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

glacial 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 ...

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 ...

. 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 i ...

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 ...

, 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 Hydrostatics is the branch of fluid mechanics that studies fluids at hydrostatic equilibrium and "the pressure in a fluid or exerted by a fluid on an immersed body". The word "hydrostatics" is sometimes used to refer specifically to water and o ...

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 units of cubic meters per second (m³/s) or cubic feet per ...

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 Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice shee ...

of North America and Europe after the last ice age (e.g.,

Lake Agassiz Lake Agassiz ( ) was a large proglacial lake that existed in central North America during the late Pleistocene, fed by meltwater from the retreating Laurentide Ice Sheet at the end of the last glacial period. At its peak, the lake's area wa ...

and the

English Channel The English Channel, also known as the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France. It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busi ...

), 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 ( – removal) is the 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, including spacecraft material for as ...

(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 during the last Weichselian glaciation.

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 material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...

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 (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

. 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 measurement related to liquid pressure (normalized by specific weight) and the liquid elevation above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22, eq.3.2a. It is usually meas ...

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 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 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 Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent between 26,000 and 20,000 years ago. Ice sheets covered m ...

Iceland

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 ...

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 . *The

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

volcano frequently causes large jökulhlaups from

. The 1996 eruption of Gjálp sent melt water southwards into Grímsvötn, that caused a jökulhlaup with a peak flow of and lasted for several days. This is the largest Grímsvötn glacial flood ever recorded. * 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 ...

volcano can cause jökulhlaups. The 2010 eruption caused a jökulhlaup with a peak flow of about . Work in Iceland has categorised jökulhlaups by origin and size. The categories of origin are: *From an ice-dammed marginal lakes such as when an outlet glacier closes off an ice-free side valley. ** Grænalón was a former example of such a lake. *From a supraglacial lake formed by accumulation of melt water in a depression on the surface of the glacier. **Such jökulhlaups tend to be small in Iceland *From a subglacial lake. **Tend to be formed by geothermal activity as found in the eastern and western Skaftá ice cauldrons and

. *From a volcanic eruption underneath a glacier (subglacial eruption). ** While melt water might flow immediately away from the eruption site, it might also accumulate near the site creating an unstable reservoir as has happened in the jökulhlaup from Eyjafjallajökull in 2010 and Katla eruptions underneath Mýrdalsjökull. *From melting after a

pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...

onto snow and ice in explosive eruptions in

stratovolcano A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with ...

es. **This type of flood may be a

lahar A lahar (, from ) is a violent type of mudflow or debris flow composed of a slurry of Pyroclastic rock, pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a valley, river valley. Lahars are o ...

and has happened at

Hekla Hekla (), or Hecla, is an active stratovolcano in the south of Iceland with a height of . Hekla is one of Iceland's most active volcanoes; over 20 eruptions have occurred in and around the volcano since the year 1210. During the Middle Ages, th ...

. *From a glacier surge into a proglacial lake or at the end of the surge when the subglacial drainage system re-establishes itself. **The 1999 surge of Langjökull at its outlet glacier of Eystri-Hagafellsjökull was into a lake which then flooded downstream. *From a landslide. Substantial potential energy is released in such slides, which can cause melting of ice and creation of flood water either if the slide falls onto a glacier or displaces water in a glacier dammed lake. **The 1967 rockslide onto the Steinsholtsjökull outlet glacier of

caused such a flood.

North America

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

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

Coast Mountains The Coast Mountains () 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 British Columbia Coast, Coast of British Columbia sout ...

, 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, 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, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. 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 ( ) are a massif of mountains in Northeastern New York which form a circular dome approximately wide and covering about . The region contains more than 100 peaks, including Mount Marcy, which is the highest point in Ne ...

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. Description The lake was essentially an enlargement of the present Lake Ontario that formed because the St. ...

drained to the Atlantic in catastrophic

Hudson Valley The Hudson Valley or Hudson River Valley comprises the valley of the Hudson River and its adjacent communities in the U.S. state of New York (state), New York. The region stretches from the Capital District (New York), Capital District includi ...

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 a glacially deposited rock (geology), rock differing from the type of country rock (geology), rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by gla ...

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 oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...

, with subsequent drainage events routed through the

Champlain Sea The Champlain Sea () 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 what are now the Canadi ...

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 current, ocean circulation driven by global density gradients formed by surface heat and freshwater fluxes. The name ''thermohaline'' is derived from ''wikt:thermo-, thermo-'', r ...

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 state ...

, dubbed the Missoula Floods. * Since 2011, periodic glacial floods have occurred from the Suicide Basin through the Mendenhall Glacier in

Juneau, Alaska Juneau ( ; ), officially the City and Borough of Juneau, is the List of capitals in the United States, capital of the U.S. state of Alaska, located along the Gastineau Channel and the Southeast Alaska, Alaskan panhandle. Juneau was named the ...

multiple times each year, with major such floods occurring in the summer of 2023 and 2024.

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.) Nanda Devi is the 23rd-highest peak in the world and ranked 74t ...

Glacier broke away in the 2021 Uttarakhand glacier burst, triggering

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

Sweden

Around 9500 BC the Baltic Ice Lake was tapped on water as the ice front retreated north of mount Billingen.

References

External links

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

Durham University Durham University (legally the University of Durham) is a collegiate university, collegiate public university, public research university in Durham, England, founded by an Act of Parliament (UK), Act of Parliament in 1832 and incorporated by r ...

NOAA. Jokulhlaup Brochure.
Jökulhlaup in the United States.