Merrill Ice Cave is a cave defined by something that is no longer there. Its floor once held an ice sheet large enough to skate on, and people did. It is gone now, and the Park Service is direct about it: historically there was an ice floor big enough to skate on, and now there is not.
That loss is the interesting part. Ice caves in lava tubes are not simply cold holes. They work as cold traps: dense winter air sinks into the tube and cannot flow back out, so the cave stays below freezing through summer and water seeping through the rock freezes and accumulates year on year. The ice is a record of the climate above it, and it takes very little warming, or a change in how air moves through a passage, to tip a cave from accumulating ice to losing it.
Several caves at Lava Beds still hold ice. Merrill is the one that shows what happens when the balance goes the other way, which makes it a more informative stop than a cave that simply looks impressive.
The monument sits on the flank of Medicine Lake Volcano in northeastern California and was established on 21 November 1925, covering more than 46,000 acres. It holds an enormous concentration of lava tubes, 27 of them with marked entrances.
Merrill is ranked among the less demanding caves here, but a permit is still required, free from the visitor centre, and the rules about lights and helmets apply everywhere in the monument. Check the current closure list before you go: caves here close seasonally for bat protection and for safety.
Other places on the map within a couple of hours.
