https://phys.org/news/2021-08-thwaites-glacier-significant-geothermal-beneath.html
Le mer. 18 août 2021 12:47, Andrew Lockley <andrew.lock...@gmail.com> a écrit : > > > https://www.newscientist.com/article/dn13583-melting-ice-caps-may-trigger-more-volcanic-eruptions/ > > > Menu > Melting ice caps may trigger more volcanic eruptions > EARTH 3 April 2008 > By Catherine Brahic > > New Scientist Default Image > Vatnajökull in the south-east is the largest ice cap in Iceland and > conceals several volcanoes > > (Image: NASA) > > A warmer world could be a more explosive one. Global warming is having a > much more profound effect than just melting ice caps – it is melting magma > too. > > Vatnajökull is the largest ice cap in Iceland, and is disappearing at a > rate of 5 cubic kilometres per year. > > Carolina Pagli of the University of Leeds, UK, and Freysteinn Sigmundsson > of the University of Iceland have calculated the effects of the melting on > the crust and magma underneath. > > > They say that, as the ice disappears, it relieves the pressure exerted on > the rocks deep under the ice sheet, increasing the rate at which it melts > into magma. An average of 1.4 cubic kilometres has been produced every > century since 1890, a 10% increase on the background rate. > > ADVERTISING > > Frequent eruptions > In Iceland there are several active volcanoes under the ice. The last big > eruption was in 1996 at Gjàlp, and before then in 1938 – a gap of 58 years. > But Pagli and Sigmundsson say that the extra magma produced as the ice cap > melts could supply enough magma for similar eruptions to take place every > 30 years on average. > > Predicting the eruptions precisely will be tricky, though, as the rate of > magma migration to the surface is unknown. > > > The situation in Iceland does not necessarily mean magma will be melting > faster around the world. Vatnajökull sits atop a boundary between plates in > the Earth’s crust, and it is this configuration that is allowing the > release in pressure to have such a great effect deep in the mantle. > > But the thinning ice has another effect on volcanoes which will be more > widespread. > > As the amount of weight on the crust changes, geological stresses inside > the crust will also change, increasing the likelihood of eruptions. “Under > the ice’s weight, the crust bends and as you melt the ice the crust will > bounce up again,” explains Bill McGuire of University College London in the > UK, who was not involved in the study. > > Unexpected activity > Pagli say places likely to be at increased risk of eruption due to > ice-melt include Antarctica’s Mount Erebus, the Aleutian Islands and other > Alaskan volcanoes. > > The shifting stress might even cause eruptions in unexpected places. > > “We think that during the Gjàlp eruption, magma reached the surface at an > unusual location, mid-way between two volcanoes, because of these stress > changes,” says Pagli. > > McGuire thinks the Vatnajökull study is based on “perfectly reasonable” > physics. However, he says that climate change presents an even more > explosive threat. “It’s not just unloading the crust that triggers volcanic > activity but loading as well.” > > He and his team are looking into the effects that rising sea-levels – also > a consequence of melting ice caps – will have on volcanoes. “We are going > to see a massive increase in volcanic activity globally,” he told New > Scientist. “If we look back at previous warm periods, that is what > happened.” > > Journal reference: Geophysical Research Letters (in press) > > On Tue, 17 Aug 2021, 12:43 , <david.sev...@carbon-cycle.co.uk> wrote: > >> Stuart, >> >> >> >> I read the paper that you kindly sent as a reference. I can see some >> issues that are relevant to compare Iceland ice loss to loss of ice in >> Marie Byrd land above the super volcano: >> >> >> >> 1. The ice sheet thickness in Iceland is an average of 400 metres and >> a maximum thickness. The Western Antarctica ice sheet above the super >> volcano is 5 or 6 times this thickness. The response could be greater as a >> result? >> 2. The super volcano currently is active as it provides heat that is >> responsible for half the ice flow from this glacier. I am unsure exactly >> how to line up this level of activity with potential magma levels that >> would mean that it is “primed” for eruption if the ice is removed. >> 3. The last time that Western Antarctica was ice free was 35 million >> years ago. I don’t know where we could look to for a similar situation >> where this thickness of ice is removed from on top of a super volcano. >> While I am sure this has happened before, I am unaware of this happening >> in >> the near geological time period which will likely mean that getting >> detailed predictions of what might happen over dozens/centuries of time >> from what has previously occurred may not be possible. >> >> >> >> A significant concern is that we are placing a lot of hopes for the >> future on the current climate models. If what I fear does happen, then we >> are going to enter completely unknown and potentially quite dangerous >> territory. If there is delay in the volcanic activity uptick after the loss >> of ice we may also only discover the folly of what has occurred when it is >> far too late. >> >> >> >> Undertaking an experiment of this danger is very foolish. At the very >> least we should investigate this further, quantify the danger, and revisit >> our climate models and explore the impact of this occurring. Flying blind >> into a future without understanding this is madness. >> >> >> >> >> >> David Sevier >> >> >> >> Carbon Cycle Limited >> >> 248 Sutton Common Road >> >> Sutton, Surrey SM3 9PW >> >> England >> >> >> >> Tel 44 (0) 208 288 0128 >> >> >> >> >> >> >> >> >> >> *From:* geoengineering@googlegroups.com <geoengineering@googlegroups.com> >> *On Behalf Of *Stuart Haszeldine >> *Sent:* 17 August 2021 02:40 >> *To:* David Sevier <david.sev...@carbon-cycle.co.uk> >> *Cc:* geoengineering <geoengineering@googlegroups.com> >> *Subject:* Re: [geo] New threat from Climate change and the use of >> Geo-engineering >> >> >> >> Hello David, I can certainly relate to your line of arguement. I guess >> that the hazard depends on the unloading by ice melt being sufficient in >> pressure change to trigger eruptions - initially from magma at critical >> balance near-surface. >> >> >> >> Heres two thoughts, and then a piece of information. >> >> 1) your reasoning will apply to any past rapid warming, to unload ice >> sheets. Haas anybody looked for changes in volcanism frequency or size >> during past glacial cycles, or coming out of glacial periods into warmer >> millennia. >> >> >> >> 2) If a super-volcano erupts, then its probably goodbye - but humans and >> most species did survive Mt Taupo about 22kyr ago. I think magma >> reservoirs need about 50% liquid for a large scale eruption - so if there >> has been geophysics across the Antarctic that may be able to inform us if >> its ready to trigger or not. >> >> >> >> 3) As additional information, the Quaternary record of tephra from >> Iceland has been investigated during the ast couple of decades to test a >> similar theory that unroofing ice load from volcanoes with shallow depth >> magma can trigger eruptions. 2km ice melt is 20 MPascal pressure change - >> so a big change on magma at 2km (50 MPa). Less significant at 8km depth >> of magma chamber for Yellowstone or Taupo super volcanoes where the >> pressure is 200MPa, though a 10% change within hundreds of years ice >> melting is still a good trigger. >> >> >> >> This is C.L. Cooper and G.T Swindles Quaternary Sciences Advances >> >> May 2020. https://doi.org/10.1016/j.qsa.2020.100004 And the >> correlation (attached) does appear to have some linkage by eye - though I’m >> sure that time series analysts in this group can do a better statistical >> job than that. >> >> >> >> >> >> >> >> Stuart >> >> Stuart Haszeldine OBE FRSE C.Geol >> >> Professor of Carbon Capture and Storage >> >> School of GeoSciences >> University of Edinburgh >> Scotland UK, EH9 3FE >> >> >> >> >> >> >> >> >> >> >> >> >> >> On 16 Aug 2021, at 17:35, <david.sev...@carbon-cycle.co.uk> < >> david.sev...@carbon-cycle.co.uk> wrote: >> >> >> >> *This email was sent to you by someone outside the University.* >> >> You should only click on links or attachments if you are certain that the >> email is genuine and the content is safe. >> >> I believe that I have identified a new feedback loop/threat that emerges >> from the current trends of climate change. This new threat is likely to >> eclipse the already identified impacts of climate change and changes the >> moral calculation about whether to use geoengineering to cool the planet. >> It becomes immoral to fail to use geo-engineering to prevent this dangerous >> feedback loop from occurring. >> >> We are in the process of increasing vulcanism of approximately 100 >> volcanoes and a super volcano as large as Yellowstone in the Southwestern >> Antarctica. The eruption of a large super volcano will potentially release >> greater than 10,000 cubic kilometres of lava and ash (for perspective, Mt >> St Helen’s eruption was about 1 cubic kilometre). To make matters worse, >> the glaciers of this region are inherently unstable because they are >> grounded below sea level – meaning they can rapidly collapse. Approximately >> half the flow of ice to the sea from the ice sheet above Marie Byrd land is >> estimated to be the result of the melt water created by the heat of the >> super volcano below the ice. The Marie Byrd Land ice sheet is largely held >> back by the Thwaites ice sheet which is sometimes call the disaster glacier >> because it is considered to be unstable and could collapse relatively >> rapidly and raise world sea levels by 0.6 metres. >> >> The Thwaites and Marie Byrd Land Ice sheets are up to three kilometres >> thick. They have lost between 60 to 100 metres of ice thickness as a result >> of climate change already. Data from the melting of Iceland’s glaciers >> indicates that roughly speaking, the land rises approximately 1 metre for >> every 1 metre of ice that is melted over time. Therefore, when the weight >> of the ice sheet is removed from the underlying super volcano, the land >> could rise by kilometres over time. It would be a reasonable expectation >> that such a large land movement risk awaking the super volcano and the >> large number of volcanoes beneath Southwestern Antarctica. >> >> *The feedback loop of concern is as follows:* >> >> 1. *The weight of the ice sheet above the super volcano and 100 other >> volcanoes reduces. This causes the land below to rise and increases the >> volcanic activity.* >> 2. *The increased volcanic activity increases the release of heat >> from the super volcano and other volcanoes which then increases the volume >> of meltwater below the ice sheet.* >> 3. *Increased melt water lubricates the flow of the ice sheets >> resulting in increased flow of ice out of the ice sheets leading to >> further >> loss of mass from the ice sheet which then further increases volcanic heat >> flux.* >> 4. *This occurs until the ice sheets in Marie Byrd land and >> Southwestern Antarctica transition to rapid collapse from the below sea >> level portion of the ice sheet. Melting these ice sheets will raise sea >> levels and threaten coastal cities across the world.* >> 5. *Collapse of the ice sheet removes the kilometres of ice weight >> from on top of the super volcano and the other volcanoes. Potentially the >> land will rise kilometres to seek equilibrium from the loss of the ice >> weight. Vulcanism increases significantly as a result.* >> 6. *The rising of the land fully awakens the super volcano, and a >> long period of potentially very disruptive volcanism results.* >> >> *It is worth noting that there has not been a large super volcano >> eruption since before our species evolved into being and could potentially >> be a significant threat to our civilization/survival. The rapid collapse of >> the ice sheets outlined would flood most of the world’s major cities. If it >> occurred within a short period of time such as a few decades, it would have >> severe economic and social disruption. A super volcano reawaken by the loss >> ice kilometres thick would likely be active for an extended period of time >> while the land was out of pressure equilibrium. From a human perspective of >> time, the awakening of a super volcano risks creating near permanent >> changes to the Earth’s climate. A super volcanic eruption could not be >> stopped once started.* >> >> I am unaware of any climate models that take the described feedback loop >> into account. I fear the impacts described will result in very different >> outcomes from the current models. >> >> The use of geo-engineering to prevent what I have outlined from occurring >> is moral. To not act to prevent this is immoral. Once the feedback loop >> passes a certain tipping point, it will be impossible to stop. The risk of >> this occurring eclipses the risk that there will be a delay in ending the >> burning of fossil fuels. Geo-engineering should NOT wait until the end of >> the decade to undertake trials. To do so risks passing dangerous tipping >> points. It should be used at scale as soon as practicable and prevent this >> deeply worrying feedback loop from happening. I strongly believe that when >> presented with this new threat and the use of geo-engineering to try to >> prevent this threat from occurring, the public will strongly back the use >> of geo-engineering. I also believe that it will focus the minds of >> politicians to finally act to cut carbon emissions. >> >> >> >> David Sevier >> >> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "geoengineering" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email togeoengineering+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/geoengineering/022301d792bc%24c1b8a710%244529f530%24%40carbon-cycle.co.uk >> <https://groups.google.com/d/msgid/geoengineering/022301d792bc%24c1b8a710%244529f530%24%40carbon-cycle.co.uk?utm_medium=email&utm_source=footer> >> . >> >> <Antarctic-BEDMAP2-topography-Fretwell-et-al-2013-rebounded-after-the-removal-of.png><Antarctic-ice-thickness-change-between-1992-and-2017.jpg><Schematic-map-of-separate-volcanoes-and-volcanic-provinces-in-Western-Antarctica-position.png><Trends >> in Antarctic Ice Sheet Elevation and Mass.pdf><marie-byrd position.jpg> >> >> >> >> The University of Edinburgh is a charitable body, registered in Scotland, >> with registration number SC005336. Is e buidheann carthannais a th’ ann an >> Oilthigh Dhùn Èideann, clàraichte an Alba, àireamh clàraidh SC005336. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "geoengineering" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to geoengineering+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/geoengineering/B6C94D44-E5DD-414A-A203-A99E2CB62E5C%40ed.ac.uk >> <https://groups.google.com/d/msgid/geoengineering/B6C94D44-E5DD-414A-A203-A99E2CB62E5C%40ed.ac.uk?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "geoengineering" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to geoengineering+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/geoengineering/00f401d7935d%240d3d4600%2427b7d200%24%40carbon-cycle.co.uk >> <https://groups.google.com/d/msgid/geoengineering/00f401d7935d%240d3d4600%2427b7d200%24%40carbon-cycle.co.uk?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to geoengineering+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/CAJ3C-04m-Ta%3D2rV3Pu-r%3DP3XSYo2OotEL6G0SgKTqhQdBQQdqw%40mail.gmail.com > <https://groups.google.com/d/msgid/geoengineering/CAJ3C-04m-Ta%3D2rV3Pu-r%3DP3XSYo2OotEL6G0SgKTqhQdBQQdqw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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