Geobulletin alpha

News from the Geoblogosphere feed

New from Snet: Lithologs, a new tool to create lithological/sedimentological logs online..

Blog post recommendation

Katla Next Icelandic Volcano to Blow?

Monitoring of the Icelandic Katla volcano, beneath the Mýrdalsjökull glacier, has been intensified following the March 2010 eruption of a fissure volcano beneath the Eyjafjallajökull glacier. The eruption of this nearby long-dormant volcano in March 2010 prompted fears among some geophysicists that it may trigger an eruption at Katla.

Eyjafjalla has blown three times in the past thousand years – in 920, 1612 and around 1823. Each time it set off Katla. An eruption at Katla could melt huge amounts of ice and cause massive floods.

Katla volcano is one of the most dangerous volcanoes in Iceland. It is located near the southern end of Iceland's eastern volcanic zone, hidden beneath the Myrdalsjökull glacier. The subglacial basaltic-to-rhyolitic volcano is one of Iceland's most active and is a frequent producer of damaging jökulhlaups. A large 10 x 14 km subglacial caldera with a long axis in a NW-SE direction is up to 750 m deep. Its high point reaches 1380 m, and three major outlet glaciers have breached its rim. Although most historical eruptions have taken place from fissures inside the caldera, the Eldgjá fissure system, which extends about 60 km to the NE from the current ice margin towards Grímsvötn volcano, has been the source of major Holocene eruptions. (Eldgjá means "fire canyon" in Icelandic). An eruption from the Eldgjá fissure system about 934 AD produced a voluminous lava flow of about 18 km3, one of the world's largest known Holocene lava flows. Katla has been the source of frequent subglacial basaltic explosive eruptions that have been among the largest tephra-producers in Iceland during historical time and has also produced numerous dacitic explosive eruptions during the Holocene. The Katla volcano normally erupts every 40–80 years.

Because Iceland is the subaerial extension of the Mid-Atlantic Ridge, it is one of the world's most active sites for basaltic fissure eruptions. For this reason, fissure eruptions are also known as Icelandic eruptions. The largest lava flow in recorded history was generated by a fissure eruption in south central Iceland in 1783. Known as the Laki flow, it erupted from a 25-kilometer-long fissure to produce 12 km of lava, filling two deep river valleys and covering an area greater than 500 km2. It was quite clear from the TV-pictures of the March 2010 eruptions that we were dealing with fissure eruptions. Because they are not central volcanoes it can be a bit difficult to locate their exact whereabouts - giving rise to some apparent confusion when the first eruption started. Problems with understanding Icelandic place names may add to the confusion. The satellite image below (cropped from a NASA Earth Observatory image) shows where the eruption end March 2010 was located at the Fimmvörduháls Pass between the Eyjafjallajökull ice field to the west (left) and the Mýrdalsjökull ice field to the east.

The plural of fjall (mountain), which is fjöll is used of a mountain with many peaks, like Eyja-fjöll. Jökul means glacier. So Eyjafjallajökull is the glacier on the Eyja-mountain. Mýr means marsh, and dal means valley, so Mýrdalsjökull literally means the glacier of the marsh valley. The Myrdal must not be confused by Mýdal, the valley of midges, a that also crops out in the name Mývatn, the lake of midges - vatn meaning water or lake.

Eyafjallajökull volcano is in short a 1666 m high shield volcano crowned by a small caldera and an ice cap that reaches down to 1000 m above sea level. The Eyafjallajökull volcano has been active for at least 800 000 years.

To simplify the geography I have drawn my own simplified map of the most important locations mentioned in this post. It more or less covers the same area as the satellite image for comparison.

For more information about the March 2010 eruptions, as such, at Fimmvörduháls I am happy to refer you to the excellent coverage by Ralph Harrington at The Volcanism Blog and by Erik Klemetti at Eruptions. Thank you for sharing your knowledge with the rest of us.

And finally my personal advice: VISIT ICELAND ! | Impressum