Page "Ethiopian Highlands" Paragraph 7

Around 30 million years ago, a flood basalt plateau began to form, piling layers upon layers of voluminous fissure-fed basaltic lava flows.

Most of the flows were tholeiitic, save for a thin layer of alkali basalts and minor amounts of felsic ( high-silica ) volcanic rocks, such as rhyolite.

In the waning stages of the flood basalt episode, large explosive caldera-forming eruptions also occurred.