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The tale of the mantle-plume thermal anomaly and the lost landscape 14 July 2011

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Using three-dimensional seismic reflection data, UK scientists have recovered the topography of a landscape that has been buried beneath the sea-floor sediments of the North Atlantic for 55 million years. The researchers, from the Bullard Laboratories and the BP Institute in Cambridge, have traced the coast, drainage patterns and contours of a landform that emerged north of what is now Scotland some 57-55 Myr ago, and have reconstructed the sequence through which the land was uplifted and, after about 1 million years of exposure, reburied. Their results are published in Nature Geoscience (see references below). They conclude that the driving force behind the rapid rise and fall of this large landmass was a thermal anomaly in the Icelandic mantle plume flowing beneath the lithospheric plate. The uplifted mass was located ~600 km from the centre of the Icelandic plume: a short-period thermal anomaly in the plume produced pulses of hot mantle material that spread out radially and caused the elevation of the landmass at the rapid rate of ~1km over two million years, and then its equally rapid subsequent disappearance.

The power of convective mantle processes is demonstrated once again. The result: a lost landscape sunk beneath the waves, just like Atlantis.

References
Ross A. Hartley, Gareth G. Roberts, Nicky White & Chris Richardson, ‘Transient convective uplift of an ancient buried landscape’, Nature Geoscience 2011 (advanced online publication, link to abstract only) doi:10.1038/ngeo1191
Heather Poore, Nicky White & John Maclennan, ‘Ocean circulation and mantle melting controlled by radial flow of hot pulses in the Iceland plume’, Nature Geoscience 2011 (advanced online publication, link is to abstract only) doi:10.1038/ngeo1161

News
A lost world? Atlantis-like landscape discovered – Live Science, 10 July 2011
Lost landscape discovered off the Scottish coast – BBC News, 14 July 2011

The Volcanism Blog

Volcanology audio slideshow at the BBC 9 June 2011

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Dr Tamsin Mather is a volcanologist in the Department of Earth Sciences at the University of Oxford (here’s her departmental web page). Dr Mather will be talking about her research at the Cheltenham Science Festival this week (ugly web page here), and gives a summary of what volcanology is, how it is done and what she in particular has been up to in this excellent BBC News audio slideshow — a miracle of concision at under five minutes, with great images and an accessible, informative expert commentary. Highly recommended.

Audio slideshow: Volcano visitors – BBC News, 9 June 2011

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Volcanic arcs: it’s all in the melt 8 October 2010

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We all know that volcanic arcs are related to subduction zones: the areas of the Earth’s surface where an oceanic lithospheric plate comes up against another plate and moves beneath it, ultimately being re-absorbed into the mantle in a vast geological recycling scheme. The oceanic rock is full of water, which begins to be released as it reaches greater depths and becomes subject to increased heat and pressure, entering the overlying mantle wedge that lies between it and the continental lithosphere and lowering its melting point, producing melt that ascends to feed volcanoes above the subduction zone. In offshore island arcs and continental volcanic arcs the line of volcanoes is always offset some way from the point at which the subducted plate makes its dive, which is marked by an oceanic trench.

Various explanations have been put forward for why the volcanoes appear where they do, usually connected to theories as to the locations of the points of highest temperature in the zone where the upper surface of the subducted slab and the mantle wedge are in contact with each other. No-one has really got to the bottom of it, however (so to speak). But two researchers from the University of Oxford Department of Earth Sciences, Philip C. England and Richard F. Katz, have been working on this problem in a new way, by applying a mathematical model of heat transport in this zone to establish where the areas of highest temperature, and thus of melt production, occur. Their conclusion is that the locations of subduction zone volcanoes can only be explained if they emerge above regions in which mantle is melting in the absence of water. Hydrous melting — melting associated with the presence of water — pervades the mantle wedge, but the conventional models of arc formation suggest that there is a particular point at which the degree of hydrous melting increases rapidly because of conditions of temperature and/or pressure, and that the arc front forms above this point. Yet these processes of hydrous melting occur not in a restricted area of the wedge but across a broad region of the mantle core, raising the issue of how the melt then becomes concentrated to feed a relatively narrow volcanic arc. England and Katz avoid that difficulty by invoking the crystallization of rising magma as it reaches the thermal boundary layer at the top of the wedge. This deflects the magma back towards the trench and into the ‘nose’ of the mantle wedge, whence it makes its way upwards by thermal erosion, opening pathways for hydrous melt which drives the volcanism of the arc.

The paper, ‘Melting above the anhydrous solidus controls the location of volcanic arcs’ by can be found in the 7 October 2010 issue of Nature. It’s subscribers only of course: the link below will give you the abstract, to read further you need to log in or pay up.

  • Philip C. England & Richard F. Katz, ‘Melting above the anhydrous solidus controls the location of volcanic arcs’, Nature, 700–703 (07 October 2010), doi:10.1038/nature09417. [abstract]

The Volcanism Blog

Stress change may provide clues to possible eruption locations 27 September 2010

Posted by admin in Africa, current research, Ethiopia, geoscience, volcano monitoring, volcanology.
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It’s all rifts, dykes and magmatic intrusions at Nature Geoscience right now. Along with the paper by Pallister et al on the Saudi quake swarms of 2009, the journal is hosting advanced online publication of a paper on a recent episode of dyke emplacement in the Afar region of north-eastern Africa: ‘Stress transfer between thirteen successive dyke intrusions in Ethiopia‘, by Ian J. Hamling et al.

The study looks at the emplacement of thirteen magmatic dykes in north-eastern Ethiopia between 2006 and 2009. A rift zone produced by the spreading boundary between the African and Arabian plates runs through this region; most such rift zones are situated on the ocean floor, so this remote area provides a valuable opportunity to study the processes associated with spreading plate boundaries without getting one’s feet wet. A team led by Ian Hamling of Leeds University measured changes in ground tension associated with each successive dyke emplacement, and found that subsequent eruptions were most likely in locations where the tension had been increased. Although the initial level of stress along a rift zone that becomes active is unknown, measurements of stress transfer will reveal whether eruptions in one location cause compressive stress change (clamping) or tensile stress change (unclamping) elsewhere. New dyking would be expected in locations subject to unclamping – in other words, where the ground has been stretched and is under increased tension – and the study shows that such is indeed the case: ‘the mean percentage of opening in unclamped sections of the rift has been 70%, with seven of 12 dykes having over 75% of their opening in regions unclamped by the previous intrusion’. The study concludes: ‘This result indicates that the stress change, induced by a new dyke, is a controlling factor on the location of future events and should therefore be incorporated into routine volcanic hazard monitoring’.

  • Ian J. Hamling, Tim J. Wright, Eric Calais, Laura Bennati & Elias Lewi, ‘Stress transfer between thirteen successive dyke intrusions in Ethiopia’, Nature Geoscience, published online: 26 September 2010 | doi:10.1038/ngeo967 [abstract]

News
Pinpointing where volcanic eruptions could strike – EurekAlert, 26 September 2010

The Volcanism Blog

Fire, ice, and Eyjafjallajökull 23 September 2010

Posted by admin in current research, Eyjafjöll, geoscience, Iceland, natural hazards, volcanology.
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A fascinating article in Science News, magazine of the Society for Science and the Public, explores the role of ice in volcanism with particular reference to the eruption of Iceland’s Eyjafjallajökull earlier this year. When Eyjafjallajökull erupted on 20 March 2010 it began with a fissure eruption characterized by relatively quiet effusive activity and limited ash emissions. This changed in mid-April when the seat of the eruption moved west to an area beneath the ice-cap. As the eruption became sub-glacial, explosivity and ash production increased, with the disruptive consequences that we are all familiar with.

The Science News article, an excellent piece of work by Alexandra Witze, looks at some of the research that is now going on in the wake of the Eyjafjallajökull eruption to explore the crucial issue of glaciovolcanism – the interaction between volcanic activity and ice.

Eyjafjallajökull’s eruption has refocused attention on a small but rapidly growing subset of volcanology: the study of volcano-ice interactions. Ice-covered volcanoes, or “glaciovolcanoes,” are not fundamentally different from other volcanoes in terms of plumbing or eruptive style. But they distinguish themselves the moment magma breaks through the crust and meets ice.

One reason to study icy volcanoes is to better understand their risks. Nobody died in the Eyjafjallajökull eruption, but in 1985 an eruption beneath an icy mountain in the Colombian Andes sent massive mudflows coursing downstream, killing more than 20,000 people. Dozens of volcanoes mantled with ice are scattered around the world, each posing a distinct hazard.

The volcano responsible for that killer eruption of 1985 was of course Nevado del Ruiz; the 25th anniversary of that event will be on 13 November this year. At Nevado del Ruiz human failings in monitoring and communication (along with unfortunate weather conditions that obscured the summit) rather than geology were to blame for the scale of the disaster, but the eruption certainly illustrates the particularly hazardous nature of ice-capped volcanoes.

News
Fire & ice: volcanoes and frozen lands make an explosive combo – Science News, 25 September 2010

The Volcanism Blog

Volcano-related topics at GSA Portland (2) 20 October 2009

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A couple more presentations on volcanic themes from the current Geological Society of America 2009 Fall Meeting in Portland, Oregon (18-21 October 2009).

Magmatic plumbing of a ‘supervolcano’ exposed to a depth of 25 km (James E. Quick, Southern Methodist University) – the exposure through uplift of a Permian caldera in the Sesia Valley (PDF) reveals the magmatic plumbing system to 25 km depth. (More about this here at The Volcanism Blog, at Eruptions, and at Outside The Interzone here and here.)

Giant impact near India – not Mexico – may have doomed dinosaurs (Sankar Chatterjee, Texas Tech University) – the Shiva basin off the west coast of India may be a meteorite impact crater: as well as killing off the dinosaurs, the crust-vaporizing bang could have enhanced the Deccan Traps eruptions.

UPDATE. I should mention that Callan Bentley of the always-excellent NOVA Geoblog is posting regular reports on the Portland geo-jamboree: GSA update 1, GSA update 2, GSA update 3, GSA update 4. PLUS Jessica at Magma Cum Laude has a list of geobloggers presenting papers, and ongoing updates from the conference. AND Erik at Eruptions has a GSA pre-update.

The Volcanism Blog

Volcano-related topics at GSA Portland (1) 19 October 2009

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The Geological Society of America is currently holding its 2009 Fall Meeting in Portland, Oregon (18-21 October 2009) and with volcanoes featuring prominently in its title, ‘From volcanoes to vineyards – living with dynamic landscapes’, it’s no surprise that there are plenty of volcanic topics in the programme.

Information on particular presentations is regularly updated on the Portland meeting news release page, but as a service to those chiefly interested in things volcanic (and who don’t feel like working their way through the list opening PDF after PDF) I will be summarizing the volcano-related stuff here.

This first post lists contributions from United States Geological Service scientists: the source is this USGS PDF.

Experimental results of carbon sequestration in basaltic rocks (Robert Rosenbauer, USGS) – exploiting the carbon dioxide sequestration potential of basaltic volcanic rocks.

Entrances to tubular caves on Mars? (Glen Cushing, USGS) – imagery from Mars may show entrances to tunnels, possibly volcanic lava tubes.

Can static decompression of magma trigger volcanic eruptions? (Michael Poland, USGS) – the March 2008 explosion at Kilauea may have been triggered by static decompression caused by lava withdrawal from a reservoir beneath the summit caldera: a mechanism that has implications for volcanic hazards worldwide.

A major explosive eruption and aftermath in the Aleutians (Chris Waythomas, USGS) – the geomorphic and ecological impact of the 2008 Kasatochi eruption, particularly in relation to seabirds.

Communicating health hazards of volcanic ash fall (Kristi Wallace, USGS) – a method for significantly improving public hazard communication in relation to volcanic ash fall and air quality hazards.

Virtual volcano tours and geologic concepts (Dina Venezky, USGS) – the use of Google Map technology to provide real-time information about volcanoes around the world.

The Perfect debris flow (Richard Iverson, USGS) – large-scale experiments examining debris-flow dynamics.

Evaluating debris flow hazards by helicopter (Carol Finn, USGS) – dangling experiments over volcanoes from helicopters to evaluate hydrothermal alteration of rocks, which can contribute to destructive debris-flow hazards on volcanic flanks.

The Volcanism Blog

Chaitén magma’s surprising speed 8 October 2009

Posted by admin in Chaitén, Chile, current research, eruptions, geoscience, natural hazards.
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New research just published in Nature indicates that the magma feeding the eruption of Chaitén that began in May 2008 rose from the magma chamber to the surface much faster than anyone thought, and much faster than sticky, viscous rhyolite magma has any right to move. This makes the Chaitén eruption even more interesting than it was already, and suggests that rhyolitic volcanoes may spring nasty surprises on us in the future by building up to eruption very quickly.

Blognote: Dr Erik Klemetti has all you need to know about Chaitén’s racy rhyolite over at Eruptions, and offers the opportunity to put your questions to one of the authors of the Nature study, Dr Jonathan Castro.

For all our Chaitén coverage: Chaitén « The Volcanism Blog.

Information
Global Volcanism Program: Chaitén – summary information for Chaitén (1508-41)
SERNAGEOMIN – Servicio Nacional de Geología y Minería (Spanish)
Erupción del Volcán Chaitén – extensive coverage of the Chaitén eruption

The Volcanism Blog

More on climate change and volcanism from ‘Nature’ 18 September 2009

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The possible connection between climate change and increased volcanism has been attracting some attention recently. Now Nature takes a look at the issue in a news article headed ‘Volcanoes stirred by climate change‘: the point being that a reduction in ice cover may be related to more explosive eruptive activity from volcanoes (or, as Nature calls them, ‘these unstable magmatic beasts’).

Volcanoes stirred by climate changeNature, 17 September 2009

The Volcanism Blog

Scientists map Sierra Negra magma chamber 22 August 2009

Posted by admin in Ecuador, Galapagos, geoscience.
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Sierra Negra volcano in the Galápagos erupting, 22 October 2005 (NASA Earth Observatory image: Terra/MODIS)

Sierra Negra volcano on Isla Isabela in the Galápagos is one of the most active volcanoes in the Galápagos archipelago: its most recent eruption was in October 2005 (shown in the NASA Earth Observatory image above).

An interdisciplinary team of scientists (University of Miami, University of Rochester, University of Idaho and the Instituto Geofísico of Ecuador) has just returned from Isla Isabela, where they have been busy deploying a seismic network the data from which will help to determine precisely where Sierra Negra’s magma chamber is located and how far it extends, as Dr Falk Amelung of the University of Miami’s Rosenstiel School of Marine and Atmospheric Science explains:

‘With the satellite data we regularly collect here at the University of Miami, using a technique called satellite radar interferometry, we are able to see the underground location of the magma chamber. The new seismic data will allow us to corroborate our information and obtain proof that the magma chamber is actually 2 km down and to what depth it extends. Petrologists suggest that the chamber may extend to a depth of 10 km, whereas geophysicists believe it might go only to a depth of 3 km or so’.

Much fun was evidently had by the team, coming and going in helicopters and on horses, and trekking across jagged, boot-shredding lava fields. The project was funded by the National Science Foundation, and in an admirable example of science-schools partnership an additional NSF grant funded the presence of Lisa Hjelm, science teacher from The Girls’ Middle School, Mountain View, California, who will be using data from the study to create a visualization of the volcano’s interior as an educational project.

The Volcanism Blog

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