Q:

How do volcanoes form?

A:

Quick Answer

Commonly, volcanoes form at points where the Earth's crust is thinnest. This is normally near fault lines, but has been known to occur in the middle of tectonic plates or even in subduction zones, where one plate is pushing another plate down under it.

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Full Answer

Volcanoes begin as vents on the ocean floor or geothermal hot spots on the Earth's surface. Hawaii's volcanic activity is one example of molten rock finding its way to the surface through vents in the ocean floor. Meanwhile, Mount St. Helens is an example of a subduction zone volcano. In both instances, magma has pushed its way up from the mantle and into the upper crust. With vent formations, lava builds up over time, layering on top of itself, and eventually a mountainous formation develops. With subduction zone volcanoes, the mountain forms first, with molten rock pushing up through thin layers of crust. This was part of why the eruption of Mount St. Helens was so dangerous, as the pressure of the heated magma built up over time and caused the top portion of the mountain to be blasted away. Of course, every volcanic eruption is dangerous, though the characteristic lava eruptions make much slower progress than the energetic activity found in previously dormant volcanoes.

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Related Questions

  • Q:

    What are some facts about underwater volcanoes?

    A:

    One interesting fact about underwater volcanoes is that they deposit about 75 percent of the annual magma output on Earth. The molten magma and hardened lava shape the ocean floor and create the edges of the new plates on the ocean floor.

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  • Q:

    Where does lava come from?

    A:

    According to the American Geophysical Union, lava forms in the Earth's mantle and flows to the surface through volcanoes. Internal gas pressure within the volcano causes it to spew lava with the amount of pressure depending on how much and how quickly.

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  • Q:

    How many volcanoes are there?

    A:

    The number of potential active volcanoes on Earth is estimated to be about 1500, with 550 of these having erupted in recorded history. The total number of volcanoes throughout the entire world is unknown, because not all volcanoes are accessible, known and recorded.

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  • Q:

    How do volcanoes work?

    A:

    Volcanoes are vents in the Earth's crust that allow liquid lava from inside the planet to travel to the surface. According to Reference.com, the word "volcano" applies to both the vent and the cylindrical cone the lava forms.

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