Geologists believe the cave was formed sometime between 650,000 and 700,000 years ago when molten lava erupted from a volcanic vent in nearby Hart Prairie. The top, sides and bottom of the flow cooled and solidified, while lava in the middle flowed out, leaving a hollow space to form the cave. Examples of both ʻAʻā and Pāhoehoe basaltic lava can be seen in the cave.
