Mýrdalsjökull (pronounced [ˈmirˌtalsˌjœːkʏtl̥] , 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 the smaller ice cap Eyjafjallajökull. Between these two glaciers is the Fimmvörðuháls pass. The glacier contributes to the most serious natural hazard area of Iceland.
Setting The icecap of the glacier covers an active volcano. The caldera of Katla has a diameter of 10 km (6 mi) and the volcano erupts usually every 40–80 years. The last eruption took place in 1918. Scientists are actively monitoring the volcano, particularly after the eruption of nearby Eyjafjallajökull began in April 2010. There is a further historic relationship with Eyjafjallajökull as the two glaciers were continuous as a single ice cap at the end of the 19th century and only separated into the larger Mýrdalsjökull and smaller Eyjafjallajökull in the middle of the twentieth century. Since the year 930, 16 eruptions have been documented and in the last 8400 years about 300 explosive basalt eruptions are known to have originated from Katla. While Katla mountain is 30–35 km (19–22 mi) in diameter at its base, more relevant to the present ice cover is its diameter closer to 20 km (12 mi) at 700 m (2,300 ft) elevation. The lowest pass out of the caldera is at 740 m (2,430 ft). This caldera is between 650–750 m (2,130–2,460 ft) deep and is surrounded by a rim of 1,300–1,380 m (4,270–4,530 ft) high mountains. Ice cauldrons are found within the caldera. The glacier's recent peak ice cover has reached 1,493 m (4,898 ft) in height and in the year 1980 it covered an area of approximately 595 km2 (230 sq mi). In 2016 the covered area of Mýrdalsjökull was believed to be 540 km2 (210 sq mi). The area was 520 km2 (200 sq mi) in 2019. The volume of ice is about 140 km3 (34 cu mi). The Eldgjá, a volcanic eruption fissure about 30 km (19 mi) long, which erupted in the year 939, is part of the same volcanic system. Before the Hringvegur (the main ring road round the island) was built, people feared traversing the plains in front of the volcano because of the frequent jökulhlaups (glacial floods) and the deep rivers to be crossed, although the road is still vulnerable to major events. Especially dangerous was the glacial flood after the eruption of 1918 when the coastline was extended by 5 km (3.1 mi) by laharic flood deposits. Mýrdalsjökull is an exceedingly high precipitation location, with models suggesting parts of it receive more than 10 metres of rainfall equivalent annually.
Glaciation History The last glacial period came to an end 11,500 years ago and was followed by the Holocene. Mýrdalsjökull is likely to have been present throughout the Holocene and definitely the last 8400 years as there is no evidence of degassed erupted tephra from Katla. Jökulhlaup's 8000 to 6000 years ago took a path over the highest pass in the caldera wall which does not support a crater lake source but would happen with an ice cap. Until the development of remote satellite imaging it was impossible to monitor to annual accuracy the mass balance of Mýrdalsjökull. Such techniques allowed it to be determined for Mýrdalsjökull that it is the summer temperatures that are the predominant driving factor in the recent recession of the glacier. However past proxy means of measurement such as outlet length of the Sólheimajökull outlet glacier were also consistent with this. Any such studies related to climate change have to be qualified as past volcanic processes have resulted in the loss of up to 5% of the ice cap on more than one occasion.
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