Tag Archives: Haukadalur

Langjökull quaking and NTV Riddle and the return of Alan’s Evil Riddle

Post by Inge B.

Photo and Copyright IngeB

Photo and Copyright IngeB

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:

  1. glacier mass balance
  2. plate spreading
  3. volcanism

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.

Wikimedia Commons: Present and former rift zones of Iceland. 1v: Western Rift Zone (WRZ); 1n: Northern Rift Zone (NRZ); 2: former Snæfellsnes-Skagi Rift Zone (SRZ); 3: former Westfjords Rift Zone (WRZ); 4: Eastern Volcanic Zone (EVZ) - most likely a future rift zone.

Wikimedia Commons: Present and former rift zones of Iceland. 1v: Western Rift Zone (WRZ); 1n: Northern Rift Zone (NRZ); 2: former Snæfellsnes-Skagi Rift Zone (SRZ); 3: former Westfjords Rift Zone (WRZ); 4: Eastern Volcanic Zone (EVZ) – most likely a future rift zone.

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.

Image Wikimedia Commons: Hagavatn – View from the southeast on the eastern part of the lake. In the background Hagafell and a glacier tongue of Langjökull, in the foreground the outflow of the lake with the remains of a destroyed bridge.

Image Wikimedia Commons: Hagavatn – View from the southeast on the eastern part of the lake. In the background Hagafell and a glacier tongue of Langjökull, in the foreground the outflow of the lake with the remains of a destroyed bridge.

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

Langjökull Glacier

Langjökull Glacier

Source:http://commons.wikimedia.org/wiki/File:Kjolur.jpg

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?

Sources:

re. the glacier

re. the volcanism beneath:

http://www.soest.hawaii.edu/GG/FACULTY/SINTON/publications/wvz_g3.pdf

Inge B.

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NTV Riddle

*** 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

Points …

Diana Barnes 2, Grimmster 3, Inge B 2, El Nathan 2

Kilgharrah

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Alan’s Evil Riddle ….

All this stone writing could really give printers the bird!

For a change, 3 alternative answers, so what are they?

Alan C

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Hekla Eruption Sweepstake …. Who’s gonna wear the ‘bragging rights’ T?

NOT ….
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

Kilgharrah

Odd strain at Hekla

Photograph by Eggert Norddahl, used under exclusive permission. All rights reserved. To use this or any other image by Eggert, contact Volcano Cafe or Eggert Norddahl directly.

Hekla have one of her days today. It all started at 08.56 with a small earthquake located at Árnes close to Haukadalur SIL-station. The earthquake was clearly tectonic and at a respectable depth of 6.2km. The earthquake will most likely be revised later as it is of low probability due to low energy released. What makes this earthquake interesting in relation to what followed is that during the weeks before Hekla 2000 the area had a small number of low energy earthquakes.

Image by Icelandic Met Office (IMO). Location of the very small earthquake that started todays festivities.

A couple of minutes later the new (installed after the 2000 eruption) borehole strainmeter at Hekla registered a medium sized, but long lasting negative mountain strain transient. During the last eruption the largest recorded strain was recorded at the more distant Búrfell. The idea of installing Hekla borehole strainmeter was to see if it is possible to pick up pre-cursor strain falls. As I am writing this the negative drop in strain is still ongoing.

Image by IMO. The initial stages of the mountain strain recorded by the Hekla Borehole strainmeter.

A couple of small spikes are showing on the Mjóaskard SIL-station, but they are to small to pinpoint them as earthquakes, at least the exact location. Also, a small tremor ranging from 1,5Hz and upwards started at 11.35 local time.

Image by IMO. Strain at -6E+04 and counting. Negatve mountain strain building up.

Is this then the run up for an eruption? Sofar it is not likely. We still miss the tell tale swarm of small earthquakes (0.2 to 2.0M), a large negative strain drop at Búrfell borehole strainmeter, and of course a rapid increase in harmonic tremor on all stations. This can though change at any time. As mountain strain builds up the likelyhood of earthquakes increase over time.

I would not recommend climbing Hekla today.

CARL

Hekla – Changes in rapid strain

Image from Icelandic Met Office. One can easily see here how the rapid strain movements increased in amplitude and energy during the last couple of day. In the beginning you can see the normal value.

During the last 48 hours Hekla has suffered an increase in rapid strain movements. On the images below you see two types of motion. The first type that is creating a sinusoidal movement (wave-like) is a phenomenon called earth-tides. They are normal and do not influence even the most agitated volcano. The second type of motion is rapid motion of strain changes as the mountain makes small trembles. Those small trembles are actually rapid mountain strain changes.

Image from Icelandic Met Office. The big "downfalls" are most likely a result from the strainmeter resetting itself after it was repaired a few days ago.

Rapid mountain strain changes are normally seen as a warning sign of unrest in an active volcanic system. However, I have not found any data stating that Hekla exhibits this pattern before an eruption. The only reference is Páll Einarsson stating the previous instance as the reason behind the July 2011 Hekla alert from IMO (Icelandic Met Office). Hekla then suffered an episode like this that ended with a 2.2 earthquake in Hekla proper.

Image from Icelandic Met Office. Storolfsvoll is showing a slightly different patter of rapid strain movements, but the increase pattern is still the same. It is just that the attack of the transients are slower.

Also, before the 1991 there was a set of shallow earthquakes at Haukadalur the week before onset of eruption. And during the last couple of weeks there has been another pattern of similar earthquakes, but at a slightly greater depth.

Photograph by Eggert Norðdahl, copyright reserved. Used by permission, for usage in print contact either Volcanocafé via email or Eggert Norðdahl directly. This stunning aerial photography of the third day of the 2000 eruption gives the enormous scale of a Hekla eruption in plain view. Expect many stunning photographs from the upcoming Icelandic eruptions by our "house" photographer Eggert Norðdahl.

This increase in rapid strain movements might be interpreted as increased unrest in the volcanic plumbing of Hekla. But we still lack the tell-tale earthquakes at Hekla proper that normally start 30 to 60 minutes before onset of eruption. The earthquake will be in Hekla proper, or within a couple of kilometers.

Please, keep the question coming for our GPS Q&A with Professor Sigrún Hreinsdottir!