In reality, these two phenomena rarely occur in the same volcano. Volcanic eruptions tend to be one or the other. Imagine the devastation and force caused by the atom bomb dropped on Nagasaki at the end of World War II in which over 40, people died. Now imagine an explosion 10, times as powerful. Explosive volcanic eruptions can be that powerful Figure 8. As hot magma beneath the surface interacts with water, gases accumulate and the magma pressure builds up.
This pressure grows and grows until these dissolved gases cause it to burst in an enormous explosion. This great explosion takes with it the magma and volcanic gases, which can shoot many kilometers into the sky and forms a mushroom cloud, similar to that formed by a nuclear explosion Figure 8. The debris travels up into the air at very high speeds and cools in the atmosphere to form solid particles called pyroclasts. Some of these particles can stay in the atmosphere for years, which can disrupt weather patterns and affect the temperature of the Earth.
The rest of the debris comes falling back to Earth where it rains down for kilometers and kilometers around. Redoubt in Alaska, This huge mushroom cloud reached 45, feet and caught a Boeing in its plume. Sometimes secondary explosions occur that are even greater than the first. Additionally, volcanic gases like water vapor, carbon dioxide, sulfur dioxide, hydrogen sulfide, and hydrogen chloride can form poisonous and invisible clouds that roam about the atmosphere.
In the Cascade Range, the explosive eruption of Mount St. Helens was preceded by the eruption of Lassen Peak, one of the three Cascade Volcanoes in northern California. On May 22, , an explosive eruption sent a column of ash and gas 30, feet into the air and triggered a high-speed pyroclastic flow, which melted snow and created a lahar.
Lassen continues to have geothermal activity and could erupt explosively again. Shasta erupts every to years. An eruption would most likely to create a large pyroclastic flow, and perhaps a lahar. However, the volcano could explode like Mt. Mazama, which blew itself in an eruption about 42 times more powerful than Mount St.
Helens in , to create Crater Lake. A second type of volcanic eruption is a non-explosive or effusive eruption Figure 8. Because the composition of magma is different in different volcanoes, the properties of the lava are different. In effusive eruptions, lava flows are relatively calm and do not explode out of the volcano. As a result, people generally have a great deal of warning before lava reaches them, so non-explosive eruptions are much less deadly.
That does not keep them from being destructive, however. Even when we know that a lava flow is approaching, there are few ways of stopping it, given the huge quantity and temperature of lava. All igneous rock comes from magma or lava.
The next time you go hiking near a volcanic zone, you might try to identify the types of lava that the volcano erupted, based on the types of igneous rocks you find. Magma Deep beneath the Earth, magma forms as the first stage in creating a volcano. This occurs because rock below the surface is subjected to great amounts of pressure from gravity. The decay of radioactive materials generates additional heat.
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Subscriber Exclusive Content. Why are people so dang obsessed with Mars? 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.
Numerous hazards result from eruptions and they can have a range of consequences. The most dangerous are the pyroclastic clouds, which destroy anything in their path. Other hazards include ash clouds, ash rain, mudslides, earthquakes, tsunamis, odd weather patterns and glacial flooding. Originally published by Cosmos as Why do volcanic eruptions occur?
Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Other hazards include ash fall, and lahars mud or debris flows. Volcanoes often cause population displacement and food shortages. Learn your volcano risks and warning signs and look out for unusual physical changes around volcanoes, such as increased ash fall or vegetation drying up.
Learn and participate in early warning systems and develop plans for both evacuating and sheltering in place. Be aware of secondary hazards such as landslides, lahars mudflows , ash and thunderstorms. Protect your home from volcanic ash and cover water sources if time allows. Avoid driving during and after ash fall when visibility can be very low and roads are slippery. Protect your lungs and eyes by wearing protective gear such as goggles and masks.
Pay particular attention to vulnerable people and support them to evacuate or shelter in place.
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