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54-413: Fortuna Glacier is a tidewater glacier at the mouth of Cumberland Bay on the island of South Georgia . It flows in a northeast direction to its terminus just west of Cape Best , with an eastern distributary almost reaching the west side of Fortuna Bay , on the north coast of South Georgia. It was named in about 1912, presumably after the whale catcher Fortuna , and is notable for two major events in

108-406: A 'calving law'. Variables used in models include properties of the ice such as thickness, density, temperature , c-axis fabric , and impurity loading. A property known as 'ice front normal spreading stress' may be of key importance, despite it not normally being measured. There are currently several concepts upon which to base a predictive law. One theory states that the calving rate is primarily

162-446: A first-order control on the advance/retreat cycle of calving glaciers during most of the advance retreat cycle, but there are climate insensitive periods as well. Pelto (1987) examined the terminus behavior of 90 Alaskan glaciers and found that the terminus behavior of all 90 were correctly predicted based on the AAR and calving rate. If we begin at the stable retracted position at the end of

216-400: A full mile across a calving face three miles (five kilometers) wide. Adam LeWinter and Jeff Orlowski captured this footage, which is featured in the film Chasing Ice . First conceived in 1995 by Ryan Casey while filming for IMAX , this sport involves a surfer being towed into range by a jet ski and waiting for a mass of ice to calve from a glacier. Surfers can wait for several hours in

270-514: A function of the ratio of tensile stress to vertical compressive stress, i.e., the calving rate is a function of the ratio of the largest to smallest principle stress. Another theory, based on preliminary research, shows that the calving rate increases as a power of the spreading rate near the calving front. In October, 1988, the A-38 iceberg broke away from the Filchner-Ronne Ice Shelf. It

324-466: A glacier, AAR, is the percentage of a glacier that is a snow-covered accumulation zone at the end of the summer melt season. This percentage for large Alaskan glaciers is between 60 and 70 for non-calving glaciers, 70-80 for moderately calving glaciers and up to 90 for very high calving rate glaciers. By using accumulation area ratio (AAR) data for Alaskan tidewater calving glaciers, Pelto (1987) and Viens (1995) produced models showing that climate acts as

378-474: A glacier, above which snow accumulates faster than it ablates, and below which, the reverse is the case. This altitude shift, in turn, prompts a retreat or advance of the terminus toward a new steady-state position. However, this change in terminus behavior for calving glaciers is also a function of resulting changes in fjord geometry, and calving rate at the glacier terminus as it changes position. Calving glaciers are different from land terminating glaciers in

432-400: A land terminating glacier to offset this higher loss from calving. The calving rate is largely controlled by the depth of the water and the glacier velocity at the calving front. The process of calving provides an imbalance in forces at the front of the glaciers, that raises velocity. The depth of the water at the glacier front is a simple measure that allows estimation of calving rate, but is

486-543: A loud cracking or booming sound before blocks of ice up to 60 metres (200 ft) high break loose and crash into the water. The entry of the ice into the water causes large, and often hazardous waves. The waves formed in locations like Johns Hopkins Glacier can be so large that boats cannot approach closer than three kilometres ( 1 + 1 ⁄ 2 nautical miles). These events have become major tourist attractions in locations such as Alaska . Many glaciers terminate at oceans or freshwater lakes which results naturally with

540-424: A major retreat of 8.5 km in those 25 years as a result of rapid thinning [1] . At some point the glacier reaches a pinning point where calving is reduced due to a fjord narrowing or shoaling and the glacier's AAR is near 100. This is occurring with LeConte Glacier and Yahtse Glacier . Le Conte Glacier currently has an AAR of 90, is at a retracted position and seems likely to be set to advance after building

594-493: A reduced rate of 37 m⋅a . In 1990, the Taku Glacier's AAR was 82 high enough, to prompt Pelto and Miller to conclude that the Taku Glacier would continue to advance for the remaining decade of the 20th century. From 1986 to 2005, the equilibrium line altitude on the glacier rose without a significant terminus shift causing the AAR to decline to about 72. Pelto and Miller concluded that the current reduction in rate of advance

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648-460: A terminus shoal. The drop in calving rate allows the glacier to reestablish equilibrium. The Taku Glacier provides a good example of this cycle. It was at its maximum extent near 1750. At this point it had closed off Taku Inlet . Subsequently, calving retreat commenced. By the time John Muir saw the glacier in 1890, it was near its minimum extent, at a location where the fjord narrowed, with deep water in front. About 1900, its AAR of 90 led to

702-408: A tidewater glacier cycle the glacier will have a moderate calving rate and a high AAR, above 70. The glacier will build a terminus shoal of sediment further reducing the calving rate. This will improve the glacier mass balance and the glacier can begin to advance due to this change or an increase in ice flux to the terminus due to increasing snowfall or reduced snow melt. As the advance proceeds

756-454: Is a calving coefficient (27.1±2 a ), H w {\displaystyle H_{w}} is the mean water depth at glacier front (m) and D {\displaystyle D} is a constant (0 m⋅a ). Pelto and Warren (1991) found a similar calving relationship with tidewater glaciers observed over longer time periods, with slightly reduced calving rate to the mainly summer rates noted by Brown et al. (1982). Calving

810-586: Is an important form of ablation for glaciers that terminate in freshwater , also. Funk and Röthlisberger determined a relationship between calving speed and water depth based on analysis of six glaciers that calve into lakes. They found that the same basic calving relationship developed for tidewater calving glaciers was true for freshwater calving glaciers, only the calving coefficients led to calving rates 10% of that for tidewater glaciers. Observations of Alaskan tidewater calving glaciers prompted Austin Post to describe

864-541: Is defined, whereby upward buoyant forces cause this ice foot to break off and emerge at the surface. This process is extremely dangerous, as it has been known to occur, without warning, up to 300 m (980 ft) from the glacier terminus. Though many factors that contribute to calving have been identified, a reliable predictive mathematical formula is still under development. Data is currently being assembled from ice shelves in Antarctica and Greenland to help establish

918-539: Is not sensitive to climate during the advancing and drastically retreating phases of its cycle. In the same region, disparate terminus responses are observed amongst tidewater calving glaciers, but not land terminating glaciers. This is exemplified by the 17 major glaciers of the Juneau Icefield , 5 have retreated more than 500 m since 1948, 11 more than 1000 m, and one glacier the Taku has advanced. This difference highlights

972-440: Is since 1970 is attributable to the laterally expanding terminal lobe as opposed to declining mass balance and that the primary force behind the Taku Glacier's advance since about 1900 is due to positive mass balance. The recent lack of positive mass balance will eventually slow the retreat if it persists. The size of tidewater glaciers is such that the tidewater glacier cycle is several hundred years in length. A tidewater glacier

1026-655: Is slightly larger than the City of Manhattan . This large ice shelf, located in the Weddell Sea , extending along the east coast of Antarctic Peninsula , consists of three segments, two of which have calved. In January 1995, the Larsen A Ice Shelf containing 3,250 km (1,250 sq mi) of ice 200 m (660 ft) thick calved and disintegrated. Then the Larsen B Ice Shelf calved and disintegrated in February 2002. Also known as

1080-415: Is the breaking of ice chunks from the edge of a glacier. It is a form of ice ablation or ice disruption . It is the sudden release and breaking away of a mass of ice from a glacier , iceberg , ice front , ice shelf , or crevasse . The ice that breaks away can be classified as an iceberg, but may also be a growler, bergy bit, or a crevasse wall breakaway. Calving of glaciers is often accompanied by

1134-461: Is the large retreat of Glacier Bay and Icy Bay glaciers in Alaska that occurred rapidly via this process. Muir Glacier retreated 33  km from 1886 to 1968 featuring extensive calving the entire time. It reversed its retreat briefly 1890—1892. In 1968, Muir Glacier was still 27 km long, less than half of its length in 1886. The retreat continued an additional 6.5 km by 2001. Today,

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1188-414: Is the main factor affecting the behavior of all glaciers, additional factors affect calving ( iceberg -producing) tidewater glaciers. These glaciers terminate abruptly at the ocean interface, with large pieces of the glacier fracturing and separating, or calving , from the ice front as icebergs. Climate change causes a shift in the equilibrium line altitude (ELA) of a glacier. This is the imaginary line on

1242-585: The Antarctic Peninsula . There they were stranded. Shackleton and five others crammed into a lifeboat, the James Caird , sailed across the Scotia Sea for 800 miles (1,300 km), reaching South Georgia two weeks later. They landed on the island's uninhabited west side at King Haakon Bay . Poor weather prevented them from setting sail again to one of the whaling stations on the island's east side, which were

1296-494: The Fleet Air Arm Museum at Yeovilton , Somerset ) held 16 personnel instead of its normal 4 capacity. 54°6′S 36°51′W  /  54.100°S 36.850°W  / -54.100; -36.850 [REDACTED]  This article incorporates public domain material from "Fortuna Glacier" . Geographic Names Information System . United States Geological Survey . Tidewater glacier While climate

1350-403: The 20th century. In mid-April 1915, explorer Ernest Shackleton 's ship Endurance , carrying the 27 members of his Antarctic expedition, became locked in the polar ice in the Weddell Sea just off Antarctica . In the spring of 1916, as the ice warmed and drifted north, the ship was crushed. The party used the lifeboats to get to Elephant Island , a desolate, uninhabited island at the edge of

1404-479: The Ilulissat Glacier or Sermeq Kujalleq in western Greenland, in an ongoing event, 35 billion tonnes of icebergs calve off and pass out of the fjord every year. Photographer James Balog and his team were examining this glacier in 2008 when their cameras caught a piece of glacier the size of Lower Manhattan fall into the ocean. The calving event lasted for 75 minutes, during which time the glacier retreated

1458-475: The Taku Glacier onset of advance, at the same time that the remaining Juneau Icefield glaciers continued receding. This advance continued at a rate of 88 m⋅a , advancing 5.3 km from the 1900 minimum until 1948, all the while building and then riding up on a substantial outwash plain beneath its calving face. After 1948, the now non-calving Taku Glacier, possessed an AAR only slightly reduced (86 and 63). This drove 1.5 km of further advance at

1512-454: The amount of flotation of the glacier at the front that is the specific physical characteristic that is important. Water depth at the glacier terminus is the key variable in predicting calving of a tidewater glacier. Debris flux and sediment recycling at the glacier grounding-line, particularly rapid in the temperate glaciers of Alaska, can alter this depth, acting as a second-order control on terminus fluctuations. This effect contributes to

1566-487: The beginning of the 20th century, the coastline was nearly straight and the bay non-existent. The entrance of the bay was filled by a tidewater glacier face that calved icebergs directly into the Gulf of Alaska. A century later glacier retreat has opened a multi-armed bay more than 30 miles long. The tidewater glacier has divided into three independent glaciers, Yahtse, Tsaa and Guyot Glacier. Other examples of glaciers currently in

1620-431: The calving of large numbers of icebergs. Calving of Greenland 's glaciers produce 12,000 to 15,000 icebergs each year alone. Calving of ice shelves is often preceded by a rift. An ice shelf in steady state calves at roughly the same rate as the influx of new ice, and calving events may occur on sub-annual to decadal timescales to maintain an overall average mean position of the ice shelf front. When calving rates exceed

1674-402: The calving process; this increases the export of icebergs from the glacier. Large calving retreats are initiated by warming conditions causing ice thinning. The resulting retreat to a new equilibrium conditions can be far more extensive than will be regained during the next advance stage. A good example of this is Muir Glacier. Next to Glacier Bay, Icy Bay has had the most extensive retreat. At

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1728-542: The case of Brady Glacier. Usually substantial thinning occurs before retreat from the shoal commences. This allowed the prediction in 1980, by the United States Geological Survey (USGS), of the retreat of the Columbia Glacier from its terminus shoal. The glacier had remained on this shoal throughout the entire 20th century. The USGS was monitoring the glacier due to its proximity to Valdez, Alaska ,

1782-416: The cycle. Taku Glacier which has been advancing for 120 years no longer calves. Hubbard Glacier still has a calving front. The glacier will then expand until the AAR is between 60 and 70 and equilibrium of the non-calving glacier is achieved. The glacier is not very sensitive to climate during the advance as its AAR is quite high, when the terminus shoal is limiting calving. At the maximum extended position

1836-418: The entire shelf calved from the northern edge of Ellesmere Island . Since 1900, about 90% of Ellesmere Island's ice shelves have calved and floated away. This event was the biggest of its kind for at least the past 25 years. A total of 87.1 km ( 33 + 5 ⁄ 8  sq mi) of ice was lost in this event. The largest piece was 66.4 km ( 25 + 5 ⁄ 8  sq mi) in area, which

1890-527: The following day by a Wessex 3 (Antrim) and two Wessex V (Tidespring) helicopters, the Wessex V aircraft crashed in extreme weather conditions. The Wessex 3, crewed by Lt Cdr Ian Stanley, Lt Chris Parry , Sub Lt Stewart Cooper and PO ACMN David Fitzgerald, succeeded in rescuing all troops and aircrew in an amazing feat of flying and navigation just before dark. On returning to Antrim , the Wessex 3 (which can be seen at

1944-443: The full thickness of the ice, calving will occur. Longitudinal stretching is controlled by friction at the base and edges of the glacier, glacier geometry and water pressure at the bed. These factors, therefore, exert the primary control on calving rate. Second and third order calving processes can be considered to be superimposed on the first order process above, and control the occurrence of individual calving events, rather than

1998-415: The glacier is near the head of its fjord and with minimal calving the glacier may be stable at this retracted position. The best current example is illustrated by the United States Geological Survey study of Columbia Glacier. They noted that the average calving rate from Columbia Glacier increased from 3 km ⋅a in the second half of 1983 to 4 km ⋅a during the first nine months of 1984. This rate

2052-419: The glacier is once again sensitive to changing climate. Brady Glacier and Baird Glacier are examples of glaciers currently at this point. Brady Glacier has been thinning during the last two decades due to the higher equilibrium line altitudes accompanying warmer conditions in the region, and its secondary termini have begun to retreat. A glacier can remain at this position for sometime, a century at least in

2106-416: The glacier retreats from the shoal, causing ever more rapid glacier flow, calving and retreat. A glacier is comparatively insensitive to climate during this calving retreat. However, in the case of San Rafael Glacier , Chile , a switch from retreat (1945–1990) to advance (1990–1997) was noted. Current examples of this retreat are Columbia Glacier and Guyot Glacier . The most famous recent example of this

2160-408: The glacier would retreat 32 km before stabilizing. By 2006, it has retreated 16 km. The water remains deep and the calving rate and glacier velocity very high, indicating retreat will continue. At this point, just like having a balloon payment in an adjustable rate mortgage, the glacier has to pay a whole new portion of its balance via icebergs. The glacier accelerates as flow is enhanced by

2214-413: The influx of new ice, ice front retreat occurs, and ice shelves may grow smaller and weaker. It is useful to classify causes of calving into first, second, and third order processes. First order processes are responsible for the overall rate of calving at the glacier scale. The first order cause of calving is longitudinal stretching, which controls the formation of crevasses . When crevasses penetrate

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2268-452: The insensitivity of a glacier to climate when its terminus is either retreating or advancing in deep water. Austin Post was one of the first to propose that water depth at the calving margin strongly affects the rate of iceberg calving. Glaciers that terminate on a morainal shoal are generally stable, but once a glacier retreats into water that deepens as the ice front recedes, calving rate increases rapidly and results in drastic retreat of

2322-587: The island in ' Operation Paraquet ', thereby removing the Argentinian military presence and restoring the island to British Sovereignty. It was decided to land a mountain troop of Special Air Service and 42 Royal Marine Commandos on the glacier , to approach Grytviken from the most unlikely direction. After the troops were landed on the glacier in conditions of extremely poor visibility and gale extreme force winds on 21 April, their conditions deteriorated rapidly still further. During several repeated rescue attempts

2376-601: The only human habitation on South Georgia. Instead they had to cross the largely unknown interior of the island. Shackleton beached his boat and with two others made his traverse of the island, crossing the Fortuna Glacier in the process. Thirty-six hours later they reached Stromness whaling station. When Argentina militarily occupied the Falkland Islands and South Georgia, the British Armed Forces recaptured

2430-407: The overall rate. Melting at the waterline is an important second order calving process as it undercuts the subaerial ice, leading to collapse. Other second order processes include tidal and seismic events, buoyant forces and melt water wedging. When calving occurs due to waterline melting, only the subaerial part of the glacier will calve, leaving a submerged 'foot'. Thus, a third order process

2484-520: The port for crude oil export from the Alaskan Pipeline . At some point a decline in mass balance will trigger a retreat from the shoal into deeper water at which point calving will ensue. Based on the recent thinning it is suggested that Brady Glacier is poised to begin retreat. The calving rate will increase as the glacier retreats from the shoal into the deeper fjord just cleared by the glacier during advance. The water depth initially increases as

2538-538: The retreat phase are South Sawyer and Sawyer Glaciers in Alaska, retreating 2.1 and 2.3 km respectively from 1961 to 2005. In Patagonia an example of a rapidly retreating glacier is the Jorge Montt Glacier which drains into Baja Jorge Montt in the Pacific Ocean. The glacier's ice thinning, at low elevations, from 1975 to 2000 reached 18 m⋅a at the lowest elevations. The glacier calving front experienced

2592-489: The terminus shoal will be pushed in front of the glacier and continue to build, keeping the calving rate low. In the case of the most glaciers such as the Taku Glacier the glacier will eventually build a terminus shoal that is above water and calving will essentially cease. This will eliminate this loss of ice from the glacier and the glacier can continue to advance. Taku Glacier and Hubbard Glacier have been in this phase of

2646-429: The terminus. Using data collected from 13 Alaskan tidewater calving glaciers, Brown et al. (1982) derived the following relationship between calving speed and water depth: V C = C H w + D {\displaystyle V_{C}=CH_{w}+D} , where V C {\displaystyle V_{C}} is the mean calving speed ( m ⋅ a ), C {\displaystyle C}

2700-430: The tidewater calving glacier advance/retreat cycle: (1) advancing, (2) stable-extended, (3) drastically retreating, or (4) stable-retracted. The following is a detailed review of the tidewater glacier cycle derived by Post, with numerous cited examples, the cycle is based on observations of temperate tidewater glaciers in Alaska, not outlet glaciers from large ice sheets or polar glaciers. The accumulation area ratio of

2754-451: The unique impacts on terminus behavior of the tidewater glacier cycle, which has caused the Taku Glacier to be insensitive to climate change in the last 60 years. Concurrently, in both Patagonia and Alaska, there are tidewater glaciers that have advanced for a considerable period, tidewater glaciers undergoing rapid retreat and stable tidewater glaciers. Ice calving Ice calving , also known as glacier calving or iceberg calving ,

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2808-536: The variation in velocity along their length. Land terminating glacier velocities decline as the terminus is approached. Calving glaciers accelerate at the terminus. A declining velocity near the terminus slows the glacier response to climate. An accelerating velocity at the front enhances the speed of the glaciers response to climate or glacier dynamic changes. This is observed in Svalbard , Patagonia and Alaska . A calving glacier requires more accumulation area than

2862-651: Was about 150 km x 50 km. A second calving occurred in May 2000 and created an iceberg 167 km x 32 km. A major calving event occurred in 1962 to 1963. Currently, there is a section at the front of the shelf referred to as the 'loose tooth'. This section, about 30 km by 30 km is moving at about 12 metres (39 ft) per day and is expected to eventually calve away. The largest observed calving of an ice island happened at Ward Hunt Ice Shelf. Sometime between August 1961 and April 1962 almost 600 km (230 sq mi) of ice broke away. In 2005, nearly

2916-447: Was four times greater than that measured at the end of 1977 and increased again in 1985. The glacier flow, i.e., the movement of the ice toward the sea, also increased, it was inadequate to keep pace with the break-up and expulsion of icebergs. The increase in speed instead seemed to just feed the ever faster conveyor to the terminus for iceberg production. This prompted the USGS to predict that

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