Surge (glacier)
Encyclopedia
Glacial surges are short-lived events where a glacier
can advance substantially, moving at velocities up to 100 times faster than normal. Surging glaciers are clustered around a few areas. High concentrations of surging glaciers can be found in Svalbard
, Canadian Arctic islands, Alaska
and Iceland. In some glaciers, surges can occur in fairly regular cycles with 15 to 100 or more surge events per year. In other glaciers, surging is unpredictable. In some glaciers, however, the period of stagnation and build-up between two surges typically lasts 10–200 years and is called the quiescent phase. During this period the velocities of the glacier are significantly lower, and the glaciers can retreat
substantially.
Surges in Svalbard typically exhibit different behavior. Svalbard surges are typically associated with slower onset with an acceleration phase, rising to a maximum velocity which is typically slower (up to four or five meters per day) than Alaskan surges, and a return to quiessence often taking years. Features observed during the active or surge phase include pothole
s, known as lacunas and medial moraines.
containing hundreds of glaciers. Svalbard is more than 60% covered by glaciers and of these glaciers, hundreds have been observed to surge.
Glacial surges in Karakoram occur in the presence of "extreme uplift and denudation."
In 1980, there were several mini-surges of Variegated Glacier in Alaska. Mini surges typically show lag times of basal flow of 5–10 hours, which correlates to differences between the surging part of a glacier and the output of water and sediment. When the 1982 surge ended on July 5, there was a large flood event that day, and more flooding in the following days. What Humphrey found in his study is that behind the glacial surge zone, there are predominantly low basal water velocities, and high sliding rates before the rapid release of large quantities of water.
s, geothermal heating of the bed, conduction of heat into the glacier and latent heat transfers. There is a positive feedback between velocity and friction at the bed, high velocities will generate more frictional heat and create more meltwater. Crevassing
is also enhanced by greater velocity flow which will provide further rapid transmission paths for meltwater flowing towards the bed. Humphrey found no precise correlation, however, between ice-slow down and the release of water inside of a glacier.
The evolution of the drainage system under the glacier plays a key role in surge cycles.
of the underlying country rock may dictate surge frequency. For example, poorly consolidated sedimentary rocks are more prone to failure under stress; a sub-glacial "landslip" may permit the glacier to slide. This explains why surging glaciers tend to cluster in certain areas.
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
can advance substantially, moving at velocities up to 100 times faster than normal. Surging glaciers are clustered around a few areas. High concentrations of surging glaciers can be found in Svalbard
Svalbard
Svalbard is an archipelago in the Arctic, constituting the northernmost part of Norway. It is located north of mainland Europe, midway between mainland Norway and the North Pole. The group of islands range from 74° to 81° north latitude , and from 10° to 35° east longitude. Spitsbergen is the...
, Canadian Arctic islands, Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and Iceland. In some glaciers, surges can occur in fairly regular cycles with 15 to 100 or more surge events per year. In other glaciers, surging is unpredictable. In some glaciers, however, the period of stagnation and build-up between two surges typically lasts 10–200 years and is called the quiescent phase. During this period the velocities of the glacier are significantly lower, and the glaciers can retreat
Glacier retreat
Glacier retreat or glacial retreat is discussed in several articles, depending on the time frame of interest, and whether the climatological process or individual glaciers are being considered. Articles on these topics include:...
substantially.
Types of glacier surges
Glacier surges have been divided into two categories depending on the character of the surge event. Glaciers in Alaska exhibit surges with a sudden onset, extremely high (tens of meters/day)maximum flow rate and a sudden termination, often with a discharge of stored water. These are called Alaskan-type surges and it is suspected that these surges are hydrologically controlled.Surges in Svalbard typically exhibit different behavior. Svalbard surges are typically associated with slower onset with an acceleration phase, rising to a maximum velocity which is typically slower (up to four or five meters per day) than Alaskan surges, and a return to quiessence often taking years. Features observed during the active or surge phase include pothole
Pothole
A pothole is a type of disruption in the surface of a roadway where a portion of the road material has broken away, leaving a hole.- Formation :...
s, known as lacunas and medial moraines.
Examples of glacial surge events
In the Norwegian Arctic, Svalbard is an archipelagoArchipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
containing hundreds of glaciers. Svalbard is more than 60% covered by glaciers and of these glaciers, hundreds have been observed to surge.
Glacial surges in Karakoram occur in the presence of "extreme uplift and denudation."
In 1980, there were several mini-surges of Variegated Glacier in Alaska. Mini surges typically show lag times of basal flow of 5–10 hours, which correlates to differences between the surging part of a glacier and the output of water and sediment. When the 1982 surge ended on July 5, there was a large flood event that day, and more flooding in the following days. What Humphrey found in his study is that behind the glacial surge zone, there are predominantly low basal water velocities, and high sliding rates before the rapid release of large quantities of water.
Hydrological control
Surges may be caused by the supply of meltwater to the base of a glacier. Meltwater is important in reducing frictional restrictions to glacial ice flow. The distribution and pressure of water at the bed modulates the glacier's velocity and therefore mass balance. Meltwater may come from a number of sources, including supraglacial lakeSupraglacial lake
A supraglacial lake is any pond of liquid water on the top of a glacier. Although these pools are , they may reach kilometers in diameter and be several meters deep...
s, geothermal heating of the bed, conduction of heat into the glacier and latent heat transfers. There is a positive feedback between velocity and friction at the bed, high velocities will generate more frictional heat and create more meltwater. Crevassing
Crevasse
A crevasse is a deep crack in an ice sheet rhys glacier . Crevasses form as a result of the movement and resulting stress associated with the sheer stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement...
is also enhanced by greater velocity flow which will provide further rapid transmission paths for meltwater flowing towards the bed. Humphrey found no precise correlation, however, between ice-slow down and the release of water inside of a glacier.
The evolution of the drainage system under the glacier plays a key role in surge cycles.
Thermal regime
Glaciers that exhibit surges like those in Svalbard; with slower onset phase, and a longer termination phase may be thermally controlled rather than Hydrologically controlled. These surges tend to last for longer periods of time than Hydrologically controlled surges.Deformable bed hypothesis
In other cases, the geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
of the underlying country rock may dictate surge frequency. For example, poorly consolidated sedimentary rocks are more prone to failure under stress; a sub-glacial "landslip" may permit the glacier to slide. This explains why surging glaciers tend to cluster in certain areas.