Intrusive rock Intrusive rock Intrusive rock (also called plutonic rock) is formed when magma crystallizes and solidifies underground to form "intrusions", for example plutons, batholiths, dikes, sills, laccoliths, and volcanic necks. Intrusive rock forms within Earth's crust from the crystallization of magma. Many mountain ranges, such as the Sierra Nevada in California, are formed mostly from large granite (or related rock) intrusions; see Sierra Nevada batholith. Intrusions are one of the two ways igneous rock can form; the other is extrusive rock, that is, a volcanic eruption or similar event. Technically speaking, an intrusion is any formation of intrusive igneous rock; rock
Cave type of solutional cave. They were formed by HS (hydrogen sulfide) gas rising from below, where reservoirs of oil give off sulfurous fumes. This gas mixes with groundwater and forms HSO (sulfuric acid). The acid then dissolves the limestone from below, rather than from above, by acidic water percolating from the surface. Caves formed at the same time as the surrounding rock are called primary caves. Lava tubes are formed through volcanic activity and are the most common primary caves. As lava flows downhill, its surface cools and solidifies. Hot liquid lava continues to flow under that crust, and if