Intrusive rock formed from magma that cools and solidifies within the crust of the planet. In contrast, an "extrusion" consists of extrusive rock; rock formed above the surface of the crust. Large bodies of magma that solidify underground before they reach the surface of the crust are called plutons. Plutonic rocks form 7% of the Earth's current land surface. Coarse-grained intrusive igneous rocks that form at depth within the earth are called "abyssal" while those that form near the surface are called subvolcanic or "hypabyssal". Intrusive structures are often classified according to whether or not they are parallel to the bedding planes
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