On our last program, we introduced a mysterious geological feature that can be found on the slopes of Mount Rainier, a volcano in Washington state. Flows of hardened lava cling to the tops of ridges as they wind down the mountainside, ignoring deep valleys to either side. Why Didn’t The lava Flow Down The Valleys, As Any Other Liquid Would? The key to this is the epoch in which these features formed. They formed during an ice age, which means that this curious geography is the result of a tremendous, elemental battle between fire and ice–a battle which ice won. Imagine a volcano, besieged by glaciers. The glacial ice is thickest where it’s filling deep valleys on the mountainside, and thinnest where there are ridges that almost poke their rocky spines up through the ice sheet.