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 100 miles from Eyjafallajokull, which gained notoriety when it erupted spectacularly two years ago.
The ash released into the atmosphere over Europe during the Eyjafallajokull 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 eruption’s widespread impact had a somewhat unexpected result: a surge in tourism to Icelandic volcanoes.
Many new tours offer visitors experiences on Iceland’s volcanoes. Last year, on the anniversary of the Eyjafallajokull eruption, a visitor center opened at Eyjafallajokull 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, 400 feet 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 650 feet 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 160-by-220 feet at the base and about 325 feet 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 in Earth’s volcanoes.
Magma supplied to a volcano is usually 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, where the reservoir has been seismically imaged to be at least 3,600 cubic miles.
On the other end of the spectrum, the volume of the shallow reservoir beneath Halemaumau 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 one and seven 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.
Kilauea activity update
A lava lake present within the Halemaumau Overlook vent during the past week resulted in nighttime glow visible from the Jaggar Museum overlook. The lake, which is normally about 260 to 380 feet below the floor of Halemaumau Crater and visible by HVO’s webcam, rose and fell slightly during the week in response to a series of deflation-inflation cycles.
On Kilauea’s east rift zone, surface lava flows were active on the pali and coastal plain over the past week. By Monday, the flows had just entered Hawaii Volcanoes National Park. As of Thursday, these flows were advancing slowly toward the ocean and were about 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. April 20 located 9 miles northwest of Naalehu at a depth of 3 miles. A magnitude 2.7 earthquake occurred at 4:42 p.m. Monday located 12 miles southwest of Makena, Maui at a shallow depth.
Visit hvo.wr.usgs.gov for detailed Kilauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes and more; call 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov.
Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.