Misplaced Pages

#98901

96-502: It is partially responsible for creating the 1958 Lituya Bay megatsunami . The glacier, which has receded over the years, carved Lituya Bay into a unique topographic phenomenon with steep walls, a very deep submerged bottom, and a very narrow entrance to the ocean which created the opportunity for a megatsunami to occur. The glacier is also the namesake of the Alaska Marine Highway ferry M/V Lituya . This article about

192-540: A cabin was damaged beyond repair. Sand boils and fissures occurred near the coast southeast of there, and underwater cables that supported the Alaska Communication System were cut. Lighter damage was also reported in Pelican and Sitka . It ripped limbs off trees and swept many away, decimating the shoreline's surrounding forest and leaving the high tide line barren and with few upright surviving trees except on

288-498: A code of conduct for ice drilling expeditions and in situ (on-site) measurements and sampling of subglacial lakes. This code of conduct was ratified at the Antarctic Treaty Consultative Meeting (ATCM) of 2011. By the end of 2011, three separate subglacial lake drilling exploration missions were scheduled to take place. In February 2012, Russian ice-core drilling at Lake Vostok accessed the subglacial lake for

384-423: A fishing boat died from a wave in the bay. Two more persons, a fishing boat captain and his seven-year-old son, were struck by the wave and lifted hundreds of feet into the air by the swell. Remarkably, both survived with minimal injuries. In Yakutat , the only permanent settlement close to the epicenter at the time, infrastructure such as bridges, docks, and oil lines all sustained damage. A wave tower collapsed and

480-420: A flat surface around the northern border of Lake Vostok, and the data collected from ERS-1 further built the geographical distribution of Antarctic subglacial lakes. In 2005, Laurence Gray and a team of glaciologists began to interpret surface ice slumping and raising from RADARSAT data, which indicated there could be hydrologically “active” subglacial lakes subject to water movement. Between 2003 and 2009,

576-402: A former subglacial lake. The water in a subglacial lake can have a floating level much above the level of the ground threshold. In fact, theoretically a subglacial lake can even exist on the top of a hill, provided that the ice over it is thin enough to form the required hydrostatic seal . The floating level can be thought of as the water level in a hole drilled through the ice into the lake. It

672-535: A height of several hundred meters into the bay, creating a megatsunami. The impact of the rockslide included the creation of wave run up that shaved up to 400m of ice off the front of the Lituya Glacier and eroded or completely eradicated its rocky deltas. After the earthquake it was observed that a subglacial lake , located northwest of the bend in the Lituya Glacier at the head of Lituya Bay, had dropped 100 ft (30 m). This proposed another possible cause to

768-584: A location in the Hoonah-Angoon Census Area, Alaska is a stub . You can help Misplaced Pages by expanding it . This article about a glacier in Alaska is a stub . You can help Misplaced Pages by expanding it . 1958 Lituya Bay megatsunami The 1958 Lituya Bay earthquake occurred on July 9, 1958, at 22:15:58 PST with a moment magnitude of 7.8 to 8.3 and a maximum Mercalli intensity of XI ( Extreme ). The strike-slip earthquake took place on

864-567: A maximum perceived intensity of XI ( Extreme ) on the Mercalli intensity scale . The epicenter of the quake was at latitude 58.37° N, longitude 136.67° W near the Fairweather Range , 7.5 miles (12.1 km) east of the surface trace of the Fairweather fault, and 13 miles (21 km) southeast of Lituya Bay. This earthquake was the strongest in over 50 years for this region, since

960-452: A prominent scientist studying polar lakes, has called Antarctica's subglacial ecosystems "our planet's largest wetland .” Microorganisms and weathering processes drive a diverse set of chemical reactions that can drive a unique food-web and thus cycle nutrients and energy through subglacial lake ecosystems. No photosynthesis can occur in the darkness of subglacial lakes, so their food webs are instead driven by chemosynthesis and

1056-602: A survey of long-track measurements of ice-surface elevation using the ICESat satellite as a part of NASA's Earth Observing System produced the first continental-scale map of the active subglacial lakes in Antarctica. In 2009, it was revealed that Lake Cook is the most hydrologically active subglacial lake on the Antarctic continent. Other satellite imagery has been used to monitor and investigate this lake, including ICESat , CryoSat-2 ,

SECTION 10

#1733084660099

1152-685: Is Lake Vostok with other lakes notable for their size being Lake Concordia and Aurora Lake. An increasing number of lakes are also being identified near ice streams. An altimeter survey by the ERS-2 satellite orbiting the East Antarctic Ice Sheet from 1995 to 2003 indicated clustered anomalies in ice sheet elevation indicating that the East Antarctic lakes are fed by a subglacial system that transports basal meltwater through subglacial streams . The largest Antarctic subglacial lakes are clustered in

1248-694: Is an ice-scoured tidal inlet with a maximum depth of 722 feet (220 m). The narrow entrance of the bay has a depth of only 33 feet (10 m). The two arms that create the top of the T-shape of the bay are the Gilbert and Crillon inlets and are a part of a trench on the Fairweather Fault. In the past 170 years Lituya Bay has had four tsunamis over 100 ft (30 m): 1854 (395 ft or 120 m), 1899 (200 ft or 60 m), 1936 (490 ft or 150 m), and 1958 (1,720 ft or 520 m). Near

1344-858: Is based on a small number of samples, mostly from Antarctica. Inferences about solute concentrations, chemical processes, and biological diversity of unsampled subglacial lakes have also been drawn from analyses of accretion ice (re-frozen lake water) at the base of the overlying glaciers. These inferences are based on the assumption that accretion ice will have similar chemical signatures as the lake water that formed it. Scientists have thus far discovered diverse chemical conditions in subglacial lakes, ranging from upper lake layers supersaturated in oxygen to bottom layers that are anoxic and sulfur-rich. Despite their typically oligotrophic conditions, subglacial lakes and sediments are thought to contain regionally and globally significant amounts of nutrients, particularly carbon. Air clathrates trapped in glacial ice are

1440-455: Is created when the ice is so much higher around the lake that the equipotential surface dips down into impermeable ground. Water from underneath this ice rim is then pressed back into the lake by the hydrostatic seal. The ice rim in Lake Vostok has been estimated to a mere 7 meters, while the floating level is about 3 kilometers above the lake ceiling. If the hydrostatic seal is penetrated when

1536-402: Is equivalent to the level at which a piece of ice over it would float if it were a normal ice shelf . The ceiling can therefore be conceived as an ice shelf that is grounded along its entire perimeter, which explains why it has been called a captured ice shelf . As it moves over the lake, it enters the lake at the floating line, and it leaves the lake at the grounding line. A hydrostatic seal

1632-401: Is found under a glacier , typically beneath an ice cap or ice sheet . Subglacial lakes form at the boundary between ice and the underlying bedrock , where liquid water can exist above the lower melting point of ice under high pressure. Over time, the overlying ice gradually melts at a rate of a few millimeters per year. Meltwater flows from regions of high to low hydraulic pressure under

1728-464: Is known in downstream areas where ice streams are known to migrate, accelerate or stagnate on centennial time scales and highlights that subglacial water may be discharged over the ice sheet grounding line. Russian revolutionary and scientist Peter A. Kropotkin first proposed the idea of liquid freshwater under the Antarctic Ice Sheet at the end of the 19th century. He suggested that due to

1824-755: Is mainly carried out by chemolithoautotrophic microbes. Like plants, chemolithoautotrophs fix carbon dioxide (CO 2 ) into new organic carbon, making them the primary producers at the base of subglacial lake food webs. Rather than using sunlight as an energy source, chemolithoautotrophs get energy from chemical reactions in which inorganic elements from the lithosphere are oxidized or reduced . Common elements used by chemolithoautotrophs in subglacial ecosystems include sulfide , iron , and carbonates weathered from sediments. In addition to mobilizing elements from sediments, chemolithoautotrophs create enough new organic matter to support heterotrophic bacteria in subglacial ecosystems. Heterotrophic bacteria consume

1920-436: Is of particular interest to scientists studying astrobiology , as well as the history and limits of life on Earth. In most surface ecosystems, photosynthetic plants and microbes are the main primary producers that form the base of the lake food web . Photosynthesis is impossible in the permanent darkness of subglacial lakes, so these food webs are instead driven by chemosynthesis . In subglacial ecosystems, chemosynthesis

2016-880: Is only one order of magnitude smaller than the amount of organic carbon in all surface freshwaters (5.10 x 10 petagrams). This relatively smaller, but potentially more reactive, reservoir of subglacial organic carbon may represent another gap in scientists’ understanding of the global carbon cycle . Subglacial lakes were originally assumed to be sterile , but over the last thirty years, active microbial life and signs of higher life have been discovered in subglacial lake waters, sediments, and accreted ice. Subglacial waters are now known to contain thousands of microbial species, including bacteria , archaea , and potentially some eukaryotes . These extremophilic organisms are adapted to below-freezing temperatures, high pressure, low nutrients, and unusual chemical conditions. Researching microbial diversity and adaptations in subglacial lakes

SECTION 20

#1733084660099

2112-624: Is perhaps the best known subglacial lake beneath the Vatnajökull ice cap. Other lakes beneath the ice cap lie within the Skatfá, Pálsfjall and Kverkfjöll cauldrons. Notably, subglacial lake Grímsvötn's hydraulic seal remained intact until 1996, when significant meltwater production from the Gjálp eruption resulted in uplift of Grímsvötn's ice dam. The Mýrdalsjökull ice cap, another key subglacial lake location, sits on top of an active volcano- caldera system in

2208-432: Is slow. Oxic or slightly suboxic waters often reside near the glacier-lake interface, while anoxia dominates in the lake interior and sediments due to respiration by microbes. In some subglacial lakes, microbial respiration may consume all of the oxygen in the lake, creating an entirely anoxic environment until new oxygen-rich water flows in from connected subglacial environments. The addition of oxygen from ice melt and

2304-467: Is suspected that there is a possibility of more. Subglacial lakes have also been discovered in Greenland, Iceland, and northern Canada. Scientific advances in Antarctica can be attributed to several major periods of collaboration and cooperation, such as the four International Polar Years (IPY) in 1882-1883, 1932-1933, 1957-1958, and 2007-2008. The success of the 1957-1958 IPY led to the establishment of

2400-536: Is the largest and most significant megatsunami in modern times; it forced a re-evaluation of large-wave events and the recognition of impact events , rockfalls , and landslides as causes of very large waves. Lituya Bay is a fjord located on the Fairweather Fault in the northeastern part of the Gulf of Alaska . It is a T-shaped bay with a width of 2 miles (3 km) and a length of 7 miles (11 km). Lituya Bay

2496-536: Is unclear. Certainly on the Greenland Ice Sheet subglacial water acts to enhance basal ice motion in a complex manner. The "Recovery Lakes" beneath Antarctica's Recovery Glacier lie at the head of a major ice stream and may influence the dynamics of the region. A modest (10%) speed up of Byrd Glacier in East Antarctica may have been influenced by a subglacial drainage event. The flow of subglacial water

2592-483: The Advanced Spaceborne Thermal Emission and Reflection Radiometer , and SPOT5 . Gray et al. (2005) interpreted ice surface slumping and raising from RADARSAT data as evidence for subglacial lakes filling and emptying - termed "active" lakes. Wingham et al. (2006) used radar altimeter (ERS-1) data to show coincident uplift and subsidence, implying drainage between lakes. NASA's ICESat satellite

2688-549: The American Geophysical Union Chapman Conference in Baltimore. The conference allowed engineers and scientists to discuss the equipment and strategies used in ice drilling projects, such as the design of hot-water drills, equipment for water measurement and sampling and sediment recovery, and protocols for experimental cleanliness and environmental stewardship . Following this meeting, SCAR drafted

2784-469: The Antarctic Ice Sheet have accumulated an estimated ~21,000 petagrams of organic carbon, most of which comes from ancient marine sediments. This is more than 10 times the amount of organic carbon contained in Arctic permafrost and may rival the amount of reactive carbon in modern ocean sediments, potentially making subglacial sediments an important but understudied component of the global carbon cycle . In

2880-597: The Cape Yakataga earthquake on September 3, 1899, which was estimated to be magnitude 8.2 on the Richter scale. The shock was felt in southeastern Alaskan cities over an area of 400,000 square miles (1,000,000 km ), as far south as Seattle , Washington, and as far east as Whitehorse, Yukon , Canada. The earthquake caused a subaerial rockfall in the Gilbert Inlet. Over 30 million cubic meters of rock fell from

2976-423: The Fairweather Fault and triggered a rockslide of 30 million cubic meters (40 million cubic yards) and about 90 million tons into the narrow inlet of Lituya Bay , Alaska. The impact was heard 80 kilometers (50 mi) away, and the sudden displacement of water resulted in a megatsunami that washed out trees to a maximum elevation of 524 meters (1,719 feet) at the entrance of Gilbert Inlet. This

Lituya Glacier - Misplaced Pages Continue

3072-579: The Scientific Committee on Antarctic Research (SCAR) and the Antarctic Treaty System , paving the way to formulate a better methodology and process to observe subglacial lakes. In 1959 and 1964, during two of his four Soviet Antarctic Expeditions , Russian geographer and explorer Andrey P. Kapitsa used seismic sounding to prepare a profile of the layers of the geology below Vostok Station in Antarctica. The original intent of this work

3168-565: The Subglacial Antarctic Lakes Scientific Access (SALSA) team announced they had reached Lake Mercer after melting their way through 1,067 m (3,501 ft) of ice with a high-pressure hot-water drill. The team collected water samples and bottom sediment samples down to 6 meters deep. The majority of the nearly 400 Antarctic subglacial lakes are located in the vicinity of ice divides , where large subglacial drainage basins are overlain by ice sheets. The largest

3264-473: The geothermal heating at the bottom of the ice sheets, the temperature beneath the ice could reach the ice melt temperature, which would be below zero. The notion of freshwater beneath ice sheets was further advanced by Russian glaciologist Igor A. Zotikov , who demonstrated via theoretical analysis the possibility of a decrease in Antarctic ice because of melting of ice at a lower surface. As of 2019, there are over 400 subglacial lakes in Antarctica , and it

3360-594: The limiting nutrient that constrains growth in the ecosystem, although co-limitation by both nitrogen and phosphorus supply seems most common. However, evidence from subglacial Lake Whillans suggests that nitrogen is the limiting nutrient in some subglacial waters, based on measurements showing that the ratio of nitrogen to phosphorus is very low compared to the Redfield ratio . An experiment showed that bacteria from Lake Whillans grew slightly faster when supplied with phosphorus as well as nitrogen, potentially contradicting

3456-460: The sediment on the floor of the bay, creating a large crater. The study concluded that: The giant wave runup of 1,720 feet (520 m) at the head of the Bay and the subsequent huge wave along the main body of Lituya Bay which occurred on July 9, 1958, were caused primarily by an enormous subaerial rockfall into Gilbert Inlet at the head of Lituya Bay, triggered by dynamic earthquake ground motions along

3552-599: The Antarctic Ice Sheet took place again between 1971–1979. During this time, a US-UK-Danish collaboration was able to survey about 40% of East Antarctica and 80% of West Antarctica – further defining the subglacial landscape and the behavior of ice flow over the lakes. In the early 1990s, radar altimeter data from the European Remote-Sensing Satellite (ERS-1) provided detailed mapping of Antarctica through 82 degrees south. This imaging revealed

3648-729: The Dome C-Vostok area of East Antarctica, possibly due to the thick insulating ice and rugged, tectonically influenced subglacial topography . In West Antarctica , subglacial Lake Ellsworth is situated within the Ellsworth Mountains and is relatively small and shallow. The Siple Coast Ice Streams, also in West Antarctica, overlie numerous small subglacial lakes, including Lakes Whillans , Engelhardt , Mercer , Conway , accompanied by their lower neighbours called Lower Conway (LSLC) and Lower Mercer (LSLM). Glacial retreat at

3744-462: The Fairweather Fault. The large mass of rock, acting as a monolith (thus resembling high-angle asteroid impact), struck with great force the sediments at bottom of Gilbert Inlet at the head of the bay. The impact created a large crater and displaced and folded recent and Tertiary deposits and sedimentary layers to an unknown depth. The displaced water and the displacement and folding of the sediments broke and uplifted 1,300 feet (400 meters) of ice along

3840-516: The available methane. There is also evidence for active methane production and consumption beneath the Greenland Ice Sheet . Antarctic subglacial waters are also thought to contain substantial amounts of organic carbon in the form of dissolved organic carbon and bacterial biomass. At an estimated 1.03 x 10 petagrams, the amount of organic carbon in subglacial lake waters is far smaller than that contained in Antarctic subglacial sediments, but

3936-450: The base of the ice sheet through the storage of supraglacial meltwater, is thought to influence the rate of ice flow and overall behavior of the Greenland Ice Sheet. Much of Iceland is volcanically active, resulting in significant meltwater production beneath its two ice caps . This meltwater also accumulates in basins and ice cauldrons, forming subglacial lakes. These lakes act as a transport mechanism for heat from geothermal vents to

Lituya Glacier - Misplaced Pages Continue

4032-405: The bay, and the additional energy of waves, especially at the western end of the bay. The paper's authors suggest that core samples may show a 70-meter (230-foot) deep layer of reworked sediment if this model is correct. 58°38′33″N 137°33′54″W  /  58.64250°N 137.56500°W  / 58.64250; -137.56500 Subglacial lake A subglacial lake is a lake that

4128-399: The bay. Four or five megatsunamis are believed to have occurred at Lituya Bay during a 150-year period: There is an ongoing debate in scholarly circles regarding whether the megatsunami was a result of the rockfall generated by the earthquake, or a result of the earthquake itself. Various analyses to determine the true cause have been conducted. The mechanism giving rise to megatsunamis

4224-644: The bottom of the ice caps, which often results in melting of basal ice that replenishes any water lost from drainage. The majority of Icelandic subglacial lakes are located beneath the Vatnajökull and Mýrdalsjökull ice caps, where melting from hydrothermal activity creates permanent depressions that fill with meltwater. Catastrophic drainage from subglacial lakes is a known hazard in Iceland, as volcanic activity can create enough meltwater to overwhelm ice dams and lake seals and cause glacial outburst flooding . Grímsvötn

4320-936: The cold temperatures in subglacial lakes, which slow down microbial metabolism and reaction rates. The variable redox conditions and diverse elements available from sediments provide opportunities for many other metabolic strategies in subglacial lakes. Other metabolisms used by subglacial lake microbes include methanogenesis , methanotrophy , and chemolithoheterotrophy , in which bacteria consume organic matter while oxidizing inorganic elements. Some limited evidence for microbial eukaryotes and multicellular animals in subglacial lakes could expand current ideas of subglacial food webs. If present, these organisms could survive by consuming bacteria and other microbes. Subglacial lake waters are considered to be ultra- oligotrophic and contain low concentrations of nutrients , particularly nitrogen and phosphorus . In surface lake ecosystems, phosphorus has traditionally been thought of as

4416-400: The consumption of ancient organic carbon deposited before glaciation. Nutrients can enter subglacial lakes through the glacier ice-lake water interface, from hydrologic connections, and from the physical, chemical, and biological weathering of subglacial sediments . Since few subglacial lakes have been directly sampled, much of the existing knowledge about subglacial lake biogeochemistry

4512-460: The consumption of oxygen by microbes may create redox gradients in the subglacial lake water column, with aerobic microbial mediated processes like nitrification occurring in the upper waters and anaerobic processes occurring in the anoxic bottom waters. Concentrations of solutes in subglacial lakes, including major ions and nutrients like sodium , sulfate , and carbonates , are low compared to typical surface lakes. These solutes enter

4608-576: The crest of the Fairweather Mountains sit the Lituya and the North Crillon glaciers. They are each about 12 miles (19 km) long and 1 mile (1.6 km) wide with an elevation of 4,000 feet (1,200 m). The retreats of these glaciers form the present "T" shape of the bay, the Gilbert and Crillon inlets. The major earthquake that struck on the Fairweather Fault had a moment magnitude of 7.8 and

4704-423: The earthquake hit, the resulting rocking of his boat woke Ulrich up. He observed the wave's formation from the deck, hearing a very loud smash at the base of Lituya Bay. In his record of the wave he notes the appearance of it and how it formed: The wave definitely started in Gilbert Inlet, just before the end of the quake. It was not a wave at first. It was like an explosion, or a glacier sluff. The wave came out of

4800-430: The energy and height of the waves. Scientists concluded that there had been a "dual slide" involving a rockfall which also triggered a release of 5 to 10 times its volume of sediment trapped by the adjacent Lituya Glacier, a ratio comparable with other events where this "dual slide" effect is known to have happened. Lituya Bay has a history of megatsunami events, but the 1958 event was the first for which sufficient data

4896-524: The entire crustal block on which Lituya Bay was situated, generated the giant solitary gravity wave which swept the main body of the bay. This was the most likely scenario of the event – the "PC model" that was adopted for subsequent mathematical modeling studies with source dimensions and parameters provided as input. Subsequent mathematical modeling at the Los Alamos National Laboratory ( Mader , 1999, Mader & Gittings, 2002) supported

SECTION 50

#1733084660099

4992-464: The entire front of the Lituya Glacier at the north end of Gilbert Inlet. Also, the impact and the sediment displacement by the rockfall resulted in an air bubble and in water splashing action that reached the 1,720-foot (520 m) elevation on the other side of the head of Gilbert Inlet. The same rockfall impact, in combination with the strong ground movements, the net vertical crustal uplift of about 3.5 feet [1.1 meters], and an overall tilting seaward of

5088-501: The event of ice sheet collapse , subglacial organic carbon could be more readily respired and thus released to the atmosphere and create a positive feedback on climate change . The microbial inhabitants of subglacial lakes likely play an important role in determining the form and fate of sediment organic carbon. In the anoxic sediments of subglacial lake ecosystems, organic carbon can be used by archaea for methanogenesis , potentially creating large pools of methane clathrate in

5184-401: The famous SPRI-NSF-TUD surveys undertaken until the mid-seventies. Since this original compilation several smaller surveys has discovered many more subglacial lakes throughout Antarctica, notably by Carter et al. (2007), who identified a spectrum of subglacial lake types based on their properties in (RES) datasets. In March 2010, the sixth international conference on subglacial lakes was held at

5280-791: The first time. Lake water flooded the borehole and froze during the winter season, and the sample of re-frozen lake water (accretion ice) was recovered in the following summer season of 2013. In December 2012, scientists from the UK attempted to access Lake Ellsworth with a clean access hot-water drill; however, the mission was called off because of equipment failure. In January 2013, the US-led Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) expedition measured and sampled Lake Whillans in West Antarctica for microbial life. On 28 December 2018,

5376-598: The floating level is high, the water will start flowing out in a jökulhlaup . Due to melting of the channel the discharge increases exponentially, unless other processes allow the discharge to increase even faster. Due to the high hydraulic head that can be achieved in some subglacial lakes, jökulhlaups may reach very high rates of discharge. Catastrophic drainage from subglacial lakes is a known hazard in Iceland, as volcanic activity can create enough meltwater to overwhelm ice dams and lake seals and cause glacial outburst flooding . The role of subglacial lakes on ice dynamics

5472-540: The glacial lake through a glacial tunnel flowing directly in front of the glacier, though neither the rate of drainage nor the volume of water drained could produce a wave of such magnitude. Even if a large enough drainage were to take place in front of the Gilbert Glacier, the run-off would have been projected to be on the opposite side in Crillon Inlet. After these considerations it was determined that glacial drainage

5568-500: The ice and pools, creating a body of liquid water that can be isolated from the external environment for millions of years. Since the first discoveries of subglacial lakes under the Antarctic Ice Sheet , more than 400 subglacial lakes have been discovered in Antarctica , beneath the Greenland Ice Sheet , and under Iceland 's Vatnajökull ice cap. Subglacial lakes contain a substantial proportion of Earth's liquid freshwater , with

5664-402: The ice surface at around x10 of the surface slope angle, as this is required for hydrostatic stability. In the late 1960s, they were able to mount RES instruments on aircraft and acquire data for the Antarctic Ice Sheet. Between 1971 and 1979, the Antarctic Ice Sheet was profiled extensively using RES equipment. The technique of using RES is as follows: 50-meter deep holes are drilled to increase

5760-492: The ice-sheet base, stronger than adjacent ice- bedrock reflections; 2) echoes of constant strength occurring along the track, which indicate that the surface is very smooth; and 3) a very flat and horizontal character with slopes less than 1%. Using this approach, 17 subglacial lakes were documented by Kapista and his team. RES also led to the discovery of the first subglacial lake in Greenland and revealed that these lakes are interconnected. Systematic profiling, using RES, of

5856-629: The last glacial period had been identified in Canada. These paleo-subglacial lakes likely occupied valleys created before the advance of the Laurentide Ice Sheet during the Last Glacial Maximum . However, two subglacial lakes were identified via RES in bedrock troughs under the Devon Ice Cap of Nunavut, Canada. These lakes are thought to be hypersaline as a result of interaction with

SECTION 60

#1733084660099

5952-419: The layer of glacial ice above the subglacial lake also supplies underlying waters with iron , nitrogen , and phosphorus -containing minerals , in addition to some dissolved organic carbon and bacterial cells. Because air clathrates from melting glacial ice are the primary source of oxygen to subglacial lake waters, the concentration of oxygen generally decreases with depth in the water column if turnover

6048-557: The level where the pressure melting point of water intersects with the temperature gradient. In Lake Vostok , the largest Antarctic subglacial lake, the ice over the lake is thus much thicker than the ice sheet around it. Hypersaline subglacial lakes remain liquid due to their salt content. Not all lakes with permanent ice cover can be called subglacial, as some are covered by regular lake ice. Some examples of perennially ice-covered lakes include Lake Bonney and Lake Hoare in Antarctica's McMurdo Dry Valleys as well as Lake Hodgson ,

6144-494: The lower part, and looked like the smallest part of the whole thing. The wave did not go up 1,800 feet, the water splashed there. The wave made its way to his boat 2–3 minutes after he saw it and carried the Edrie down to the southern shore and then back near the center of the bay. Ulrich was able to control the boat once the main wave passed, maneuvering through subsequent waves up to 20 ft high until he could finally exit

6240-486: The main source of oxygen entering otherwise enclosed subglacial lake systems. As the bottom layer of ice over the lake melts, clathrates are freed from the ice's crystalline structure and gases such as oxygen are made available to microbes for processes like aerobic respiration . In some subglacial lakes, freeze-melt cycles at the lake-ice interface may enrich the upper lake water with oxygen concentrations that are 50 times higher than in typical surface waters. Melting of

6336-523: The margins of the Antarctic Ice Sheet has revealed several former subglacial lakes, including Progress Lake in East Antarctica and Hodgson Lake on southern Alexander Island near the Antarctic Peninsula . The existence of subglacial lakes beneath the Greenland Ice Sheet has only become evident within the last decade. Radio-echo sounding measurements have revealed two subglacial lakes in

6432-447: The megatsunami was caused by a massive and sudden impulsive impact when about 40 million cubic yards of rock several hundred meters above the bay was fractured from the side of the bay, by the earthquake, and fell "practically as a monolithic unit" down the almost vertical slope and into the bay. The rockfall also caused air to be dragged along due to viscosity effects, which added to the volume of displacement, and further impacted

6528-526: The north glacier, the one they call Lituya Glacier. I know you can't ordinarily see that glacier from where I was anchored. People shake their heads when I tell them I saw it that night. I can't help it if they don't believe me. I know the glacier is hidden by the point when you're in Anchorage Cove, but I know what I saw that night, too. The glacier had risen in the air and moved forward so it was in sight. It must have risen several hundred feet. I don't mean it

6624-489: The northern and southern edges. The megatsunami flooded the entire bay and created a damage line up to 213 m (699 ft) around the outline of the bay, with evidence of this damage line still visible from space to this day. At 22:15 hours PST on July 9, 1958, which was still daylight at that time of year, an earthquake with a magnitude of 7.8 struck the Lituya Bay area. The tide was ebbing at about plus 1.5 m and

6720-435: The northwest section of the ice sheet. These lakes are likely recharged with water from the drainage of nearby supraglacial lakes rather than from melting of basal ice. Another potential subglacial lake has been identified near the southwestern margin of the ice sheet, where a circular depression beneath the ice sheet evidences recent drainage of the lake caused by climate warming. Such drainage, coupled with heat transfer to

6816-412: The organic material produced by chemolithoautotrophs, as well as consuming organic matter from sediments or from melting glacial ice. Despite the resources available to subglacial lake heterotrophs, these bacteria appear to be exceptionally slow-growing, potentially indicating that they dedicate most of their energy to survival rather than growth. Slow heterotrophic growth rates could also be explained by

6912-787: The overlying glacier, after which these sulfides are oxidized to sulfate by aerobic or anaerobic bacteria, which can use iron for respiration when oxygen is unavailable. The products of sulfide oxidation can enhance the chemical weathering of carbonate and silicate minerals in subglacial sediments, particularly in lakes with long residence times. Weathering of carbonate and silicate minerals from lake sediments also releases other ions including potassium (K ), magnesium (Mg ), sodium (Na ), and calcium (Ca ) to lake waters. Other biogeochemical processes in anoxic subglacial sediments include denitrification , iron reduction , sulfate reduction , and methanogenesis (see Reservoirs of organic carbon below). Subglacial sedimentary basins under

7008-417: The potential to change their hydrology and circulation patterns. Areas with the thickest overlying ice experience greater rates of melting. The opposite occurs in areas where the ice sheet is thinnest, which allows re-freezing of lake water to occur. These spatial variations in melting and freezing rates lead to internal convection of water and circulation of solutes, heat, and microbial communities throughout

7104-416: The production of the 100 ft (30 m) wave which caused destruction as high as 1,720 ft (520 m) above the surface of the bay as its momentum carried it upslope. The wave caused damage to the vegetation up the headlands around the area where the rockfall occurred, up to a height of 524 meters, as well as along the shoreline of the bay. It is possible that a good amount of water drained from

7200-417: The proposed mechanism – as there was indeed sufficient volume of water and an adequately deep layer of sediments in the Lituya Bay inlet to account for the giant wave runup and the subsequent inundation. The modeling reproduced the documented physical observations of runup. A 2010 model examined the amount of infill on the floor of the bay, which was many times larger than that of the rockfall alone, as well as

7296-465: The rockfall and sediment disturbed by it, and the energy of the resulting waves from the rockfall and stirred-up sediment would not have been sufficient. The study concluded that, instead, a "dual slide" event was more likely – the rockfall, impacting very close to the head of the Lituya Glacier , caused around 400 meters (1,300 feet) of ice from the glacial toe to break off (as shown in photographs from

7392-531: The sediments that could be released during ice sheet collapse or when lake waters drain to ice sheet margins. Methane has been detected in subglacial Lake Whillans, and experiments have shown that methanogenic archaea can be active in sediments beneath both Antarctic and Arctic glaciers. Most of the methane that escapes storage in subglacial lake sediments appears to be consumed by methanotrophic bacteria in oxygenated upper waters. In subglacial Lake Whillans, scientists found that bacterial oxidation consumed 99% of

7488-428: The signal-to-noise ratio in the ice. A small explosion sets off a sound wave , which travels through the ice. This sound wave is reflected and then recorded by the instrument. The time it takes for the wave to travel down and back is noted and converted to a distance using the known speed of sound in ice. RES records can identify subglacial lakes via three specific characteristics: 1) an especially strong reflection from

7584-608: The southernmost part of the Katla volcanic system . Hydrothermal activity beneath the Mýrdalsjökull ice cap is thought to have created at least 12 small depressions within an area constrained by three major subglacial drainage basins . Many of these depressions are known to contain subglacial lakes that are subject to massive, catastrophic drainage events from volcanic eruptions, creating a significant hazard for nearby human populations. Until very recently, only former subglacial lakes from

7680-524: The subglacial lake reservoir. Longer residence times, such as those found beneath the interior Antarctic Ice Sheet, would lead to greater contact time between the water and solute sources, allowing for greater accumulation of solutes than in lakes with shorter residence times. Estimated residence times of currently studied subglacial lakes range from about 13,000 years in Lake Vostok to just decades in Lake Whillans. The morphology of subglacial lakes has

7776-403: The subglacial lake, which will vary among subglacial lakes of different regions. Subglacial sediments are primarily composed of glacial till that formed during physical weathering of subglacial bedrock . Anoxic conditions prevail in these sediments due to oxygen consumption by microbes, particularly during sulfide oxidation . Sulfide minerals are generated by weathering of bedrock by

7872-412: The sun. Subglacial lakes and their inhabitants are of particular interest in the field of astrobiology and the search for extraterrestrial life . The water in subglacial lakes remains liquid since geothermal heating balances the heat loss at the ice surface. The pressure from the overlying glacier causes the melting point of water to be below 0 °C. The ceiling of the subglacial lake will be at

7968-445: The time), and possibly injected considerable water under the glacier. The glacier, lightened, rose before stabilizing in the water, and a large amount of trapped infill (subglacial and proglacial sediment) that was trapped under the glacier and had already been loosened by the earthquake was released as an almost immediate and many times larger second slide. The debris released was estimated by the study as being between 5 and 10 times

8064-611: The underlying salt-bearing bedrock, and are much more isolated than the few identified saline subglacial lakes in Antarctica. Unlike surface lakes, subglacial lakes are isolated from Earth's atmosphere and receive no sunlight. Their waters are thought to be ultra- oligotrophic , meaning they contain very low concentrations of the nutrients necessary for life. Despite the cold temperatures, low nutrients, high pressure, and total darkness in subglacial lakes, these ecosystems have been found to harbor thousands of different microbial species and some signs of higher life. Professor John Priscu ,

8160-492: The volume of Antarctic subglacial lakes alone estimated to be about 10,000 km , or about 15% of all liquid freshwater on Earth. As ecosystems isolated from Earth's atmosphere , subglacial lakes are influenced by interactions between ice , water , sediments , and organisms . They contain active biological communities of extremophilic microbes that are adapted to cold, low- nutrient conditions and facilitate biogeochemical cycles independent of energy inputs from

8256-562: The volume of the initial rockfall, a bulking ratio comparable with that of other events such as the September 2002 Kolka-Karmadon rock ice slide (estimated ratio between 5 and 10), the November 1987 Parraguirre landslide (est. ratio 2.5) and the May 1970 Huascarán landslide (est. ratio 4). This additional volume would explain the large changes in the underwater shape of the sea floor in

8352-479: The water column from glacial ice melting and from sediment weathering. Despite their low solute concentrations, the large volume of subglacial waters make them important contributors of solutes, particularly iron, to their surrounding oceans. Subglacial outflow from the Antarctic Ice Sheet , including outflow from subglacial lakes, is estimated to add a similar amount of solutes to the Southern Ocean as some of

8448-407: The weather was clear. Anchored in a cove near the west side of the entrance of the bay, Bill and Vivian Swanson were on their boat fishing when the earthquake hit: With the first jolt, I tumbled out of the bunk and looked toward the head of the bay where all the noise was coming from. The mountains were shaking something awful, with slide of rock and snow, but what I noticed mostly was the glacier,

8544-481: The world's largest rivers. The subglacial water column is influenced by the exchange of water between lakes and streams under ice sheets through the subglacial drainage system; this behavior likely plays an important role in biogeochemical processes, leading to changes in microbial habitat, particularly regarding oxygen and nutrient concentrations. Hydrologic connectivity of subglacial lakes also alters water residence times , or amount of time that water stays within

8640-401: Was a big wall of water going over the point. The wave started for us right after that and I was too busy to tell what else was happening up there. When the earthquake struck, Howard G. Ulrich and his 7-year-old son were in Lituya Bay aboard their boat, the Edrie. They were anchored in a small inlet on the southern side of the bay. The two had gone out on the water at 20:00 hours PST and when

8736-524: Was analyzed for the Lituya Bay event in a study presented at the Tsunami Society in 1999. Although the earthquake which caused the megatsunami was very energetic and involved strong ground movements, several possible mechanisms were not likely or able to have caused the resulting megatsunami. Neither water drainage from a lake, nor landslide, nor the force of the earthquake itself led to the megatsunami, although all of these may have contributed. Instead,

8832-418: Was captured and was responsible for the deaths of 5 people. A subsequent analysis to the 1999 one that examined the wider impact of the event found that the rockfall itself was inadequate to explain the resulting accounts and evidence. In particular, the amount of sediment apparently added to the bay, judging by the sea-floor shape, was much greater than could be explained by the rockfall alone, or even

8928-442: Was just hanging in the air. It seems to be solid, but it was jumping and shaking like crazy. Big chunks of ice were falling off the face of it and down into the water. That was six miles away and they still looked like big chunks. They came off the glacier like a big load of rocks spilling out of a dump truck. That went on for a little while—it's hard to tell just how long—and then suddenly the glacier dropped back out of sight and there

9024-496: Was key in developing this concept further and subsequent work demonstrated the pervasiveness of this phenomenon. ICESat ceased measurements in 2007 and the detected "active" lakes were compiled by Smith et al. (2009) who identified 124 such lakes. The realisation that lakes were interconnected created new contamination concerns for plans to drill into lakes ( see the Sampling expeditions section below ). Several lakes were delineated by

9120-483: Was not the mechanism that caused the giant wave. The Lituya Bay megatsunami caused damage at higher elevations than any other tsunami, being powerful enough to push water up the tree covered slopes of the fjord with enough force to clear trees to a reported height of 524 m (1,719 ft). A 1:675 recreation of the tsunami found the wave crest was 150 m (490 ft) tall. Five people were killed, many people were injured, and many homes destroyed. Two people on

9216-472: Was to conduct a broad survey of the Antarctic Ice Sheet. The data collected on these surveys, however, was used 30 years later and led to the discovery of Lake Vostok as a subglacial lake. Beginning in the late 1950s, English physicists Stan Evans and Gordon Robin began using the radioglaciology technique of radio-echo sounding (RES) to chart ice thickness. Subglacial lakes are identified by (RES) data as continuous and specular reflectors which dip against

#98901