Vulcanism

Vulcanism, which is the second of the greatest earth forming movements, does not concern mining geology as much as other forces of nature do. Vulcanism is just another word for volcanos. A volcano is a gap, or rupture, in the surface or crust of the earth, which permits hot, molten rock, ash and gases to flee from deep underneath the surface. Volcanic activity that has to do with the extrusion of rock is likely to produce mountains or features that are similar to mountains over a phase of time. Volcanoes are in general located where tectonic plates pull apart or are coming together. A mid-oceanic ridge, such as the Mid Atlantic Ridge, has examples of volcanoes created by convergent tectonic plates that have pulled apart; the Pacific Ring of Fire has illustrations of volcanoes that have been brought about by these convergent tectonic plates coming together. On the other hand, volcanoes are generally not formed where two tectonic plates slide past one another. Volcanoes can also shape where there is a stretching of the crust of the earth and where the crust grows thin, like in the African Rift Valley, the European Rhine Graben with its Eifel volcanoes, the Wells Gray-Clearwater Volcanic Field as well as the Rio Grande Rift in North America.

“Mantle plumes”, or the well known, “hotspots”, can originate volcanoes; these hotspots can take place far from plate boundaries, like in the Hawaiian Islands. Tectonism is the third biggest earth forming movement that takes place when the crust of the earth becomes deformed due to great amounts of pressure. This type of movement normally takes place over a long period of time and cannot be perceived by people. Even in cases when the movements are quicker, such as like what occurred in the sinking of Long Beach, California because of the removing of enormous pools of oil underneath the city, the movement that occurs might not be noticed for a number of years. It is known though that tectonic movements can occur very quickly and can actually take place in a matter of seconds and when this does happen, the end result is what we know as earthquakes. The most known of types of tectonism are epeirogeny and orogeny. Epeirogenic movements consist of the slow modifications that can take up to centuries and eons for them to make a change that can be perceived in the crust of the earth. Orogenic movements are what are known as mountain making movements. These are in general a bit more rapid than epeogenic changes however; they are still slow and can take up to thousands of years. The deformation of rocks that occurs from orogenic and epeirogenic movements is very vital to prospectors. The following terms are words that can be found in geological reports in mining.