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

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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

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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

New light on Mammoth Mountain and Long Valley Caldera 3 March 2010

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New research (link to abstract) in the March 2010 issue of the Geological Society of America Bulletin sheds new light on the volcanism of the Long Valley caldera complex in eastern California, clarifying the eruptive sequence and the character of eruptive activity over the last 190,000 years.

Four eruptive sequences have been identified by Gail Mahood of Stanford University and her co-researchers, who used argon isotopes to study the lavas at Long Valley Caldera and Mammoth Mountain, which straddles the caldera’s south-west rim: the western moat sequence (~190,000–160,000 years ago), the Mammoth sequence (~120,000–58,000 years ago), the northwest caldera sequence (~41,000–29,000 years ago) and the Inyo chain sequence (from ~9,000 years ago to the present). This dating of the silicic lavas in the north-west sector of the caldera to ~41,000-29,000 years ago shows them to be rather younger than previously thought.

Interestingly, mafic and silicic lavas were produced simultaneously during the eruptions: ‘in each eruptive sequence mafic and silicic lavas erupted contemporaneously from spatially associated vents’. The authors suggest that if alkali basalt intruding into the crust caused the silicic eruptions, potentially small-volume silicic eruptions may be produced by this mechanism in future, producing explosive eruptions but within a limited area: they note that ‘In the past 40,000 years, eruptions have occurred along a N-S linear trend less than 10 km wide, limiting the zone subject to volcanic hazards’. This is useful information when it comes to planning for future eruptive activity. The eruption of basalt lava also indicates that no large magma body, which would absorb the basaltic material, is present below the caldera, Professor Mahood told the keen supervolcano fans at Discovery News.

The authors also note that their results provide ‘equivocal support for a suggested anticorrelation between volcanism and glaciation for the past 800,000 years in eastern California’ – that is, the theory that glaciation and volcanism alternated over that period, with maximum volcanism occurring during interglacial periods.

  • Gail A. Mahood, Joshua H. Ring, Simone Manganelli & Michael O. McWilliams, ‘New 40Ar/39Ar ages reveal contemporaneous mafic and silicic eruptions during the past 160,000 years at Mammoth Mountain and Long Valley caldera, California’, Geological Society of America Bulletin, vol. 122, nos. 3-4 (March 2010), pp. 396-407. [doi: 10.1130/B26396.1]. Link to abstract.

News
California supervolcano has split personalityDiscovery News, 2 March 2010

Information
Global Volcanism Program: Long Valley – information summary for Long Valley Caldera (120314-A)
Global Volcanism Program: Mammoth Mountain – information summary for Mammoth Mountain (1203-15-)
USGS Long Valley Observatory – website for the LVO, which keeps an eye on what the caldera is up to
Geological history of the Long Valley Caldera – from the LVO

The Volcanism Blog

Seamounts galore in Oceanography special issue 24 February 2010

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Oceanography special issue: Mountains in the Sea (23:1 Mar 2010)

The latest issue (vol. 23, no. 1, March 2010) of the official magazine of The Oceanography Society, Oceanography, is devoted to the study of undersea mountains or seamounts. This special issue is entitled, not surprisingly, ‘Mountains in the Sea’ and features fascinating content by some very distinguished contributors, and, best news of all, the online version is free!

Seamount volcanism is an important theme in many of the articles, as might be expected. The following focus particularly on volcanic matters (links are direct to the PDFs):

There are also spotlight articles on particular seamounts, including the volcanically active Loihi, Vailulu’u and Northwest Rota-1 seamounts (links are direct to the PDFs).

The table of contents for this special issue of Oceanography gives direct links to all the content, and USGS director Marcia McNutt provides a foreword (PDF). Also: Oceanography home page, The Oceanography Society home page, and a press release at ScienceDaily.

The Volcanism Blog

Five new volcanoes discovered in Ecuador 18 December 2009

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The South American republic of Ecuador, spanning the northern Andes, is not exactly short of volcanoes: more than 50 Ecuadorian volcanoes are known, while the Global Volcanism Program lists 20 volcanoes with Holocene activity, including such great names as Cayambe, Reventador, Cotopaxi, Chimborazo and Tungurahua.

Well, there are going to be some additions to the list with the news that no fewer than five previously unknown volcanoes have just been discovered in north-central Ecuador by volcanologists Patricia Mothes and Minard Hall.

The newly identified ‘Cosanga Volcanoes’ are located in the Cordillera Real between Baez and Cosanga, about 75 km south-east of the Ecuadorian capital, Quito, and have been named Lavas de Bermejo, El Dorado, Domos de Huevo de Chivo, Centro Pumayacu and Centro Cosanga. Of these five Mothes and Hall report that at least one, Pumayacu, is potentially active – more work is needed before the potential activity level of the other four can be determined. The Cosanga volcanoes are relatively low features, between 2,800 and 3,700 metres, and are also relatively young, having formed between 2,000 and 20,000 years before the present. Around Pumayacu pottery fragments of the Cosanga culture have been excavated, which Hall suggests indicates that inhabitants of the area around 2,000 years ago may have had to leave because of volcanic eruptions at that time.

The identification of these unknown volcanoes was sparked by the discovery of obsidian in the Cosanga region. Further studies are planned, and Mothes and Hall do not rule out discovering yet more hidden Ecuadorian volcanoes.

[Thanks go to Volcanism Blog commenter Guillermo.]

News
Descubren cinco nuevos volcanes en Ecuador – BBC Mundo, 18 December 2009
Descubren 5 nuevos volcanes en Ecuador – Ecuador Ciencia, 13 December 2009
Descubren cinco nuevos volcanes en Ecuador – AFP, 13 December 2009

Information
Global Volcanism Program: volcanoes of Ecuador – Holocene volcanoes in Ecuador
Ecuador volcanoes and volcanics – information from the USGS Cascades Volcano Observatory

The Volcanism Blog

Pre-eruption rumbles help volcano forecasting 17 December 2009

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Before a volcano erupts it rumbles and shakes the ground, just as an angry dog growls before it bites, says this press release.

The point is that different volcanoes behave in different ways – some rumble consistently, some stop and start, some rumble and erupt straightaway, others rumble for ages before they do anything, and others never get round to erupting at all – and understanding that behaviour helps with eruption forecasting and the issuing of alarms.

Volcano observatories often have a good understanding of these behaviours in the case of their local volcanoes: now Emily Brodsky, associate professor of earth and planetary sciences at the University of California, Santa Cruz, working with Luigi Passarelli of the University of Bologna and Stephanie Prejean of the USGS Alaska Volcano Observatory, has been trying to ‘stitch together those empirical rules with the underlying physics and find some sort of generality’. Professor Brodsky is presenting her findings at the AGU Fall Meeting in San Francisco.

Physics, of course, is only part of the problem with effective forecasting and warning of volcanic eruptions. Psychology is also an issue. The Pasto volcanological observatory in Colombia, which keeps watch on Galeras, has an excellent understanding of Galeras’s behaviour and always issues timely and appropriate warnings, but the local inhabitants do not respond to the alerts because they also feel that they know the volcano very well and don’t believe, from their experience, that its activity will do them any harm. They also weigh up the potential risks of volcanic activity (rather remote) against the risks of leaving their homes, farms and businesses unattended for an unknown length of time (very real) and decide to stay put.

(Press release re-heated here, here and here.)

The Volcanism Blog

Undersea explosive eruptions named ‘neptunian’ 5 July 2009

Posted by admin in current research, geoscience, volcanology.
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Two researchers from the School of Earth Sciences and Centre of Excellence in Ore Deposits (CODES) at the University of Tasmania have come up with the name ‘neptunian’ to describe undersea explosive volcanic eruptions, says a report at ScienceDaily.

These eruptions are sustained and driven by gas exsolved from magma … Neptunian eruptions differ dramatically from magmatic-gas-driven explosive eruptions on land, reflecting the important influence of confining pressure and the higher heat capacity, density, and viscosity of water compared to air.

The original article (abstract here) by Sharon R. Allen and Jocelyn McPhie of CODES can be found in Geology: Sharon R. Allen and Jocelyn McPhie, ‘Products of neptunian eruptions’, Geology, July 2009, pp. 639-642 [DOI 10.1130/G30007A.1].

N.B. Not to be confused with Neptunism.

The Volcanism Blog

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