The gritty ash feels like fine sand, or dust.

Deadlier than red-hot lava, it spews from volcanoes by the ton. It can lay a suffocating blanket on the land nearby, or it can travel for thousands of miles, carried by wind currents to taint the air on the other side of the world.

In the past, volcanic ash has buried entire cities, hiding them for thousands of years—like the Roman towns Pompeii and Herculaneum. And while we’re safer in many ways from volcanoes today, some modern technology is particularly vulnerable to airborne ash; an eruption of the Icelandic volcano, Eyjafjallajökull, in 2010 was so dangerous to airplanes that much of the air traffic in Europe was shut down for a week.

But it just looks like dust… So what makes volcanic ash so dangerous? Read on to learn more!

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