What Makes Decade Volcanoes So Hazardous?

etna — Mount Etna, a Decade Volcano off the coast of Sicily, erupts, in an undated photo. Wead/Shutterstock

We humans have long been wary of volcanoes, and with good reason. We can't hear about Vesuvius' victims in the ancient Roman city of Pompeii or hear about the wide-ranging aftereffects of Indonesia's Mount Tambora eruption in 1815 — one of the most monstrous volcanic eruptions in recorded history — without feeling a little nervous.

So, we humans keep a list of worrisome volcanoes to keep tabs on and study — they're called the Decade Volcanoes, but not because they erupt every decade.

"The so-called Decade Volcanoes project was an initiative that began in the 1990s as part of the United Nations International Decade for Natural Disaster Reduction," says Jon Major, lead scientist at the Cascades Volcano Observatory in Vancouver, Washington. "As part of that proposed initiative, the international volcano community, through an organization called International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI), identified 16 volcanoes worldwide as being worth more intensive study, owing to their history of destructive eruptions, the hazards they posed and their proximity to densely populated areas."

Volcanologists use a variety of tools to assess the state of a volcano. They watch for earthquakes using seismometers, monitor for changes in ground surface elevation using GPS and satellite radar technology, and keep an eye on the release of volcanic gases that may indicate the movement of magma toward the surface.

"This instrumentation network allows us to detect the earliest possible signs of potential volcanic activity so that we can inform emergency management authorities and the public," says Major.

Here, in alphabetical order (and not order of destructive potential), are the 16 Decade Volcanoes:

Contents

Avachinsky — Kamchatka, Russia
Colima — Jalisco and Colima, Mexico
Etna — Sicily, Italy
Galeras — Nariño, Colombia
Mauna Loa — Hawai'i, U.S.
Merapi — Central Java, Indonesia
Nyiragongo — Democratic Republic of Congo
Rainier — Washington, U.S.
Sakurajima — Kagoshima Prefecture, Japan
Santa Maria — Guatemala
Santorini (Thera) — Cyclades, Greece
Taal — Luzon, Philippines
Teide — Canary Islands, Spain
Ulawun — New Britain, Papua New Guinea
Unzen — Nagasaki Prefecture, Japan
Vesuvius — Naples, Italy

1. Avachinsky — Kamchatka, Russia

On the Kamchatka peninsula on the eastern coast of Russia sits a giant stratovolcano — a type of steep-sided conical volcano that's more likely to produce an explosive eruption than some others. Avachinsky and its neighboring volcano, Koryaksky, can be seen from Petropavlovsk-Kamchatsky, Kamchatka's most populous city. Since its first eruption in 1737, Avachinsky has erupted at least 16 times, the largest eruption in 1945 producing glowing lava flows from its mouth, which would be something to see. Its last eruption was in 2001.

2. Colima — Jalisco and Colima, Mexico

Colima volcano — Volcan de Colima looks calm and quite benign, though it is an active volcano, erupting often and causing frequent temporary evacuations of nearby villagers due to threatening volcanic activity. Cavan-Images/Shutterstock

On the border of the Mexican states of Colima and Jalisco, only 75 miles (125 kilometers) south of the city of Guadalajara, sits the Colima Volcanic Complex. These two stratovolcanoes, the Nevado de Colima and Volcan de Colima, are both active, but the younger of the two, Volcan de Colima, is more active and has erupted at least 30 times since the 16th century. It has been erupting often since 2013, but an explosive eruption in 1913 blew a giant crater in the top.

3. Etna — Sicily, Italy

Mount Etna erupts, spewing lava and ash from the southeast crater, Dec. 22, 2018, in Catania, Italy. Fabrizio Villa/Getty Images

Located on the Mediterranean island of Sicily, Italy, Mount Etna is the most active volcano in Europe and has the longest recorded history of eruptions of any volcano in the world — there is ancient documentation of Etna erupting in 1,500 B.C.E. The 21st century has seen a lot of action from Mount Etna; it has been erupting almost continually since 2001.

4. Galeras — Nariño, Colombia

Galeras in Colombia is a very old stratovolcano with a collapsed caldera — scientists think it has been active for at least a million years. Spanish conquistadors recorded eruptions, and it was probably a sight to behold even if it wasn't erupting, because Galeras is almost always belching humongous steam plumes. Located just west of the City of Pasto, Colombia, an eruption in 1993 killed nine people.

5. Mauna Loa — Hawai'i, U.S.

Mauna Loa covers half the island of Hawai'i — its name means "Long Mountain'' in Hawaiian, and it's the largest active volcano on the planet. Much of Mauna Loa is underwater, and its submarine portion makes up most of its height; from base to summit the volcano is 10.5 miles (17 kilometers) high. One of the two Decade Volcanoes in the United States, Mauna Loa has erupted 34 times since 1843, and lava flows often come precariously close to human population centers like Hilo.

6. Merapi — Central Java, Indonesia

Merapi is on the Indonesian island of Java, the world's most populous island. It's understandable, then, that scientists would want to monitor a volcano that's been erupting since 1987. Of its 67 historic eruptions, 32 have come with dangerous nuée ardentes, a French term meaning "glowing cloud," which is a huge, fast-moving cloud of scalding hot gas and ash.

7. Nyiragongo — Democratic Republic of Congo

The Nyiragongo volcano is one of the most locally destructive in the past century. Located in the Democratic Republic of Congo, it contains a deep lava lake, and its lava is particularly fluid. On Jan.10, 1977, the wall of the volcano containing the lava lake ruptured and spilled up to 176 million cubic feet (5 million cubic meters) of lava into the surrounding landscape in a half an hour. Luckily, the lava drained mostly away from populated areas, although it did reach the outskirts of Goma, the nearest town.

8. Rainier — Washington, U.S.

Mount Rainier is the most hazardous volcano in the contiguous U.S., but it used to be much taller. During an eruption 5,600 years ago, the summit collapsed into itself, creating a gigantic crater which later eruptions filled back in.

"Ranier has erupted many times in the past 10,000 years and has a history of shedding large volcanic mudflows known as lahars that can travel many tens of miles," says Major. "It is infamous for shedding what is called the Osceola Mudflow — a large volcanic mudflow that occurred about 5,600 years ago and traveled all the way to the Puget Sound covering a vast swath of what is now densely populated area."

9. Sakurajima — Kagoshima Prefecture, Japan

The Sakurajima volcano near Kagoshima, Japan, is very powerful and has been in a state of nearly constant eruption since its first recorded eruption in the year 708 C.E. Sakurajima used to be on an island, but lava flows from a giant eruption in 1914 connected it with the mainland close by.

10. Santa Maria — Guatemala

Near the Guatemalan city of Quetzaltenango sits the Santa Maria volcano, whose eruption in 1902 was one of the most powerful eruptions of the 20th century. This huge explosion blew a mile-wide (1.5 kilometer-wide) crater on the mountain's southwestern side that's been constantly active since 1922. Before the 1902 eruption, the volcano had been mostly quiet for 500 years.

11. Santorini (Thera) — Cyclades, Greece

In the Aegean Sea, on the Greek island of Santorini, lies the site of one of the most destructive volcanic events in human history. Shaped like the letter "C", the island (at one time called Thera) had its center blown out in a volcanic explosion around 1610 B.C.E. Although the island was populated at the time, there are no written accounts of the event — this might be because not many survived it. Archaeologists have found clues that some of the islanders had enough warning to leave the island before it blew, but when it did, it was with the force of dozens of atomic bombs.

12. Taal — Luzon, Philippines

The Taal volcano is a giant caldera, located 31 miles (50 kilometers) south of Manila, the capital of the Philippines. Part of the Pacific Ring of Fire, a region characterized by volcanic activity and earthquakes due to the intersection of several tectonic plates, Taal has erupted at least 34 times since 1572, including the giant eruption in 1911 which killed 1,335 people. Taal is still restless today and an active threat to the people of the Philippines.

13. Teide — Canary Islands, Spain

On the Canary Islands sits the Teide volcano, rising 12,188 feet (3,715 meters) over the ocean, the highest point in Spain. A few of its vents have erupted since the island was populated early in the 15th century, the most recent eruption being in 1909. None of these eruptions have been very destructive, however.

14. Ulawun — New Britain, Papua New Guinea

Ulawun sits right above a subduction zone, a place where two tectonic plates meet, in the southwestern Pacific Ocean. Though it has not been historically very destructive, it is active and sits 81 miles (130 kilometers) from the town of Rabaul.

15. Unzen — Nagasaki Prefecture, Japan

Mount Unzen is actually a group of overlapping stratovolcanoes on Kyushu, an island on the southern tip of Japan. In 1792, one of its domes collapsed and the resulting avalanche slid into the ocean, causing a tsunami that killed nearly 15,000 people. It was completely silent until 1990, when its eruption caused 12,000 people to evacuate their homes. A 1991 eruption of Mount Unzen killed 45 scientists and journalists.

16. Vesuvius — Naples, Italy

Mount Vesuvius is famous for destroying the wealthy city of Pompeii in 79 C.E., but the city of Naples — only 5.6 miles (9 kilometers) west of the mountain — was unscathed due to the prevailing winds. Naples is home to over 3 million residents, and though Vesuvius doesn't erupt often, there's evidence that a large eruption has happened every 2,000 years for the past 25,000 years. Vesuvius has been pretty quiet for the past two millennia, so it's possible that Naples might feel it heating up soon.