Glossary · Khoa học Trái Đất
Lava tube
A long, hollow tunnel that forms when molten lava flows beneath a field of cooled lava, when a crust forms over a river of lava, or when lava cracks its way through the underground. After the volcanic activity stops, the tunnel remains as caves of different sizes.
Lava tubes are found on Earth and very probably on the Moon and Mars. If the ceiling of a solidified tube collapses, it opens a pit that can lead into the rest of the tunnel. Pits were first discovered on the Moon in 2009; according to a research team using data from NASA's LRO (2022), about 16 of the more than 200 pits are probably collapsed lava tubes. On Earth, lava tunnels are typically 10–30 m across; a 2020 comparative study found those on the Moon and Mars to be 100 to 1,000 times larger, and holds that low gravity explains their enormous size. On Mars, where gravity is about a third of Earth's, lava tubes seem to be smaller than on the Moon — though still bigger than on Earth — and collapse more often.
Since the pits were found, scientists have wondered whether they lead to caves that could be explored or used as shelters: the pits or caves would offer some protection from cosmic rays, solar radiation and micrometeorites. LRO data combined with computer modelling show that in the permanently shadowed reaches of one pit in Mare Tranquillitatis, the temperature fluctuates only slightly, around 17 °C, while the surface heats to about 127 °C by day and cools to about −173 °C at night; if a cave extends from the bottom of the pit, it would have that temperature too.