Post by Inge B.
Photo from Kalidalur highland road, Langjökull (western side) left, Presthnúkur in the middle, Þórisjökull to the right
There was a unusual swarm of about 20 quakes which took place between Langjökull ice cap and the highland road Kjölur on the western side of the ice cap these last days and it made a new start now.
This is a region which has not been very active lately regarding earthquakes or eruptions.
Source: Icelandic Met Office (IMO), 5 April 2013
There are three main factors influencing Langjökull and its surroundings also regarding the earthquakes occurring there:
- glacier mass balance
- plate spreading
Langjökull is the next biggest Icelandic ice cap (after Vatnajökull), its dimensions being acc. to Wikipedia 925 km² at an volume of 195 km³ and up to 580 m (1,900 ft) thickness. This big glacier though has been receding heavily these last years, probably due to climate change. Scientists even prognosticate this glacier being reduced to next to nothing very soon, if the tend in climate change is continued.
This will of course have an influence on the glacier and its surroundings, eg. due to glacier rebound. This last technical term means that when the enormous weight of the glacier is lifted in a rather short time span, the earth’s crust beneath will move upwards. Near Höfn in the east under Vatnajökull, there has been measured a uplift of over 11 cm in the last years.
Earthquakes may be caused by this kind of “resettling” of earth’s crust.
From commons.wikimedia.org <, 1n=NVZ; 1v=WVZ with Reykjanes; 2 and 3 are former rift zones; 4=EVZ
Then there is the spreading which influences the MAR (Middle Atlantic Ridge) and all parts of Iceland on active spreading ridges. These ridges have been going through several rift jumps in some millions of years. The active rift zone was placed over Snaefellsnes and Vatnsnes, till it shifted over to today’s location which is divided in the south into a Western Volcanic Zone (WVZ) – with Langjökull as its center – and an Eastern Volcanic Zone comprising a.o. the more active volcanoes Hekla, Katla and Grímsvötn. This rift zone has been active now for about 2 million years. Northwards this continues in the NVZ (Northern Volcanic Zone) reaching from the Vatnajökull, over Askja and other volcanic systems out to the sea where it combines with the Kolbeinsey Ridge.
The WVZ has been less active than the Eastern Volcanic Zone during the Holocene, so it is proposed that the spreading zone, the rift is again “jumping” in the south of Iceland. In the whole there were only 17 eruptions representing 64% of its whole production and these took place from around 10.000 BP till about 7000 years ago.
Nevertheless, Langjökull is part of one main zone of the Icelandic rift and MAR, so these quakes could also be part of a rifting episode.
And finally, as with all the big ice caps in the centre of Iceland, also Langjökull is concealing some mysteries. The ice of its cap is not flat. There are mountain tops, nunataks and strange indentations. And after some screening done, scientists discovered not only one, but at least two volcanic systems stretching out under the ice with two calderas under the glacier and two high temperature areas near its edge. There could also be a big table volcano under the ice. And a further high temperature area, the one at Geysir in Haukadalur perhaps connected to one of the systems.
The known volcanic systems under Langjökull are
a) Prestahnúkur, in the southwest, there was sometimes talk about it having some quake swarms in the vicinity and someone – was it Newby – intended to drive up there in a high-wheeler. The volcano’s tentacles in the form of dikes are reaching at least under Geitlandsjökull, an outlet glacier.
b) Hveravellir in the northeast. This is a famous stop-over for people traversing the country on the Kjölur highland road, with an high temperature area forming sinter terraces.
Lake Hagavatn, not far from the hypocenters.
The hypocenters of the ongoing quake swarm are placed beneath an old lava shield.
Where the deeds are done
The last eruptions in the Langjökull area took place around the time of settlement in the 10th century when 2 craters on the northwestern side of the glacier shield produced an impressive lava field called Hallmundarhraun (length around 50 km).
Will there soon be another?
re. the glacier
- Comparison of energy balance and degree-day models of
- summer ablation on the Langjökull ice cap, SW-Iceland by Sverrir Guðmundsson, Helgi Björnsson, etal. (2006?)
- Geometry, Mass balance and climate change response of Langjökull, Iceland, by Helgi Björnsson, etal. (Conference poster, Obergurgl) [https://docs.google.com/viewer?a=v&q=cache:ltfiXqdsA7AJ:www.raunvis.hi.is/~sg/langj1.pdf+Langj%C3%B6kull&hl=de&pid=bl&srcid=ADGEEShVpiITP8jVmBZbPlTCNnegXWpIVioUEPomrjsCqi3ciYV7cOFS_HjK085M5c69YZ4jahI9cD3GMs9YBa3Ja9pwQ90sFghnGPuqWHzWTa5ZUOFeI_bZque_XSyOxHcJnAuON5Ne&sig=AHIEtbTzFsBz4pRIsoQG4u4V-TfJmCYxBw]
- Holocene climate conditions and glacier variation in central Iceland from physical modelling and empirical evidence by Gwenn E. Flowers, etal. (2008; paywalled)
re. the volcanism beneath:
- GVP zu Hveravellir: http://www.volcano.si.edu/world/volcano.cfm?vnum=1701-08=
- GVP zu Prestahnúkur: http://www.volcano.si.edu/world/volcano.cfm?vnum=1701-07=
- Th. Thordarsson, Armann Hoskudsson: Iceland. Geology of Europe 3. Harpenden 2002 (book)
- Jon Sinton, etal. Postglacial eruptive history of the Western Volcanic Zone, 2005.
*** Beware the red herrings ….
1 point for the volcano 1 point for the red herring
No 1 – Pixar; Sakhalin Oblast; 2001; Citroen; SOLVED Nemo Peak
No 2 – Yellow alert; Dog breed; D.O.C.; Licking County; SOLVED Mt Etna
No 3 – Shield volcano; Scenic railroad; Lahar alert system; Ice caves; SOLVED Mt Rainier
No 4 – Mosquitoes; Inaccessible; Desert; Salt lakes; SOLVED Waw an Namous
No 5 – Spiders; Tiger flowers; Smoke rings; Local Capital; SOLVED Colima
Diana Barnes 2, Grimmster 3, Inge B 2, El Nathan 2
Alan’s Evil Riddle ….
All this stone writing could really give printers the bird!
For a change, 3 alternative answers, so what are they?
Chryphia March 26th at 19.17
Islander March 26th/27th up to 4pm
Jamie March 26th 23pm to midnight
LAKAT March 27th anytime
Diana Barnes March 27th at 7.30am
Lamiah87 March 27th 12.37
Talla March 28th at 2pm
Georgiade March 29th at 2.30pm
Sam March 29th 4pm onwards
Karenz. March 30th 4pm tp 5pm
Stoneyard April 1st midnight to 4am
Spica April 1st 00am to 06am
Floodwarn April 1st/2nd midday to midday
Inannamoon667 April 1st midday to midnight
CJWINWIN April 2nd anytime
Ursh April 2nd anytime
BUT MAYBE ….
Irpsit April 6th at 8.30am
Newby April 7th 3am to 7am
Cowboy Andre April 9th 1pm to 5pm
El Nathan April 9th late afternoon
Barbara Germany April 12th 6am to 8am
harrie April 12th/13th 8pm to 4am
Bobbi April 14th 2am to 6am
Stephanie Alice Halford April 14th 5.05pm
Denise April 17th midday to midnight
Jim Ludwell April 17th 4am to 11am
Lughduniense April 19th, in the (late) morning
Kilgharrah April 19th midday
Kobba April 20th 9pm and 10pm
Schteve42 April 23rd 6am to 8am
Christian Thordin April 27th 3.30am
Tyler Mannison April 30th midday and 5pm
Bo Minik May 2nd 1pm to 3pm
microcollector May 18th at 8.32am Granyia May18th daylight hours
Grimmster May 21st anytime
Alison May 25th midnight to midday
Summer May 30th anytime
GeoLurking June 25th anytime
Bruce Stout July 1st 1pm
Stefan August 16th 00am to 6am