Wednesday, June 1, 2011

800-Mile-Wide Hot Anomaly Found Under Seafloor off Hawaii




So much for another veryattractive and convincing theory.  Againwe are back to knowing nothing about what is actually happening around hotspots and have to put our imaginations on hold. It was fun while it lasted and I certainly bought into it to the extentof struggling to work around the problem when I considered the evidence forcrustal migration.

Suddenly the idea of a very deepplume is plausibly replaced by a large zone of hotter rock that may havedeveloped as a concentration point in the center of the pacific plate.    The question then is this feeding heat bothhorizontally and vertically to the island chain which certainly shows amigrating plume of some sort at work there.

Fitting this all together isgoing to provide headaches for some time. That is the nature of seriously contradictory new evidence. 

Where did the heat come from orare we looking at the artifact of a chemical separation that we have yet tofigure out.  After all this is a basalticevent.

800-Mile-Wide Hot Anomaly Found Under Seafloor off Hawaii

findings contradict long-held theory that a plume directly fuels Hawaii.



Hot lava spills into the sea from under a hardened lava crust on the Big Islandof Hawaii(file picture).

Photograph by Patrick McFeeley, National Geographic
Dave Mosher

Updated May 27, 2011 (First posted May 26, 2011)



Hawaii'straditional birth story—that the volcanic islandswere, and are, fueled by a hot-rock plume running directly to Earth's scorchingcore—could be toast, a new study hints.
Scientists say they've found solid evidence of a giant mass of hot rockunder the seafloor in the region. But it's not a plume running straight fromthe core to the surface—and it's hundreds of miles west of the nearest Hawaiianisland.

Until now, the researchers say, good seismic data on the region hasbeen scarce, so it was tough to question the traditional explanation: that astream of hot rock directly from around Earth's core formed the 3,100-mile-long(5,000-kilometer-long) chain of islands and undersea mountains in the Pacific Ocean.

As Earth's crust slid over the plume, as if on a conveyor belt, theerupting seafloor built mounts, mountains, and islands out of layers of cooledlava over tens of millions of years—or so the conventional wisdom goes.

But after analyzing 20 years' worth of earthquake data,geophysicists say they've found an 800-mile-wide (1,300-kilometer-wide) regionof hot rock in the Hawaiian region—but nothing beneath the Big Island of Hawaii.The island, the youngest in the chain, is traditionally thought to be above thepurported plume.

Although the new evidence flies in the face of the giant-plume theory,"we can't rule out a narrow plume below the island, but the main sourcecomes from a different place. It can't be linked directly below," saidgeophysicist Robert van der Hilst of MIT, co-author of the new study, led byhis colleague Qin Cao and appearing online today in the journal Science.


Hawaii Plume Takes Deep Detour?

Volcano formation starts where Earth's mantle—the planet's thickestrock layer—meets the molten outer core, some 1,800 miles (2,900 kilometers)below the surface.

The outer core heats the mantle's bottom rocks into buoyant putty,which rises toward the crust, as if in a lava lamp. Within a few miles of thecrust, the rock decompresses, melts, and often oozes—or erupts—out of theEarth's surface.
A technique called seismic tomography uses the sounds of earthquakesrippling through the planet and bouncing around to detect such plumes, or hotspots. But this kind of data has been limited for Hawaii.

"It's been very difficult to image the mantle below Hawaii, simply becauseit's so far away from [large] seismic-sensor networks," van der Hilstsaid. Data suggesting a plume directly below the island is very limited andbased on relatively narrow sampling by seismic waves, he said.

By contrast, Van der Hilst said, the new study analyzed two decades'worth of seismic data and extracted subtle but clear signals.

Those signals point to the giant anomaly, about 410 miles (660kilometers) down: a relatively disklike segment of rock between 540 and 720degrees Fahrenheit (300 and 400 degrees Celsius) hotter than its surroundingsand between 370 miles (600 kilometers) and 1,000 miles (1,600 kilometers) westof the Big Island.

The team suspects the plume is pooling at the boundary between theupper and lower mantle, then snaking its way to the crust below the archipelagobefore rising to feed Hawaii'svolcanic islands.

More evidence is needed before it's known for sure what's stoking thevolatile island chain, but at the least, the new study "shows the processof how our planet loses heat is more complicated than we thought," van derHilst said. It may also help explain how other Pacific seamounts came to be, headded.



Magma Chamber Surprisingly Close to Hawaii's Surface?

Lava source found within two miles of surface, research suggests.



Lava glows through a hole in the crust of Kilauea volcano on the Big Islandof Hawaii
Photograph from Photolibrary
Richard A. Lovett in San Francisco
Published December 23, 2010


A giant magma chamber burning beneath the Hawaiian Islands is closer tothe surface than any other magma chamber yet measured—as little as 1.9 to 2.5miles (3 to 4 kilometers) below the surface, scientists say.


But Hawaiians don't need to worry about plunging into the magma below,say, during an earthquake—two miles of solid rock is more than enough to keepthat from happening, according to geology undergraduate Julie Ditkof, whopresented the findings December 14 at a meeting of the American GeophysicalUnion in San Francisco.
Ditkof, of Ohio State University, determined the chemical compositionof crystals in a thousand samples of volcanic rock taken from Hawaii'smost volcanically active regions, the BigIsland (map) and an adjacent undersea volcano calledLoihi.

Using a method developed in Iceland—another volcanic island—by MichaelBarton, Ditkof's advisor and research partner at Ohio State, she paidparticular attention to olivine, the first mineral in Earth's crust tocrystallize as temperatures and pressures drop.

The ratios of certain elements in each olivine sample told her how deepthe lava had been when it left the magma chamber and began crystallizing—andtherefore the depth of the magma itself, said Ditkof, whose findings have notbeen published in a peer-reviewed journal.

Heated Debate

The magma-depth discovery may settle a longstanding debate.

In 2008 workers doing exploratory drilling for a geothermal plantreported that they had accidentallybroken through to a shallow magma chamber near the Big Island's Kilauea volcano.

Even after the incident, though, scientists were unsure as to thegeneral depth of the magma chamber, or chambers, that produce most of the Big Island'slava, as magma is called once it hits the surface.

Some prior studies of other minerals in Hawaiian volcanic rock, forexample, had suggested that the local lava comes from as deep as perhaps 11 to25 miles (18 to 40 kilometers) down.

But seismicstudies appeared to show magma chambers at much shallower depths—about 1.2to 3.7 miles (2 to 6 kilometers).

"We wanted to prove one right or one wrong," Ditkof said.

Magma to Power Hawaii?

The discovery of magma so close to the surface suggests that Hawaii might have agood, fairly accessible source of alternative energy.\

That could be good news for the state, which generates 90 percent ofits power from imported oil, "resulting in electricity that costs fivetimes more than the national average," accordingto Scientific American.

Ditkof said, "Very shallow magma chambers mean there is a veryshallowgeothermal heatsource that could be tapped," for example to generate steam to powerturbines in electrical plants, she said.

"If someone could utilize that, you have amazing geothermalpotentials."


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