New paper suggests volcanoes are causing Antarctic ice loss from below

The average temperature on the surface of Antarctica is -45C [-49F], and thus the atmosphere and greenhouse gases cannot melt the surface of most of the interior. However, this new paper discovered by accident an active volcano that may cause significant ice melt 1 kilometer below the surface. There could be many other such undiscovered volcanoes below the ice caps of both Antarctica and Greenland melting the ice naturally from below. 

Melt water from the new volcano will drain into the MacAyeal Ice Stream, labeled above as ice stream E, its original designation. This radar image of West Antarctica (see box on the inset at bottom right for location) has been color-coded to indicate the speed at which the ice is moving. Red marks the fast-moving centers of the ice streams and black lines outline each stream’s catchment area. By greasing the skids with water, the new volcano might increase the rate of ice loss from the MacAyeal Ice Stream. Courtesy: NASA. 

Could volcanoes be causing Antarctic ice loss?

by Staff WritersParis (AFP) Nov 17, 2013

Accelerating ice loss from the Antarctic icesheet could be due in part to active volcanoes under the frozen continent's eastern part, a study said on Sunday.

From 2002 to 2011, the average annual rate of Antarctic icesheet loss increased from about 30 billion tonnes to about 147 billion tonnes, the UN's panel of climate scientists reported in September.

The icesheet is a mass of glacial land ice -- one such sheet covers most of Greenland and the other Antarctica, and together they contain most of the freshwater on Earth.

The sheets are constantly moving, slowly flowing downhill and seawards under their own weight. Portions that extend out over the water are called ice shelf.

Previous research has blamed warmer seas swirling in a circular fashion around Antarctica for the quicker pace of icesheet loss from the southernmost continent.

These waters erode ice shelves, went the theory. And as more of the shelves disappeared, the quicker the sheet would flow and lose ice to the sea.

But in a new paper in the journal Nature Geoscience geologists led by Amanda Lough at Washington University in St. Louis, Missouri, suggested that, in West Antarctica, the faster flow may be also be due to volcanoes.

These heat the underside of the ice, causing melting that lubricates the flow, they suggested.

Evidence for this comes from recently deployed sensors that recorded two "swarms" of seismic activity under Mary Byrd Land, a highland region of West Antarctica, in 2010 and 2011.

Using ice-penetrating radar, the team found an intriguing elliptically-shaped deposit, measuring about 1,000 square kilometres (386 square miles) in the area, at a depth of 1,400 metres (4,550 feet).

The deposit is believed to be volcanic ash, spewed out by an enormous eruption some 8,000 years ago -- an estimate reached on the assumption it has since been covered by ice accumulating at the rate of 12.5 centimetres (five inches) a year.

"Together, these observations provide strong evidence for ongoing magmatic activity and demonstrate that volcanism continues to migrate southwards."

Several volcanoes were known to exist in West Antarctica, but none were thought to be active.

"Eruptions at this site are unlikely to penetrate the 1.2 to two-km (0.75-1.2-mile) -thick overlying ice, but would generate large volumes of melt water that could significantly affect ice stream flow," said the study.

from Science Daily:

Volcano Discovered Smoldering Under a Kilometer of Ice in West Antarctica: Heat May Increase Rate of Ice Loss

Nov. 17, 2013 — It wasn't what they were looking for but that only made the discovery all the more exciting.

In January 2010 a team of scientists had set up two crossing lines of seismographs across Marie Byrd Land in West Antarctica. It was the first time the scientists had deployed many instruments in the interior of the continent that could operate year-round even in the coldest parts of Antarctica.

Like a giant CT machine, the seismograph array used disturbances created by distant earthquakes to make images of the ice and rock deep within West Antarctica.

There were big questions to be asked and answered. The goal, says Doug Wiens, professor of earth and planetary science at Washington University in St. Louis and one of the project's principle investigators, was essentially to weigh the ice sheet to help reconstruct Antarctica's climate history. But to do this accurately the scientists had to know how Earth's mantle would respond to an ice burden, and that depended on whether it was hot and fluid or cool and viscous. The seismic data would allow them to map the mantle's properties.

In the meantime, automated-event-detection software was put to work to comb the data for anything unusual.

When it found two bursts of seismic events between January 2010 and March 2011, Wiens' PhD student Amanda Lough looked more closely to see what was rattling the continent's bones.

Was it rock grinding on rock, ice groaning over ice, or, perhaps, hot gases and liquid rock forcing their way through cracks in a volcanic complex?

Uncertain at first, the more Lough and her colleagues looked, the more convinced they became that a new volcano was forming a kilometer beneath the ice.

The discovery of the new as yet unnamed volcano is announced in the Nov. 17 advanced online issue of Nature Geoscience.

Following the trail of clues

The teams that install seismographs in Antarctica are given first crack at the data. Lough had done her bit as part of the WUSTL team, traveling to East Antarctica three times to install or remove stations in East Antarctica.

In 2010 many of the instruments were moved to West Antarctica and Wiens asked Lough to look at the seismic data coming in, the first large-scale dataset from this part of the continent.

"I started seeing events that kept occurring at the same location, which was odd, "Lough said. "Then I realized they were close to some mountains-but not right on top of them."

"My first thought was, 'Okay, maybe its just coincidence.' But then I looked more closely and realized that the mountains were actually volcanoes and there was an age progression to the range. The volcanoes closest to the seismic events were the youngest ones."

The events were weak and very low frequency, which strongly suggested they weren't tectonic in origin. While low-magnitude seismic events of tectonic origin typically have frequencies of 10 to 20 cycles per second, this shaking was dominated by frequencies of 2 to 4 cycles per second.

Ruling out ice

But glacial processes can generate low-frequency events. If the events weren't tectonic could they be glacial?

To probe farther, Lough used a global computer model of seismic velocities to "relocate" the hypocenters of the events to account for the known seismic velocities along different paths through the Earth. This procedure collapsed the swarm clusters to a third their original size.

It also showed that almost all of the events had occurred at depths of 25 to 40 kilometers (15 to 25 miles below the surface). This is extraordinarily deep -- deep enough to be near the boundary between the earth's crust and mantle, called the Moho, and more or less rules out a glacial origin.

It also casts doubt on a tectonic one. "A tectonic event might have a hypocenter 10 to 15 kilometers (6 to 9 miles) deep, but at 25 to 40 kilometers, these were way too deep," Lough says.

A colleague suggested that the event waveforms looked like Deep Long Period earthquakes, or DPLs, which occur in volcanic areas, have the same frequency characteristics and are as deep. "Everything matches up," Lough says.

An ash layer encased in ice

The seismologists also talked to Duncan Young and Don Blankenship of the University of Texas who fly airborne radar over Antarctica to produce topographic maps of the bedrock. "In these maps, you can see that there's elevation in the bed topography at the same location as the seismic events," Lough says.

The radar images also showed a layer of ash buried under the ice. "They see this layer all around our group of earthquakes and only in this area," Lough says.

"Their best guess is that it came from Mount Waesche, an existing volcano near Mt Sidley. But that is also interesting because scientists had no idea when Mount Waesche was last active, and the ash layer is sets the age of the eruption at 8,000 years ago. "

What's up down there?

The case for volcanic origin has been made. But what exactly is causing the seismic activity?

"Most mountains in Antarctica are not volcanic," Wiens says, "but most in this area are. Is it because East and West Antarctica are slowly rifting apart? We don't know exactly. But we think there is probably a hot spot in the mantle here producing magma far beneath the surface."

"People aren't really sure what causes DPLs," Lough says. "It seems to vary by volcanic complex, but most people think it's the movement of magma and other fluids that leads to pressure-induced vibrations in cracks within volcanic and hydrothermal systems."

Will the new volcano erupt?

"Definitely," Lough says. "In fact because of the radar shows a mountain beneath the ice I think it has erupted in the past, before the rumblings we recorded.

Will the eruptions punch through a kilometer or more of ice above it?

The scientists calculated that an enormous eruption, one that released a thousand times more energy than the typical eruption, would be necessary to breach the ice above the volcano.

On the other hand a subglacial eruption and the accompanying heat flow will melt a lot of ice. "The volcano will create millions of gallons of water beneath the ice -- many lakes full," says Wiens. This water will rush beneath the ice towards the sea and feed into the hydrological catchment of the MacAyeal Ice Stream, one of several major ice streams draining ice from Marie Byrd Land into the Ross Ice Shelf.

By lubricating the bedrock, it will speed the flow of the overlying ice, perhaps increasing the rate of ice-mass loss in West Antarctica.

Washington University in St. Louis (2013, November 17). Volcano discovered smoldering under a kilometer of ice in West Antarctica: Heat may increase rate of ice loss. ScienceDaily. Retrieved November 17, 2013, from http://www.sciencedaily.com­/releases/2013/11/131117155609.htm

from Nature Geoscience:

VOLCANOLOGY Mobile magma under Antarctic ice Volcanoes have been active under the West Antarctic Ice Sheet for millions of years, and there is evidence for  recent activity. Now swarms of tiny earthquakes detected in 2010 and 2011 hint at current magma movement in  the crust beneath the ice.

By John C. Behrendt

The West Antarctic Ice Sheet is losing 

 mass as the climate warms and the 

 surrounding floating ice shelves that 

 buttress the land-based ice are eaten away 

 at their base by warmer ocean waters1. 

 However, the ice can also melt from below 

 on land, where subglacial volcanic activity 

 causes a high flow of heat through the 

 crust2–5. Writing in Nature Geoscience, 

 Lough et al.6 use observations of hundreds 

 of small seismic events in the crust beneath 

 the West Antarctic Ice Sheet to infer 

 current magma movement in a volcanic 

 system beneath the ice, which may bring 

 heat up to the rock–ice interface and thus 

 affect ice flow.

 Late Cenozoic volcanic activity 

 associated with the West Antarctic Riff 

 System7 extended over a wide area of West 

 Antarctica, including beneath the West 

 Antarctic Ice Sheet (WAIS) that flows 

 through it. In general, the volcanic activity 

 seems to have migrated southwards, 

 along north–south-oriented fractures, 

 away from the Marie Byrd Land dome8. 

 Active volcanism has also been reported 

 in a few other places in the West Antarctic 

 Riff System4,5, and aeromagnetic surveys 

 provide evidence for a number of volcanic 

 centres beneath the WAIS (ref. 2), but it has 

 been unclear whether magmatic activity 

 continues today.

 Lough et al.6 analysed seismic data 

 recorded by a deployment of 37 seismic 

 stations in Marie Byrd Land, a highland 

 region of West Antarctica (Fig. 1). Tey 

 identifed two swarms  of earthquakes 

 about one year apart, in 2010 and 2011. 

 The swarms were comprised of hundreds 

 of small seismic events, with magnitudes 

 between 0.8 and 2.1. Te quakes occurred 

 at depths of about 25 to 40 km, close 

 to the boundary between the crust and 

 mantle beneath Marie Byrd Land, much 

 deeper than normal crustal earthquakes. 

 Tese characteristics, as well as the 

 observed wave frequencies, are typical for 

 deep long-period earthquakes that have 

 been associated with active volcanoes 

 worldwide9–12. Lough and colleagues  therefore interpret the observed seismic 

 activity as a sign of magma movements 

 within an active subglacial magmatic 

 system, though it is unclear whether the 

 observed swarm activity presages an 

 imminent eruption.

 Te earthquake swarms originated 

 beneath a subglacial mountain complex 

 with elevation of about 1,000 m above the 

 surrounding low-lying areas. Aeromagnetic 

 data show a 400 nf magnetic anomaly 

 at the high point, suggesting that rocks 

 in this region are highly magnetized. 

 Shallow-source magnetic anomalies from 

 rocks are ofen a sign of a volcanic origin, 

 so Lough et al. interpret the subglacial 

 mountain complex as a volcanic edifce. 

 Tey also identify a prominent 20 × 50 km 

 elliptical layer of ash in the ice above the 

 subglacial peak, about 400 to 1,400 m 

 below the ice surface. Given modern 

 ice accumulation rates of about 12.5 cm  per year, the authors estimate that the 

 ash layer formed about 8,000 years ago 

 and was probably sourced from nearby 

 Mount Waesche.

 Radar ice-sounding data provide 

 measurements of ice thickness in West 

 Antarctica, but gaps in the data — the

aerogeophysical data lines are spaced about 

 15 km apart — lead to uncertainties. Deep 

 long-period earthquakes can occur up to 

 5 km away from active volcanic vents9–12, 

 and at this distance away from the source 

 of the earthquakes the ice is about 1,100 m 

 thick. Lough and colleagues show that 

 only an exceptionally large eruption could 

 breach the ice sheet in Marie Byrd Land 

 and vent to the surface.

 Te earthquake swarms, magnetic 

 anomaly and ash layer are all  located 

 about 55 km south of Mount Sidley in the 

 Executive Committee mountain range, 

 south of the area of Holocene volcanic ...