Lava flows may surge or back up due to a constriction downflow and flow out of windows or entrances. Often this lava leaves a lining deposit around the edge as evidence of its passing, and may even deposit lava balls that were being carried along, around the edges of the entrance or window. A different sort of upwelling can occur from floors of tubes when segregations boil out of the semi-solid floor. Sometimes these resemble miniature volcanoes or even lava roses.
In the photo below, lava has upwelled from a lower level through a window and sealed the window shut as it cooled. In the lower photo are some features upwelled on a floor.


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Created: August 4, 2000
Author: Dave Bunnell