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Tuesday, 8 May 2001 Lecture Global
Natural Catastrophes. |
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Professor Bill McGuire gave an excellent talk as he guided us through three different types of catastrophes that could trigger mass extinction phases on Earth. He covered Volcanic eruptions, Giant Tsunami and Asteroid/Comet impacts. We were introduced to the classification of Volcanic eruptions, VEI scale (Volcanic Eruption Index) from 0 - 8. Every step represented a tenfold increase in magnitude. Mount St Helens = 5 on the scale whilst the Lake Oregon Caldera = 8, some 1000 times more powerful than St Helens! This maximum of 8 represented some truly mind boggling figures like ejection rates of 1 Billion kg per second, duration of eruption 2 weeks, heights for ejected material typically 25km and possibly as high as 45 -50 km. Tephra ejection (total volume of everything ejected) in Trillions of cubic metres and other factors I can't remember. Another example quoted was the eruption of Toba, some 74,000 years ago. A size 7 on the scale. This has been postulated to have caused a mass extinction of the then human population to below 5000 individuals, some studies suggest as few as 40 individuals survived, from which we all descend. These numbers were derived from studies of mitacondrial DNA. (If I remember correctly the walls of all human cells are composed of this DNA, which is passed on to offspring via the female line, mother to child. There being no male DNA involved in the construction of the cell wall.) Another table showed how often we could expect the various events. Scale 7 events appear to occur every 100,000 years! Bill went on to discuss
the various magma chamber requirements for these eruptions and said that
currently about 45 locations were being monitored however another 1500
were not! |
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Giant Tsunami An Horizon program last year featured Bill discussing his work on the possible collapse of the west flank of one of the Canary Islands initiating an underwater avalanche and a 1000m high Giant Tsunami. In the geological past there is evidence to show that this occurred and that the Bahamas were swamped with sands and boulders as the Tsunami passed over the Islands. Some of these boulders weigh 100 tons and now rest 30m above see level. (What was the sea level then?) Bill said that placing a great circle over the deposits of this event point to the Canaries as the source of the Giant Tsunami (Great circles? These are constructed by plotting all your evidence and connecting a line through all the similarities. If they begin to look like an arc of a circle that would encompass the Earth you can extrapolate back to the centre of the circle and get a point on the Earth's surface. If you are still unsure check a text book.) All this could happen again to the Caribbean, Florida, and most of East Coast USA. Don't worry, Bill only reckons it will be about 40m high as pass up the Thames (and over my house!). Bill is currently using Satellite surveillance to watch the west flank of one of the islands and he says it's only slipping at 1cm per year. The Spanish Government couldn't care less. Another interesting aside was the result of the studies of Tsunami that have occurred within modern times. They have shown that the victims had been "sand blasted" by the debris mobilized by the wave! |
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Asteroids & Comets We were introduced to a range of tables and charts for all sizes and frequency occurrences for Asteroids. They ranged from the energy released and the area of damage that could be expected. Again these were all big numbers! Bill discussed what you could expect from a very large impact. In some ways the effects on the atmosphere and light absorption where similar to large volcanic events. One point made was that secondary impacts could be expected. (I think he mentioned the breakup of an asteroid/comet and the sub-orbital paths of ejecta from the impact but, my memories going a bit!) However, Bill did cover the KT event and concluded the amino acid ( of what? I presume in deposits at the boundary paralleled with studies of meteorites and encounters with comets.) was more indicative of a comet impact. In respect of the high iridium layer both comet and asteroid are thought to be similar enough to have the same effect. During question time, our Chairman mentioned the Volcanic Ash deposits at Walton & Harwich. Bill perked up and said he remembered hearing about this some 20 odd years ago ( this probably means 30 plus years ago) and asked for any reference to published papers. Our very own Bill George is familiar with the published material on Essex Geology and has agreed to collate all the references for our guest speaker on this occasion. Our Chairman mentioned the Volcanism in NW Scotland probably occurred too early to be responsible for the Ash deposits. Our speaker hedged his bets. (I have this nagging feeling that I've read about North Sea volcanism but the age eludes me, anyhow one can't dismiss Europe as a source for the Ash deposits. The evidence should be worth studying.) (If you want to know more join our Society and if your interested in Essex & geology get a copy of Gerald Lucy's book.) That about covers the lecture at least the salient points. Professor Bill McGuire is well published and his current book still in print is titled "Apocalypse" and is available via any book shop (suggested was AMAZON at £11.95, slightly cheaper than the high street.) Our Chairman said he might buy a copy ( gasps & laughter all round as we now him too well!) Incidentally, Bill starts a new radio programme on Radio 4 in early July called "SUPER HEROES". (Check the Field Trips Programme as some updates where announced. A very enjoyable meeting. RC)
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