What type of lava does a shield volcano have

Eruptions of these volcanoes are not generally explosive, but are more like liquid overflowing around the edges of a container. The world's largest volcano, Mauna Loa in Hawaii , is a shield volcano, according to the U. Mauna Loa is about 55, feet 17, meters from its base beneath the ocean to the summit, which is 13, feet 4, meters above sea level. It is also one of the Earth's most active volcanoes and is carefully monitored. The most recent eruption was in Lava domes are built up when the lava is too viscous to flow , according to the U.

A bubble or plug of cooling rock forms over a fissure. This cooler, thick lava usually rises near the end of an explosive eruption and lava domes often form within the craters of stratovolcanoes.

Helens has several well-defined lava domes inside the crater , according to NASA. Besides well-known symmetrical volcanoes such as Mount Fuji in Japan and Kilimanjaro in Tanzania, volcanic activity is responsible for several other distinctive landforms. Calderas : A caldera is a bowl-shaped depression formed when a volcano collapses into the void left when its magma chamber is emptied. There are three types , according to San Diego State University.

The first type is a crater lake caldera. This is the result of a stratovolcano collapsing into its magma chamber during a violent eruption. Basaltic calderas have a concentric ring pattern resulting from a series of gradual collapses rather than a single event. They are often found at the summit of shield volcanoes such as the craters at the tops of Mauna Loa and Kilauea. Resurgent calderas are the largest volcanic structures on Earth.

They are the result of catastrophic eruptions that dwarf any eruptions ever recorded by human beings. Yellowstone caldera, sometimes called a "super volcano," is one example. Volcanic plugs : When magma solidifies in the fissure of a volcano the hard dense rock may form a " neck " that remains when softer surrounding rock has been eroded away, according to the U.

Ash released from shield volcanoes often builds up around the vent forming a steep, round hill known as a cinder cone. A lava tube may also form, beneath the surface of the ground, when low viscosity lava develops a hard crust through which lava flows.

A caldera is a large-scale volcanic crater that could be several kilometres in diameter. It is formed either when the magma chamber is emptied and the roof collapses, or through a massive explosive volcanic eruption.

Due to the higher viscosity of magmas erupted from these volcanoes, they are usually more explosive than shield volcanoes. Stratovolcanoes sometimes have a crater at the summit that is formed by explosive ejection of material from a central vent. Sometimes the craters have been filled in by lava flows or lava domes, sometimes they are filled with glacial ice, and less commonly they are filled with water.

Cinder Cones also called Tephra Cones. Parts of the crater walls eventually collapse back into the crater, the vent is filled with loose material, and, if the crater still is deeper than the water table, the crater fills with water to form a lake, the lake level coinciding with the water table. Volcanic Domes also called Lava Domes. Blocks of nearly solid lava break off the outer surface of the dome and roll down its flanks to form a breccia around the margins of domes.

The surface of volcanic domes are generally very rough, with numerous spines that have been pushed up by the magma from below. Calderas are much larger depressions, circular to elliptical in shape, with diameters ranging from 1 km to 50 km. Calderas form as a result of collapse of a volcanic structure. The collapse results from evacuation of the underlying magma chamber.

In shield volcanoes, like in Hawaii, the evacuation of the magma chamber is a slow drawn out processes, wherein magma is withdrawn to erupt on from the rift zones on the flanks. If magma leaks back to the surface during this resurgent doming, then eruptions of small volcanic domes can occur in the area of the resurgent domes. A fumarole is vent where gases, either from a magma body at depth, or steam from heated groundwater, emerges at the surface of the Earth.

Since most magmatic gas is H 2 O vapor, and since heated groundwater will produce H 2 O vapor, fumaroles will only be visible if the water condenses. H 2 O vapor is invisible, unless droplets of liquid water have condensed. Hot springs or thermal springs are areas where hot water comes to the surface of the Earth.

Cool groundwater moves downward and is heated by a body of magma or hot rock. A hot spring results if this hot water can find its way back to the surface, usually along fault zones. Minerals dissolved in the high temperature water are often precipitated when the water cools at the surface. This produces spectacular deposits of travertine chemically precipitated calcite, or siliceous sinter.

Bacteria forming microbial mats under the water are responsible for the coloration often seen in hot springs. Different species, with different colors thrive at different temperatures. A geyser results if the hot spring has a plumbing system that allows for the accumulation of steam from the boiling water.

When the steam pressure builds so that it is higher than the pressure of the overlying water in the system, the steam will move rapidly toward the surface, causing the eruption of the overlying water.

Some geysers, like Old Faithful in Yellowstone Park, erupt at regular intervals. The time between eruptions is controlled by the time it takes for the steam pressure to build in the underlying plumbing system. Plateau or Flood basalts are extremely large volume outpourings of low viscosity basaltic magma from fissure vents. The basalts spread huge areas of relatively low slope and build up plateaus. The only historic example occurred in Iceland in , where the Laki basalt erupted from a 32 km long fissure and covered an area of km 2 with 12 km 3 of lava.

As a result of this eruption, homes were destroyed, livestock were killed, and crops were destroyed, resulting in a famine that killed people. Volcanoes and Plate Tectonics.

In the discussion we had last lecture about how magmas form, we pointed out that since the upper parts of the Earth are solid, special conditions are necessary to form magmas. These special conditions do not exist everywhere beneath the surface, and thus volcanism does not occur everywhere. If we look at the global distribution of volcanoes we see that volcanism occurs four principal settings. Along divergent plate boundaries, such as Oceanic Ridges or spreading centers.

In areas of continental extension that may become divergent plate boundaries in the future. Along converging plate boundaries where subduction is occurring.

They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world.

Schematic representation of the internal structure of a typical cinder cone. Explosive eruptions caused by gas rapidly expanding and escaping from molten lava formed cinders that fell back around the vent, building up the cone to a height of 1, feet. The last explosive eruption left a funnel-shaped crater at the top of the cone.

After the excess gases had largely dissipated, the molten rock quietly poured out on the surrounding surface of the cone and moved downslope as lava flows. This order of events--eruption, formation of cone and crater, lava flow--is a common sequence in the formation of cinder cones. S ome of the Earth's grandest mountains are 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, feet above their bases.

Helens and Mount Rainier in Washington. M ost 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. T he 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.