Author Topic: Helium Leaking from Earth in Southern California  (Read 600 times)

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Helium Leaking from Earth in Southern California
« on: July 05, 2015, 06:25:06 PM »

Stephanie Pappas    7 hrs ago

Helium Leaking from Earth in Southern California

A natural helium leak in Southern California reveals that the Newport-Inglewood fault is deeper than once thought — with a direct line from the Earth's surface to the planet's hot, dense mantle.

Scientists have found high levels of helium-3 in oil wells up to 3 kilometers (1.8 miles) deep in Orange County, along a 30-mile (48 kilometers) stretch from Los Angeles' Westside to Newport Beach. Helium-3 comes only from the Earth's mantle, the semisolid rock layer beneath the crust.

"The fault, which I don't think people had anticipated, was deeply connected," said Jim Boles, a professor emeritus of earth sciences at the University of California, Santa Barbara.

The results have implications for the underground structure of the Los Angeles basin. Geologists believed the area to be underpinned by a low-angle thrust fault, but the Newport-Inglewood fault appears to plunge down deep, Boles told Live Science. [In Photos: Ocean Hidden Deep in Earth's Mantle]

What the study does not do — despite some breathless media coverage otherwise — is alter earthquake predictions about southern California.

Hot rock

Discovering helium-3 at the Newport-Inglewood fault is undeniably odd. About 30 million years ago, the fault was the site of a subduction zone, a region in which one continental plate is pushing under another, driving a layer of crust down toward the mantle like a conveyer belt. Boles and his colleagues found a layer of a metamorphic rock called blueschist at the bottom of deep wells in the Newport-Inglewood fault zone. The minerals in blueschist form only in very particular conditions in which rock gets pushed deep underground and then rapidly resurfaces, before having time to "cook" under the high temperatures deep in the crust, according to the U.S. Geological Survey. These conditions exist in subduction zones.

© Sonia Fernandez The Newport-Inglewood fault in California is leaking helium-3, researchers have found.
But subduction zones are not typically places where high levels of helium-3 are found, Boles said. Helium anomalies are most often found in spreading centers in the deep ocean, where the Earth's crust is pulling apart, or in volcanic hotspots such as the Hawaiian islands or Yellowstone National Park, where the hot mantle gets close to the Earth's surface.

The Newport-Inglewood fault "could have had a connection" to the mantle 30 million years ago when it was an active subduction zone, Boles said, "but the fact that the connection looks like it's still there is pretty interesting."

Complicated faults

What the new findings suggest is that the Newport-Inglewood fault runs deep. A previous hypothesis held that the LA Basin was underpinned by a low-angle thrust fault, but this study contradicts that notion, Boles said. Essentially, the underground structure of the region may be far different than once thought.

Despite scattered news reports linking the new findings to an earlier USGS report that raised the risk of a large quake in the next three decades from about 4.7 percent to 7 percent, the helium discovery at the Newport-Inglewood fault is not cause for panic. The discovery does not speak to the seismicity of the region, Boles said, and a lot more data is needed to even determine the implications of the findings for the area's geologic structure.

"The only thing you can say is that this fault looks like it's a more significant fault than people thought in terms of how deep it goes and what it communicates with," Boles said.

The researchers reported their findings in the online journal Geochemistry, Geophysics, Geosystems, also known as G-Cubed.


Greenland’s ice can generate glacial earthquakes

Giant earthquakes are shaking Greenland — and scientists just figured out the disturbing reason why

By Chris Mooney June 25,2015

If Greenland goes, it is becoming clear that it won’t go quietly.

Scientists have already documented entire meltwater lakes vanishing in a matter of hours atop the vast Greenland ice sheet, as huge crevasses open beneath them. And now, they’ve cast light on the mechanisms behind another dramatic geophysical effect brought on by the rumbling and melting of this mass of often mile-thick ice: earthquakes.

In a new paper in the journal Science, a team of researchers from Swansea University in the UK, the Lamont-Doherty Earth Observatory at Columbia University, and several other institutions explain how the loss of Greenland’s ice can generate glacial earthquakes. In brief: When vast icebergs break off at the end of tidal glaciers, they tumble in the water and jam the glaciers themselves backwards. The result is a seismic event detectable across the Earth.

[Scientists finally have an explanation for why huge lakes atop Greenland are vanishing]

“These are all around magnitude 4.6 to 5.2, they’re all pretty close to magnitude 5,” says Meredith Nettles of the Lamont-Doherty Earth Observatory at Columbia University, a co-author of the study. “Which is a pretty big earthquake.”

Granted, these earthquakes aren’t caused by faults – they’re caused by massive movements of ice and how those impact the ground beneath. Compared with the early 1990s, Nettles says, scientists are now measuring seven times as many of these glacial earthquakes coming from Greenland — the rate has shot up as the ice sheet has begun to lose more mass from the calving of icebergs at the front end of glaciers.

To understand the dynamics behind how these glacial earthquakes are happening, the researchers put GPS instruments atop Greenland’s fast moving Helheim Glacier, which is located in the southeast part of Greenland, across the Denmark strait from Iceland. They also monitored the glacier’s calving front, where it meets the water, by camera, and used global seismic data to track earthquake occurrences.

To get a better sense of what they discovered, you first have to wrap your mind around how big these calving icebergs actually are. The amount of ice mass that breaks off in large iceberg calvings from Helheim Glacier, explains Nettles, is around a gigaton, or a billion metric tons. “If you took the whole National Mall, and covered it up with ice, to a height about four times as high as the [Washington] monument,” says Nettles, you’d have about a gigaton of ice. “All the way down from the Capitol steps to the Lincoln Memorial.”

Measured in space rather than mass, a big iceberg breaking off Helheim can be 4 kilometers in length — or over two miles. So maybe it is no surprise that a body this large can shake the Earth when it moves — and especially when it throws its weight against another solid object, as occurs during iceberg calving.

[Alaska’s glaciers are now losing 75 billion tons of ice every year]

The iceberg, when it breaks off from the glacier front, is tall and relatively thin (compared with the glacier, anyway) and in effect “standing” up vertically.  If you could see a cross section of what was happening when it breaks off, it might look like cutting a fairly thick slice from a loaf of bread. But as soon as the iceberg is detached, it quickly begins to capsize.

As that happens, its top (above water) falls and pushes back against the glacier, even as its bottom (below water) rises up to the surface, eventually leaving the iceberg floating flat in the water. Or at least, that’s the usual process. Here’s a video of the process being simulated, by the researchers, in a tank:

vid at link

In this video, which has been slowed down by five times its real speed, a plastic iceberg undergoes capsizing while being digitally tracked through two black dots. The rigid wall to the right measures the hydrodynamic pressure in the water, which plays a major role in the source of glacial earthquakes generated by iceberg capsize. (Justin C. Burton and L. Mac Cathles)

During this capsizing, two massive forces are generated. The first and most obvious one occurs as the tumbling top of the iceberg pushes against the glacier, and actually drives the sheet of ice backwards and inland. “During the earthquakes, the region near the calving front shows a dramatic reversal of flow, moving upglacier for several minutes while simultaneously moving downward,” the authors write.

“The horizontal and vertical motion then rebound rapidly,” they continue. But in the meantime, it’s enough to shake the Earth. “That calving iceberg is pushing the remaining part of the glacier backwards hard enough that we can actually measure that, hard enough that it reverses the whole flow of the front of the glacier temporarily,” says Nettles. “And it’s that force pushing on the remaining glacier and the rocks beneath it that gives us the seismic [activity].”

There’s also a second force involved. As the iceberg separates from the glacier, that opens up a gap for water to rush into. The region has lower water pressure, so that lessens the push of water and ice downward on the Earth. And this results in “an upward force acting on the solid Earth, as observed in our seismic analysis,” note the researchers.

As if all of this not enough, the events also create a “big tsunami,” says Nettles. This occurs as the tumbling and rolling iceberg pushes water outwards through the fjord leading up to the glacier. “The tsunami is caused because the iceberg has to move a lot of water out of the way as it tips over,” Nettles explains.

Setting aside the drama of tsunamis and glacial earthquakes, what’s most fundamental is how all of this contributes to rising seas — because of course, it is happening over and over again. Over 55 days in the late summer of 2013, the researchers observed “ten  large calving events and corresponding earthquakes” — and a total retreat of Helheim Glacier by 1.5 kilometers. And Helheim is just one of many Greenland glaciers that are losing ice.

Each gigaton sized iceberg would be equivalent to roughly a quarter of a percent of Greenland’s estimated 378 gigaton annual ice loss. It takes 360 gigatons to raise the global sea level by a millimeter, so Greenland is doing that roughly annually, as icebergs fall into the sea and glaciers retreat further. (In all, the ice sheet contains enough water to raise global sea levels by 6 meters, or 20 feet.)

The loss of ice occurs both through iceberg calving — which explains almost half of Greenland’s total loss, according to the new study — and mechanisms like simple drainage. Here, as meltwater atop the ice sheet finds ways of flowing down to its base (sometimes through sudden lake drainage), it then makes its way to the ocean. But both mechanisms have their explosive elements — earthquakes, tsunamis, lake vanishings — albeit in very different ways.

“The earthquakes are not themselves destabilizing the ice sheet,” says Nettles, “but they are a marker of the fact that the ice sheet is getting smaller and retreating.”

And that’s where the admittedly tiny piece of good news from all of this comes in. Because these earthquakes are so big, and detectable anywhere with seismic equipment, they can actually be used to track how much ice Greenland is losing. They’re like the  pulse of ice loss. So because Greenland will not go quietly, at least we will know how fast it is leaving us.
« Last Edit: July 05, 2015, 06:36:57 PM by space otter » USA, LLC
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