Mýrdalsjökull with Katla
Mýrdalsjökull with Katla in summer
The Katla (k ʰ ahtla ) is one of the most active volcanoes in Iceland. He is under the glacier shield of Mýrdalsjökull in the south of the country.
The name Katla is a female derivative of the Icelandic Ketill (German tank ), but also a common in Iceland woman's name.
According to a popular legend Katla, a notorious for their vicious temperament worker had in the nearby Þykkvabæjarklaustur miracle pants that made those never get tired, which she wore. A shepherd boy named Bardi pants borrowed without permission from Katla's because he had to look for sheep in the mountains. When he returned with the animals, Katla killed him and left his body in a barrel with skyr, an Icelandic Magerquark disappear. When the skyr during the winter was on the decline, feared Katla to be discovered, ran to the neighboring mountain, disappeared inside and unleashed a glacier run from the volcano. The five -kilometer-long fissure Kötlugjá up on the glacier is also named after her.
The volcano is located in the south of Iceland about 50 km east of the town Hvolsvöllur and about 10 km north of the village of Vik í Mýrdal. He's mostly from Mýrdalsjökull covered the. Having a surface area of 580 km ² fourth largest glacier dome Islands
Topography and Geology
Katla is the central volcano of a volcanic system, which is about 100 km long. The central volcano dominated by volcanic column system ranges from Eldgjá in the north east to the south coast of the upstream Westman Islands.
The central volcano is located on the eastern edge of the eastern volcanic zone, above the intersection of the linear rift zone and a steep rise in Erdkrustendicke. (see also: Geology of Iceland )
The 200 to 700 m thick sheet of ice of the glacier Mýrdalsjökull also fills the caldera. The vents in the most active volcanic fissure Kötlugjá are also covered by ice. Currently the caldera comprises about 80 km ² at 10 km wide and 14 km in length along an axis in NW- SE direction and 500 to 700 m depth. The mountain peaks on its edge, mostly rhyolitic lava domes are up to 1380 m high.
Seismological experiments point to a relatively just below the surface ( at 2 km depth) down -reaching up to about 3 km depth magma chamber with a capacity of about 10-12 km ³.
Between the peaks of the caldera rim rich valley glaciers down to the plains and valleys. The best known of them are Entujökull in the northwest and Sólheimajökull in the south. By far the largest valley glacier is the outpouring located to the east Kotlujokull, which is also known under the false name Höfðubrekkujökull.
The volcano erupted in the last 1000 years from about twenty times, while on average about twice per century. Immense glacier runs above the surrounding lowlands, especially poured over the Mýrdalssandur.
The volcano is current state of knowledge on the one hand is the second largest of Iceland, on the other hand, also the one who has produced some of the most explosive volcanic eruptions in the history of the country.
The generated by the coincidence of ice and magma due to the location under the glacier hydro- magmatic eruptions of Katla are very explosive and have also sizable and widespread ash deposits particularly devastating glacial cycles (Icelandic: Jökulhlaup ) result.
Activities of the volcano can be traced back over at least 200,000 years. This produces large quantities of basaltic magma were produced, but also significant proportions of rhyolitic lavas and ignimbrites (such as on the Sólheimasandur ) or dacitic tephra.
Around the volcano you will find the traces of over 100 basaltic and rhyolitic tephra layers at least twelve, which, in subglacial eruptions from the Ice Age to the colonization of Iceland ie were ejected in the last 10000-1000 years. In addition, it was discovered the traces of five to ten effusive eruptions, which is mainly lava leaked on the northern edge of the Mýrdalsjökull.
The Sólheimar eruption 10600 BC
Approximately 10,600 BC, the most powerful known eruption of Katla took place, the so-called Sólheimar eruption, which was a Plinian eruption in type, the only previously documented on this volcano. This produced 10 km ³ rhyolithscher tephra. Lahars streamed down Mýrdal as well as pyroclastic flows, which can be recognized by numerous volcanic pile of loose materials and the so-called Sólheimar - ignimbrites. The traces of loose materials extend far to the south to the sea and are thus evidence of the most violent eruptions, which are known at all in Iceland.
Presumably, the caldera of the volcano has formed on this occasion by breaking a magma chamber during its emptying or it has been at least greatly enlarged.
The ash from this eruption can be found all around the North Atlantic and they are used to Tephrochronologie under the international name "ash 1", in other Scandinavian countries called in Iceland Skoga - tephra Vedde - tephra.
Eldgjá eruption 934 AD
Eldgjá is associated with the volcano Katla volcano column, starting ranges discontinuously from Mýrdalsjökull almost to the southwest edge of the glacier Vatnajökull. Its center forms an eruption column of eight kilometers long and 150 m depth, the Eldgjá, dt the fire column is called. This is an old grave system that was reactivated by the historic outbreak in the years of probably 934-940. The eruption also had some explosive phases and sent a total of about 219 million tons of sulfur dioxide into the atmosphere, which is about 24 times the amount of the eruption of Mount Pinatubo in 1991.
In this first outbreak of Katla after the settlement of Iceland in the 9th century. produced about 18 km ³ of lava that flowed in two streams to the sea. This so-called Eldgjá - Hraun is now mostly under newer lavas about the eruptions of Laki, eg northwest of Kirkjubæjarklaustur, and you can in the Eldgjá - Palagonitlage the ground for post-glacial volcanic cinders see, some of which date from lava fountains.
A Lavaflut similar to the Eldgjá was also produced by the so-called Hólmsá - fire in the year 6600 BC.
From the 12th century
Here the volcanic activity of Katla volcano concentrated on the column Kötlugjá.
During the late Middle Ages, the source location is rather poor, is improving this in modern times. Relatively well documented are the eruptions of 1580, 1612, 1625, 1660, 1721, 1755, 1823, 1860 and 1918.
The outbreaks were very different degrees. In particular, the eruptions of 1262, 1625, 1721 and 1755 caused major damage with tephra - fall, which reached to the Scandinavian mainland. Numerous farms were destroyed or had to be relocated, pasture desolate because of a large area of glacial deposits and tephra fell over Scandinavia and Western Europe down.
The pastor Jón Steingrímsson, which became known as the so-called fire preacher and chronicler of the volcanic disaster of Laki, wrote about the eruption of Katla of 1660, that this little ash and unconsolidated materials have produced but have had for a considerable glacier run result. Here, for example, were the Church and Farm Höfðabrekka swept away by the floods. Then, all located on the Mýrdalssandur farms were abandoned and even the time of Jón Steingrímsson at the end of the 18th century the area was uninhabited. The nowadays existing farms there are subsequent start-ups.
In 1721 one of the largest explosive eruptions took place with an enormous glacier run. This triggered waves caused damage on the Vestmannaeyjar ( Westman Islands dt ). After the annals However, there were no casualties among the local residents.
Subsequent outbreaks are different well documented and researched. Some with minor glacier runs and little Tephraniederfall found in the 19th century instead of (1823 and 1860 ).
Controversial is the ever encountered thesis, an eruption of Eyjafjallajökull in 1821 have prepared the outbreak of the Katla 1823.
The last eruption was clearly assignable in 1918 and had a large glacier run result. It is estimated the amount of down at his peak over the Sander flowing liquid ( water and mud ) to approximately 200,000 m³ / s (compared to runoff volume at the mouth of the Amazon 175.000 m³ / s).
In this case, condensation water collected under the glacier, this floating on the water broke through the front ice barrier and spilled out with tremendous force on the Mýrdalssander. The case also transported Eisklötze were up to 200 meters long and 18 meters high.
The outbreak announced at the October 12, 1918 by 13 clock with a strong earthquake on. About two hours later could be seen to ascend a 14 km high eruption column from the Kötlugjá. The Tephraausfall was so strong that it destroyed the farm Búlandssel in Skaftártunga.
Around the same time you could in two places at Kotlujokull, a side glacier of Mýrdalsjökull see break out the first glacier runs. The level of Mýrdalssandur was largely covered by water. The tidal waves were divided into two main streams, one of the river Múlakvísl east of the island mountain Hafursey followed over, told before Hjörleifshöfði again and the other Inselsberg included. The second flowed from Kriki, a valley between two western side glaciers, from the WSW after and followed the course of the river Kúðafljót into the sea.
A second major tidal wave followed by 17 clock and so did much ice with that positioned on hills observers spoke of here, " snow-covered hills spin along (via the Sander ) " would. The tidal waves moving at a speed of 15-20 km / h The total volume of the glacier run is estimated to be three to five cubic kilometers, and covered more than 50 % of the Mýrdalssandur (400 km ²). The surface of the Mýrdalssandur raised by the surviving material (0.5-1 km ³ of volcanic ash and deposits ) by about one meter.
The eruptions of Katla held on for another 23 days. Overall, about 0.7 cubic kilometers of tephra was distributed, which corresponds to a volume of 0.3 cubic kilometers of magma.
From the 50s of the 20th century
It is assumed that minor eruptions in 1955 and 1999.Im June 1955 destroyed two bridges on the glacier runs Mýrdalssandur. Tactics involved a glacier run on the Sólheimasandur to a smaller subglacial eruption of Katla in 1999. Characteristic of this glacier run also was a very rapid swelling of the amount of water to 4400 m³ / s within an hour, an effect of the one dam failure gleichkam.Geodätische and other surveillance of known intrusion kettle on the Mýrdalsjökull showed between 2001 and 2004 an increase in the boiler due to stronger geothermal activity, which was accompanied by a swelling of the volcano. After 2005, this development has stagnated at first and you put on one of the boiler opposite trend firmly.
On 20 April 2010, the Icelandic President Olafur Grimsson warned in an interview with the BBC before another outbreak for which there are already signs. This could exceed the impact of the time of the interview current Eyjafjallajokull eruption several times in his force. For this statement, which can be based on any clear facts, the president was strongly criticized by various parties. A more differentiated assessment of the situation showed about geochemist and geographer Trausti Ari Guðmundsson, who pointed out that an eruption of Katla in the sequence would certainly possible, but not predictable in its facticity is still in its strength.
Glacier run in July 2011
On 9 July 2011, there was a glacier run in the river Múlakvísl, who had already announced hours and days earlier in a series of earthquakes up to ten kilometers deep in the Katla region. The glacier run came from three burglary boilers in the southeast of Mýrdalsjökull. Presumably, a small volcanic eruption had occurred beneath the glacier similar to 1955.
The glacier run again destroyed the only good 20 -year-old bridge on the ring road Múlakvísl. Due to a glacial overflow warning by a water level warning system, the road was blocked already about an hour before the destruction of the bridge to traffic, so that no one was hurt, although the water level according to one of the stations of the Icelandic Meteorological Office ( IMO) to 5 meters increased. Around 200 people were evacuated as a precaution, but it could return to their homes soon. On July 10, the water level went during the day back to normal height.
On 11 July 2011, the tremor under the Katla had calmed down.
On 15 July 2011 1,500 men were transported by special vehicles by a ford across the Múlakvísl. Meanwhile, a temporary bridge over the river is completed. It was taken on July 16, 2011 at noon in operation.
When flying over the glacier 18 July 2011 geologists discovered next to the slump boilers, from which the glacier run had come, another new and presented in general a decrease in the glacier surface firmly. Because of the large number of new crevasses should the southeastern Mýrdalsjökull currently meiden.Gleichzeitig keep the earthquake series under the Mýrdalsjökull to.
In September 2011, the geologist Einar Kjartansson defined by the Icelandic Meteorological Office IMO the glacier run as a result of a small eruption of Katla. However, this opinion does not seem to be shared by the Dean of the Volcanological Institute of the University of Iceland Magnús Tumi Guðmundsson, who said in an interview with the same newspaper on September 7th 2011, the eruption of Katla could, in accordance with typical and currently existing features such as clustering of earthquakes and expansion imminent.
Typical sequence of a volcanic eruption of Katla glacier run
The location of the volcano under a glacier makes the observability of small eruptions, some of which probably could go unnoticed, as long as they produced only less significant glacier runs.
Since the last major eruption took place in 1918, had as yet no opportunity to analyze a larger outbreak of Katla during the event with scientific methods.
According to the annals of the larger eruptions of Katla usually terminate with a series of earthquakes, including one or more fairly strong earthquake in. This takes about a day before the actual outbreak. Presumably, this is related to the melting of up to 750 m, but usually at least 300-600 m thick ice on the outbreak sites. Following this, a strong explosive eruption phase follows with columns that can reach a height of at least 10-15 km. The tephra consists in most cases of dark mafic rock. Depending on their chemical composition, they can certainly cause health damage in humans and animals.
As observed in the last explosive eruption of Eyjafjallajökull in April 2010, characterize frequent lightning in the eruption column and thundering and crashing sounds this outbreak phase.
Finally, however, is just the Mýrdalsjökull with the Katla in Iceland particularly notorious for the problems associated with major outbreaks glacier runs.
Therefore, a volcanic eruption under a glacier a glacier run result, because the heat of the magma melts ice on large quantities. The contact of the melt water with hot lava leads to massive steam explosions, so-called phreatomagmatic explosions in which the volcanic material is broken up into tiny particles. Furthermore, enormous amounts arise melt water. If accumulated enough, the mixture breaks the ice barrier, the glacier floats on the mixture, and the tidal wave breaks out from under him, as you could see about even with the glacier runs from the Grímsvötn caused by the outbreak in Gjálp 1996.
The glacier runs of Katla are different from those of other glacial volcanoes that they do not last long, but carry a lot of liquid ( mixture of water, mud, ice, etc.). Simultaneously, the strong gradient from the glaciers to the sea, that the tidal waves move very quickly. You can run in their icebergs of 200 m length and 18 m in height with tear to take but usually only a few hours.
Of the 17 previously documented glacier runs, 15 poured in an easterly direction over the Mýrdalssandur and only two in south direction over the Sólheima or Skógasandur. Only one flood flooded 1600 years ago in the west the plain of the River Markarfljót. The gorge Tröllagjá was created in the Emstrur (see Laugavegur ).
Shift of the beach line
Due to the eruptions of the volcano every time be transported enormous amounts of volcanic ash and sediment into the sea, making the beach line in part is considerably advanced. Despite constant erosion of the beach by ocean currents between the outbreaks, the shoreline in front of the island mountain Hjörleifshöfði has been shifted to net about 5 km into the sea since the beginning of the conquest from 870 AD.
Research and monitoring of the volcano
The volcano is currently the most watched in the country. Numerous seismic stations to measure earth movements. The water from the surrounding rivers is regularly examined for its mineral content, gas content and the electrical conductivity.
Geologists also have numerous investigations concerning the location and the shape of the glacier subsurface hired to find the exact appearance of the caldera. Due to the fact based calculations, and it has accumulated knowledge about the functioning of the volcano, it is believed that during a future eruption, most of the flood will fall back on the Mýrdalssandur, with ten percent probability falls a flood on the valley of the river Markarfljót, especially from page glacier Entujökull starting and twelve percent probability attributable to a glacier run on the Sólheima and the Skógasandur. :