Answer:
When two oceanic plates collide one oceanic plate is eventually subducted under the other. Where one plate slides under the other is referred to as the 'subduction zone'. As the subducting plate descends into the mantle where it is being gradually heated a benioff zone is formed. This benioff zone is a zone of shallow,intermediate and deep focused earthquakes. Some deep focused earthquakes that occur at ocean ocean- collision boundaries can be as deep as 670 kilometres. As the subducted plate descends into the mantle it is gradually heated allowing the formation of magma. The magma that forms is andesitic in composition and begins to form when the subducted plate reaches a depth of 100 kilometres. This andesitic magma is formed from the partial melting of the asthenosphere just above the subduction zone. This partial melting of the subducting plate is due to the loss of water as it descends into the mantle. The andesitic magma is now less dense than the surrounding material so it rises through the crust and erupts to form an arc of volcanoes called an island arc. The distance between the trench and the island arc depends greatly upon where the subducting plate reaches the 100 kilometer depth. If the subduction angle is steep then the distance between the arc and the trench will be short.If the suduction angle is shallow the distance is longer. The main features are indicated in the diagram below. The swell is seen by a bulge in the in the downgoing plate where it is subducted into the mantle.where the plate subducts into the mantle is known as the trench.the forearc ridge contains highly deformed sedimentary and metemorphic rock. The backarc region is located behind the arc and can be compressed or extended.
Explanation:
Divergent boundaries are the tectonic boundaries that results two tectonic plates pulling apart.
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Hello!
The correct answer is: About 80,000
(I believe there are almost 90,000 now)
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<span>What is one reason why democracies in sub-Saharan Africa tend to be fragile?
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c. Ethnic conflicts, made worse by poorly drawn borders, destabilize many attempts at government.
Democracy is known as a "government by the people". In the sub-Saharan Africa scenario corruption is rampant. It is most especially rampant in the government level. That is why their democracy is very fragile because those who are tasked to keep law and order are the ones breaking the laws to fill their own pockets and satisfy their own interests to the detriment of the people.
The Yellowstone caldera differs from most other volcanoes in that it is classified with a Volcanic Explosivity Index(VEI) of 8. What this means is that the volcano can potentially have a volcanic ejecta mass of over 1,000,000,000,000 tons. Now compare this to the VEI of some other volcanoes:
<span>Eyjafjallajökull: 4
</span>Mt. St. Helens: 5
Krakatoa: 6
Tambora: 7
There is only a small number of known VEI 8 eruptions, only around 42 in the last 36 million years with the last known one being 25,360 years ago. In other words, Yellowstone is really dangerous and should be monitored closely.
