ARCHIVE 174 – A CONTINENT SPLITS APART
August 25, 2015 8 Comments
In today’s cheap and superficial hype – too often the triumph of style over substance – many things are marketed as having various specified advantages “and so much more”. Well, here is a photograph that really does have “so much more”. It was taken from the eastern wall of the rift valley, near Kijabe in Kenya, looking down westwards towards the rift’s floor, sometime in the late 1970s. The rift wall here is not a single escarpment, but a series of small escarpments that gradually descend to the rift’s floor like a flight of huge steps.
This photo was taken from the top of the escarpment, looking down upon the top of the first of these steps which, because it still has sufficient altitude to attract rain and mist, is green and fertile. This green but restricted area of land is covered in a close patchwork of cultivated plots, and dwellings roofed with thatch or corrugated iron. Beyond this step, the floor of the rift can be seen, browner and drier, many hundreds of feet below. Rising from these pale, dry lowlands is the dark and jagged bulk of Mt Longonot, a dormant volcano which last erupted around 1860. In the far distance, behind Longonot, the abrupt line of hills is the rift valley’s western wall.
So far so good, but there really is so much more here, for the fact is that the eastern edge of the African continent has been breaking apart for a long time. The island of Madagascar broke away from the rest of Africa many millions of years ago and, during this lengthy isolation from the mainland, many unique (i.e. endemic) forms of life have evolved there, e.g. the Lemurs.
But that is not all. The Eastern Rift Valley (the one in Kenya) and and the Western Rift constitute further incipient splits in the eastern side of the African continent and, as I took this picture, I was standing on the western edge of another part of the continent that may split away to become an island like Madagascar in (the millions of) years to come.
The floor of the rift is new crust that has moved upwards from the Earth’s extremely hot interior to ‘seal up the cracks’ in the disintegrating continent. And hence the reason for the many volcanoes (including Mt Longonot) in this area – these were formed where the molten rock (magma) moving up from the Earth’s interior burst out (erupted) onto the Earth’s surface, as lava. There are also numerous natural steam vents on the rift valley floor – these are the result of rainwater and groundwater coming into contact with the extremely hot rocks present not far below the surface of the ground.
UPDATE: I became an enthusiastic collector of rocks, minerals and fossils from somewhere around the age of five and went on to become a professional geologist – lecturing and research. I’m very grateful for that background because it has given me a very solid idea of who, where and what I am in what might be termed “The Grand Scheme Of Things”. To put it another way, if I’ve reached the “grand old age of 65”, then the Earth’s lifespan of 4,500,000,000 years make my lifetime seem like less than the blink of an eyelid – which is exactly what it is. A knowledge of geology also makes for new insights into landscapes.