Tubular lava stalactites are common in many lava tubes and have a concentric tubular shape, are (initially) hollow, and range in diameter from .4 to 1 cm.  They are formed by "segregations extruded by expanding gas into cave passages" (Allred & Allred, 1998) as the lava tube cools. In the cooling walls of the cave, some minerals solidify first, forming a coarse, porous matrix. Boiling causes gases to force the remaining segregated liguid material out of the walls, forming tubular lava stalactites. Growth rings are found on the skin of the stalactites, each ring formed from dripping. Considerable material may be carried out of the stalactite and pile up on the floor beneath, forming a drip stalagmite.
In the first photo a single stalactite shows a bit of vermiform character, but doesn't full grade into a tubular lava helictite. The middle photo shows a stalactite that deflated when either the hot gases filling it suddenly escaped, or draining of liquid lava caused it to collapse. The lower photo shows a group of stalactites that have merged with their respective drip stalagmites to form the analogy of a column as found in limestone caves.



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Created: August 4, 2000
Author: Dave Bunnell