How do volcanoes erupt

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Create Account See Subscription Options. Continue reading with a Scientific American subscription. Sometimes the plates collide, pull apart, or slide alongside each other; resulting in convergent boundaries, divergent boundaries, and transform boundaries. This activity is what drives geological activity, which includes earthquakes and volcanoes.

In the case of the former, subduction zones are often the result, where the heavier plate slips under the lighter plate — forming a deep trench. Over millions of years, this rising magma creates a series of active volcanoes known as a volcanic arc. In short, volcanoes are driven by pressure and heat in the mantle, as well as tectonic activity that leads to volcanic eruptions and geological renewal. The prevalence of volcanic eruptions in certain regions of the world — such as the Pacific Ring of Fire — also has a profound impact on the local climate and geography.

For example, such regions are generally mountainous, have rich soil, and periodically experience the formation of new landmasses. We have written many articles about volcanoes here at Universe Today.

Want more resources on the Earth? Skip to content. Like this: Like Loading Over time these gases expand to times their original size, increasing the pressure on the chamber lid to such an extent that an eruption occurs. This is similar to when you shake a soft drink and it explodes when opening the lid — by shaking it you are separating carbon dioxide molecules, causing a build-up of gas and pressure.

Typically, it will also form pyroclastic clouds: cascades of hot ash, gas and molten rock fragments, which are around degrees Celsius and travel around kilometres per hour.

The fundamental concept of an eruption is that an increase in pressure on the chamber lid causes the magma to be released from beneath it. However, there are variances in the cause of this magma movement and the type of eruption generated.

These can either spread apart and leave a gap in the surface, or they can push underneath one another — a process called subduction. When the plates separate, magma rises slowly in order to fill the gap through a gentle explosion of thin basaltic lava, which is at temperatures from to degrees Celsius. However, when one plate pushes underneath the other, this forces molten rock, sediment and seawater down into the magma chamber. The rock and sediment are melted into fresh magma, and eventually overfill the chamber until it erupts, releasing sticky and thick andesitic lava, at temperatures from to degrees Celsius.

Decreasing temperatures can cause old magma to crystalise and sink to the bottom of the chamber, forcing fresh liquefied magma up and out — similar to what happens when a brick is dropped in a bucket of water. A decrease in external pressure on the magma chamber may also allow for an eruption by minimising its ability to hold back increasing pressures from the inside. This is often caused by natural events, such as typhoons, that decrease rock density, or by glacial melting on top of the chamber lid, which alters molten rock composition.

The volcanoes found in the Hawaiian islands are of this sort. Ultimately, the size of an eruption will depend on the thickness of the magma, the density of gases it contains and the amount of new magma being pushed into the magma chamber.

Basaltic lava allows gas to escape easily, resulting in smaller eruptions, while andesitic and rhyolotic lava makes it harder for the gas to escape, leading to larger eruptions. Lava is often thought to be the main danger of a volcanic eruption, but this is not the case.