Start at the Beginning:

Steamy bathrooms have vents, well-made pie crusts have vents and our planet’s surface has vents – we call them volcanoes.

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We live on a thin crust of solid rock sitting atop a thick layer of much denser, flowing molten rock called magma. Big temperature variations (from 870°C to 2200°C) in the magma cause pressure to build up, pushing it upwards to the surface. Finding a weak spot it breaks through, relieving the pressure. This is easiest in the places where shifting tectonic plates meet, which is why most of the volcanoes we need to worry about are dotted around the ‘Ring of Fire’ bordering the Pacific Ocean. Of the global population at risk from volcanoes, 95% are in just seven countries: Indonesia, the Philippines, Japan, Mexico, Guatemala, Ethiopia and Italy.

Are All Volcanoes Dangerous?

Depending how long since their last eruption, volcanoes are regarded as extinct (no known eruptions in at least 10,000 years and none considered likely); dormant (they haven’t erupted recently, maybe not for thousands of years, but could do so at some point); and active (showing signs of unrest up to and including erupting). But unless tectonic movements have left them far from the thinnest parts of the Earth’s crust, even supposedly extinct volcanoes can spring back to life.

Why Do They Affect Planes?

While travellers and airlines hate it, there are good reasons to ground planes if they’re at risk from volcanic ash clouds, which can rise 30 km and travel more than 1500 km. Unlike normal clouds, ash clouds consist of minute glass particles and pulverised rock. If sucked into a plane engine these can melt and then solidify, causing numerous problems including potential engine failure. The US$1.7 billion loss to the aviation industry from cancelling 100,000 flights after the 2010 eruption of Iceland’s Eyjafjallajökull spurred efforts to develop better detection and avoidance systems.

Everything You Need to Know About Volcanoes


How Much Damage Can They Do?

A lot. The largest eruption of the past 500 years was Mount Tambora, Indonesia, in 1815. The eruption killed about 70,000 people; 90,000 more died from the catastrophic global cooling that followed.

“It is not possible to predict when or where the next eruption will take place. What is certain is that it will happen.”
Magnús Tumi Gudmundsson, from Iceland’s Institute of Earth Sciences

By the Numbers

Approximate number of volcanoes with the potential to erupt each year:

  • 1000

Average number of eruptions annually:

  • 50-70

Percentage of people whose lives are at risk from volcanoes live in Indonesia:

  • 66%

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