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Volcanoes: Top 10 Questions

November 2015

Thanks to Jeffrey Johnson, associate research professor of geophysics, Boise State University; and Brittany Brand, assistant professor in the department of geophysics, Boise State University for the answers.

1: Why do volcanoes erupt?

Magma is a liquid. It is stored within the crust and because it is a liquid, it is less dense than the surrounding rock. Therefore, it is going to rise buoyantly through the crust toward the surface. When it gets to the surface, the pressure inside that intrusion of magma gets so high that it finally exceeds the ability of the rock to hold it in. It's like filling up a water balloon too full. Eventually it's going to pop and open. So essentially, volcanoes erupt when the lava, or the magma, gets so close to the surface that it punches out. (From Natalie at Cole Valley Christian School in Boise)

2: How many active volcanoes are there in the world?

Active volcanism is defined as a volcano that has erupted in the last 10,000 years. This means there are 1,500 active volcanoes, and about 500 of those have erupted during historic times. Today, there are about 20 volcanoes world wide that are in eruption. (From Ashland at Longfellow Elementary School in Boise)

3: What makes lava rise?

We call magma when it's in the ground, "molten rock." "Lava," is what we call it when it erupts onto the ground. Magma rises like a hot air balloon rises. This is because it's less dense than the surrounding rock. It rises through the crust until it makes its way to the surface to erupt. (From Alex at Edahow Elementary School in Pocatello)

4: What are the signs of a volcano when it's about to erupt?

Volcanologists are very interested in understanding and forecasting volcanic eruptions. They look at four main things to understand if a volcano is getting ready to erupt. They watch the earthquake activity underneath the ground. They study the deformation of a volcano. They also check to see if the volcano is growing in size. Finally, they look at the gasses and temperature coming out of a volcano. These four things together help us determine if a volcano may soon erupt. (From Emma at Lewis and Clark Elementary School in Pocatello)

5: How far do volcanoes shoot lava?

If lava is coming out of a volcano, it doesn't shoot up into the sky. It flows across the ground. When lava, or magma, becomes explosive, it's because it has gas in it. The gases expand and rip the lava apart, shooting up into the air. It can go anywhere from a couple hundred feet all the way up to 30 miles into the atmosphere. (From Nathan at River Valley Elementary School in Meridian)

6: How hot is liquid magma?

Liquid magma is really hot. In order to melt rock and create magma or lava, you need to have temperatures of at least 1,500 degrees Fahrenheit. Some lava is as hot as 2,200 degrees Fahrenheit. (From Ryan at Cynthia Mann Elementary School in Boise)

7: How many times can a volcano erupt?

A volcano can erupt as long as it has a supply of magma from depth. So, really it can erupt many times. They can erupt continuously for years, or they can erupt over the course of a few days and then stop for many hundreds of years. It really depends on the characteristics of the specific volcano. (From Jeff at Cynthia Mann Elementary School in Boise)

8: How many different kinds of lava are there?

There are more types of lava on earth than there are flavors of ice cream. You can have lava that is very thick and sticky. This lava doesn't flow very easily and might just pile up inside a volcanic crater. Lava can also be really fluid and flow quite far from the volcano. Two styles of lava that you might be familiar with are pahoehoe and a'a. These lavas have the same composition, but one of them, pahoehoe, moves very slowly across the ground and forms smooth surfaces. A'a, on the other hand, usually moves faster and tumbles around forming really rough surfaces. (From Nick at Anser Charter School in Boise)

9: How do people know when a volcano is extinct?

We can't be absolutely certain that a volcano won't erupt again. Generally, when a volcano hasn't erupted for 10,000 years, we declare that volcano to be dead. However, in many cases, we don't know that the volcano hasn't erupted for that many years. In other cases, a volcano that has been quiet for 10,000 years may awaken. There have been plenty of examples of volcanoes that were thought to be extinct that have erupted. (From Adrianna at Cynthia Mann Elementary School in Boise)

10: Could volcanoes be a renewable thermal energy source?

Volcanic areas are one of the premier examples of renewable energy resources. A common misconception is that the geothermal energy that comes from volcanic areas taps into the actual magma, and this is not true. We tap into the hot ground surrounding the volcanic area. One country that does an exceptionally good job with harvesting geothermal energy from volcanoes is Iceland. (From Kai at North Junior High School in Boise)


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