Monday, December 13, 2010

Erta Ale: The Gateway to Hell

In the north of Ethiopia, about a hundred miles west of the southern end of the Red Sea, is a bubbling caldera known as "The Gateway to Hell." To get to it you must travel by camel train through some of the hottest, harshest terrain on Earth while keeping one eye open for the locals with a reputation for hostility.

This is Erta Ale, one of the Earth's oldest continuously active basaltic shield volcanoes so called for their shape resembling a warrior's shield. At the center of the volcano is a perpetually-bubbling lava lake every bit as menacing as it sounds.

Shield volcanoes form when rock deep in the Earth heats to its melting point and rises through conduits and fractures until it punches through the crust. Unlike explosive stratovolcanoes, like Mount St. Helens in Washington state, lava oozes out of shield volcanoes at a more lethargic pace.

Shield volcanoes are the biggest volcanoes on earth. They are short but wide with widths 20 times their heights. Their typical gradient is gentle at the bottom, near 2-3 degrees, with a steeper slope of 10 degrees near the top and they level out at the summit, producing the shield-like shape.

Erta Ale, which translates to "smoking mountain" in the local language, has been active since 1906. Its mile-wide elliptical summit resembles more a muddy quarry than a hazardous volcano, excepting, of course, the churning lava lake at one end. The lake is only one of five in the world, making the volcano quite a rarity.

With a viscosity a thousand times that of water, lava creeps along slowly enough to give humans enough time to get out of the way. Agriculture and infrastructure are common casualties of shield volcano lava, though, especially on the Hawaiian Islands - the most notable assembly of shield volcanoes.

Simmering at almost 2000 degrees Fahrenheit - 10 times hotter than boiling water - the molten rock at Erta Ale first fills up its circular chamber before spilling over, emptying out and receding back into the hole. The process repeats over and over like a giant piston in the Earth's crust.

In 2005, a major eruption at Erta Ale killed 250 heads of livestock and forced thousands of locals to evacuate but no humans were killed. Another eruption in 2008, however, resulted in two missing persons.

In 2009, a team of scientists led by Dougal Jerram from Durham University in the U.K. visited Erta Ale to map it. Using lasers, the team created a hi-res 3D photograph of the volcano's interior, obtaining the first laser scan of the inside of an active volcano.

The lava lake gateway to the underworld is just one of several exciting geophysical wonders in that part of Africa. In 2005, the nearby Dabbahu Fissure appeared overnight, spewing noxious volcanic gasses from the Earth's crust.

Both the volcano and the fissure lie along the Great Rift Valley, a geologically active area where the African plate is splitting apart, tearing the Horn of Africa away from the mainland. Though continental drift happens on a scale of eons, evidence of its violent nature can be seen in this extreme and ominous example in northern Africa. As long as you're willing to travel by camel train.