock, and time to allow the whole process to happen. Now let’s

examine the geology of the mountains above Kalk Bay.

The Table Mountain Sandstone that forms the top layer of the rocks of the Cape Peninsula is

a sedimentary rock. At some time in the distant past the sand part of the sandstone was laid
down in fairly thick beds, possibly at the bottom of a lake or a sea. As the earth’s crust bent

and buckled through the millennia, these beds of sandstone were thrust deep beneath the top

layer of the crust, and were subjected to immense heat and pressure. This heat treatment
caused the sand to coalesce into rock, and then fuse into quartzite. During various upshifts

and downshifts through the layers of the earth’s crust, the beds flexed slightly. This flexing

caused cracks to form in the brittle rock, just as a face-pack might crack when its wearer
smiles. In geological terms, these cracks are referred to as joints. These joints, however small,

provide entry points for water to penetrate the rock beds.

There is much geological evidence to show that the whole of what is now the Southern

African region was once much hotter and wetter than it is now. (Marker and Swart, 1995.)

The geological evidence also tells us that this period lasted for a relatively long time. If we
can assume that the quartzite beds were close to the earth’s surface at the same time that the

area was enduring a hot, wet topical climate, then we have another two ingredients for our

cave formation: lots of water, for a long time.

The only thing left for us to show is that quartzite is soluble, and we will have explained the
origin of the Kalk Bay caves. Quartzite is regarded as a rock that does not dissolve easily, and

certainly not as easily as limestone rocks. In the current climate this is true but, if the

temperature of the water is raised, quartzite dissolves much more easily until, at 100 degrees
Centigrade, it is actually more soluble than limestone. (Ford and Williams, 1989.) If the water

is not only warm, but slightly acidic too, then the rock dissolves even more easily. Given the