Meru has a conical profile when viewed from the west, but there is a 4-km-wide collapse crater to the E. The summit collapse is associated with the early Holocene Momella event that resulted in debris avalanche and lahar deposits as far as the W flank of Kilimanjaro. Cones and lava domes are located on all sides; a maar field is present on the lower N flank. Activty from the Ash Cone, inside the open crater, was reported around 1878 and in 1910 CE. A second vent between it and the headwall produced lava flows that cover much of the caldera floor. Kisaka et al. (2021) identified three late Pleistocene explosive eruptions during 31-38 ka BP (cal 14C).