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North Atlantic Logbook

Looking at "Big Time"... from 20,000 BC onward

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Jönkulhlaup Paths Suggested from Eyjafjallajökull and Katla
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Veðurstofa Íslands/Icelandic Meteorological Office has prepared some strongly-worded studies about the fearsome power of jönkulhlaups (glacial burst-floods) which can be unleashed when any one of several subglacial volcanoes in Iceland erupt. Most notably, Grimsvötn under Vatnajökull; Katla under Myrdalsjökull and Eyjafjallajökull under its glacier/jökull can, under worst-case eruptive conditions, create burst-flood volumes that can rip apart highways and bridges, and completely scour the landscape.

I'm not sure to whom to credit this map.

One study in particular examines the hazards associated with a Skarrá-valley jönkulhlaup from either Katla or Eyjafjallajökull -

Evidence shows that, specifically after eruptions of Katla (and possibly Eyjafjallajökull), the shock when a big jönkulhlaup headwall hits the sea (loaded with debris and two-story-house sized blocks of ice) has created enough energy to cause tsunamis elsewhere.

Veðurstofa Íslands has also commented that on at least one occasion a jönkulhlaup in the Markarflót caused a tsunami (1721, from Katla) - (Note: this is not a letter-sized document and takes a while to download the single poster-sized sheet.)

The newest set of quakes are all focussed under areas of the glacier with approximately 100-200 metres thickness of ice. Depending upon which side of the north-south Eyjafjallajökull drainage gradient an eventual new fissure might poke through, the resulting water pool and heated steam under the jökull will exert upward pressure and ultimately burst out either under the Steinsholtsjökull glacial tongue to the north (draining into the narrow upper valley of the Krossá and down into the Markarfljót sandur) or will stream down a narrow gorge to the east of the (south) Goðasteinn peak on Eyjafjallajökull, as indicated in the inset illustration - pointed out in the Meteo poster above.

Their additional concerns, at this late winter season, are about massive ice and snow slides from the steeper southern side (slope failures similar to avalanches) triggered by the undermining of high volumes of heated water flowing downhill in this direction... and are primarily motivated by the short warning times involved. Such slides will sweep over the highway now being used by many tourists coming to the volcano, in addition to regular circumferential traffic on Highway 1. (source map below from Veðurstofa Íslands - credits noted on map)

The southeast corner of Iceland is very vulnerable to jönkulhlaups - perhaps more than any other comparable place on earth. The rare conjunction of volcanoes and covering ice caps produces some spectacular and frightening natural floods. Iceland Meteo says that the water headwall in the upper valley of the Krossá can reach 45 metres in height, dropping to 15 metres when the valley widens. The initial two hours could see water volumes to 300,000 cu.metres per second - not dissimilar to volumes pouring across the Myrdalssandur during the initial hours of a Katla eruption-caused jönkulhlaup. Such a burst flood would wipe away many of the farms built in the Markarfljót since the last Eyjafjallajökull eruption in 1821-23.

The hazard is high in the case of Eyjafjallajökull at this moment in 2010, because a jönkulhlaup in either direction (north or south) over or near the point closest to the present earthquake series would cross routes used heavily by volcano-watching tourists. Enlarge any image by clicking once to enter the gallery, and once more to see it full-size.

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Re: Olen samaa mielta

Kindly, if possible, provide an English translation of your comment so I may reply.

Thank you.

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