These formations in a lava tube are called extrusion spires and were formed when molten lava in the floor was pushed up through a hole. You can see how some of the lava traveled to the top and then spilled out and dripped down the sides. These are over six feet tall and are the largest in the US. Taken with a TL120 on Fuji ProviaF 100. Lighting was from two Vivitar 283 flashes. One was placed to the far left and triggered by a slave. The other was held just to the right of the camera.