The currently inactive Twin Calderas were part of a small, round volcano in the Imuruk volcanic field. They started out as volcanic craters. Over a period of 100,000 years, these craters erupted lava 10-20 separate times. Eventually, the volcano ran out of lava, leaving it empty and hollow. Having lost their support, the volcanic craters collapsed, creating two calderas or large, bowl-shaped depressions in the ground.
Last updated: April 29, 2015