Image of hot lava in the crater of a volcano.

Did you know? Magma is molten rock inside Earth. Once molten rock erupts from a volcano, it’s called lava. Lava will then cool into solid rock. Image: USGS

It’s no secret that volcanoes are dangerous. The recent eruption of Guatemala’s Volcán de Fuego has taken more than 110 lives. In Hawaii, lava has covered roads, destroyed cars and set fire to buildings. So it may come as a surprise to hear that people are wondering if they can use volcanoes to toast their marshmallows.

On Twitter, Jay Fur asked: “Is it safe to roast marshmallows over volcanic vents? Assuming you had a long enough stick, that is? Or would the resulting marshmallows be poisonous?”

Jay received a response from the United States Geological Survey, a government agency that studies the landscape of the United States. They wrote, “Erm…we’re going to have to say no, that’s not safe. (Please don’t try!) If the vent is emitting a lot of SO2 or H2S, they would taste BAD. And if you add sulfuric acid (in vog, for example) to sugar, you get a pretty spectacular reaction.”

It’s clear that the USGS don’t want Jay to eat volcanic marshmallows, but there’s a lot of technical language in their message that might be hard to understand. So what’s actually going on?

When a volcano erupts, it’s not just molten rock that comes out of the ground. Gases that were dissolved in magma are released on the way to the surface. It’s these gases that the USGS are worried about. SO2 (or SO2) is sulfur dioxide, a poisonous gas with a pungent smell, and H2S (or H2S) is hydrogen sulfide, a poison also known as rotten egg gas. Both of these gases are reactive, and could form poisonous chemicals in a marshmallow.

Plus, when exposed to air, sunlight and water, these gases can create a dangerous volcanic fog known as vog. The sulfur in volcanic gases and water in the air react to form H2SO4, otherwise known as sulfuric acid. In humans, vog can cause lung damage and breathing difficulties among other symptoms. It can also kill plants and harm animals.

Sulfuric acid also reacts with sugar in a way that is spectacular but dangerous. Sugar is made of hydrogen (H), oxygen (O) and carbon (C). Sulfuric acid pulls hydrogen and oxygen out of the sugar to make water (H2O), much of which is released as steam. It leaves behind a tower of carbon ash, a bunch of heat, and a cloud of poisonous fumes. You can watch videos of this reaction on the internet, but don’t try this at home.

So to wrap up, volcanoes are dangerous and no place to roast marshmallows. Volcanic gases can poison you, or create deadly fog that reacts with marshmallow to turn it to ash. Much better to roast marshmallows over a campfire instead!

Updated on 14 June 2018 to incorporate the latest information from Volcán de Fuego.

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One response

  1. super boy Avatar
    super boy

    still, I want to roast a marshmallow on a volcano still

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