Tubular Lava Stalactites
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 liquid 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. This is illustrated in the first photo, which 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.
The second photo show a pair of stalactites each formed by a small flow issuing down a tube, perhaps a pair of tree molds that collect from a segment of wall that is exuding segragations, acting as somewhat of a funnel of collected material that may come from several pores inside. These tiny channels in the rock likely result from the inherent porosity that develops from gas being ejected.
The third photo shows what may well be the longest tubular stalactite known, measured by a survey team at just over six feet long. It is in a rather remote section of a long lava tube.
The fourth photo shows a stalactite that deflated when either the hot gases filling it suddenly escaped, or draining of liquid lava caused it to collapse.
AUTHOR: Dave Bunnell