Vêlage (glaciologie)

Ice calving, also known as glacier calving or iceberg calving, 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 a loud cracking or booming sound before blocks of ice up to 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 . These events have become major tourist attractions in locations such as Alaska. Many glaciers terminate at oceans or freshwater lakes which results naturally with 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 subannual to decadal timescales to maintain an overall average mean position of the ice shelf front. When calving rates exceed 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 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.

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ENV-410: Science of climate change

The course equips students with a comprehensive scientific understanding of climate change covering a wide range of topics from physical principles, historical climate change, greenhouse gas emissions

Vêlage (glaciologie)

Plateforme de glace de Larsen

vignette| |alt=Carte de l'Antarctique indiquant l'emplacement de la barrière de Larsen. vignette|Carte de la Péninsule Antarctique.|alt=Carte de l'Antarctique indiquant l'emplacement des principaux segments de la barrière de Larsen (A, B, C et D). La Plateforme de glace de Larsen, autrefois appelée Barrière de Larsen, est une plateforme de glace flottant au nord-ouest de la mer de Weddell, s'étendant tout le le long de la côte orientale de la Péninsule Antarctique.

Glacier Thwaites

Le glacier Thwaites est un glacier d'Antarctique situé dans la Terre Marie Byrd. Il forme une barrière de glace alimentée par un courant glaciaire permettant à une partie des glaces de l'inlandsis Ouest-Antarctique de s'évacuer du plateau antarctique occidental vers la mer d'Amundsen.

Modeling the breaking-off of icebergs from tidewater glaciers

Qimin Wang

Ice calving is the breakaway process of icebergs which plays an important role in the dy- namics and the mass balance of ice sheets. Our project is to use Akantu (An open source object-oriented Finite Element library by LSMS) to reproduce the fracturing stages of the Bowdoin glacier in Greenland. Studies were first made on the mechanisms of ice calving and the provided data, to extract the key factors for our simulation. The HPC (high performance computing) simulation model was built by Python scripts, including preprocessing mesh file, applying arbitrary loading profiles, defining boundary conditions and initial conditions, pass- ing message through the simulation process, etc. The simulation scheme has been modified to better analysis the impact of water pressure and velocity field. Simulation acceleration was also implemented by amplifying the velocity field, so that the damage initiation and propagation could be explored faster. Some preliminary results about the relationship of system energy and damage propagation was analyzed. In the end, we proposed some study direction for the future researchers on the similar subject.

2019

Freshwater Flux and Spatiotemporal Simulated Runoff Variability into Ilulissat Icefjord, West Greenland, Linked to Salinity and Temperature Observations near Tidewater Glacier Margins Obtained Using Instrumented Ringed Seals

Konrad Steffen

The distribution of terrestrial surface runoff to Ilulissat Icefjord, west Greenland, is simulated for the period 2009-13 to better emphasize the spatiotemporal variability in freshwater flux and the link between runoff spikes and observed hydrographic conditions at theGreenland Ice Sheet tidewater glacier margins. Runoffmodel simulations were forced with automatic weather station data and verified against snow water equivalent depth, equilibrium line altitude, and quasi-continuous salinity and temperature observations obtained by ringed seals. Instrumented seals provide a novel platform to examine the otherwise inaccessible waters beneath the dense ice melange within the first 0-10 km of the calving front. The estimated mean freshwater flux from land was 70.6 +/- 4.2 km(3) yr(-1), with an 85% contribution of ice discharge from Jakobshavn Isbrae (also known as SermeqKujalleq), 14% from runoff, and the remaining 1% from precipitation on the fjord surface area, subglacial geothermal melting, and frictional melting due to basal ice motion. Runoff was simulated to be present from May to November and to vary spatially according to glacier cover and individual catchment size. Salinity and temperature observations correlate (significantly) with simulated runoff for the upper part of both the main fjord and southern fjord arm. Also, at the tidewater glacier margins in the northern and southern arm of Ilulissat Icefjord, salinity changes in the upper water column (upper 50 m) are significant after temporal spikes in runoff during late summer, while small-amplitude runoff variability during the recession of runoff did not create a clear signal in observed salinity variability. Also, in the southern arm near the glacier margin (between 100- and 150-m depth), the heterogeneous distribution in salinity could be because of the mixing of meltwater going upward from passing the grounding line. The effect of runoff spikes on observed salinity is less pronounced near the ice margin of Jakobshavn Isbrae than in the north and south arms.

Amer Meteorological Soc2015

The structure and effect of suture zones in the Larsen C Ice Shelf, Antarctica

Konrad Steffen

Ice shelf fractures frequently terminate where they encounter suture zones, regions of material heterogeneity that form between meteoric inflows in ice shelves. This heterogeneity can consist of marine ice, meteoric ice with modified rheological properties, or the presence of fractures. Here, we use radar observations on the Larsen C Ice Shelf, Antarctica, to investigate (i) the termination of a 25km long rift in the Churchill Peninsula suture zone, which was found to contain similar to 60m of accreted marine ice, and (ii) the along-flow evolution of a suture zone originating at Cole Peninsula. We determine a steady state field of basal melting/freezing rates and apply it to a flowline model to delineate the along-flow evolution of layers within the ice shelf. The thickening surface wedge of locally accumulated meteoric ice, which likely has limited lateral variation in its mechanical properties, accounts for similar to 60% of the total ice thickness near the calving front. Thus, we infer that the lower similar to 40% of the ice column and the material heterogeneities present there are responsible for resisting fracture propagation and thereby delaying tabular calving events, as demonstrated in the >40year time series leading up to the 2004/2005 calving event for Larsen C. This likely represents a highly sensitive aspect of ice shelf stability, as changes in the oceanic forcing may lead to the loss of this heterogeneity.

Amer Geophysical Union2014

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