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Recently there was an online news article that mentioned cold magma that was flowing on the land. What is cold magma? – Matt, 7, Illinois

Dear Matt,

When I think about volcanoes, I picture molten magma deep inside the Earth. Or burning hot lava pouring down the side of a mountain. But you’re right that there have been news reports that mention cold lava.

I talked about what that could be with my friend Katie Cooper. She’s a geologist at Washington State University.

She told me the news may be using “cold lava” to describe a lahar. That’s a mix of water and rocky debris that sometimes whooshes down the side of a volcano. It's also called a debris flow or a volcanic mud flow.

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How do volcanoes erupt? –Miles, 10, Tampa, FL

Wherever we find a volcano on the surface of our planet, we can find the source of an eruption beneath it. That’s what I found out from my friend John Wolff, a volcanologist at Washington State University. Our planet is home to all kinds of volcanoes that erupt in different ways. Some eruptions are quiet and continuous, with a slow flow of lava. Other volcanoes erupt explosively and can spew ash and lava hundreds of feet up into the sky. All of this lava has its start underground in the form of something called magma. Wolff said that scientists used to think there were large pools of hot liquid beneath volcanoes. Now we know it isn’t quite that simple. Magma is not really a liquid, but rather a kind of sludge or slurry. It helps to think of it kind of like honey. Read More ...