Erosion Control

A Long, Slow Breakup

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The surface of our planet moves in all sorts of ways. Erosion is one cause; landslides, as we’ve recently experienced, are another. Something most of us don’t think about all too often—except for those in seismically active areas—is the movement of the tectonic plates.

The Great Rift Valley runs some 3,700 miles, from Lebanon in the north all the way down to Mozambique, roughly following the path of the Red Sea. The part commonly known today as the East African Rift extends more than 1,800 miles from the Gulf of Aden down through Ethiopia, Kenya, and Tanzania. As you might have seen in various articles and photos in the popular press, a huge crack is appearing in southwestern Kenya, part of it just 30 miles from Nairobi, so far causing part of a highway to collapse and fueling lots of speculation about the future shape of the continent. It was originally thought to be a dramatic expansion of the existing rift.

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The movement of the tectonic plates created the Red Sea millions of years ago, as the African and Arabian plates moved apart. (They’re still moving about a centimeter each year.) Scientists say these same phenomena—the movement and rupture of plates—will, in a few million years, create a new sea in eastern Africa, along with a large new island offshore.

Although it’s generally accepted that this scenario will play out as predicted, some scientists think the sudden appearance of the crack, and several smaller ones nearby, is due at least in part to erosion rather than to tectonic movement. The main crack, which in most places is several yards wide and about as deep, is not continuous and the sides do not fit together like puzzle pieces—evidence, according to some, that it’s more likely caused by erosion of soft volcanic ash and sediments being transported by recent heavy rains. Several smaller cracks have also appeared in the vicinity of the main one.

You can see more photos of the fissure and an artist’s rendering of what the new island might look like here EC_bug_web


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