Dear Albert Swell from a distant source comes with long wave crests, many times the wave length. But if swell passes an island the fronts are refracted around it and the two sets of wave fronts cross each other on the down-wave side. This crossing can be observed in any lagoon with two entrances. To find an island you should sail along the bisector of the refracted fronts, trying to keep their amplitudes the same. If you understand the roll response of your boat you can do it at night.
I am sure that Polynesians will have used several navigation techniques and so we cannot use their survival to prove one of them. Stephen Emeritus Professor of Engineering Design School of Engineering and Electronics University of Edinburgh Mayfield Road Edinburgh EH9 3JL Scotland tel +44 131 650 5704 fax +44 131 650 5702 Mobile 07795 203 195 [email protected] http://www.see.ed.ac.uk/~shs Veli Albert Kallio wrote: > I think that Alan's position is right in a stable Holocene setting but > in the cycles of the ice age when large volcanic discharges occurred > this might not have been the case. > > A good picture of the frequency and fluctuation in geothermal output > is from the Pacific Ocean where its human occupancy was guided by the > rise of constant steam columns. > > In order to navigate through the ocean the mushroom clouds of the > newly forming islands must have had a far more frequent event at times > in the past than it is today. > > No one in their right mind today would try to navigate the pacific on > basis of rising columns of steam as most of these are just large storm > clouds in a horison, a bit like seeing water in Sahara. In order to > successfully colonise, the ratio of real steam columns to normal anvil > clouds had to be very high as from a very long distance all they look > a pretty much similar. > > Of course, many polynesians lost their lives chasing "steam colums" > which turned out to be just a storm cloud in a horison, but even for > allowing for this, the Holocene stability cannot be extrapolated to > the large fluctuations in earth's geothermal output. > > Therefore, the First Nations' complaint on ice sheet mass balance and > geothermal fluctuations remain firmly on our agenda during the various > meetings in the UN and will obviously have all the support from the > Polynesian people who disagree European ideas. > (And for good reasons.) > > We cannot today navigate anywhere in the Pacific between islands by > using smoke stacks to hop from island group to another. At current > rate of geothermal heat and output and lack of columns no Polynesian > would never have discovered dry land under their feet. They would all > have been lost at sea just chasing storm clouds in the far horizons - > and become soon extinct like the Neanderthals. > > Kind regards, > > Albert > > > > Date: Fri, 18 Sep 2009 12:29:26 -0400 > > From: [email protected] > > To: [email protected] > > CC: [email protected]; [email protected]; > [email protected]; [email protected] > > Subject: [geo] Re: Colloquium report: hazards from global warming > > > > > > Dear All, > > > > If you want to learn about volcanic eruptions and climate, I recommend > > my review article: > > > > Robock, Alan, 2000: Volcanic eruptions and climate. Rev. Geophys., 38, > > 191-219. > > > > http://climate.envsci.rutgers.edu/pdf/ROG2000.pdf > > > > http://climate.envsci.rutgers.edu/pdf/ROGcorrection2007RG000232.pdf > > > > > > Ward is wrong. Eruptions do not cause warming, except as Alvia > > explained through outgassing of CO2 over geologic time scales. > > > > Volcanic dust falls out in weeks and then if it fell on ice or snow > > would be quickly covered by clean snow, so would not warm the surface. > > Sulfate aerosols fall as acid rain or snow and again, would not warm. > > > > Wind patterns from tropical eruptions do produce a positive mode of the > > Arctic Oscillation with warming of continents in winter, but that is a > > regional pattern on the backdrop of global cooling. > > > > Alan > > > > Alan Robock, Professor II > > Director, Meteorology Undergraduate Program > > Associate Director, Center for Environmental Prediction > > Department of Environmental Sciences Phone: +1-732-932-9800 x6222 > > Rutgers University Fax: +1-732-932-8644 > > 14 College Farm Road E-mail: [email protected] > > New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock > > > > > > On Fri, 18 Sep 2009, John Nissen wrote: > > > > > > > > > > > Hi Andrew, > > > > > > The passage you are referring to is this: > > > > > > "But too many eruptions, too close together, may have the opposite > effect and quicken global warming, said U.S. vulcanologist Peter Ward." > > > > > > > > > The same gentleman has views that stratospheric aerosols will have a > > > heating effect, and various other odd-ball ideas. This view of the > > > effect of many eruptions was not challenged at the meeting, but I > think > > > it was not challenged because people were not taking him too > seriously. > > > (Bill can correct me on this.) Of course there is some truth in his > > > assertion, in that eruptions produce water vapour and CO2 which have a > > > long-term warming effect. But this is true for a single eruption as > > > well as multiple eruptions. > > > > > > There is another short term effect to consider. The volcanic dust may > > > spread to polar regions and reduce snow and ice albedo. For a > > > Pinatubo-like eruption, I would expect that effect to last at most a > > > couple of years, similar to the effect of the stratospheric aerosols > > > from the eruption. So with Pinatubo, at any rate, the cooling > effect of > > > the aerosols dominated over other effects for two years. But I'm not a > > > vulcanologist. (I'm copying this email to Seb Watt, who is one, > and who > > > was at the meeting.) > > > > > > Cheers, > > > > > > John > > > > > > > > > > > > Andrew Lockley wrote: > > >> This raises interesting points about the limits of SRM > geoengineering. > > >> Perhaps the experts on the list could explain why frequent volcanic > > >> eruptions cause a warming effect? Can we be sure that H2S > > >> geoengineering techniques we propose cannot result in this > 'blowback'? > > >> > > >> A > > >> > > >> 2009/9/17 John Nissen <[email protected]>: > > >> > > >>> This is a press report on the first day of the Hazards > Colloquium, organised > > >>> by Bill McGuire, at UCL, London. > > >>> > > >>> http://planetark.org/wen/54708 > > >>> > > >>> Global Warming May Bring Tsunami And Quakes: Scientists > > >>> > > >>> Date: 17-Sep-09 > > >>> Country: UK > > >>> Author: Richard Meares > > >>> > > >>> LONDON - Quakes, volcanic eruptions, giant landslides and > tsunamis may > > >>> become more frequent as global warming changes the earth's > crust, scientists > > >>> said on Wednesday. > > >>> > > >>> Climate-linked geological changes may also trigger "methane > burps," the > > >>> release of a potent greenhouse gas, currently stored in solid > form under > > >>> melting permafrost and the seabed, in quantities greater than > all the carbon > > >>> dioxide (CO2) in our air today. > > >>> > > >>> "Climate change doesn't just affect the atmosphere and the > oceans but the > > >>> earth's crust as well. The whole earth is an interactive > system," Professor > > >>> Bill McGuire of University College London told Reuters, at the > first major > > >>> conference of scientists researching the changing climate's > effects on > > >>> geological hazards. > > >>> > > >>> "In the political community people are almost completely unaware > of any > > >>> geological aspects to climate change." > > >>> > > >>> The vulcanologists, seismologists, glaciologists, climatologists and > > >>> landslide experts at the meeting have looked to the past to try > to predict > > >>> future changes, particularly to climate upheaval at the end of > the last ice > > >>> age, some 12,000 years ago. > > >>> > > >>> "When the ice is lost, the earth's crust bounces back up again > and that > > >>> triggers earthquakes, which trigger submarine landslides, which > cause > > >>> tsunamis," said McGuire, who organized the three-day conference. > > >>> > > >>> David Pyle of Oxford University said small changes in the mass > of the > > >>> earth's surface seems to affect volcanic activity in general, > not just in > > >>> places where ice receded after a cold spell. Weather patterns > also seem to > > >>> affect volcanic activity - not just the other way round, he told the > > >>> conference. > > >>> > > >>> LONDON'S ASIAN SUNSET > > >>> > > >>> Behind him was a slide of a dazzlingly bright orange painting, > "London > > >>> sunset after Krakatau, 1883" - referring to a huge Asian > volcanic eruption > > >>> whose effects were seen and felt around the world. > > >>> > > >>> Volcanoes can spew vast amounts of ash, sulphur, carbon dioxide > and water > > >>> into the upper atmosphere, reflecting sunlight and sometimes > cooling the > > >>> earth for a couple of years. But too many eruptions, too close > together, may > > >>> have the opposite effect and quicken global warming, said U.S. > vulcanologist > > >>> Peter Ward. > > >>> > > >>> "Prior to man, the most abrupt climate change was initiated by > volcanoes, > > >>> but now man has taken over. Understanding why and how volcanoes > did it will > > >>> help man figure out what to do," he said. > > >>> > > >>> Speakers were careful to point out that many findings still > amounted only to > > >>> hypotheses, but said evidence appeared to be mounting that the > world could > > >>> be in for shocks on a vast scale. > > >>> > > >>> Tony Song of NASA's Jet Propulsion Laboratory in California > warned of the > > >>> vast power of recently discovered "glacial earthquakes" -- in > which glacial > > >>> ice mass crashes downwards like an enormous landslide. > > >>> > > >>> In the West Antarctic, ice piled more than one mile above sea > level is being > > >>> undermined in places by water seeping in underneath. > > >>> > > >>> "Our experiments show that glacial earthquakes can generate far more > > >>> powerful tsunamis than undersea earthquakes with similar > magnitude," said > > >>> Song. > > >>> > > >>> "Several high-latitude regions, such as Chile, New Zealand and > Canadian > > >>> Newfoundland are particularly at risk." > > >>> > > >>> He said ice sheets appeared to be disintegrating much more > rapidly than > > >>> thought and said glacial earthquake tsunamis were > "low-probability but > > >>> high-risk." > > >>> > > >>> McGuire said the possible geological hazards were alarming > enough, but just > > >>> one small part of a scary picture if man-made CO2 emissions were not > > >>> stabilized within around the next five years. > > >>> > > >>> "Added to all the rest of the mayhem and chaos, these things > would just be > > >>> the icing on the cake," he said. "Things would be so bad that > the odd > > >>> tsunami or eruption won't make much difference." > > >>> > > >>>>> > > >>> > > >>> > > > > > > > > > > > > > -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
