Geology And Geophysics

Active Volcanoes



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Some of the most beautiful places in the world owe their existence to volcanoes. The lush greenery of Hawaii, for instance, thrives in soil that formed in fire, as the incandescent glow from Kilauea’s ongoing eruption reminds us. Eruptions that are more explosive, like Mount St. Helens in May 1980 or Iceland’s Eyjafjallajökull during the spring of 2010, are very exciting to watch from a safe distance but also cause a lot of trouble and can be deadly.

Where are the active volcanoes of the world? Which ones might make a good vacation destination, and which are most likely to be disruptive and dangerous?

♦ Volcano facts

At any given moment, some 20 eruptions are going on throughout the world (not counting sea floor volcanism), according to the Smithsonian’s  Global Volcanism Program. There are, however, far more than 20 active volcanoes in the world.

Scientists call a volcano active if it has erupted in the last 10,000 years or so, during what geologists call the Holocene period. The Smithsonian volcanologists say that upwards of 1500 eruptions have happened over that time. If you check out their interactive map of these Holocene volcanoes, you will see that most run in rather curvy lines that mark the edges of huge tectonic plates that cover Earth’s surface, while a few volcanoes are instead found far from a plate edge.

This distribution isn’t accidental. Plate tectonic processes of pulling apart (rifting), where hot material wells up and fills the resulting gap, and collision, where a piece of Earth’s rocky crust is forced down (subducted) into the hot interior and melts, are the ultimate causes of volcanoes. These processes happen most often on the edges of tectonic plates. Scientists speculate that volcanoes found far from the edges, for example in Hawaii or at Yellowstone, form when some sort of a very hot plume of material from inside the Earth rises up to the surface at a “hot spot."

There are two special cases: Iceland, where the seafloor rift zone comes up on land, and East Africa, where the continent is actually breaking apart in a rift zone that includes Kilimanjaro and many other volcanoes. In both these areas, eruptions happen frequently and can be either explosive (the so-called “gray lava” type of eruption) or effusive (the “red lava” style that Hawaiian volcanoes have made famous).

Fortunately for us, very few of these active volcanoes have erupted recently according to the human time scale. A few, though, have been erupting so long, they are almost like old, if somewhat cantankerous friends.

♦ Popular volcanoes

Two Hawaiian volcanoes lead the lists for activity and size. Both Kilauea and Mauna Loa are “hotspot” volcanoes and erupt frequently, but Kilauea may be the most active volcano on Earth, having erupted 34 times since 1952, and has now been in continuous eruption since 1983. Nearby Mauna Loa hasn’t erupted since 1984, but it has had 33 documented eruptions since 1843. It is the tallest volcano in the world, and if measured from its base on the sea floor, it would also be the tallest mountain in the world at some 56,000 feet (17 km). In comparison, Mount Everest is a little over 29,000 feet (almost 9 km) high.

Near Italy, where the African and Eurasian tectonic plates collide, the volcano/island of Stromboli has been in almost continuous eruption for thousands of years, earning the name “Lighthouse of the Mediterranean.” It has a unique type of eruption with mild explosions along with a lot of gas venting and volcanic “bombs” being ejected; in fact, similar volcanoes all over the world are called “strombolian” volcanoes. Etna, on the east coast of Sicily, has frequent eruptions, some of which can be very violent, as well as occasional flank collapses, but during its quiet phases, this volcano supports resorts and wineries.

Yasur volcano, rising where the Pacific and Australian plates collide, is sometimes called the Southern Hemisphere’s version of Stromboli. both for its eruptive style and its popularity among travelers. Yasur has been erupting steadily at least since 1774, when Captain Cook saw it.

Other frequently erupting volcanoes that are near population centers and draw tourists include Vesuvius in Italy, Arenal in Costa Rica, Popocatepetl and Colima in Mexico, some South American volcanoes, Soufriere Hills on Montserrat, several volcanoes in the Philippines and Indonesia, and a number of volcanoes in Alaska and the Pacific Northwest.

While many of these well-known volcanoes are beautiful, they are also dangerous and frequently cause havoc.

♦ Volcanic hazards

Volcanic ash and jet engines don’t mix. While European authorities were criticized for the extent of their restrictions on flights during the most recent eruption of Eyjafjallajökull , the US Geological Survey reported in 2008 that 7 of the 80 encounters commercial aircraft had with volcanic ash over a 15-year period resulted in loss of engine power that nearly led to a crash. In 1982, British Airways Flight 9 had all four of its engines quit within a minute after flying into a cloud of volcanic ash. Fortunately the crew was able to restart the engines and safely land the jet, although the ash had also scoured the aircraft’s window, making the emergency landing much more difficult.

Today, Volcanic Ash Advisory Centers (VAAC) across the world constantly monitor for signs of a volcanic eruption that would affect aircraft.

Some volcanoes, such as Vesuvius near Naples and Rainier near Seattle/Tacoma, also threaten large population centers, and increasingly, a volcano observatory will be established nearby to watch for signs of unrest. This isn’t always a building, but a monitoring center staffed by earth scientists and other experts. The first such observatory developed in Hawaii around the turn of the 20th century. Today, the US Geological Survey runs the Volcano Hazards Program, including observatories for Yellowstone and Long Valley calderas, as well as ones for Alaskan volcanoes, including Redoubt and Augustine, and the Cascade range, including Rainier and Mount St. Helens. There are also many volcano observatories throughout the world.

A volcano observatory sends out warnings to local emergency managers as well as to aviation centers and keeps the media informed when there is an increase in volcanic activity. It is also a center for studying volcanoes and educating the public about these fascinating fire mountains.

There are up to 1500 active volcanoes in the world. A few erupt frequently and are dangerous. Some are incredibly beautiful. They bring us sorrow and destruction but also provide us with many benefits. Humanity has always had a complex relationship with volcanoes, but as we learn more about them, we are beginning to understand how to minimize the risks and maximize our enjoyment of them.

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ARTICLE SOURCES AND CITATIONS
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