A jökulhlaup ( ) (literally "glacial run") is a type of

glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

outburst flood In geomorphology, an outburst flood—a type of megaflood—is a high-magnitude, low-frequency catastrophic flood involving the sudden release of a large quantity of water. During the last deglaciation, numerous glacial lake outburst floods were ca ...

. 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 Vatnajökull ( Icelandic pronunciation: , literally "Glacier of Lakes"; sometimes translated as Vatna Glacier in English) is the largest and most voluminous ice cap in Iceland, and the second largest in area in Europe after the Severny Island ice ...

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...

, 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. Since jökulhlaups emerge from

hydrostatic Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...

ally sealed lakes with floating levels far above the threshold, their peak discharge can be much larger than that of a marginal or extra-marginal lake burst. The

hydrograph A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs). It can als ...

of a jökulhlaup from Vatnajökull typically either climbs over a period of weeks with the largest flow near the end, or it climbs much faster during the course of some hours. These patterns are suggested to reflect channel melting, and sheet flow under the front, respectively. Similar processes on a very large scale occurred during the deglaciation of North America and Europe after the last ice age (e.g.,

Lake Agassiz Lake Agassiz was a large glacial lake in central North America. Fed by glacial meltwater at the end of the last glacial period, its area was larger than all of the modern Great Lakes combined. First postulated in 1823 by William H. Keating, it ...

and the

English Channel The English Channel, "The Sleeve"; nrf, la Maunche, "The Sleeve" (Cotentinais) or ( Jèrriais), (Guernésiais), "The Channel"; br, Mor Breizh, "Sea of Brittany"; cy, Môr Udd, "Lord's Sea"; kw, Mor Bretannek, "British Sea"; nl, Het Kana ...

), and presumably at earlier times, although the geological record is not well preserved.

Formation process

Subglacial water generation

Subglacial meltwater may be produced on the glacier surface (supraglacially), below the glacier (basally) or in both locations.

Ablation Ablation ( la, ablatio – removal) is removal or destruction of something from an object by vaporization, chipping, erosion, erosive processes or by other means. Examples of ablative materials are described below, and include spacecraft materi ...

(surface melting) tends to result in surface pooling. Basal melting results from geothermal heat flux out of the earth, which varies with location, as well as from friction heating which results from the ice moving over the surface below it. In 1997 analyses concluded that, based on basal meltwater production rates, the annual production of subglacial water from one typical northwestern Germany catchment was 642x10⁶ m³ during the last

Weichselian glaciation The Weichselian glaciation was the last glacial period and its associated glaciation in northern parts of Europe. In the Alpine region it corresponds to the Würm glaciation. It was characterized by a large ice sheet (the Fenno-Scandian ice sheet) ...

Supraglacial and subglacial water flow

Meltwater may flow either above the glacier (supraglacially), below the glacier (subglacially/basally) or as groundwater in an

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...

below the glacier as a result of the hydraulic transmissivity of the subsoil under the glacier. If the rate of production exceeds the rate of loss through the aquifer, then water will collect in surface or subglacial ponds or lakes. The signatures of supraglacial and basal water flow differ with the passage zone. Supraglacial flow is similar to stream flow in all surface environments—water flows from higher areas to lower areas under the influence of

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

. Basal flow under the glacier exhibits significant differences. In basal flow the water, either produced by melting at the base or drawn downward from the surface by gravity, collects at the base of the glacier in ponds and lakes in a pocket overlain by hundreds of metres of ice. If there is no surface drainage path, water from surface melting will flow downward and collect in crevices in the ice, while water from basal melting collects under the glacier; either source can form a subglacial lake. The

hydraulic head Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22. It is usually measured as a liquid surface elevation, expressed in units of length, ...

of the water collected in a basal lake will increase as water drains through the ice until the pressure grows high enough either to force a path through the ice or to float the ice above it.

Episodic releases

If meltwater accumulates, the discharges are episodic under continental ice sheets as well as under Alpine glaciers. The discharge results when water collects, the overlying ice is lifted, and the water moves outward in a pressurized layer or a growing under-ice lake. Areas where the ice is most easily lifted (i.e. areas with thinner overlying ice sheets) are lifted first. Hence the water may move up the terrain underlying the glacier if it moves toward areas of lower overlying ice. As water collects, additional ice is lifted until a release path is created.Wingham2006 If no preexisting channel is present, the water is initially released in a broad-front jökulhlaup which can have a flow front that is tens of kilometres wide, spreading out in a thin front. As the flow continues, it tends to erode the underlying materials and the overlying ice, creating a

tunnel valley A tunnel valley is a U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages. They can be as l ...

channel even as the reduced pressure allows most of the glacial ice to settle back to the underlying surface, sealing off the broad front release and channelizing the flow. The direction of the channel is defined primarily by the overlying ice thickness and second by the gradient of the underlying earth, and may be observed to "run uphill" as the pressure of the ice forces the water to areas of lower ice coverage until it emerges at a glacial face. Hence the configuration of the various tunnel valleys formed by a specific glaciation provides a general mapping of the glacier thickness when the tunnel valleys were formed, particularly if the original surface relief under the glacier was limited. The rapid, high-volume discharge is highly erosive, as evidenced by the debris found in tunnels and at the mouth of tunnels, which tends to be coarse rocks and boulders. This erosive environment is consistent with creation of tunnels over 400 m deep and 2.5 km wide, as have been observed in the Antarctic. Piotrowski has developed a detailed analytic model of the process, which predicts a cycle as follows: # Meltwater is produced as a result of geothermal heating from below. Surface ablation water is not considered as it would be minimal at the glacial maximum and evidence indicates that surface water does not penetrate more than 100 meters into a glacier. # Meltwater initially drains through subglacial aquifers. # When the hydraulic transmissivity of the substratum is exceeded, subglacial meltwater accumulates in basins. # Water accumulates sufficiently to open the ice blockage in the tunnel valley which accumulated after the last discharge. # The tunnel valley discharges the meltwater excess—turbulent flow melts out or erodes the excess ice as well as eroding the valley floor. # As the water level drops, the pressure decreases until the tunnel valleys again close with ice and water flow ceases.

Human triggered

A subglacial lake in Iceland was inadvertently triggered by a borehole drilled through the overlying ice. The authors suggested that

hydrofracturing Frost weathering is a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedg ...

crevasses and flooding of moulins by precipitation events may be natural triggers of jökulhlaups.

Examples

Twisted bridge Skaftafell due to Glacial lake outburst flood

Whilst jökulhlaups were originally associated with Vatnajökull, they have been reported in the literature over a broad range of locations including the present day Antarctic, and there is evidence that they also occurred in the Laurentian ice sheet and the Scandinavian ice sheet during the

Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eur ...

Iceland

Mýrdalsjökull Mýrdalsjökull (pronounced , Icelandic for "(the) mire dale glacier" or "(the) mire valley glacier") 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 t ...

is subject to large jökulhlaups when the subglacial volcano Katla erupts, roughly every 40 to 80 years. The eruption in 1755 is estimated to have had a peak discharge of 200,000 to 400,000 m³/s. *The

Grímsvötn Grímsvötn (; ''vötn'' = "waters", singular: ) is a volcano with a (partially subglacial) fissure system located in Vatnajökull National Park, Iceland. The volcano itself is completely subglacial and located under the northwestern side of the Va ...

volcano frequently causes large jökulhlaups from

. The 1996 eruption caused a peak flow of 50,000 m³/s and lasted for several days. * The

Eyjafjallajökull 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 . The volcan ...

volcano can cause jökulhlaups. The 2010 eruption caused a jökulhlaup with a peak flow of about 2,000 to 3,000 m³/s.

North America

In July 1994, an ice-dammed surface lake drained via a subglacial tunnel through , in the

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

Coast Mountains The Coast Mountains (french: La chaîne Côtière) are a major mountain range in the Pacific Coast Ranges of western North America, extending from southwestern Yukon through the Alaska Panhandle and virtually all of the Coast of British Columbia ...

, resulting in a jökulhlaup. The flood surge of from 100 to 300 m³/second flowed 11 km through Farrow Creek to terminate in

Chilko Lake Chilko may refer to: *Chilko River The Chilko River is a river in the Chilcotin District of the Central Interior of British Columbia, Canada, flowing northeast from Chilko Lake to the Chilcotin River. Its main tributary is the Taseko River. Th ...

, causing significant erosion. The ice dam has not reformed. Similar British Columbian jökulhlaups are summarized in the table below. As the Laurentide Ice Sheet receded from its maximum extent from around 21,000 to 13,000 years ago, two significant meltwater rerouting events occurred in eastern

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. Though there is still much debate among geologists as to where these events occurred, they likely took place when the ice sheet receded from the

Adirondack Mountains The Adirondack Mountains (; a-də-RÄN-dak) form a massif in northeastern New York with boundaries that correspond roughly to those of Adirondack Park. They cover about 5,000 square miles (13,000 km2). The mountains form a roughly circular ...

and the St. Lawrence Lowlands. * First,

Glacial Lake Iroquois Glacial Lake Iroquois was a prehistoric proglacial lake that existed at the end of the last ice age approximately 13,000 years ago. The lake was essentially an enlargement of the present Lake Ontario that formed because the St. Lawrence River down ...

drained to the Atlantic in catastrophic

Hudson Valley The Hudson Valley (also known as the Hudson River Valley) comprises the valley of the Hudson River and its adjacent communities in the U.S. state of New York. The region stretches from the Capital District including Albany and Troy south to ...

releases, as the receding ice sheet dam failed and re-established itself in three jökulhlaups. Evidence of the scale of the meltwater discharge down the Hudson Valley includes deeply incised sediments in the valley, large sediment deposit lobes on the continental shelf, and

glacial erratic A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by glacial ice, often over distances of hundred ...

boulders greater than 2 metres in diameter on the outer shelf. * Later, when the St. Lawrence Valley was deglaciated, Glacial Lake Candona drained to the

North Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe and ...

, with subsequent drainage events routed through the

Champlain Sea The Champlain Sea (french: Mer de Champlain) was a prehistoric inlet of the Atlantic Ocean into the North American continent, created by the retreating ice sheets during the closure of the last glacial period. The inlet once included lands in ...

and St. Lawrence Valley. This surge of meltwater to the North Atlantic by jökulhlaup about 13,350 years ago is believed to have triggered the reduction in

thermohaline circulation Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to temper ...

and the short-lived Northern Hemisphere Intra-Allerød cold period. * Finally,

was an immense glacial lake located in the center of North America. Fed by glacial runoff at the end of the last glacial period, its area was larger than all of the modern Great Lakes combined, and it held more water than contained by all lakes in the world today. It drained in a series of events between 13,000 BP and 8,400 BP. * Also, into the Pacific Ocean, large drainage events took place through the

Columbia River Gorge The Columbia River Gorge is a canyon of the Columbia River in the Pacific Northwest of the United States. Up to deep, the canyon stretches for over as the river winds westward through the Cascade Range, forming the boundary between the sta ...

, dubbed the

Missoula Floods The Missoula floods (also known as the Spokane floods or the Bretz floods or Bretz's floods) were cataclysmic glacial lake outburst floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ...

India

On 7 February 2021, part of

Nanda Devi Nanda Devi is the second-highest mountain in India, after Kangchenjunga, and the highest located entirely within the country (Kangchenjunga is on the border of India and Nepal). It is the 23rd-highest peak in the world. Nanda Devi was consid ...

Glacier broke away in the 2021 Uttarakhand glacier burst, triggering

sweeping away a power plant. More than 150 people were feared dead.

Sweden

Around 9 500 BC the

Baltic Ice Lake The Baltic Ice Lake is a name given by geologists to a freshwater lake that evolved in the Baltic Sea basin as glaciers retreated from that region at the end of the last ice age. The lake existed between 12,600 and 10,300 years Before Present ...

was tapped on water as the ice front retreated north of mount

Billingen Billingen is the largest of the thirteen mesas in the Swedish county of Västra Götaland, with a maximum altitude of . The mesa extends in a north-southerly direct with a length of and a width of . Billingen is divided into two parts by an eas ...

References

External links

Video of a jökulhlaup at Eyjafjallajokull volcano, Iceland
14 April 2010, Blog of Professo
Dave Petley

Durham University , mottoeng = Her foundations are upon the holy hills (Psalm 87:1) , established = (university status) , type = Public , academic_staff = 1,830 (2020) , administrative_staff = 2,640 (2018/19) , chancellor = Sir Thomas Allen , vice_chan ...

NOAA. Jokulhlaup Brochure.
Jökulhlaup in the United States.