The Ethiopian and Somali plateaux are composed of flood basalts sitting unconformably above the upwarped Mesozoic sediments. Rifting had probably begun by the early Miocene and certainly by the late Miocene. This may have been produced by calderas in the Rift Valley, including Awassa. Quaternary basaltic volcanism in the MER has produced fields of monogenetic cinder cones and lava flows. Some phreatomagmatic eruptions have occurred, producing maars.
Tectonic activity makes the interpretation of strand-line evidence problematic.
With a network of geodetic stations, Asfaw et al. Higher altitudes experience elevated precipitation and reduced evaporation. Limited areas near the Red Sea coast receive most of their precipitation during this season from moisture evaporated off the Red Sea. May. The ITCZ is associated with easterly winds, which bring the short rains from the Indian Ocean. The dry season begins as the ITCZ retreats southwards across Ethiopia.