Divergent plate boundaries At the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust is being formed by hot molten rock slowly cooling and solidifying. The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates. The release of pressure due to the thinning of the crust leads to adiabatic expansion, and the partial melting of the mantle causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, therefore most volcanic activity is submarine, forming new seafloor. Black smokers or deep sea vents are an example of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, Iceland. Lava enters Pacific at the Big Island of Hawaii Convergent plate boundaries Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, creating magma. This magma tends to be very viscous due to its high silica content, so often does not reach the surface and cools at depth. When it does reach the surface, a volcano is formed. Typical examples for this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire. Flood A flood is an overflow of an expanse of water that submerges land, a deluge.[1] In the sense of "flowing water", the word is applied to the inflow of the tide, as opposed to the outflow or "ebb". It is usually due to the volume of water within a body of water, such as a river or lake, exceeding the total capacity of the body, and as a result some of the water flows or sits outside of the normal perimeter of the body. It can also occur in rivers, when the strength of the river is so high it flows right out of the river channel , usually at corners or meanders. These of course, are not applicable in such instances as sea flooding. The word comes from the Old English flod, a word common to Teutonic languages, compare German Flut, Dutch vloed from the same root as is seen in flow, float. The term "The Flood" usually refers to the great Universal Deluge described in Genesis and is treated at Deluge. The Power of Nature Man’s power to create or destroy is nothing compared with nature’s Tornadoes. These spinning clouds of dust and debris have wind speeds reaching 300 mph. tornadoes can flatten buildings as well as pick up cars and houses and toss them around like toys. Most tornadoes occur in the Midwestern United States. Everything in the path of a tornado is destroyed, yet areas nearby can be left untouched. On a single day in 1999, around 1,500 people were either killed or injured from tornadoes in Tornado Alley. Earthquakes People can do nothing to prevent or stop an earthquake. When the earth shakes, w ... ...
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