Ice cauldron

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Ice cauldrons of Katla volcano, Myrdalsjokull glacier in 2009 Myrdalsjokull 1 Iceland.JPG
Ice cauldrons of Katla volcano, Mýrdalsjökull glacier in 2009
Newly formed ice cauldrons at Katla during unrest period in 2011 Myrdalsjokull Katla August 2011.jpg
Newly formed ice cauldrons at Katla during unrest period in 2011

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 bowl shaped depressions).

Contents

Their existence is connected to ice-volcano interaction in two possible ways: They can be formed in the course of a subglacial eruption or on top of a continuously active subglacial high temperature geothermal area.

In both cases, a jökulhlaup may be produced in connection with them.

Formation and continued existence of ice cauldrons

Ice cauldrons and subglacial eruptions

When an eruption takes place under a bigger glacier, eg. an ice cap, it normally begins with an effusive stage. The heat forms an ice cave and pillow lava is produced. After some time, the eruption has reached a stage where the pressure drops within the ice vault and the eruption style changes to become explosive. Hyaloclastite is produced and the heat is transferred to the meltwater. „At this stage, the surface ice begins to act brittle and creates concentric fractures that cave in towards the meltwater reservoir. This is referred to as the ice cauldron." [1]

When the eruption continues, “the meltwater reservoir becomes so large that the ice cauldron collapses inward towards the edifice, exposing the meltwater reservoir and allowing the breach of both the reservoir and the explosive lava, releasing plumes of gasses and jets of hyaloclastites “. [1] The ice cauldron can develop further into an ice canyon, as was the case during the 1996 Gjálp eruption. It can continue to exist after the meltwater has left the eruption site and the eruption is terminated. But in most cases, ice flow will fill up the ice cauldron again and make it disappear as soon as the eruption products have cooled down enough. [2]

Ice cauldrons on top of subglacial geothermal areas

Another case are ice cauldrons situated on top of geothermal areas. "(…) hydrothermal systems are created that bring heat up from a magma body, continuously melting ice into water that may be stored at the glacier bed until it breaks out in jökulhlaups." [3]

Many examples for a decades long existence of such ice cauldrons are to be found in Iceland.

Ice cauldrons around the world

Examples from Iceland

Aerial view of Vatnajokull. Skafta cauldrons as slight identations to the east of Hamarinn. Sylgjokull Hamarskriki 4 Iceland.JPG
Aerial view of Vatnajökull. Skaftá cauldrons as slight identations to the east of Hamarinn.
Ice cauldrons at Katla caldera Location of Katlas caldera.png
Ice cauldrons at Katla caldera

Skaftárkatlar (Skaftá cauldrons)

These are two depressions in the ice cover above two subglacial lakes in the southwestern part of Vatnajökull. [4]

In the whole, many cauldrons are to be found within Vatnajökull glacier (8,100 km2 in 2015), the largest of which in the western part of the ice cap are the Skaftá cauldrons. [5]

These ice cauldrons "are created by melting at subglacial geothermal areas". [6] The meltwater accumulates in lakes "under the cauldrons until it drains every 2–3 years in a jökulhlaup" of normally up to 2,000 m3/sec. [5]

An unusually big outburst flood (jökulhlaup) was recorded in 2015. The eastern Skaftá cauldron had accumulated meltwater in this case during around 5 years. It was discharged down the Skaftá river in September 2015 with a peak of 3,000 m3/sec or even more. The cauldron then partially collapsed and formed a depression of up to 110 m deep in its center and a max. width of 2.7 km. [7]

Katla

Famous examples from Iceland are the ice cauldrons within the Katla caldera.

Katla is an important caldera and central volcano situated under the Mýrdalsjökull glacier cap in the southern part of Iceland's East Volcanic Zone. 150–200 eruptions during Holocene have been attributed to her, and 17 of these happened since Settlement of Iceland in the 8th century. Most of the eruptions had their origin in the ice covered caldera. The last contested big eruption took place in 1918 and initiated a jökulhlaup with an estimated peak discharge of 300,000 m3/sec. [8]

Within the caldera 12–17 ice cauldrons are supra- and inglacial manifestations of a near-surface magmatic storage system. [8] K. Scharrer even explains that "twenty permanent and 4 semi-permanent ice cauldrons could be identified on the surface of Mýrdalsjökull indicating geothermally active areas in the underlying caldera." [9]

They have a depth of 10–40 m and a width of 0.6–1.6 km. In 1955, 1999 and 2011 small to medium sized jökulhlaup originated from some new ice cauldrons. It is still subject of discussion if they were eruption caused or initiated by heating up of the geothermal areas under these cauldrons. [8] "The geothermal heat output is in the order of a few hundred megawatt." [10]

Ice cauldrons in other environments

Fourpeaked Mountain, Alaska Fourpeaked - Fumarole on NW side (2007-02-22).jpg
Fourpeaked Mountain, Alaska

Ice cauldrons of course do not form only in Iceland, but also at many other places where there is subglacial volcanic activity, eg. in Alaska (Mount Redoubt, Mount Spurr). [11]

Ice cauldrons and volcano monitoring

As deepening and widening of the ice cauldrons eg. at Katla volcano, and esp. in combination with increased seismic activity at the sites, are interpreted as signs of magma inflow, the cauldrons are closely monitored. [10]

See also

Related Research Articles

Vatnajökull Icelandic glacier

Vatnajökull is the largest and most voluminous ice cap in Iceland, and the second largest in area in Europe after the Severny Island ice cap of Novaya Zemlya. It is in the south-east of the island, covering approximately 8% of the country.

Mýrdalsjökull Glacier in Iceland

Mýrdalsjökull is an ice cap in the south of Iceland. It is to the north of Vík í Mýrdal and to the east of the smaller ice cap Eyjafjallajökull. Between these two glaciers is Fimmvörðuháls pass. Its peak reaches 1,493 m (4,898 ft) in height and in the year 1980 it covered an area of approximately 595 km2 (230 sq mi).

Eyjafjallajökull Glacier and volcano in Iceland

Eyjafjallajökull, sometimes referred to as 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 with a summit elevation of 1,651 metres (5,417 ft). The volcano has erupted relatively frequently since the Last Glacial Period, most recently in 2010, when, although relatively small for a volcanic eruption, it caused enormous disruption to air travel across northern and western Europe for a week.

Katla (volcano) Large volcano in Southern Iceland

Katla is a large volcano in southern Iceland. It is very active; twenty eruptions have been documented between 930 and 1918, at intervals of 20–90 years. It has not erupted violently for 104 years, although there may have been small eruptions that did not break the ice cover, including ones in 1955, 1999, and 2011.

Öræfajökull

Öræfajökull is an ice-covered volcano in south-east Iceland. The largest active volcano and the highest peak in Iceland at 2,110 metres (6,920 ft), it lies within the Vatnajökull National Park and is covered by part of the glacier.

Grímsvötn

Grímsvötn is a volcano with a fissure system located in Vatnajökull National Park, Iceland. The volcano itself is completely subglacial and located under the northwestern side of the Vatnajökull ice cap. The subglacial caldera is at 64°25′N17°20′W, at an elevation of 1,725 m (5,659 ft). Beneath the caldera is the magma chamber of the Grímsvötn volcano.

Jökulhlaup Type of glacial outburst flood

A jökulhlaup 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 floods from Vatnajökull, Iceland, which are triggered by geothermal heating and occasionally by a volcanic subglacial eruption, but it is now used to describe any large and abrupt release of water from a subglacial or proglacial lake/reservoir.

Subglacial volcano Volcanic form

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 in Iceland and Antarctica; older formations of this type are found also in British Columbia and Yukon Territory, Canada.

Geology of Iceland

The geology of Iceland is unique and of particular interest to geologists. Iceland lies on the divergent boundary between the Eurasian plate and the North American plate. It also lies above a hotspot, the Iceland plume. The plume is believed to have caused the formation of Iceland itself, the island first appearing over the ocean surface about 16 to 18 million years ago. The result is an island characterized by repeated volcanism and geothermal phenomena such as geysers.

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 areas, including Iceland, Alaska, and parts of the Andes. Jökulhlaups have been identified as the most frequently occurring volcanic hazard in Iceland, with major events where peak discharges of meltwater can reach 10,000 – 100,000 m3/s occurring when there are large eruptions beneath glaciers.

Esjufjöll Volcano in Iceland

The subglacial Esjufjöll volcano is located at the SE part of the Vatnajökull icecap. Esjufjöll is a strict nature reserve

Vatnajökull National Park

Vatnajökull National Park is one of three national parks in Iceland. It encompasses all of Vatnajökull glacier and extensive surrounding areas. These include the national parks previously existing at Skaftafell in the southwest and Jökulsárgljúfur in the north.

Glaciovolcanism

Glaciovolcanism is volcanism and related phenomena associated with glacial ice. The ice commonly constrains the erupted material and melts to create meltwater. Considerable melting of glacial ice can create massive lahars and glacial outburst floods known as jökulhlaups.

Loki-Fögrufjöll

Loki-Fögrufjöll is a subglacial volcano under the Vatnajökull glacier.

Skaftá River in Iceland

The Skaftá is a river in South Iceland. It is primarily glacial in origin and has had its course modified by volcanic activity; as a result of both, it often floods because of glacial melting.

Helgafell (Hafnarfjörður)

Helgafell is a mountain on Reykjanes peninsula, Iceland. The height of the mountain is 338 m.

Sveifluháls

Sveifluháls is a mafic hyaloclastite ridge of 397 m height in the southwest of Iceland in Gullbringusýsla. It is part of Krýsuvík volcanic system and of the protected area Reykjanes Fólkvangur.

1996 eruption of Gjálp

Gjálp is a hyaloclastite ridge (tindar) in Iceland under the Vatnajökull glacier shield. It originated in an eruption series in 1996 and is probably part of the Grímsvötn volcanic system, though not all the scientists involved are of this opinion.

References

  1. 1 2 S. E. Ackiss: Investing the Mineralogy and Morphology of Subglacial Volcanoes on Earth and Mars. Dissertation. Department of Earth, Atmospheric, & Planetary Sciences West Lafayette, Indiana May 2019. 28 August 2020.
  2. Pall Einarsson, Bryndis Brandsdottir, Magnus Tumi Gudmundsson, Helgi Bjornsson, Karl Gronvold and Freysteinn Sigmundsson: Center of the Icelandic Hospot experiences Volcanic Unrest. Eos, Vol. 78, No. 35, September 2, 1997 Retrieved 30 August 2020.
  3. Helgi Björnsson: Subglacial lakes and jökulhlaups in Iceland. Global and Planetary Change 35 (2002) 255–271 Retrieved 31 August 2020.
  4. For a map see: I. Galeczka, etal.: The effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the Skaftá river, Iceland. Journal of Volcanology and Geothermal Research 301 (2015) 253–276. Retrieved 31 August 2020.
  5. 1 2 I. Galeczka, etal.: The effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the Skaftá river, Iceland. Journal of Volcanology and Geothermal Research 301 (2015) 253–276. Retrieved 31 August 2020.
  6. S. Jónsson etal.: Effects of Subglacial Geothermal Activity Observed by Satellite Radar Inferometry. Geophysical Research Letters, Vol. 25, No.7, pages 1059–1062, April 1, 1998. Retrieved 30 August 2020.
  7. Ultee L., Meyer C., Minchew B. (2020). Tensile strength of glacial ice deduced from observations of the 2015 eastern Skaftá cauldron collapse, Vatnajökull ice cap, Iceland. Journal of Glaciology 1–10. https://doi.org/10.1017/jog.2020.65
  8. 1 2 3 McCluskey, O (2019) Constraining the characteristics of a future volcanogenic Jökulhlaup from Katla, Iceland, through seismic analysis and probabilistic hydraulic modelling, Master's thesis, School of Earth and Environmental Sciences, University of Portsmouth
  9. K. Scharrer: Monitoring ice-volcano interactions in Iceland using SAR and other remote sensing techniques. Dissertation der Fakultät für Geowissenschaften der Ludwig-Maximilians-Universität München. 4 Sept. 2007 Retrieved 30 August 2020.
  10. 1 2 Magnús T. Guðmundsson, etal.: Geothermal activity in the subglacial Katla caldera, Iceland, 1999–2005, studied with radar altimetry. Annals of Glaciology 45 2007. Retrieved 30 August 2020.
  11. J. Barr. Volcanic impacts on modern glaciers: a global synthesis. Preprint. Manchester University. (2018)