Rock cycle called intrusive or plutonic and cools very slowly, producing a coarse-grained texture such as the rock granite. As a result of volcanic activity, magma (which is called lava when it reaches Earth's surface) may cool very rapidly while being on the Earth's surface exposed to the atmosphere and are called extrusive or volcanic rocks. These rocks are fine-grained and sometimes cool so rapidly that no crystals can form and result in a natural glass, such as obsidian, however the most common fine grained rock would be known as basalt. Any of the three main types of rocks (igneous, sedimentary, and
West Crater imply that they resulted from the same movement of magma and were possibly fed by the same magma chambers. The lava dome likely formed before the lava flows erupted, suggested by its steep western side and the appearance of rock from the dome on the western lava flow. The dome's deep depression may have formed when the dome's top collapsed as lava moved out of the volcano during the eruption of the two flows. The human population within of West Crater is slightly more than 500 people, but more than 14,000 people live within of the volcano, and more than