What are the Differents Types or Classes of Volcano according to their Shape and mode eruption!!!????

Question

Pls. Help me . Its my Home work.

Answer 1

1. Composite volcanoes -- sometimes called stratovolcanoes.

They are typically steep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above their bases.

The essential feature of a composite volcano is a conduit system through which magma from a reservoir deep in the Earth's crust rises to the surface. The volcano is built up by the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash, etc., are added to its slopes.

Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents. Lavas either flow through breaks in the crater wall or issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dikes that act as ribs which greatly strengthen the cone.

Examples of composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, Mount St. Helens and Mount Rainier in Washington. Mt Mayon in Philippines

2. Sheild Volcanoes

Shield Volcanoes

Shield volcanoes are the largest volcanoes on Earth that actually look like volcanoes (i.e. not counting flood basalt flows). The Hawaiian shield volcanoes are the most famous examples.

Shield volcanoes are almost exclusively basalt, a type of lava that is very fluid when erupted. For this reason these volcanoes are not steep (you can't pile up a fluid that easily runs downhill).

Eruptions at shield volcanoes are only explosive if water somehow gets into the vent, otherwise they are characterized by low-explosivity fountaining that forms cinder cones and spatter cones at the vent, however, 90% of the volcano is lava rather than pyroclastic material.

Shield volcanoes are the result of high magma supply rates; the lava is hot and little-changed since the time it was generated. Shield volcanoes are the common product of hotspot volcanism but they can also be found along subduction-related volcanic arcs or all by themselves.

Examples of shield volcanoes are Kilauea and Mauna Loa (and their Hawaiian friends), Fernandina (and its Galápagos friends), Karthala, Erta Ale, Tolbachik, Masaya, and many others.

Answer 2

Ancient volcanic activity in Big Bend is recorded by volcanic ash and extensive lava flows. Molten rock found many ways to intrude into the country rock 30 to 40 million years ago. The oldest rocks in the area are around 500 million years old, so 10 million years of volcanic activity is a relatively short amount of time. The volcanic activity is directly related to a period of mountain building in the park. For example, Burro Mesa and the Chisos Mountain range are a result of volcanic
activity. Large or small amounts of molten rock slowly made underground magma tunnels through the rock strata. The magma that did not reach the surface finally cooled and hardened. These areas are known as igneous intrusions which commonly form as either laccoliths or sills. Laccoliths form from lateral spreading of the magma into mushroom shaped intrusions, whereas sills simply spread laterally and remain as a flat intrusion of igneous rock in the country rock. Another pathway for magma to travel is through fractures or faulting. Dikes fill available space from the faulting and cut through the strata at high angles. In Big Bend National Park, a few of these magma masses reached the surface with great explosions of ash, cinder and lava. However, the typical scene was much more calm. Lava flowed quietly and slowly from most of the vents. The more explosive and impressive eruptions would have come from composite type volcanoes, whereas the source of the more quite and slow eruption would have come from shield volcanoes.

Composite volcanoes represent some of the greatest and most violent types of volcanoes on earth's surface. A typically composite volcano is a steep sided, large structure with a symmetrical cone. The cone is built from alternating layers of lava flow, volcanic ash, cinders, blocks, and bombs. This layering system can result in cones as tall as 8,000 feet above sea level.
There are two routes lava can flow from a composite volcano. The first is by breaking through the crater walls from fissures on the sides of the cone. The lava then cools once it has filled the fissures and acts as a dike. This cooling activity acts as a benefit to the cone because it adds in its strength and stability. The other direction of flow is simply from the crater at the opening of the volcano.
The most distinctive characteristic of the composite volcano is the conduit system. The conduit system allows for a magma reservoir deep inside the earth's crust. The pressure and the volume of magma is allowed to build up under the crust until it is released in a violent eruption. The eruptions of ash, lava, and cinder are responsible for the continuing growth of a volcano.
However, large composite cones can not be seen in Big Bend today. So, what happened to these giant mountains? When a composite volcano becomes dormant, erosion because the most powerful player. The cone is destroyed and the hardened magma in the fissures and conduit becomes exposed. This hardened magma, usually a basalt, is also subject to erosion, but the erosion is much slower because the rock is more resistant. All that remains of the ancient composite volcanoes are plugs and dike structures raising above the land surface.
The shape of a shield volcano is very distinctive, and is the direct result of the characteristics of its lava flows. The cone is very wide but not nearly as tall as a composite volcano and is built almost entirely from lava flow. The lava flows in all directions from a central vents and from many other side vents. After thosands of these small and gentle flows, a broad, gentle sloping dome is built. The highly fluid lava flow that is typical of shield cones is called basalt lava. Basalt lava spreads over a great distance and cools very slowly as thin sheets with gentle dips. Even though the lava flow is not as explosive as the composite volcanoes, shield volcanoes can still reach very large sizes. Present shield volcanoes can have diameters of 3 to 4 miles and heights up to 2,000 feet above sea level.