Volcano Watch: Volcano tourism plumbs new depths

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

Iceland’s Eyjafjallajökull Volcano burst into life for the first time in 190 years on March 20, 2010. A 500-meter- (2,000-foot) long fissure opened in the Fimmvörduháls pass to the west of the ice-covered summit of Eyjafjallajökull. Lava fountains erupted fluid magma, which quickly built several hills of bubble-filled lava rocks (scoria) along the vent. A lava flow spread northeast, spilling into Hrunagil Gully. Photo courtesy of NASA.

Iceland’s Eyjafjallajökull Volcano burst into life for the first time in 190 years on March 20, 2010. A 500-meter- (2,000-foot) long fissure opened in the Fimmvörduháls pass to the west of the ice-covered summit of Eyjafjallajökull. Lava fountains erupted fluid magma, which quickly built several hills of bubble-filled lava rocks (scoria) along the vent. A lava flow spread northeast, spilling into Hrunagil Gully. Photo courtesy of NASA.

Adventurous tourists have an opportunity this summer for an experience reminiscent of the classic book and movie “Journey to the Center of the Earth”—the chance to explore the interior of a volcano. The volcano is Thrihnukagigur, one of Iceland’s numerous (and unpronounceable) volcanoes. It is about 160 km (about 100 miles) from Eyjafjallajökull, which gained notoriety when it erupted spectacularly two years ago.

The ash released into the atmosphere over Europe during the Eyjafjallajökull eruption caused global havoc. Air traffic was banned for 10 days, affecting millions of travelers and causing large losses of revenue for the airline industry and for a multitude of international businesses.

The widespread impact of the eruption had a somewhat unexpected result: a surge in tourism to Icelandic volcanoes.

Many new tours offer experiences to visitors on Iceland’s numerous volcanoes. Last year, on the anniversary of the Eyjafjallajökull eruption, a visitor center opened at Eyjafjallajökull and offered tours that highlight the transformations of the landscape caused by the eruption.

By far the most unique volcano tour in Iceland, and perhaps the world, is being offered this summer at Thrihnukagigur, which is considered a dormant, but not extinct, volcano. It last erupted about 4,000 years ago, apparently draining at least part of its shallow magma system and leaving an open pathway to the surface.

Visitors will be lowered via an open elevator system (similar to that used for window-washing on skyscrapers) 120 m (400 ft) down into the open conduit leading to the volcano’s magma chamber, the reservoir that supplies the molten rock that erupts at the surface as lava or ash.

Scientists have descended 200 m (650 ft) into Thrihnukagigur. In addition to exploring the cavity left by the evacuated magma, they found several lateral conduits, which hint at the complexity of a volcano’s magma plumbing system.

The size of the cavity at Thrihnukagigur is about 50×70 m (160 x 220 ft) at the base and about 100 m high. While this must be an awe-inspiring space —approximately the size of a football field and the height of the Statue of Liberty—it’s actually an extremely small volume (a small fraction of a cubic kilometer) compared to estimated magma reservoir volumes at Earth’s volcanoes.

A river with volcanic black sand banks meanders to the sea through farm fields near the southern coast of Iceland. Photo courtesy of the CIA

A river with volcanic black sand banks meanders to the sea through farm fields near the southern coast of Iceland. Photo courtesy of the CIA

Magma supplied to a volcano is usually (although not always) stored in reservoirs at various depths below the surface prior to intrusion or eruption. The volumes of these reservoirs vary widely. The largest reservoirs lie under “supervolcanoes,” such as Yellowstone, whose reservoir has been seismically imaged to be at least 15,000 cubic kilometers (about 3,600 cubic miles).

On the other end of the spectrum, the volume of the shallow reservoir beneath Halema`uma`u Crater in Kilauea caldera is probably about one cubic kilometer. There is another, deeper and larger reservoir beneath the southern part of Kilauea caldera, estimated to be between 3 and about 30 cubic kilometers (1-7 cubic miles) in volume.

One of the reasons for the large uncertainty in the volume estimates is that magma reservoirs are almost certainly not 100 percent magma. Instead, they contain a mixture of solid and molten rock and volcanic gas.

In recent years, our methods of imaging the subsurface plumbing systems of volcanoes have vastly improved, giving us a better appreciation of the complexity of magma storage reservoirs.

While the accessible cavity under Iceland’s Thrihnukagigur is very likely only a small part of the volcano’s magma plumbing system, it is doubtless an awesome journey into the earth.


Time-lapse movie of Kilauea Caldera from the Hawaiian Volcano Observatory. Hawaii’s own volcanic display has brought millions of visitors to Hawaii Volcanoes National Park.

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