Volcanism throughout the solar system.

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AA2281 Exploring the Solar System

Assessment

F: Volcanism throughout the solar system

"Volcanism is one of the major processes, whereby a planet transfers heat produced in its interior outward to the surface" (Encyclopedia of the solar system).Volcanism is part of the process of bringing material up from the deep interior of a planet and spilling it forth on the surface where it cools and becomes solid. At least three quarters of the surface rocks on earth and Venus can be attributed to volcanic activity. There are two styles of volcanic activity explosive or effusive. Explosive is when magma is disrupted into fragments which are called pyroclasts by the expansion of exsolved gases. Effusive eruption is when magma escapes through a vent, there is no significant disruption, but a lava flow is formed. To understand the volcanic processes of the earth the products of volcanic activity have been studied under a wide range of environmental conditions such as gravity and atmospheric pressure. There are quite a few other planets which have volcanoes on the surface, including Venus, Mars, and Jupiter's moon Io. Other planets exhibit the results of volcanic activity. These include Mercury, the Earth's Moon, Jupiter's moon Europa, and perhaps Neptune's moon Triton. Planetary bodies, like Jupiter's moon Europa also exhibit icy volcanism where water takes the place of lava.

Eruptions allow fresh gases to the surface from the melted material below. Volcanism is part of the process by which a planet cools off. Even though they are not volcano's, geysers and hot springs are also part of the volcanic process, involving water and hydrothermal activity. Much of the earth's surface especially the crust of the ocean floor consisted of very young rocks, geologically. The rocks came from long lines of volcanoes, which were located along ridges near centres of ocean basins, within the last 300 million years. When this was concluded the theory of plate tectonics was developed, this explained the locations and distributions of volcanoes on Earth. Volcanoes that erupted basalt tended to be located along midocean ridges, this marks constructional margins of Earth's rigid crust plates. There are several ways in which a volcano forms, just as there are several different kinds of volcanoes.

Hot magma, rising from lower reaches of the Earth, eventually, but not always, erupts onto the surface. During the eruption lava and ash form a cone. This cone is what we know as a volcano. Strong earthquakes accompany rising magma just before an Eruption. Among the different kinds of volcanoes are shield volcanoes, cinder cones and composite volcanoes. On Earth, the most general cause of volcanism is caused by lithospheric subduction which are composite volcanoes. These volcanoes form as a result of subduction of the nearby lithosphere.

The Earth's Moon has no large volcanoes like Hawaii or Mount St. Helens. However, vast plains of basaltic lava cover much of the lunar surface. Volcanism on the Moon differs in several ways from volcanism on the Earth. First, there is the matter of age. Volcanism on the Earth is an ongoing process. Many of Earth's volcanoes are quite young in geologic terms, often less than a few 100,000 years old. In contrast, most volcanism on the Moon appears to have occurred between 3 and 4 billion years ago. Typical mare samples are ~3,500,000,000 years old. Even the youngest mare flows have estimated ages of nearly 1 billion years. These "young" rocks have not been sampled or directly dated, so this age is could be incorrect. For comparison, the oldest dated rock on the Earth is ~3.9 billion years old. The oldest sea floor basalts on Earth are only about 200 million years old. Because the Moon does not show any evidence for recent volcanic or geologic activity, it is sometimes referred to as the "dead" planet.
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The settings of mare volcanism reveal another major difference from volcanism on the Earth. Specifically, Earth's volcanoes mostly occur within long linear mountain chains. Mountain chains like the Andes mark the edge of a lithospheric plate. Mountain chains like the Hawaiian Islands mark past plate movements over a mantle hotspot. In contrast, the mare typically occur in the bottoms of very large, very old impact craters. Thus, most of the mare are nearly circular in shape. Further, lunar mountain chains form the edges of these impact basins and tend to surround the lunar mare. There is no evidence ...

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