fredag 16. april 2010

Katla - Eyjafjallajøkuls sinte storesøster

J.R.R. Tolkien konstaterte i The Hobbit at: "It does not do to leave a live dragon out of your calculations, if you live near him."

Den islandske journalisten Iris Erlingsdottir minner oss om faren ved å ha drager i nærheten i The Huffington Post. Dragene er islandske vulkaner som potensielt kan gjøre veldig mye mer skade enn å stanse flytrafikken i et par dager:

"The 934 AD lava flow from the Eldgjá fissure system unleashed the largest flood of basalt on the planet in historic times. The Laki eruption in 1783 had the largest outflow of lava since then. It emitted fluoride that poisoned half of Iceland's livestock, resulting in a famine that killed approximately a quarter of Iceland's population, and thrust vast quantities of sulfur dioxide into the atmosphere, directly causing many deaths in Western Europe, and contributing to several years of extreme weather in Europe. It is often credited as an indirect cause of the French Revolution."

Det ekspertene er redd for nå og som kan forandre situasjonen vesentlig, er et vulkanutbrudd i Katla. Glasiolog Helgi Björnsson sier til Iceland Review Online at:

The maximum flow in glacial bursts caused by Katla can be fifty or one hundred times more voluminous than what we have seen flow out of Gígjökull [an Eyjafjallajökull glacial tongue]. When the flood comes you better make a run for it,” Björnsson told mbl.is. Katla is hidden underneath the Mýrdalsjökull icecap.“There are eruption channels between Eyjafjallajökull and Katla and magma could shoot into the Katla volcano. Katla might only need a nudge,” Björnsson said."

Alle som kan sin Astrid Lindgren vil huske at Katla er dragen som bor i Katlagrotten og som må nedkjempes av Brødrene Løvehjerte Karl og Jonathan. Men Katla er også en vulkan på Island som har sovet en stund, en av de to "sinte søstrene". Katla har historisk har hatt et stort utbrudd en gang hvert 40-80 år, siste i 1918. Alle de tre siste gangene den mye mindre Eyjafjallajøkull har hatt utbrudd har også Katla hatt et utbrudd. BBC skriver om the two so called Angry Sisters, Hekla og Katla:

"The most ominous thing about Eyjafjallajoekull is that its eruptions have historically preceded eruptions by one of Iceland's most feared volcanoes, Katla. Fortunately, Katla, one of the two so-called Angry Sisters, has shown no sign of unusual activity in 2010. Katla is located under the vast Myrdalsjoekull glacier. One of the highest volcanoes in Europe at 1,512m (4,961 ft), its crater has a diameter of 10km. Any eruption would raise fears of major flooding due to the melting of the glacier.Its last major eruption occurred in 1918, with a smaller eruption in the 1950s. Historically, it tends to erupt every 40-80 years."

Iris Erlingsdottir skriver dette om sjansene for at Katla skal eksplodere:

"Each of the previous three Eyjafjallajökull eruptions since Iceland's settlement (920, 1612, and 1821-23) has been followed by a major Katla eruption. Maybe Katla will explode, and maybe it won't. Maybe the new volcano will continue to grow, like Parícutin, until it towers over the landscape, but maybe it will just fizzle out over the next few months. There are simply some events over which we have no control."

Nå er det jo ikke slik at man skal gå rundt og regne med at det kommer katastrofer. Ekstremtilfellene, det vi kaller "black swans", kommer jo nesten aldri. Men det kan være greit å være klar over at de kan inntreffe. Slik som The Year Without a Summer som inntraff i 1816 etter det største vulkanutbruddet de siste 1600 årene i Mount Tambora i Indonesia, et utbrudd der asken førte til lavere temperaturer og omfattende sultproblemer over hele kloden.