As the sediments subduct, the water rises into the overlying mantle material and lowers its melting point. Melting in the mantle above the subducting plate leads to volcanoes within an island or continental arc. Why does melting occur at convergent plate boundaries? This water lowers the melting point of the mantle material, which increases melting. Volcanoes at convergent plate boundaries are found all along the Pacific Ocean basin, primarily at the edges of the Pacific, Cocos, and Nazca plates.
Trenches mark subduction zones, although only the Aleutian Trench and the Java Trench appear on the map in figure 3. Remember your plate tectonics knowledge. Large earthquakes are extremely common along convergent plate boundaries. Of course, these volcanoes are caused by the abundance of convergent plate boundaries around the Pacific.
Figure 3. The Cascade Range is formed by volcanoes created from subduction of oceanic crust beneath the North American continent. The Pacific Ring of Fire is where the majority of the volcanic activity on the Earth occurs. A description of the Pacific Ring of Fire along western North America is a description of the plate boundaries. This incredible explosive eruption of Mount Vesuvius in Italy in A. Trenches mark subduction zones. The Cascades are a chain of volcanoes at a convergent boundary where an oceanic plate is subducting beneath a continental plate.
The volcanoes are located just above where the subducting plate is at the right depth in the mantle for there to be melting Figure 3. The Cascades have been active for 27 million years, although the current peaks are no more than 2 million years old. The volcanoes are far enough north and are in a region where storms are common, so many are covered by glaciers. The Cascades are shown on this interactive map with photos and descriptions of each of the volcanoes.
At divergent plate boundaries hot mantle rock rises into the space where the plates are moving apart. As the hot mantle rock convects upward it rises higher in the mantle. The rock is under lower pressure; this lowers the melting temperature of the rock and so it melts. Lava erupts through long cracks in the ground, or fissures. Why does melting occur at divergent plate boundaries? Hot mantle rock rises where the plates are moving apart. This releases pressure on the mantle, which lowers its melting temperature.
Volcanoes erupt at mid-ocean ridges, such as the Mid-Atlantic ridge, where seafloor spreading creates new seafloor in the rift valleys. Where a hotspot is located along the ridge, such as at Iceland, volcanoes grow high enough to create islands figure 5. They cause more damage in poorer countries, where there are fewer resources to predict and prepare for them.
Where are volcanoes found? Volcanoes usually form along plate boundaries , where tectonic plates are either moving towards or away from one another: Constructive boundary or divergent boundary - this is where two plates move away from one another. Volcanoes are one kind of feature that forms along convergent plate boundaries, where two tectonic plates collide and one moves beneath the other. This photo shows an explosion near the summit of the West Mata volcano within the Pacific Ocean; the image area is about 1.
Download larger version jpg, 1. Heat within the asthenosphere creates convection currents that cause tectonic plates to move several centimeters per year relative to each other. If two tectonic plates collide, they form a convergent plate boundary. These subduction zone s can create deep trench es. As the denser plate edge moves downward, the pressure and temperature surrounding it increases, which causes changes to the plate that melt the mantle above, and the melted rock rises through the plate, sometimes reaching its surface as part of a volcano.
Over millions of years, the rising magma can create a series of volcanoes known as a volcanic arc. The majority of volcanic arcs can be found in the Ring of Fire , a horseshoe-shaped string of about volcanoes that edges the Pacific Ocean. If you were to drain the water out of the Pacific Ocean, you would see a series of deep canyon s trenches running parallel to correspond ing volcanic island s and mountain ranges.
These mountains are continually built up as the Nazca plate subducts under the South American plate. For many years, scientists have been trying to explain why some volcanoes exist thousands of kilometers away from tectonic plate boundaries.
The dominant theory, framed by Canadian geophysicist J. These hot spot s are able to independently melt the tectonic plate above them, creating magma that erupts onto the top of the plate. In hot spots beneath the ocean, the tectonic activity creates a volcanic mound.
Over millions of years, volcanic mounds can grow until they reach sea level and create a volcanic island. The volcanic island moves as part of its tectonic plate. The hot spot stays put, however. As the volcano moves farther from the hot spot, it goes extinct and eventually erode s back into the ocean. For Wilson and many scientists, the best example of hot spot volcanism is the Hawaiian Islands.
Experts think this volcanic chain of islands has been forming for at least 70 million years over a hot spot underneath the Pacific plate. Of all the inhabit ed Hawaiian Islands, Kauai is located farthest from the presumed hot spot and has the most eroded and oldest volcanic rocks, dated at 5.
Hot spots can also create terrestrial volcanoes. The Yellowstone Supervolcano , for instance, sits over a hot spot in the middle of the North American plate, with a series of ancient caldera s stretching across southern Idaho. The Yellowstone hot spot fuels the geyser s, hot spring s, and other geologic activity at Yellowstone National Park, Wyoming. While volcanoes come in a variety of shapes and sizes, they all share a few key characteristics. All volcanoes are connected to a reservoir of molten rock, called a magma chamber , below the surface of the Earth.
When pressure inside the chamber builds up, the buoyant magma travels out a surface vent or series of vents, through a central interior pipe or series of pipes. These eruptions, which vary in size, material, and explosiveness, create different types of volcanoes.
Stratovolcano es are some of the most easily recognizable and imposing volcanoes, with steep, conic peaks rising up to several thousand meters above the landscape. Also known as composite volcanoes, they are made up of layers of lava, volcanic ash , and fragment ed rocks. Mount Rainier is an impressive stratovolcano that rises 4, meters 14, feet above sea level just south of Seattle, Washington.
Over the past half million years, Mount Rainier has produced a series of alternating lava eruptions and debris eruptions. These eruptions have given Mount Rainier the classic layered structure and conic shape of a composite volcano. Volcan de Fuego and Acatenango are a pair of stratovolcanoes that stand more than 3, meters 12, feet above sea level near Antigua, Guatemala. While the volcanoes are considered twins because of their similar shape and size, they are made of different types of lava and have distinct eruption histories.
While Acatenango erupts infrequent ly today, Fuego is considered to be the most active volcano in Central America, erupting more than 60 times since Shield volcano es are built almost exclusive ly of lava, which flows out in all directions during an eruption.
These flows, made of highly fluid basalt lava, spread over great distances and cool in thin layers. While they are not as eye-catching as their steep stratovolcano cousins, shield volcanoes are often much larger in volume because of their broad, expansive structure. Shield volcanoes make up the entirety of the Hawaiian Islands.
The Galapagos Islands are also made up of a series of shield volcanoes. Isabela and Fernandina islands have flatter tops than other shield volcanoes because lava erupts from fissures around their tops and along ridges at their bases. Pyroclastic cone s are the most prolific type of volcano on Earth.
They can develop as part of stratovolcanoes, shield volcanoes, or independently. Also known as cinder cone s, they form after violent eruptions blow lava into the air.
Often formed from a single eruption or short series of eruptions, pyroclastic cones only stand at heights of tens of meters to hundreds of meters. It was the first volcano to be studied for its entire life cycle. In that time, lava and ash buried the nearby town of San Juan. Lava dome s are like shield volcanoes in that they are built entirely of lava. This lava, however, is too thick and sticky to move great distances. It just piles up around the volcano vent. Lava domes are often found on the summit or flank s of a volcano, but they can also develop independently.
Like pyroclastic cones, they only reach a few hundred meters, as they are formed during singular eruptions or slow lava releases. For almost a year, a lava dome grew out of a summit crater created from the eruption, reaching a height of more than meters 1, feet. It ultimately collapse d into a pile of rubble after 11 months of growth. Some volcanoes experience such large, explosive eruptions that they release most of the material in their magma chamber.
This causes the land around the erupting vent or vents to collapse inwardly, creating circular depression s called calderas. Depending on their intensity and duration , volcanic eruptions can create calderas as much as kilometers wide. Crater Lake, Oregon, is in a caldera about 10 kilometers 6 miles wide.
The volcano's magma chamber collapsed, then filled with water from rain and snow, creating the lake. Crater Lake is the deepest lake in the United States. Deception Island, located off the coast of Antarctica, experienced a violent eruption roughly 10, years ago. The volcano summit collapsed, forming a caldera 7 kilometers 4.
The caldera gives Deception Island its horseshoe shape, which opens to the sea through a narrow channel. Much like calderas, craters are depressions left after a volcano experiences a large eruption. While calderas are formed by the collapse of material inside a volcano, craters are formed as materials explode out from a volcano.
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