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Volcanologists know more about volcanoes than anyone else on our planet. So which ones give these seasoned experts the jitters? Which future blasts do they fear the most?

Photos courtesy of volunteer Luis Salavarria. Mount Vesuvius, near Naples, Italy, has been quiet since the middle of the 20th century. However, it remains a threat to erupt at any time.

In the late 1980s, the International Association of Volcanology and Chemistry of the Earth’s Interior initiated the Decade Volcanoes project. The group of experts identified 16 dangerous volcanoes to monitor in depth throughout the 1990s (which was designated the International Decade for Natural Hazards Reduction) and beyond. A few volcanoes were left off the list because conditions—political or environmental—made them difficult to study. But, in general, the scientists targeted volcanoes that endanger large populations.

Here’s the current list, in alphabetical order.

	Digging Deeper Find out more about
Pompeii.

Avachinsky-Koryaksky, Russia

This pair of volcanoes on the Ring of Fire last erupted in 2001 and 1957, respectively. They are two of the most active stratovolcanoes on the Kamchatka Peninsula.

Colima, Mexico

This steep-sided peak can produce avalanches and fast-moving rivers of lava and ash. It’s been acting up since 2001 and has a 400-year history of eruptions, making it Mexico’s most consistently active volcano.

Mount Etna, Italy

Europe’s most active volcano, on the island of Sicily, threatens more than 300,000 residents. Small volcanic islands are especially dangerous because there’s often nowhere to escape, except out to sea.

Galeras, Colombia

It’s the youngest and most active of a five-volcano family.

Mauna Loa, Hawaii, United States

The largest volcano in the world can spew 5 million tons of lava in one hour from a massive magma chamber.

Merapi, Indonesia

It’s hard to choose among this country’s 125 or so volcanoes, but Merapi is one of the most active peaks.

Mount Nyiragongo, Congo

Near the border of Rwanda, a 2002 eruption produced a lava flow that forced almost 500,000 people to evacuate.

Mount Rainier, Washington, United States

The mountain is “rotten,” as one volcanologist described it, with soft, muddy slopes below the snowcapped peak. An explosion will unleash tremendous lahars (hot mudflows) on the heavily populated Seattle, Washington, metropolitan area.

Sakurajima, Japan

Nearly 2 million people are in harm’s way.

Santa Maria, Guatemala

This volcano formed at the junction of three tectonic plates and has been active since 1922.

Santorini, Greece

At this popular tourist destination, the volcano has a beautiful, white gleaming town perched on the crater’s rim.

Taal, Philippines

Explosive steam from a lake-filled caldera and surrounding sea makes Taal especially dangerous.

Teide, Canary Islands, Spain

It’s the third-largest volcano in the world by mass.

Ulawun, Papua New Guinea

The structure is unstable and it has been smoking and exploding since 1999, including a blast that triggered evacuations.

Mount Unzen, Japan

One of 75 active volcanoes in Japan, Unzen’s 1792 eruption was the country’s biggest volcanic disaster.

Vesuvius, Italy

The underlying limestone, which contains a lot of carbon, adds an extra dose of carbon dioxide gas to the magma. The more gas, the more explosive the volcano can be. Vesuvius buried the ancient Roman city of Pompeii in 79 CE.