Lunar lava tube Lunar lava tube Lunar lava tubes are sub-surface tunnels on the Moon that are believed to have formed during basaltic lava flows. When the surface of a lava tube cools, it forms a hardened lid that contains the ongoing lava flow beneath the surface in a conduit-shaped passage. Once the flow of lava diminishes, the tunnel may become drained, forming a hollow void. Lunar lava tubes are formed on surfaces that have a slope that ranges in angle from 0.4° to 6.5°. Lunar lava tubes may be as wide as before they become unstable against gravitational collapse. However, stable tubes
The Barrier ponded, eventually cooling to form an ice-marginal lava flow. When the ice melted away, the ice-cooled lava-flow front formed a precipitous cliff; water ponded behind the lava dam, forming Garibaldi Lake. The unstable lava formation of The Barrier has in the past unleashed several debris flows in the area below Garibaldi Lake. The most recent major landslide in 1855-1856 formed a large boulder field which gives Rubble Creek its name. At least of rock was removed from The Barrier during the 1855-1856 event. Concerns about The Barrier's instability due to volcanic, tectonic, or heavy rainfall activity prompted the provincial government