Calving

In geography and glaciology, calving refers to the process by which icebergs or large blocks of ice break off from the edge of a glacier, ice shelf, or ice tongue and fall into the sea or a lake. It is a natural part of the ice-mass loss process in polar and glacial environments and represents one of the primary mechanisms by which glaciers discharge ice into the ocean. The term is derived from the resemblance to the act of an animal giving birth, as new icebergs are “born” from the glacier front.

Definition

Calving is the mechanical separation of ice masses from the terminus (end) of a glacier or ice shelf due to internal stresses, buoyant forces, or melting at the ice–water interface. The detached ice blocks float away as icebergs if they enter the ocean, or as ice fragments in lakes or fjords.
It typically occurs where a glacier terminates in a body of water—such as a sea, fjord, or proglacial lake—though it may also take place at ice cliffs grounded on land.

Process of Calving

The calving process involves several stages, driven by a combination of glacial dynamics, melting, and mechanical failure:

1. Fracture Formation:
   • Stresses develop within the glacier due to flow velocity, buoyancy, and gravitational forces.
   • Cracks (crevasses) propagate through the ice near the glacier terminus.
2. Water Undercutting and Melting:
   • Warm ocean or lake water erodes the submerged part of the ice front, creating overhangs and cavities.
   • Undercutting weakens the glacier edge, promoting collapse.
3. Ice Break-off:
   • The overhanging ice becomes unstable and breaks away from the main glacier.
   • Large chunks of ice detach and rise to the surface if submerged, often producing waves or turbulence.
4. Iceberg Formation and Drift:
   • The broken pieces float away as icebergs or ice blocks, gradually melting and dispersing.

The process can occur gradually, with small pieces breaking off regularly, or catastrophically, when large masses calve suddenly, generating powerful waves and noise.

Causes of Calving

Calving results from a combination of environmental, mechanical, and thermal factors, including:

1. Glacier Flow and Stress:
   • Glaciers constantly move under gravity. When the flow reaches a terminus in water, internal stresses and strain rates lead to cracking.
2. Water Temperature and Erosion:
   • Warmer ocean or lake water melts the submerged glacier base, enhancing undercutting.
3. Buoyancy Forces:
   • When a glacier front extends into deep water, buoyant forces lift and weaken the ice tongue, causing it to fracture.
4. Tidal Action and Waves:
   • Repeated tidal flexing and wave impact destabilise the glacier front.
5. Climatic Warming:
   • Rising air and ocean temperatures accelerate surface melting and increase calving frequency.
6. Hydrofracturing:
   • Meltwater penetrates cracks, refreezes, and expands, deepening fractures that eventually cause breakage.

Types of Calving

1. Subaerial Calving:
   • Occurs above the water surface when large blocks fall directly from an ice cliff into the sea or lake.
2. Subaqueous Calving:
   • Takes place below the water surface when submerged ice detaches and rises to the surface, often explosively.
3. Tabular Calving:
   • Produces large, flat-topped icebergs (tabular icebergs), typical of Antarctic ice shelves.
4. Transverse or Pinnacle Calving:
   • Produces irregular, steep-sided icebergs, common in tidewater glaciers of Greenland and Alaska.

Geographic Occurrence

Calving is most common in polar and subpolar regions and in high mountain areas where glaciers terminate in water.
Major calving sites include:

• Antarctica: Edge of the Ross Ice Shelf, Filchner–Ronne Ice Shelf, and Larsen Ice Shelf.
• Greenland: Tidewater glaciers such as Jakobshavn Isbræ (one of the world’s fastest-moving glaciers).
• Alaska: Glaciers like Columbia Glacier and Hubbard Glacier.
• Patagonia: Glaciers feeding Lago Argentino and Lago Viedma in South America.
• Svalbard and Canadian Arctic: Where marine-terminating glaciers are prevalent.

Effects and Significance

1. Iceberg Production:
   • Calving is the primary source of icebergs in the oceans. These icebergs drift with currents and gradually melt, contributing to the freshwater input into the marine environment.
2. Sea-Level Contribution:
   • When the parent glacier originates on land, calving contributes indirectly to sea-level rise, as land-based ice enters the ocean.
   • Ice shelves already floating do not directly raise sea level, but their collapse can accelerate inland ice discharge.
3. Glacier Dynamics:
   • Calving can cause a glacier to retreat rapidly when the rate of ice loss exceeds the rate of ice flow toward the terminus.
4. Ecosystem Impact:
   • Icebergs affect marine ecosystems by influencing water circulation, nutrient distribution, and providing habitats for microorganisms.
5. Hazards:
   • Sudden calving events can generate large waves and pose dangers to ships, coastal infrastructure, and tourists near glacier fronts.

Calving Fronts and Ice Shelves

An ice shelf is a thick, floating extension of a continental glacier. Its seaward edge, known as the calving front, periodically loses icebergs through calving. These fronts can remain stable for long periods but may retreat dramatically if weakened by warming waters or structural fractures.

• The Larsen B Ice Shelf in Antarctica collapsed in 2002 after progressive thinning and extensive calving, highlighting the link between climate change and ice-shelf instability.

Relationship with Climate Change

Calving rates are sensitive indicators of climatic and oceanic changes. Increasing global temperatures enhance surface melting and subaqueous erosion, leading to more frequent and larger calving events.
Recent satellite observations show that many marine-terminating glaciers in Greenland and West Antarctica are retreating rapidly, primarily due to increased calving rates linked to ocean warming.

Measurement and Study

Scientists study calving processes using:

• Satellite imagery to monitor glacier front positions and iceberg formation.
• Time-lapse photography and seismometers to detect calving events.
• Field measurements of water temperature, salinity, and glacier velocity.
• Numerical models that simulate stress distribution, buoyancy forces, and ice–water interactions.