Volcano Watch — Volcano tourism plumbs new depths

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 x 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.

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 Kīlauea caldera is probably about one cubic kilometer. There is another, deeper and larger reservoir beneath the southern part of Kīlauea 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.

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Volcano Activity Update

A lava lake present within the Halema‘uma‘u Overlook vent during the past week resulted in night-time glow that was visible from the Jaggar Museum overlook. The lake, which is normally about 80–115 m (260–380 ft) below the floor of Halema‘uma‘u Crater and visible by HVO's Webcam, rose and fell slightly during the week in response to a series of deflation-inflation cycles.

On Kīlauea's east rift zone, surface lava flows were active on the pali and coastal plain over the past week. By Monday, April 23, the flows had just entered Hawai‘i Volcanoes National Park. As of Thursday, April 26, these flows were advancing slowly towards the ocean and were about 900 m (0.6 miles) from the water.

Two earthquakes beneath the Hawaiian Islands were reported felt this past week. A magnitude-1.8 earthquake occurred at 6:11 a.m., HST, on Friday, April 20, 2012, and was located 14 km (9 mi) northwest of Nā‘ālehu, Hawai‘i at a depth of 5 km (3 mi). A magnitude-2.7 earthquake occurred at 4:42 p.m., HST, on Monday, April 23, 2012, and was located 19 km (12 mi) southwest of Mākena, Maui, at shallow depth.