The rock cycle summarizes the formation and breakdown of igneous, sedimentary, and metamorphic rocks. It also shows how the formations of these rocks are interrelated. The water cycle is the movement of water within the hydrosphere (the waters of Earth's surface). The water cycle is a series of movements of water above, on, and below the surface of the Earth. I will discuss both cycles and show how the two are interrelated.
The water cycle, also called the hydrologic cycle, consists of four stages: storage, evaporation, precipitation, and runoff. Water is stored in oceans and lakes, in river channels, ice caps, glaciers, and in the ground. Evaporation, including plant respiration, changes water into water vapor. Precipitation occurs when water vapor in the air condenses in the clouds and falls to the ground as rain, snow, ice pellets, or hail. Runoff is the movement of water downhill, and includes water flowing in streams, on the ground, and in the ground. Enormous volumes of water are involved in the water cycle. There are 1.4 billion cu. km. of water on the earth. A little more than 72 percent of the water is ocean water. .
The rock cycle shows how each of the three principal types of rocks (sedimentary, metamorphic, and igneous) can evolve into either of the other two types of rock, or even into other rocks of its own type. For example, a rock may change into a sedimentary rock by eroding, and then accumulating as sediments in a new place, and then cementing into rock. Metamorphic rocks form when rock is heated or subjected to high pressure, or both, without melting, and igneous rocks form when rock melts and then cools again. The rock cycle transforms rocks from one type to another, or to a new rock of the same type, depending on temperature and pressure where these transformations occur. These conditions, in turn, depend on depth at which the transformations occur. Weathering and erosion occur at or near the Earth's surface.
