A story in sediment
These pillars of rock are found in the Afar depression in Ethiopia. The story of these rocks may be the first chapter in the story of an ocean.
The Afar Triangle is a corner of Ethiopia that buts up against the Red Sea. The Red Sea itself is a newly formed “ocean”, with two tectonic plates rifting apart and a volcanic spreading center in the center. That spreading center heads south and makes a turn out into the Indian Ocean at the point where it connects to the Afar triangle.
There are several places on earth where several mid-ocean ridge spreading centers come together; called triple junctions by geologists because 3 plates are coming together at a single spot. The Afar depression is developing as though it may become the third edge of a triple junction if East Africa fully rifts away from the continent.
The land in the Afar depression is sinking as the land rifts apart, but it is happening very slowly. These rocks are carbonate and evaporite rocks, formed when the ocean levels were high enough to flood this part of the basin.
One final interesting note: these rocks are in a rift zone formed by land that is sinking down over time, but they’re also oceanic rocks. The fact that these were deposited in an ocean implies that in recent geologic history, sea levels have been high enough to submerge this area. In other words, even though we’re in an interglacial period, at some point in recent geologic history sea levels have been higher than they are today to produce these rocks. At some point in the future, as the land continues to subside from faulting and sea levels rise from the changes humans are imposing on our atmosphere, the sea may again claim this location.
-JBB
Image credit: Achilli Family, CC BY 2.0 http://bit.ly/DallolSalt
