Geology majority of the geologic history of the Earth. There are three major types of rock: igneous, sedimentary, and metamorphic. The rock cycle illustrates the relationships among them (see diagram). When a rock crystallizes from melt (magma or lava), it is an igneous rock. This rock can be weathered and eroded, then redeposited and lithified into a sedimentary rock. It can then be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric. All three types may melt again, and when this happens, new magma is formed, from which an igneous rock
Ice-marginal lava flow ice sheet's margins. Initially, the lava flow is like any other but when the lava reaches the margins of an ice sheet, the front of the lava flow cools very quickly and thus, forms a barrier (Figure 1). Behind this barrier, the lava begins to pool, ceasing the contact between the hot lava and cold ice. The barrier is left behind as the ice retreats, leaving a thick lava front, which is just a large, steep, and unstable cliff face. The Barrier A fantastic example of a natural lava dam formed from an ice-marginal lava flow is a phenomenon aptly