Geology of Ascension Island

Rocks in the EFC constitute trachyte, rhyolite and formations such as lava domes and thick flows.

The Devil's Inkpot lava flows formed from a fissure around the same time as the Sister's Peak region 829,000 years ago.

Benmoreite scoria cones record evidence of mafic volcanism, although older rhyolite and trachyte flows, domes and pyroclastic deposits point to felsic eruptions as well.

By comparison, Green Mountain formed as recently as 395,000 years ago with trachyte flows and pyroclastics grouped around a mafic scoria cone.

The 758,000 year old intermediate bentmoreite lava flows of southwest Ascension are interspersed with scoria cones and periodically mafic ash falls.