Martian lava tube would also reduce the landed payload mass for manned missions which would be economically advantageous. Martian lava tube Martian lava tubes are natural sub-surface lava tube caverns on Mars that are believed to form as a result of fast-moving, basaltic lava flows associated with shield volcanism. Lava tubes usually form when the external surface of the lava channels cools more quickly and forms a hardened crust over subsurface lava flows. The flow eventually ceases and drains out of the tube, leaving a conduit-shaped void space which is usually several meters below the surface. Lava tubes are typically associated with extremely
Lava buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an aā flow. Accretionary lava balls as large as are common on aā flows. Aā is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into aā if it becomes turbulent from meeting impediments or steep slopes. The sharp, angled texture makes aā a strong radar reflector, and can easily be seen from an orbiting satellite (bright on Magellan pictures). Aā lavas typically erupt at temperatures of . The word is also spelled "aa", "aa", "aa", and "a-aa", and pronounced .