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Throwing a fit
Mount Erebus experiences one of its most active seasons in 165 years
Posted January 14, 2007
Mount Erebus is famous for its persistent but low-level activity as the world’s southernmost active volcano. But last year it threw one of its biggest recorded tantrums during its last 165 years.
For the second half of 2005, Erebus erupted as much as six times a day, throwing what volcanologists call “bombs,” hot rocks, out of the crater and onto the sides of the 3,794-meter-high volcano.
“A bomb hit one of our [geophysical] stations,” said Phil Kyle, a volcanologist with the New Mexico Institute of Mining and Technology who leads a team of scientists and students attempting to find out what makes Erebus tick.
Last year’s anomalous activity followed about three years of uncharacteristic silence, according to Kyle. Eruptions returned in 2004, and by the middle of 2005, the scientists knew something was up thanks to data received from a suite of about 10 seismometers located on the volcano, mostly around the rim, that operate year-round.
Capt. James Ross provided the first his¬torical record of Erebus (which he named after one of his vessels) when his log recorded lava flows on the side of the volcano. Sketches at the time even showed eruptions, Kyle said.
“We’ve not seen anything like that in our time,” he added, noting that it is hard to determine the exact level of activity based on Ross’ notes.
The only other time the volcano has kicked up such a storm occurred in 1984, when Erebus launched bombs measuring 10 meters wide and slung them as far as 3 kilometers away from the crater.
Kyle said 2005 appears to be the third most volatile period on record for the volcano, which has been active for about 1.3 million years.
“Erebus is less active this year than last year,” he said. “We don’t know why it starts and stops like this.” But the answers are coming.
Pooling it together
For more than three decades, Kyle and colleagues have explored Erebus, a “special” volcano with a number of features that make it particularly appealing to study.
Topping that list is its permanent lake of molten lava, only one of three known to exist in the world, Kyle said. The other two are located in Africa: Erta Ale in Ethiopia and Nyiragongo in the Democratic Republic of Congo.
The lake is a result of natural convection that continuously cycles magma from a chamber deeper inside the volcano to the surface.
“This is a very rare feature in volcanoes. You just don’t see these lakes,” Kyle said. “It’s a window into the magma chamber, [and] it can help us understand what’s going on.”
The 30-meter-wide lake has at least been in existence since its discovery in 1972 and aerial photographs from the 1960s indicate it was around before then, Kyle said. He believes — based on accounts from the heroic age of exploration — that the lava lake has likely been percolating for the past century.
Explorers like Robert Falcon Scott and Ernest Shackleton apparently reported seeing a red glow above the volcano’s cone during the dark winter months. What they probably saw, Kyle said, was the reflection of the lava lake on the clouds.
“I think it’s a persistent, long-lived feature. It varies, and it’s dynamic. … Each year is different for us,” Kyle explained. “Each year we don’t know what we’re going to find.”
Call a plumber
The lava itself is also rather rare. Most volcanoes contain basalt lava but the fiery liquid bubbling in Erebus is phonolite lava. The composition is particularly interest¬ing because phonolite is more explosive than basalt. Mount Vesuvius, the infamous volcano that leveled Pompeii in 79 AD, also contained phonolite lava, according to Kyle.
Such a catastrophic explosion from Erebus is extremely unlikely, however, because the magma column is exposed and not capped like Vesuvius, so there is no way for pressure to build. Also, early indications suggest there is less gas in the Erebus magma, which is the driving force of violent eruptions.
One of the goals of the team next season will be to discover more about the volcano’s plumbing, particularly the magma chamber inside Erebus that feeds the lake and the conduit that connects the two.
The researchers will install about 25 additional seismometers on the volcano next year. Seismometers measure and record the size and force of seismic waves.
By studying seismic waves, the scientists can map the interior of the volcano, much as a CAT scan images the inside of an object using X-rays.
“We can use incoming earthquakes from different places to see what happens as they pass through the volcano,” Kyle said, adding that the seismic waves produced by eruptions from the volcano itself will also be helpful for such imaging. “Hopefully we’ll get a good look at what’s inside there.”