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Ocean crust formation not such a passive business 27 November 2009

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New research indicates that the formation of ocean crust is not always a passive business, but has an important dynamic component. The study is based on analysis of seismic wave velocities in the uppermost 200 km of the mantle beneath the Gulf of California:

The seismic waves in three localized centers, spaced about 250 kilometers (155 miles) apart, traveled more slowly than waves in the surrounding mantle, implying the presence of more melt in the localized centers and thus a more vigorous upwelling. From that, the geologists determined the centers, located 40-90 kilometers (25 to 56 miles) below the surface, showed evidence of dynamic upwelling in the mantle. [from the Brown University press release]

This research is published in a letter to the current issue of Nature (home of the snappy science headline – ‘Developmental Biology: Down the tube’, ‘Meteorology: Can’t beat the heat’, etc.), available in full to subscribers.

  • Yun Wang, Donald W. Forsyth & Brian Savage, ‘Convective upwelling in the mantle beneath the Gulf of California’, Nature, vol. 462 no. 7272 (26 Nov 2009), pp. 499-501 [doi:10.1038/nature08552]. Click here for summary.

Oceanic crust formation is dynamic after all – Brown University press release, 23 November 2009

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Toba eruption deforested India 24 November 2009

Posted by admin in climate, current research, India, Indonesia, Toba.
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The Toba eruption of ~73000 years ago is perennially fascinating: the world’s largest known Quaternary eruption, this event registered VEI=8 and had a global climatic impact that may have caused the near-extinction of humanity by creating a ‘population bottleneck’ (or perhaps not). The scientist behind the population bottleneck theory, University of Illinois anthropology professor Stanley Ambrose, is a lead author for a new study in the journal Palaeogeography, Palaeoclimatology, Palaeoecology (click here for the abstract) which explores further the impact of the Toba eruption and concludes that its effects were indeed wide-ranging and (crucially for the claim that contemporary human populations were dramatically affected) long-lasting.

The study looked at pollen from a marine core taken in the Bay of Bengal which includes ash from the Toba eruption and at carbon isotope ratios in fossil soil carbonates from directly above and below the Toba ash in three locations in central India. Both analyses indicated a change in the vegetation cover in central India after the Toba eruption, from forests to more open vegetation conditions with a predominance of grasslands. The change in vegetation suggests that significantly drier conditions were produced by the Toba eruption, and that those conditions lasted for at least a thousand years.

  • Martin A.J. Williams, Stanley H. Ambrose, Sander van der Kaarsc, Carsten Ruehlemannd, Umesh Chattopadhyayae, Jagannath Pale & Parth R. Chauhanf, Environmental impact of the 73 ka Toba super-eruption in South Asia, Palaeogeography, Palaeoclimatology, Palaeoecology [article in press, corrected proof], doi:10.1016/j.palaeo.2009.10.009 (abstract)

Supervolcano eruption – in Sumatra – deforested India 73,000 years ago – EurekAlert, 23 November 2009
Supervolcano eruption in Sumatra deforested India 73,000 years ago – ScienceDaily, 23 November 2009
…. both of the above being essentially regurgitations of this University of Illinois press release.

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Volcanic origin for nickel ore deposits 21 November 2009

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Some 10% of the world’s nickel production comes from iron-nickel sulphide (or, if you prefer, sulfide) deposits laid down on seafloors between 2.5 and 3 billion years ago and found in those interesting ultramafic volcanic rocks called komatiites. How these deposits came to be there, however, has always been something of a mystery, for the ore requires sulphur to form and neither the magmas hosting the ore nor the seawater contained sufficient sulphur for the process. Clearly, if the sulphur doesn’t come from the magma or the seawater it must come from the substrate: because of the very high temperatures at which the magma was erupted (greater than 1500oC) it was able thermo-mechanically to erode its substrate, thus acquiring sulphur in areas where the substrate was sulphur-rich. But how did the sulphur come to be there in the first place?

In a paper entitled ‘Atmospheric sulfur in Archean komatiite-hosted nickel deposits’ (abstract) in the new issue of Science a team of scientists from the Carnegie Institution, Woods Hole Oceanographic Institution and the universities of Manitoba and Western Australia argue that it all starts with volcanoes. Sulphur dioxide was erupted by volcanoes into an anoxic atmosphere, where high levels of UV sunlight broke down the gas and allowed sulphur to descend via rainfall and accumulate on the seabed. There geothermal action formed it into sulphide which was combined with nickel in magmas to produce the iron-nickel sulphides found in komatiites. The unusual isotope sulphur-33, produced by the atmospheric breaking-down of the volcanic sulphur dioxide, has turned up in rocks found in Western Australia, providing scientists with the key to recreating the sulphur’s complex ancient journey.

  • Andrey Bekker, Mark E. Barley, Marco L. Fiorentini, Olivier J. Rouxel, Douglas Rumble, Stephen W. Beresford, ‘Atmospheric sulfur in Archean komatiite-hosted nickel deposits’, Science, Vol. 326. no. 5956 (20 Nov 2009), pp. 1086 – 1089. DOI: 10.1126/science.1177742. (abstract)

Early volcanoes minted nickel – ScienceNow Daily News, 21 November 2009
Rich ore deposits linked to ancient atmosphere – RedOrbit, 21 November 2009

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Thermal imaging and volcano forecasting 25 November 2008

Posted by admin in geoscience, natural hazards, volcano monitoring, volcanology.
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An article in National Geographic for 22 November 2008 reports on the use of thermal imaging to assist in forecasting volcanic behaviour: ‘Infrared technology reveals volcanoes’ secrets’.

Focusing on the workof Michael Ramsey and Adam Carter of the University of Pittsburgh, who are using a combination of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite data and images captured at ground level through a hand-held instrument called FLIR (Forward Looking Infrared Radiometer) to monitor Bezymianny volcano in Kamchatka, the article explores the ways in which thermal information can help scientists pick up the warning signs of volcanic activity more quickly and accurately, improving their ability to forecast a volcano’s likely behaviour.

For much, much more on this see top hot rocks blog Magma Cum Laude.

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