Water is the creative force behind most caves. Lava caves, however, are usually formed during the transformation of ﬂuid basalt into solid rock (the exceptions being the small caves created during the uplifting or buckling of congealing lava crust). Lava ﬂowing downhill tends to develop a central channel of faster-moving magma. This molten river forms its own levees, and cooling and congealing lava, rafting the surface, catches on the sides like a snagged log, narrowing the channel edges until they crust over in a roof. The molten river below, eroding its way deeper and deeper, is now encased in a tunnel or lava tube of its own making; where well insulated, it can continue to ﬂow for miles. If a change or an end to the eruption reduces or stops the ﬂow of lava, the ﬁery river will drain out of its tube, often leaving a series of horizontal ridges like stone bathtub rings on the walls as the ﬂuid level drops. The world’s longest lava tube cave, the Kazumura Cave on the east slope of Kilauea Volcano, Hawai‘i Island, is over thirty miles long.