Yellowstone Super Plume Enlarged

Further work using electroconductivity has hugely expanded and reshaped our understanding of the Yellowstone plume first imaged using seismic work.  Perhaps more correctly it is mapping the zoneof influence formed by the hot plume which naturally drives fluids in thesurrounding rocks generating alteration.

Henceforth geologists will wantto find similar rocks exposed on surface to map the derivative effects onmineralization.

Deep drilling will also teach usa lot now that we know the effects of a super plume naturally extends far fromthe zone of actual maximum heat flow.

It is interesting though just howflat lying the plume zone appears to be, or perhaps this is a natural misreadin which rising heat is creating a larger halo effect close to the surface.

Yellowstone supervolcano fed by bigger plume

By Paul RinconScience reporter, BBC News

13 April 2011 Last updated at 09:25 ET

http://www.bbc.co.uk/news/science-environment-13061779

The underground volcanic plume at Yellowstone in the US may be bigger than previouslythought, according to a study by geologists.

The volcanic hotspot below Yellowstone feeds the hot springs, mud pots and geysers that bring millions of visitors tothe USnational park each year.

But the Yellowstone"supervolcano" has erupted violently in the distant past and could doso again at some point.

The study is set to be published inGeophysical Research Letters journal.

In 2009, researchers used seismic waves from earthquakes to build up animage of the hotspot beneath Yellowstone, which straddles the US states of Wyoming,Montana and Idaho.

The authors of the latest work used variations in the electricalconductivity of rocks to produce a new picture of the plume.

This conductivity is a property of the molten silicate rocks and thehot briny water that is naturally present in them.

"It's like comparing ultrasound and MRI in the human body; theyare different imaging technologies," says co-author Michael Zhdanov, aprofessor of geophysics at the Universityof Utah in Salt Lake City.

Hot envelope

The 2009 images, using seismic waves, showed the plume of hot andmolten rock dipping downward from Yellowstoneat an angle of 60 degrees. This plume extended 240km (150 miles) west-northwestto a point at least 660km (410 miles) under the Montana-Idaho border.

This was as far as the seismic imaging could "see".

The new study, using electrical conductivity, can only see about 320km(200 miles) below ground.

Variations in electrical conductivity reveal the volcanic plume ofpartly molten rock

But it shows the conductive part of the plume dipping more gently, atan angle of perhaps 40 degrees to the west, and extending perhaps 640 km (400miles) from east to west.

They may look different because the two techniques image slightlydifferent things.

Seismic images highlight materials such as molten or partly-molten rockthat slow seismic waves, while the geoelectric technique displays briny fluidsthat conduct electricity.

Co-author Robert B Smith, who is also at University of Utah,said the plume was bigger in the geoelectric picture. He said it could beinferred that there were more fluids than shown by the seismic images.

Despite differences, he says, "this body that conducts electricityis in about the same location with similar geometry as the seismically imaged Yellowstone plume."

The more gentle tilt of the geoelectric plume could suggest that thehot region imaged by the seismic wave technique may be enveloped by a broader,underground envelope of partly-molten rock and liquids, the researchers say.

There have been three huge eruptions of the Yellowstonesupervolcano: 2.1 million years ago, 1.3 million years ago and 640,000 yearsago. Two of these eruptions blanketed a large area of North America with volcanic ash.

The most recent full-scale eruption of the Yellowstonesupervolcano ejected some 1,000 cubic km (240 cubic miles) of hot ash and rockinto the atmosphere. There have been smaller eruptions in between the largestoutpourings; the most recent of these occurred 70,000 years ago.