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Tree rings, volcanoes and climate 7 March 2012

Posted by admin in climate, current research.
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Is dendrochronology always a reliable guide to past climatic variations? And apropos the theory that large volcanic eruptions in the latter half of the thirteenth century AD were responsible for the cool period known as the Little Ice Age (LIA), can it perhaps be argued that the eruption did not so much begin the LIA as end the MWP (Medieval Warm Period)? That kind of conceptual re-focusing appeals to me as a historian. It is the type of game historians (well aware that all periodization is a human construct) like to play: flip the structuring principles you apply to the past around and see what difference it makes. And what do the trees say?

These musings are provoked by this article at Bits of Science. Have a look and see what you think.

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

Posted by admin in current research, geoscience.
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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

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Underwater Antarctic volcanoes discovered 12 July 2011

Posted by admin in Antarctica, current research, volcanology.
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Just a brief note (for now) on what looks to be a fascinating discovery. Scientists from the British Antarctic Survey have discovered previously unknown underwater volcanoes in Antarctica. During research cruises in RRS James Clark Ross the BAS team discovered no fewer than twelve sub-sea volcanoes, some up to 3 km high, with at least one showing signs of recent activity. The volcanoes were identified in the Southern Ocean near the South Sandwich Islands, using shipboard 3D seafloor mapping technology.

News
Huge volcanoes mapped in sea near Antarctica – MSNBC, 11 July 2011
Antarctic survey finds undersea volcanoes – UPI, 11 July 2011

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Volcanology audio slideshow at the BBC 9 June 2011

Posted by admin in current research, geoscience, volcanology.
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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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Phytoplankton flourishes as Kasatochi’s ash fertilizes the ocean 8 October 2010

Posted by admin in Alaska, current research, Kasatochi.
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The eruption of Alaska’s Kasatochi volcano in August 2008 has led to a surge in the population of phytoplankton in the North Pacific, says a paper in Geophysical Research Letters authored by a horde of scientists from institutions in Canada, the USA and the UK, led by oceanographer Roberta C. Hamme of the University of Victoria, British Columbia. An unusual storm system meant that the ash deposited by the volcano was transported across a very wide area of the north-eastern Pacific, and the iron content encouraged the growth of phytoplankton (for which iron is a key nutrient), producing one of the largest plankton blooms ever recorded in this region. Scientists have recently suggested that volcanic ash fertilization of the ocean in this way can occur, but, as Professor Hamme notes in the very useful summary of the Kasatochi paper she has made available as a PDF on her website (wish more scientists would do that), this is the first time conclusive evidence has been obtained to support the hypothesis.

Because phytoplankton (which are the basis of oceanic and freshwater food chains) consume carbon dioxide and release oxygen, seeding the oceans with iron to encourage their growth has sometimes been suggested as a means of diminishing atmospheric CO2. However, the evidence of the naturally-occurring Kasatochi seeding episode is that the process is not very efficient and that it would take a lot of iron to make even a small difference.

  • Roberta C. Hamme et al. ‘Volcanic ash fuels anomalous plankton bloom in subarctic northeast Pacific’, Geophysical Research Letters, 37 (2010), doi:10.1029/2010GL044629. [abstract]

News
How volcanoes feed plankton – ScienceNow, 5 October 2010
Effects of volcanic eruption dash promising global warming theoryGlobe and Mail, 5 October 2010
Volcano ‘seeded’ ocean bloom – UPI.com, 6 October 2010

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

Posted by admin in current research, geoscience, volcanology.
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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]

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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

Research: Fuji developing a more explosive style? 6 May 2010

Posted by admin in current research, Fuji, Japan, volcanoes, volcanology.
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‘Rumbles hint that Mount Fuji is getting angry’, says the rather sensationalized headline that New Scientist has stuck over their report of a new study of Mount Fuji. There’s no suggestion in the original research paper that Fuji is ‘getting angry’, or even slightly annoyed, just a new theorization of the processes that may be causing Fuji’s magmas to become more andesitic to dacitic, thus tending towards a more explosive eruptive style.

The paper, ‘Crypto-magma chambers beneath Mt. Fuji’ by Takayuki Kaneko et al (JVGR 2010, in press) notes that Fuji’s eruptive history has been characterized by basaltic activity with occasional explosive eruptions involving andesitic to dacitic lavas. Studies of Fuji’s lavas using air-fall scoria, however, indicate an increase in silica content over time: Kaneko proposes a two-level magma chamber system to account for this, with basaltic magma at the deep level and more silicic magma at the shallower level. The increasing level of silica, suggests Kaneko, ‘could result from the combination of repeated magma mixing between the two end-member magmas and fractional crystallization processes in each magma chamber’.

The upward trend of SiO2 … seems to continue to the present. In the last several thousand years, explosive eruptions involving a small volume of andesitic magma were repeated sporadically … Such andesitic or dacitic products have not been found from the older periods of Fuji–Ko-Fuji to the middle stage of Shin-Fuji volcanoes. This may suggest that, in the last several thousand years, the composition of the magma in the shallow chamber has become more SiO2-rich than ever.

The New Scientist article says that Kaneko interprets the low-frequency earthquakes detected beneath Fuji in 2000 and 2001 as possible evidence for magma injections into the lower chamber, ‘and adds he would not be surprised if Fuji erupts in the very near future’. That’s the ‘Fuji getting angry’ bit, and it’s stretching things somewhat on the basis of this research. The paper itself simply concludes with the suggestion that ‘Fuji may have entered a stage with the potential for explosive eruptions involving andesitic to dacitic magmas’.

  • Takayuki Kaneko, Atsushi Yasuda, Toshitsugu Fujii and Mitsuhiro Yoshimoto, ‘Crypto-magma chambers beneath Mt. Fuji’, Journal of Volcanology & Geothermal Research, article in press 2010 [doi:10.1016/j.jvolgeores.2010.04.002]

News
Rumbles hint that Mount Fuji is getting angryNew Scientist, 5 May 2010

Information
Global Volcanism Program: Fuji – information about Fuji from the GVP (0803-03=)
Volcano Research Center – the University of Tokyo’s Volcano Research Center

The Volcanism Blog

British scientists discover deepest known undersea volcanic vents 12 April 2010

Posted by admin in Caribbean, current research, submarine volcanism.
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First photograph of the world's deepest known 'black smoker' vent, erupting water hot enough to melt lead, 3.1 miles deep on the ocean floor (National Oceanography Centre)
First photograph of the world’s deepest known ‘black smoker’ vent, erupting water hot enough to melt lead, 3.1 miles deep on the ocean floor (National Oceanography Centre).

Scientists from the UK’s National Oceanography Centre (NOC) have discovered the deepest volcanic vents so far known, 5000 metres below the surface of the Caribbean Sea. The vents are located in the Cayman Trough in the western Caribbean, which reaches a maximum depth of 7,500 metres. Further research will analyse the geology and geochemistry of the vents and the marine life associated with them. NOC geochemist Dough Connelly, Principal Scientist of the expedition, says: ‘We hope our discovery will yield new insights into biogeochemically important elements in one of the most extreme naturally occurring environments on our planet’.

The Cayman Trough expedition, funded by the National Environment Research Council, is based aboard the UK’s new ocean-going research vessel RRS James Cook. For more on the expedition, see our post from August 2008: British scientists to investigate Caribbean deep-sea hydrothermal vents.

News
British scientific expedition discovers world’s deepest known undersea volcanic vents – EurekAlert, 11 April 2010
World’s deepest undersea vents discovered in Caribbean – BBC News, 12 April 2010
World’s deepest known undersea volcanic vents discovered – ScienceDaily, 12 April 2010

Information
National Oceanography Centre – website for the UK’s newly integrated National Oceanography Centre
Cayman Trough expedition – reports from the expedition team

The Volcanism Blog