Youkullhluip

Meltwater may form on the surface of a glacier, under a glacier, or both there and there ^{[3] [4]} . Abilation (melting on the surface) often leads to the formation of lakes on the surface. Bottom melting occurs due to geothermal heat of rocks under the glacier, which differs in different areas, or due to heat from friction when ice moves over rocky rocks under it.

Meltwater may flow over a glacier, between a glacier and a rock base, or as groundwater in an aquifer below the rock base of the glacier as a result of the water permeability of the base below the glacier. If the rate of formation of melt water exceeds the absorption capacity of the aquifer, surface or subglacial lakes are formed ^[5] .

Surface and subglacial flows differ in the zones of passage. The supraglacial flow is similar to terrestrial flow in all open environments — water flows from higher to lower points under the influence of gravity. The subglacial flow behaves differently - the melt water formed under the glacier or leaked from the surface under the action of gravity is collected in cavities inside or under the glacier into lakes, over which there are hundreds of meters of ice. The pressure of the water accumulating in such a lake grows until it is large enough to either make its way out or raise ice above the surface of the lake ^{[3] [6]} .

As melt water accumulates and pressure rises under continental ice sheets or alpine glaciers, occasional water discharges occur. As ice rises above the subglacial lake under pressure, the water moves to where there is less resistance. Therefore, the first to rise are the places where the ice is thinner or has cracks. Therefore, water often moves up the surface under the glacier to areas with a smaller thickness of ice. As water accumulates, the lake grows, other areas of the ice layer rise, until a way out is found ^[7] .

If there is no previously formed discharge channel, at first the water will break out with a wide youklullhluip, which may have a flow width of tens of kilometers, but a negligible thickness. With further flow, yoqualhloyp tends to blur the rock beneath the glacier and ice, forming a channel of the tunnel valley, while reducing the pressure allows the rest of the raised ice to settle down on the rock again. It interrupts the wide flow and forms a narrow channel. The direction of the channel is mainly determined by the thickness of the ice above the stream, and only secondarily, by the relief of the rock beneath it; “upward flow” is sometimes observed, since ice pressure pushes water to places with a smaller ice thickness until it appears on the surface of the glacier. This process determines the shape of many tunnel valleys, and it is possible to obtain general information about the thickness in different places of the glacier that existed at the time of the formation of the tunnel valley, especially if the initial surface under the glacier was not diverse ^{[3] [4]} .

Rapid sudden leakage of large volumes of water causes extremely large erosion, as evidenced by fragments of rocks and boulders in the tunnels and in their mouth. In the Antarctic, due to erosion, tunnels of more than 400 meters deep and up to 2.5 km wide were thus formed ^[3] .

Although youlukchleuyps were originally associated exclusively with Vatnajökull , the scientific literature asserted their existence in many places, including modern Antarctica; there is also evidence that they occurred in the Laurentian Ice Sheet ^{[8] [9] [10] [11]} and the Scandinavian Ice Sheet during the last ice age ^[12] .

Iceland

• Large-scale yoqualhlopy occur on Myrdalsyokyudla when the subglacial Katla volcano erupts - every 40-80 years. It is estimated that the eruption of 1755 caused a southwestern peak with a flow of 200,000–400,000 m³ / s.
• Grimsvötn Volcano often causes large Vatnayöküdl youkülhöypy. The 1996 eruption triggered a south-west coast with a peak flow of water of 50,000 m³ / s, which for several days made it the second (in terms of flow capacity) river in the world after the Amazon. The river Skeydara flooded the area in front of the Scaftafell . Youkülhluyp destroyed parts of the Ring Road , a stream of water carried fragments of ice weighing up to 5000 tons, and icebergs weighing 100–200 tons hit the bridge on the Ring Road and destroyed it (now the ruins of the bridge are marked with information boards and is a popular stop of tourists on the Ring Road). The water flow was up to 4 meters high and 600 meters long; he transferred 18.5 million tons of silt ^[13] . After the flow stopped, icebergs up to 10 meters high could be seen on the banks of the river.
• Eyjafjallajöküdul volcano can also cause youkülhluipa. The 2010 eruption caused a southwestern peak with a flow of 2,000–3,000 m³ / s ^{[14] [15]} .

North America

History

With the retreat of the Laurentian Ice Sheet from its maximum size in the period 21000 - 13000 years ago, two significant events occurred related to the redirection of meltwater flows in eastern North America. And, although geologists are still arguing about where these events occurred, they probably occurred when the ice sheet retreated from the Adirondack Mountains and the Laurentian Lowlands.

• At first, the Iroquois Ice Lake flowed into the Atlantic Ocean as a result of large floods along the Hudson Valley, which occurred when, during three youkülhlyuipov, the ice dam of the retreating shield was destroyed and re-created. Evidence of the scale of these events in the valley is significantly distinguished sediments, large traces of sediments on the continental shelf and erratic boulders with a diameter of more than 2 m on the outer shelf.
• Later, when the ice sheet retreated from the valley of St. Lawrence, the icy lake of Kandona flowed out into the North Atlantic, when the joulehlyuipa passed through the Sea of ​​Champlain and the valley of St. Lawrence. It is believed that the ingress of huge volumes of fresh melt water from these yoqualhleipes into the North Atlantic is approx. 13350 years ago led to a decrease in the thermohaline circulation and a short-term Allerod cooling in the Northern Hemisphere ^[16] .
• Finally, a giant ice lake Agassiz , located in the center of North America. The melt waters of glaciers at the end of the last glacial period flowed from it. Its area was larger than the area of ​​all the modern Great Lakes combined, and the volume of water exceeded the reserves in all present-day lakes of the world. Youkülhüypy occurred several times between 13,000 and 8,400 years ago.

In the west of the mainland, similar yoqualhlyuypas with runoff into the Pacific Ocean occurred along the gorge of the Columbia River and were called the Missoule floods .

Modernity

In July 1994, a surface glacier lake with a dam emerged from the ice through a subglacial tunnel through the Goddard Glacier in the Coastal Range , British Columbia , prompting a yo chullhluip. A flow of 100–300 m³ / s swept through Farrow Creek to Lake Chilko, causing significant erosion. The ice dam was not re-created. Similar yoqualhlyuipas in British Columbia are shown in the table below ^[17] :