During an increase in Earth radius from A to B, the increase in radius generates localised tangential compression at the surface interaction of each fragmented crust plus tangential extension at the base of each crust.

In geology, this process represents a primary mechanism for compression of rocks at the surface. The downward force of gravity led to extension along the East African Rift Valley, and compression of surface rocks, and magmatic eruptions along these extension-compression zones in the Oligocene (33.9 to 23 ) formed the Ethiopia-Yemen flood basalts.

The compression zones continued to be tectonically active in the Miocene, with rapid uplift of the Ethiopia-Yemen Highlands. The Miocene ape Chororapithecus abyssinicus shows high altitude adaptations by 10.5Ma, with teeth specialized for eating stems and leaves as little fruit could grow at those altitudes.

Tectonic history of Danakil in the context of the Ethiopian Plateau

Chororapithecus abyssinicus could provide palaeontological evidence for when the Danakil-Aysha block pulled away from Somalia, from that the faulting of the Chorora formation around 10.5 Ma would be a result of that the continent just north of Chorora pulled away from Somalia (or, was pulled adjacent to Somalia to the current position of the Aysha block, which has also rotated clockwise. )

The genetic estimates of a chimpanzee-human-last-common-ancestor (CHLCA) split around 6 Ma could be a marker for when the Danakil block was fully separated from the mainland.

The geology of Danakil would show tectonic stress from the compression-extension zone, where super-elevated continental crust has fractured and fragmented, with gradually collapse under the influence of gravity to adopt the new surface curvature. The entire island could have been brittle, and hence weak in tension, with a continuous faulting along the western edge to form a lower-elevation coast-line, with a coastal ecosystem where Australopithecus afarensis evolved as a “beach ape”.

The geography of Pliocene Danakil could perhaps be similar to the island of Crete, one of the most seismically active areas in the eastern Mediterranean.

References

1. New geological and palaeontological age constraint for the gorilla–human lineage split