Katla () is an active

subglacial volcano A subglacial volcano, also known as a glaciovolcano, is a volcanic form produced by subglacial eruptions or eruptions beneath the surface of a glacier or ice sheet which is then melted into a lake by the rising lava. Today they are most common i ...

in southern Iceland. This volcano has been very active historically with at least twenty documented major eruptions since 2920 BC. In its recent history though, Katla has been less active as the last major eruption occurred in 1918. These eruptions have had a

Volcanic Explosivity Index The volcanic explosivity index (VEI) is a scale used to measure the size of explosive volcanic eruptions. It was devised by Christopher G. Newhall of the United States Geological Survey and Stephen Self in 1982. Volume of products, eruption c ...

(VEI) of between 4 and 5 on a scale of 0 to 8. In comparison, the

Eyjafjallajökull Eyjafjallajökull (; "glacier of (the mountain) Eyjafjöll"), sometimes referred to by the numeronym E15, is one of the smaller ice caps of Iceland, north of Skógar and west of Mýrdalsjökull. The ice cap covers the caldera of a volcano wi ...

2010 eruption had a VEI of 4. Larger VEI-5 eruptions are comparable to Mount St. Helens 1980 eruption. These eruptions have produced very large glacial outburst floods. Several smaller (minor) events measuring VEI-1 and below have occurred since. Katla is one of the largest volcanic sources of carbon dioxide (CO₂) on Earth, accounting for up to 4% of total global volcanic carbon dioxide emissions.

Geography and physical appearances

Katla is one of the largest

volcanoes A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

. It is situated to the north of Vík í Mýrdal and to the east of the smaller

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

. Its peak reaches and is partially covered by the

Mýrdalsjökull Mýrdalsjökull (pronounced , Icelandic for "(the) mire dale glacier" or "(the) mire valley glacier") is an ice cap on the top of the Katla volcano in the south of Iceland. It is to the north of the town of Vík í Mýrdal and to the east of ...

glacier. The system has an area of . The

Eldgjá Eldgjá (, "fire canyon") is a volcano and a canyon in Iceland. Eldgjá is part of the Katla volcano; it is a segment of a long chain of volcanic craters and fissure vents that extends northeast away from Katla volcano almost to the Vatnajök ...

canyon is part of the same volcanic system, and extends as a fissure swarm to the north-east. The lavas from this eruption in 939 to 940 almost reach the south eastern coast, although are partially buried. The

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

of the Katla volcano has a diameter of and is covered with of ice. The volcano normally erupts every 40–80 years. The flood discharge at the peak of an eruption in 1755 has been estimated at 200,000–400,000 m³/s (7.1–14.1 million cu ft/sec), comparable to the combined average discharge of the

Amazon Amazon most often refers to: * Amazon River, in South America * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon (company), an American multinational technology company * Amazons, a tribe of female warriors in Greek myth ...

Mississippi Mississippi ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South regions of the United States. It borders Tennessee to the north, Alabama to the east, the Gulf of Mexico to the south, Louisiana to the s ...

Nile The Nile (also known as the Nile River or River Nile) is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa. It has historically been considered the List of river sy ...

, and

Yangtze The Yangtze or Yangzi ( or ) is the longest river in Eurasia and the third-longest in the world. It rises at Jari Hill in the Tanggula Mountains of the Tibetan Plateau and flows including Dam Qu River the longest source of the Yangtze, i ...

rivers (about 266,000 m³/s (9.4 million cu ft/sec)).

Etymology

The name ''Katla'' derives from the word '' ketill'' ("

kettle A kettle, sometimes called a tea kettle or teakettle, is a device specialized for boiling water, commonly with a ''lid'', ''spout'', and ''handle''. There are two main types: the ''stovetop kettle'', which uses heat from a cooktop, hob, and the ...

"), referring to the form of the volcano. ''Katla'' is also used as a female first name.

Historic activity

There have been up to twenty three eruptions recorded for Katla since 920 CE. Only two people are known to have died because of events directly associated with one of these eruptions in 1755. The 1918 eruption of Katla started on the late afternoon of the 12 October 1918 and lasted for 24 days, with the first day having the most dangerous events, including an extremely large flood with peak flow of . It has been graded a VEI 4 level eruption. The 1918 eruption resulted in extending the southern coast by due to laharic flood deposits. Most of these eruptions resulted in glacial floods (

jökulhlaup A jökulhlaup ( ) (literally "glacial run") is a type of glacial outburst flood. It is an Icelandic term that has been adopted in glaciological terminology in many languages. It originally referred to the well-known subglacial outburst floo ...

s). Some Mýrdalsjökull jökulhlaups have been associated with catastrophic flooding which results from peak discharges of more than , which is ten to a hundred times the size of most jökulhlaups. Apart from the 1755 and 1918 eruptions already mentioned in this regard, both of which like the majority of large floods drained onto the Mýrdalssandur plain to the volcanoes south-east, an eruption in 822 drained from the north-east aspect of the caldera down the Markarfljót river flood plain to the mountain's south-west covering an area of . This is a convoluted route that outputs on to a large flood plain, the Markarfljótsaurar. Before the Hringvegur (Iceland's Ring Road) was constructed in 1974, people feared traversing the plains in front of the volcano because of the frequent ''jökulhlaup'' (or glacier bursts) and the deep river crossings.

Recent activity

Katla has been showing signs of unrest since 1999, and geologists have concerns that it might erupt in the near future. The volcano's present

dormancy Dormancy is a period in an organism's Biological life cycle, life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolism, metabolic activity and therefore helps an organism to conserv ...

is among the longest in its known history. Particularly, monitoring has been intensified following the March 2010 eruptions of a smaller neighbouring volcano, the

glacier. The eruption of this nearby long-dormant volcano in March and April 2010 prompted fears among some

geophysicist Geophysics () is a subject of natural science concerned with the physical processes and properties of Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists conduct investigations acros ...

s that it might trigger an eruption at the larger and more dangerous Katla. In the past 1,000 years, all three known eruptions of Eyjafjallajökull have triggered subsequent Katla eruptions. Following the 2010 Eyjafjallajökull eruptions, on 20 April 2010 Icelandic President Ólafur Grímsson said "the time for Katla to erupt is coming close ... we celandhave prepared ... it is high time for European governments and airline authorities all over Europe and the world to start planning for the eventual Katla eruption". Increased earthquake activity had been noticed on Katla since the eruption at Eyjafjallajökull, but no other signs of an imminent eruption were observed. These quakes are located mainly on the northwestern rim of the caldera. On 9 October 2010, a sudden rise in harmonic tremor was observed in the stations around Katla, but although a sign of a possible impending eruption, none occurred.

2011 activity

In 2011, geologic activity led many to speculate that a very small subglacial eruption had taken place. In June 2011, harmonic tremor was again detected at Katla volcano. A few days later, an earthquake swarm took place in the caldera, indicating magma movement inside the volcano, leading to increased fears of an eruption in the near future. On 8 and 9 July, another spike in harmonic tremors occurred, as a small eruption of Katla took place. Cracks formed on the glacier, as well as a cauldron. Icelandic media reported a small

subglacial eruption Subglacial eruptions, those of ice-covered volcanoes, result in the interaction of magma with ice and snow, leading to meltwater formation, jökulhlaups, and lahars. Flooding associated with meltwater is a significant hazard in some volcanic a ...

might have started. On the morning of 9 July, a glacier flood was reported in the river Múlakvísl, and also later in the river Skálm. The bridge across Múlakvísl was destroyed as well as other parts of the road, Route 1, on the Icelandic ring road. Helicopter pilots flying over the glacier also reported cracks in the glacier. Scientists monitoring the activity said speculation that it was caused by a "very small" subglacial eruption lacked confirmation by visual or seismic evidence.

2016 and 2017 activity

Tremors were detected under Katla in late August 2016. A "Specialist Description" describing the activity on 29 August 2016 noted that there was:

... a seismic swarm in Mýrdalsjökull on the 29th of August with two events in the northern Katla caldera rim measured at magnitude 4.5. These are the biggest earthquakes in Katla volcano since 1977. Earthquake eruption checks confirmed that most earthquakes occurred between 0:40 and 1:50 PM. The big earthquakes were about thirty seconds apart at 1:47. They were followed by more than 50 aftershocks until 15:12 PM, when there was an earthquake of magnitude 3.3 and then the cycle and seismic activity in the region reduced again. No unrest was measured along these earthquakes. The geothermal has decreased in the following week and is now negligible.

An update written at 11 Sep 16:38 GMT reported:

Today, shortly before 14:00, a small earthquake swarm began in Mýrdalsjökull. The largest earthquakes of the swarm were of magnitude 3.3 and 3.0 at 16:12 and 15:57. More than 10 smaller earthquakes were detected in the swarm. All of the earthquakes were shallow and located in the caldera of Katla volcano. It is not unusual for seismic swarms of this type to occur in this area.

In February 2017, seismic activity at the volcano continued.

Other activity

As well as eruptions Katla is host to geothermal systems and these contribute to many of the smaller jökulhlaups from the mountain. Jökulhlaup triggering at Mýrdalsjökull may result from geothermal processes, and ice dams and their sudden removal by floating of the ice above a lake of melt water. Some eruptions could be secondary to the removal of overpressure by a jökulhlaup. There are currently at least 20

ice cauldron Ice cauldrons are ice formations within glaciers that cover some subglacial volcanoes. They can have circular to oblong forms. Their surface areas reach from some meters (as indentations or holes in the ice) to up to 1 or more kilometers (as b ...

s known related to the geothermal areas within the caldera. These are often manifest as depressions in the ice cap rather than full thickness to the underlying rock cauldrons and have variable activity. Geothermal waters with a high volcanic mineral and gas content are produced and can result in both gas and water pollution.

Risks

The area of the volcano contributes to the most serious natural hazard area of Iceland. The most likely large eruption had in 2019 a 89% probability of occurring within 30 years and would likely be associated with tephra production of about which can be compared with the that disrupted air travel from the second phase of the

2010 eruptions of Eyjafjallajökull Between March and June 2010 a series of Volcano, volcanic events at Eyjafjallajökull in Iceland caused Air travel disruption after the 2010 Eyjafjallajökull eruption, enormous disruption to air travel across Western Europe. The disruptions st ...

. It is most likely to occur in the months June to September, and be associated with a jökulhlaup flowing from Kotlujökull an outlet glacier to the south-east, over Mýrdalssandur to the sea where it could affect the town of Vík í Mýrdal. The 1755 and 1918 eruptions show that lightning and tephra fall are perceived as dangerous by humans in the immediate vicinity of a large eruption and have influenced jökulhlaup evacuation planning. Geothermal jökulhlaups can be large enough to damage property and infrastructure.

Monitoring

Because of such risks the volcano is intensively monitored. The Icelandic Meteorological Office updates its website with reports of quakes both at Eyjafjallajökull and Katla. Continuous monitoring includes for seismic flood tremor, water gauges and water conductivity given the flood risk. The ice cauldrons of Mýrdalsjökull are also monitored.

Folklore

In folklore, the witch named Katla is held responsible for causing the ''

'' (outburst) of the

glacier over the volcano; these events are dubbed (or "Katla's eruption"). The folktale recorded by Jón Árnason in 1862 probably dates much older since it is set in the time of the , the Catholic monastery abolished c. 1550. The short folktale entitled "Katla eða Kötlugjá" can be summarized as follows: In the pre-Reformation days when the Þykkvibær monastery was installed with an abbot, they had a cranky housekeeper there named Katla, well versed in (ancient) magic (), instilling fear in others. She owned a magical pair of breeches (, 'trousers'), which allowed its wearer to run endlessly without fatigue, but herself reserved its use for an emergency. One day in autumn, the abbot's shepherd Barði has trouble rounding up the sheep before master and the housekeep return from a banquet, and he borrows the breeches to retrieve the stray. Katla discovers the transgression and ambushes him, drowning him in a vat of sour whey (). But as winter wore on, the whey began to dwindle and Katla was heard muttering "Barði will soon appear".After "Barði will soon appear". Cf. Zoëga (1922) ''Icelandic-English dictionary'' s.v. "" : ''impers.'' ''bryddir á e-u'' something begins to appear Realizing the discovery of her crime and punishment was imminent, she put on her breeches and disappeared to the northwest, presumably diving straight into the glacier. Right afterwards a glacial outburst (''jökulhlaup'') occurred that rushed towards the monastery and . Other geologic features such as ('Katla's gorge') and the surrounding area made desolate, named also bear names alluding to the Katla folklore.

Images

Image:Myrdalsjökull glacier iceland 2005 1.JPG, The Mýrdalsjökull glacier in 2005 image: Myrdalsjökull glacier iceland 2005 3.JPG, The Mýrdalsjökull glacier in 2005 File:2008-05-24 32 Myrdalssandur with Myrdalsjökull.jpg, Katla from the Myrdalssandur flood plain in 2008 File:Volcan Katla, Suðurland, Islandia, 2014-08-17, DD 132.JPG, Katla in 2017 File:Volcán Katla, Suðurland, Islandia, 2014-08-17, DD 133.jpg, wider view of Katla in 2017

In popular culture

Katla is the subject of '' Katla'', an Icelandic TV series produced for

Netflix Netflix is an American subscription video on-demand over-the-top streaming service. The service primarily distributes original and acquired films and television shows from various genres, and it is available internationally in multiple lang ...

Notes

References

;Citations ;Bibliography * *

External links

Katla
in the "Catalogue of Icelandic Volcanoes"]
Volcanism 1

University of Iceland's Institute of Earth Sciences page about Katla

Webcams from Iceland, including Katla

Katla: preparedness for tourists

Icelandic Meteorological Office: Katla status

* (with narration audio p3 format {{Authority control Subglacial volcanoes of Iceland Subglacial calderas Active volcanoes Mountains of Iceland VEI-6 volcanoes East Volcanic Zone of Iceland 20th-century volcanic events One-thousanders of Iceland Glaciers of Iceland Volcanic systems of Iceland Calderas of Iceland Southern Region (Iceland)