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, e.g. 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.

Skaftárkatlar (Skaftá cauldrons)

These are two depressions in the ice cover above two subglacial lakes in the south-western part of Vatnajökull. [lower-alpha 1] In the whole, many cauldrons are to be found within Vatnajökull glacier (8,100 km2 (3,100 sq mi) in 2015), the largest of which in the western part of the ice cap are the Skaftá cauldrons. [4]

These ice cauldrons "are created by melting at subglacial geothermal areas". [5] 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/s (71,000 cu ft/s). [4]

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/s (110,000 cu ft/s) or even more. The cauldron then partially collapsed and formed a depression of up to 110 m (360 ft) deep in its center and a maximum width of 2.7 km (1.7 mi) [6]

Katla

Ice cauldron
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Ice cauldrons on the Mýrdalsjökull ice cap of Katla. [7] [8] [9]

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 Katla, 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 large eruption took place in 1918 and was associated with a jökulhlaup with an estimated peak discharge of about 300,000 m3/s (11,000,000 cu ft/s). [8]

Within the caldera 12–17 ice cauldrons are supra- and inglacial manifestations of a near-surface magmatic storage system. [8] K. Scharrer 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". [10] Others have also documented the change with time of ice cauldrons at Katla. [11] :71

They have a depth of 10–40 m (33–131 ft) and a width of 0.6–1.6 km (0.37–0.99 mi). 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". [11]

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, e.g. in Alaska (Mount Redoubt, Mount Spurr). [12]

Ice cauldrons and volcano monitoring

As deepening and widening of the ice cauldrons at Katla volcano, and especially in combination with increased seismic activity, are interpreted as signs of magma inflow, the cauldrons are closely monitored. [11]

See also

Notes

  1. For a map see [4]

Related Research Articles

<span class="mw-page-title-main">Mýrdalsjökull</span> Glacier in Iceland

Mýrdalsjökull 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.

<span class="mw-page-title-main">Eyjafjallajökull</span> Glacier and volcano in Iceland

Eyjafjallajökull, 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 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.

<span class="mw-page-title-main">Katla (volcano)</span> Large volcano on Southern Iceland

Katla is an active volcano 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 (VEI) of between 4 and 5 on a scale of 0 to 8. In comparison, the Eyjafjallajökull 2010 eruption had a VEI of 4. Larger VEI-5 eruptions are comparable to Mount St. Helens 1980 eruption. Several smaller (minor) eruptions measuring VEI-1 and below have occurred since, with the most recent being in 1999.

<span class="mw-page-title-main">Kverkfjöll</span> Volcano in Iceland

Kverkfjöll is a potentially active central volcano, fissure swarm, and associated mountain range situated on the northern border of the glacier Vatnajökull in Iceland.

<span class="mw-page-title-main">Öræfajökull</span> Volcano in south-eastern Iceland

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.

<span class="mw-page-title-main">Eldgjá</span> Volcanic fissure and eruption in south Iceland

Eldgjá is a volcano and a canyon in Iceland. Eldgjá is part of the Katla volcano; it is a segment of a 40 kilometres (25 mi) long chain of volcanic craters and fissure vents that extends northeast away from Katla volcano almost to the Vatnajökull ice cap. This fissure experienced a major eruption around 939 CE, which was the largest effusive eruption in recent history. It covered about 780 square kilometres (300 sq mi) of land with 18.6 cubic kilometres (4.5 cu mi) of lava from two major lava flows.

<span class="mw-page-title-main">Grímsvötn</span> Volcano in Iceland

Grímsvötn is an active 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.

<span class="mw-page-title-main">Jökulhlaup</span> 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.

<span class="mw-page-title-main">Subglacial volcano</span> 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.

<span class="mw-page-title-main">Geology of Iceland</span>

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.

<span class="mw-page-title-main">Subglacial eruption</span> Eruption of an ice-covered volcano

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. It is important to explore volcano-ice interactions to improve the effectiveness of monitoring these events and to undertake hazard assessments. This is particularly relevant given that subglacial eruptions have demonstrated their ability to cause widespread impact, with the ash cloud associated with Iceland's Eyjafjallajökull eruption in 2010 resulting in significant impacts to aviation across Europe.

<span class="mw-page-title-main">Bárðarbunga</span> Stratovolcano in Iceland

Bárðarbunga, is an active stratovolcano located under Vatnajökull in Vatnajökull National Park which is Iceland's most extensive glacier. The second highest mountain in Iceland, 2,000 metres (6,600 ft) above sea level, Bárðarbunga is also part of the Bárðarbunga-Veiðivötn volcanic system that is approximately 190 kilometres (120 mi) long and 25 kilometres (16 mi) wide.

<span class="mw-page-title-main">Thordarhyrna</span>

Thordarhyrna is one of seven subglacial volcanoes beneath the Vatnajokull glacier in Iceland. It is a paired active central volcano with Grímsvötn, and can be classified as part of the Grímsvötn-Laki volcanic system, with common fissure swarms to the south.

<span class="mw-page-title-main">Loki-Fögrufjöll</span>

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

<span class="mw-page-title-main">Skaftá</span> 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.

<span class="mw-page-title-main">Sveifluháls</span>

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.

<span class="mw-page-title-main">1996 eruption of Gjálp</span>

Gjálp is a hyaloclastite ridge (tindar) in Iceland under the Vatnajökull glacier shield. Its present form resulted from an eruption series in 1996 and it is probably part of the Grímsvötn volcanic system. However not all the scientists were of this opinion, as seismic studies are consistent with a 10 km (6.2 mi) lateral dike intrusion at about 5 km (3.1 mi) depth from Bárðarbunga being the trigger event. This does not exclude a shallower secondary intrusion from Grímsvötn being important in the subaerial eruption itself.

<span class="mw-page-title-main">Hofsjökull volcanic system</span> Volcano in Iceland

The Hofsjökull volcanic system contains the largest active central volcano in Iceland. It is called Hofsjökull, after the icecap of the same name. The system is in the west of the Highlands of Iceland and north of the dormant central volcano of Kerlingarfjöll Icelandic pronunciation:[ˈcʰɛ(r)tliŋkarˌfjœtl̥] ), which is usually regarded as part of the same volcanic system.

References

  1. 1 2 Ackiss, S. E. (May 2019). Investing the Mineralogy and Morphology of Subglacial Volcanoes on Earth and Mars. Dissertation (PDF) (Thesis). Department of Earth, Atmospheric, & Planetary Sciences West Lafayette, Indiana. Retrieved 28 August 2020.
  2. Einarsson, Pall; Brandsdottir, Bryndis; Gudmundsson, Magnus Tumi; Bjornsson, Helgi; Gronvold, Karl; Sigmundsson, Freysteinn (2 September 1997). "Center of the Icelandic Hospot experiences Volcanic Unrest". Eos. 78 (35). 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. 1 2 3 Galeczka, I.; Eiriksdottir, E.S.; Hardardottir, J.; Oelkers, E.H.; Torssander, P.; Gislason, S.R. (2015). "The effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the Skaftá river, Iceland" (PDF). Journal of Volcanology and Geothermal Research. 301: 253–276. Bibcode:2015JVGR..301..253G. doi:10.1016/j.jvolgeores.2015.05.008 . Retrieved 31 August 2020.
  5. Jónsson, S.; Adam, N.; Björnsson, H. (1 April 1998). "Effects of Subglacial Geothermal Activity Observed by Satellite Radar Inferometry". Geophysical Research Letters. 25 (7): 1059–1062. Bibcode:1998GeoRL..25.1059J. doi:10.1029/98GL50567 . Retrieved 30 August 2020.
  6. 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. doi:10.1017/jog.2020.65.
  7. "Katla - Monitoring of ice cauldrons". Institute of Earth Sciences, University of Iceland. Retrieved 15 June 2024.
  8. 1 2 3 4 McCluskey, O. (2019). Constraining the characteristics of a future volcanogenic Jökulhlaup from Katla, Iceland, through seismic analysis and probabilistic hydraulic modelling, Master’s thesis (Thesis). School of Earth and Environmental Sciences, University of Portsmouth. pp. 1–121. Retrieved 10 June 2024.:17
  9. "Search:Múlakvísl & Mýrdalssandur". Icelandic Met Office. Retrieved 15 June 2024.
  10. Scharrer, K. (4 September 2007). Monitoring ice-volcano interactions in Iceland using SAR and other remote sensing techniques. Dissertation (PDF) (Thesis). Fakultät für Geowissenschaften der Ludwig-Maximilians-Universität München. Retrieved 30 August 2020.
  11. 1 2 3 Guðmundsson, Magnús T.; Högnadóttir, Þ.; Kristinsson, A.B.; Guðbjörnsson, S (2007). "Geothermal activity in the subglacial Katla caldera, Iceland, 1999–2005, studied with radar altimetry" (PDF). Annals of Glaciology. 45. Bibcode:2007AnGla..45...66G. doi:10.3189/172756407782282444. Archived from the original (PDF) on 14 August 2020. Retrieved 14 August 2020.
  12. Barr, I.D.; Lynch, C.M.; Mullan, D.; De Siena, L.; Spagnolo, M. (2018). "Volcanic impacts on modern glaciers: A global synthesis". Earth-Science Reviews (Preprint). 182: 186–203. Bibcode:2018ESRv..182..186B. doi:10.1016/j.earscirev.2018.04.008.