In comparison, the Mt. Saint Helens eruption ejected about 1 cubic kilometer of material. The eruptions from supervolcanoes can be so large that the ash ejected into the air blocks the Sun and lowers the temperature on the entire planet.
The lowered temperatures caused by these eruptions is called a volcanic winter. One can only imagine how such a huge eruption would change the world in modern times. The largest supervolcano in North America is the Yellowstone caldera, which had three super eruptions at 2. Long Valley caldera, south of Mono Lake in California, is the second largest supervolcano in North America, erupting extremely hot and explosive rhyolite around , years ago.
An earthquake swarm in alerted geologists to the possibility of another eruption in the future, but the timing of such an event is unknown. Supervolcanoes are a fairly new idea so the exact cause of supervolcano eruptions is still debated. However, scientists believe that an entire and very large magma chamber erupts in a catastrophic explosion. This enormous eruption creates a huge hole or caldera where the surface area collapses. Skip to main content.
Search for:. Types of Volcanoes When most people think of volcanoes, they think of a tall mountain with a crater on the top, maybe a little snow at the summit and some trees scattered around the base. Lesson Objectives Describe the basic shapes of volcanoes. Compare the features of volcanoes. Describe the stages in the formation of volcanoes. Strato-volcano or Composite Volcano The picture below shows Mt. Licenses and Attributions. What is needed for there to be an enormous volcano? What does this tell us about planets with enormous volcanoes?
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The top then collapsed to form a large depression, which later filled with water and is now completely occupied by beautiful Crater Lake. A last gasp of eruptions produced a small cinder cone, which rises above the water surface as Wizard Island near the rim of the lake. Depressions such as Crater Lake, formed by collapse of volcanoes, are known as calderas. They are usually large, steep-walled, basin-shaped depressions formed by the collapse of a large area over, and around, a volcanic vent or vents.
Calderas range in form and size from roughly circular depressions 1 to 15 miles in diameter to huge elongated depressions as much as 60 miles long.
Crater Lake, Oregon; Wizard Island, a cinder cone, rises above the lake surface. The Evolution of a Composite Volcano A. Magma, rising upward through a conduit, erupts at the Earth's surface to form a volcanic cone. Lava flows spread over the surrounding area. As volcanic activity continues, perhaps over spans of hundreds of years, the cone is built to a great height and lava flows form an extensive plateau around its base.
During this period, streams enlarge and deepend their valleys. When volcanic activity ceases, erosion starts to destroy the cone. After thousands of years, the great cone is stripped away to expose the hardened "volcanic plug" in the conduit. During this period of inactivity, streams broaden their valleys and dissect the lava plateau to form isolated lava-capped mesas. Continued erosion removes all traces of the cone and the land is worn down to a surface of low relief.
All that remains is a projecting plug or "volcanic neck," a small lava-capped mesa, and vestiges of the once lofty volcano and its surrounding lava plateau. Shield volcanoes The internal structure of a typical shield volcano S hield volcanoes, the third type of volcano, are built almost entirely of fluid lava flows. 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.
And, in areas called "hot spots" that are usually located in the interior of plates, away from the plate margins. Diverging Plate Margins Active volcanism is currently taking place along all of oceanic ridges, but most of this volcanism is submarine volcanism and does not generally pose a threat to humans.
One of the only places where an oceanic ridge reaches above sea level is at Iceland, along the Mid-Atlantic Ridge. Here, most eruptions are basaltic in nature, but, many are explosive strombolian types or explosive phreatic or phreatomagmatic types. As seen in the map to the right, the Mid-Atlantic ridge runs directly through Iceland.
All around the Pacific Ocean, is a zone often referred to as the Pacific Ring of Fire, where most of the world's most active and most dangerous volcanoes occur. The Ring of Fire occurs because most of the margins of the Pacific ocean coincide with converging margins along which subduction is occurring. These are all island arcs. Hot Spots Volcanism also occurs in areas that are not associated with plate boundaries, in the interior of plates. These are most commonly associated with what is called a hot spot.
Hot spots appear to result from plumes of hot mantle material upwelling toward the surface, independent of the convection cells though to cause plate motion. Hot spots tend to be fixed in position, with the plates moving over the top. As the rising plume of hot mantle moves upward it begins to melt to produce magmas. These magmas then rise to the surface producing a volcano. But, as the plate carrying the volcano moves away from the position over the hot spot, volcanism ceases and new volcano forms in the position now over the hot spot.
This tends to produce chains of volcanoes or seamounts former volcanic islands that have eroded below sea level. Volcanism resulting from hotspots occurs in both the Atlantic and Pacific ocean, but are more evident on the sea floor of the Pacific Ocean, because the plates here move at higher velocity than those under the Atlantic Ocean.
A hot spot trace shows up as a linear chain of islands and seamounts, many of which can be seen in the Pacific Ocean. The Hawaiian Ridge is one such hot spot trace. Here the Big Island of Hawaii is currently over the hot spot, the other Hawaiian islands still stand above sea level, but volcanism has ceased. Northwest of the Hawaiian Islands, the volcanoes have eroded and are now seamounts.
The ages of volcanic rocks increase along the Hawaiian Ridge to the northwest of Hawaii. The prominent bend observed where the Hawaiian Ridge intersects the Emperor Seamount chain has resulted from a change in the direction of plate motion over the hot spot. Note that when the Emperor Seamount chain was produced, the plate must have been moving in a more northerly direction.
The age of the volcanic rocks at the bend is about 50 million years. Yellowstone appears to be over a continental hot spot that has produced a chain of volcanoes as the North American Plate moves southwestward over the hot spot.
Examples of questions on this material that could be asked on an exam. Natural Disasters. Volcanic Landforms, Volcanoes and Plate Tectonics. Volcanic Landforms Volcanic landforms are controlled by the geological processes that form them and act on them after they have formed.
Shield Volcanoes A shield volcano is characterized by gentle upper slopes about 5 o and somewhat steeper lower slopes about 10 o. Most shields were formed by low viscosity basaltic magma that flows easily down slope away form the summit vent. Most shield volcanoes have a roughly circular or oval shape in map view. Vents for most shield volcanoes are central vents, which are circular vents near the summit.
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