Tubular Lava Helictites.

Dave Bunnell has an awesome site dedicated to caves and lava – this one above is a picture of tubular lava helictites:

Helictites are an eccentric or "vermiform" form of stalactite that twists and turns rather than growing straight up and down. They typically begin as tubular lava stalactites, but crystallization of the emerging lava as it cools pushes the lava in different directions. Often groups of these helictites will bend in the same direction down the passage, suggesting an influence of wind moving through the tube.

Link