Land-forms from Lava and Ash
Shield Volcano
A shield volcano is a type of volcano usually built almost entirely of fluid magma flows. They are named for their large size and low profile, resembling a warrior’s shield lying on the ground. This is caused by the highly fluid lava they erupt, which travels and spreads on a surface. This results in the steady accumulation of broad sheets of lava, building up the shield volcano’s distinctive form. The shape of shield volcanoes is due to the low-viscosity magma. Since low-viscosity magma is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones rising from a hot spot on the ocean floor, like the Mauna Kea shield volcano; and they are common in Iceland, and Galapagos Islands, as well.
Cinder Cone Volcano
Cinder cones result from pyroclastic eruptions of mostly cinders, (hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 meters high. Cinder cones are the most common type of volcano and also the smallest type. Most cinder cones erupt only once, with the exception of the Cerro Negro volcano in Nicaragua, which is the Earth’s most historically active cinder cone. Cerro Negro has erupted more than twenty times since it was born in 1850. Parícutin in Mexico and Sunset Crater in Arizona are other examples of cinder cones. In New Mexico, Caja del Rio is a volcanic field of over 60 cinder cones.
Based on satellite images it was suggested that cinder cones might occur on other terrestrial bodies in the Solar system too; on the surface of Mars and the Moon.
Stratovolcanoes or Composite Volcanoes
Stratovolcanoes or composite volcanoes are tall conical mountains composed of lava flows and explosive eruptions of ash, cinder, and lava in alternate layers. Cinders and ash pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the process repeats. Classic examples include Mount Fuji in Japan, Mayon Volcano in the Philippines, Mount St. Helens in Washington State, and Mount Vesuvius and Stromboli in Italy. Stratovolcanoes typically form at convergent plate boundaries where subduction occurs; they are particularly abundant along the Ring of Fire, for example the high peaks of the Andes Mountains in South America.
Throughout recorded history, ash produced by the explosive eruption of stratovolcanoes has posed the greatest volcanic hazard to civilizations.
Lava Plateaus
Lava plateaus are formed by highly fluid (runny) lava during numerous successive eruptions through numerous vents without violent explosions. These eruptions are quiet because of low viscosity of lava, so that it is very fluid and contains a small amount of trapped gases. Multiple successive and extensive lava flows cover the original landscape to after millions of years form a plateau, which may contain lava fields, cinder cones, shield volcanoes and other volcanic landforms. An example is the massive Level Mountain shield volcano in northern British Columbia, Canada, which covers an area of 1,800 km 2, and another one is the Columbia River Plateau in Washington.
Caldera
Caldera it’s a type of volcanic crater (from one to dozens of kilometers in diameter); a huge hole formed by the collapse of a volcanic mountain due to an enormous eruption that may empty the main vent and the magma chamber. The mountain becomes a hollow shell and collapses inward. Usually is a very large composite volcano that after an explosive period collapses. Examples, Chicoma Mountain in New Mexico, and Mount St. Helens in Washington State, its caldera was created 1980 after an earthquake, measuring 5.1 on the Richter scale, caused an eruption that reduced the elevation of the mountain’s summit from 2,950 m to 2,549 m, replacing it with a 1.6 km wide horseshoe-shaped crater.
Land-forms from Magma
When magma forces its way through cracks in the upper crust, but fails to reach the surface and eventually cools down. Over time is exposed, because of weathering and erosion, and we can see the features formed:
1. Volcanic Necks: Looks like a giant tooth stuck in the ground. It forms when magma hardens in a volcano’s pipe. Look at the picture of Shiprock in New Mexico.
2. Dikes: When magma forces itself across rock layers hardens into a dike. Look at the picture of a dike cross-cutting horizontal layers of sedimentary rock.
3. Sills: When magma squeezes between horizontal layers of rock it forms a sill. Look at the picture of a sill cutting sandstones, in Horton Bluff, Minas Basin South Shore, Nova Scotia.
4. Batholiths: Large rock masses that form the core of many mountain ranges. Look at the figure of Castle Peak that is the highest point on the Idaho Batholith.
5. Dome Mountains: Smaller bodies of hardened magma. It forms when uplift pushes a batholith toward the surface. Look at the figure of Round Mountain in northwestern British Columbia, Canada.
Geothermal Activity
Geothermal activity it’s when magma, a few kilometers beneath Earth’s surface, heats underground water. This will result in:
Hot spring: hot water rises to the surface and collects in a natural pool. Look a the picture of Macaques enjoying an open air hot spring or “onsen” in Nagano, Japan.
2. Geysers: fountain of water and steam that erupts from the ground. Look at the figure of Steam phase eruption of Castle Geyser in Yellowstone National Park.
Sources:
1. Science Explorer Earth Science, Prentice Hall.
2. Wikipedia
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