Aymeric. Tourists exploring the underground caves created by lava in the Grand Brûlé. Cooling and crystallization of basaltic lava around the sides, bottom and top channels lava rock produces a coated conduit called a lava tube. Crystalline basalt remains relatively hot surrounds and insulates washed inside the washing tube over crystallization. The tube provides a very efficient mechanism of basaltic lava flows that travel long distances away from their source, without significant heat loss. Lava tubes are typically <1 km long, it may exceed several kilometers. The diameters of the lava tubes are also highly variable, from <1 m up to 15 m. Flow inside lava tubes in Hawaii were recorded at 35 mph. Fast moving, turbulent lava, combined with the high temperatures of lava, may result in thermal erosion inside the tube. Well insulated lava tubes can erode both downward and laterally with time. The turbulence of the fluid motion and constantly escaping gases generated spatter fragments lining the walls of many lava tubes. Over time, the eruption ceases and lava remaining in the tube will drain downhill to expose a hollow inactive lava tube. These tubes typically comprise a flat, have high marks lava canal walls. A thin layer of splashes often found in the tube walls, along with lava stalactites icicle-shaped hanging from the ceiling. Mound-like lava stalagmites from splashing drops on the floor of the tubes are less common.