Supervolcano eruptions are extremely rare in Earth history. A supervolcano must erupt more than 1, cubic km cubic miles of material, compared with 1. Helens or 25 km 3 for Mount Pinatubo, a large eruption in the Philippines in Not surprisingly, supervolcanoes are the most dangerous type of volcano. Supervolcanoes are a fairly new idea in volcanology. The exact cause of supervolcano eruptions is still debated.
However, scientists think that a very large magma chamber erupts entirely in one catastrophic explosion. This creates a huge hole or caldera into which the surface collapses Figure below. Yellowstone sits above a hotspot that has erupted catastrophically three times: 2. Yellowstone has produced many smaller but still enormous eruptions more recently Figure below.
The Yellowstone hotspot has produced enormous felsic eruptions. The Yellowstone caldera collapsed in the most recent super eruption. Long Valley had an extremely hot and explosive rhyolite about , years ago. An earthquake swarm in alerted geologists to the possibility of a future eruption, but the quakes have since calmed down.
A supervolcano could change life on Earth as we know it. Ash could block sunlight so much that photosynthesis would be reduced and global temperatures would plummet. No one knows when the next super eruption will be. Skip to main content. Search for:. Types of Volcanoes Lesson Objectives Describe the basic shapes of volcanoes. 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.
Schematic representation of the internal structue of a typical composite volcano. W hen a composite volcano becomes dormant, erosion begins to destroy the cone. As the cone is stripped away, the hardened magma filling the conduit the volcanic plug and fissures the dikes becomes exposed, and it too is slowly reduced by erosion.
Finally, all that remains is the plug and dike complex projecting above the land surface--a telltale remnant of the vanished volcano. Shishaldin Volcano, an imposing composite cone, towers 9, feet above sea level in the Aleutian Islands, Alaska. A n interesting variation of a composite volcano can be seen at Crater Lake in Oregon. From what geologists can interpret of its past, a high volcano--called Mount Mazama- probably similar in appearance to present-day Mount Rainier was once located at this spot.
These calderas are volcanic features that are formed by the collapse of a huge amount of land due to the powerful eruptions. Caldera comes from Latin word, meaning cauldron. Calderas are generally circular shaped geographic formations like the picture in figure 6. These are not singular mountains but entire geographical areas. Yellowstone National Park in Wyoming is another caldera that has blown about a hundred times in the last 16 million years.
Supervolcanoes represent the most dangerous type of volcano. An eruption from a supervolcano could change life on Earth as we know it for many years.
Supervolcanoes were not even accepted in volcanology until this millennium. Many supervolcano eruptions are thought to have occurred, the most recent in New Zealand less than years ago. That explosion was thought to have ejected about cubic kilometers of material. A supervolcano eruption near what is now Colorado was thought to have let loose over 5, cubic kilometers of material millions of years ago.
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.
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