In appearance, runners look like driblets of lava running down the wall of the cave. They are actually a form of tubular lava stalactite formed along a surface instead of free-hanging. They may also form along the edge of a stalactite. Like tubular lava stalactites, they are formed of cooling segregated lava that is extruded from semi-crystalline wall matrices, propelled by boiling and escaping gases.

The first photo shows more typical runners, with just a small opening at the top. In the second, small structures that look somewhat like lava roses have formed at the top the of the runner.

AUTHOR: Dave Bunnell