Mauna Loa is tall enough to have experienced glaciation during the last ice age, 25,000 to 15,000 years ago. Unlike Mauna Kea, on which extensive evidence of glaciation remains even today, Mauna Loa was at the time and has remained active, having grown an additional in height since then and covering any glacial deposits beneath new flows; strata of that age doesn't occur until at least down from the volcano's summit, too low for glacial growth. Mauna Loa also lacks its neighbor's summit permafrost region, although sporadic ice persists in places. It is speculated that extensive phreatomagmatic activity occurred during this time, contributing extensively to ash deposits on the summit.