If two tectonic plates collide, they form a convergent plate boundary. Usually, one of the converging plates will move beneath the other, a process known as subduction. Deep trenches are features often formed where tectonic plates are being subducted and earthquakes are common.
As the sinking plate moves deeper into the mantle, fluids are released from the rock causing the overlying mantle to partially melt. The new magma molten rock rises and may erupt violently to form volcanoes, often building arcs of islands along the convergent boundary. When two plates are moving away from each other, we call this a divergent plate boundary.
Along these boundaries, magma rises from deep within the Earth and erupts to form new crust on the lithosphere. Continental Hotspots. Text and Illustrations by Robert J. Explore This Park. Types of Plate Boundaries. Active subduction along the southern Alaska coast has formed a volcanic arc with features including the Katmai caldera and neighboring Mount Griggs. Katmai National Park and Preserve, Alaska. NPS photo. Divergent Plate Boundary Volcanic eruptions and shallow earthquakes are common where plates rip apart.
Transform Plate Boundary Shallow earthquakes and little volcanism occur where one plate slides laterally past another. Hotspot In places like Hawaii and Yellowstone, a plate rides over a rising plume of hot mantle, causing earthquakes and a chain of volcanoes. Volcanoes are most common in these geologically active boundaries. The two types of plate boundaries that are most likely to produce volcanic activity are divergent plate boundaries and convergent plate boundaries.
At a divergent boundary , tectonic plates move apart from one another. They never really separate because magma continuously moves up from the mantle into this boundary, building new plate material on both sides of the plate boundary. Here, the North American and Eurasian tectonic plates are moving in opposite directions. The upward movement and eventual cooling of this buoyant magma creates high ridges on the ocean floor.
These ridges are interconnected, forming a continuous volcanic mountain range nearly 60, kilometers 37, miles —the longest in the world. Vent s and fractures also called fissure s in these mid-ocean ridges allow magma and gases to escape into the ocean. Most submarine volcanoes are found on ridges thousands of meters below the ocean surface. Some ocean ridges reach the ocean surface and create landforms. The island of Iceland is a part of the Mid-Atlantic Ridge.
These eruptions were preceded by significant rift ing and cracking on the ground surface, which are also emblematic of diverging plate movement. Of course, divergent plate boundaries also exist on land. The East African Rift is an example of a single tectonic plate being ripped in two. Along the Horn of Africa , the African plate is tearing itself into what is sometimes called the Nubian plate to the west, including most of the current African plate and the Somali plate to the east, including the Horn of Africa and the western Indian Ocean.
At a convergent plate boundary , tectonic plates move toward one another and collide. Oftentimes, this collision forces the dense r plate edge to subduct , or sink beneath the plate edge that is less dense. 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. Craters are usually much smaller than calderas, only extending to a maximum of about one kilometer. Many volcanoes have multiple craters caused by different eruptions.
The Maly Semiachik volcano, located on the Kamchatka Peninsula in far eastern Russia, has six craters at its summit. The youngest of these craters, Troitsky, filled in with water and snowmelt, creating a lake meters feet deep.
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