When lava ponds up in a passage it cools to form a smooth-surfaced lake. Typically the ponding occurs in plunge pool basins eroded beneath lavafalls, as seen in the lower photo. They may also occur when flows have been backed up by constrictions downstream of the flow due to passage collapse, which is probably what formed the now-drained lake in the top photo.

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Created: August 4, 2000
Updated: Dec. 12, 2008
Author: Dave Bunnell