Ice shelf
Floating glacial ice platforms that moderate glacier flow.
An ice shelf is a thick, floating slab of glacial ice that extends from the coast into the ocean, fed by one or more glaciers. They develop along shorelines where the ice is not thick enough to push aside the denser seawater. The line where the floating ice shelf meets the grounded ice resting on bedrock is called the grounding line, while the edge where the shelf meets the open ocean—often covered by sea ice—is known as the ice front or calving front. The largest ice shelves on Earth are Antarctica’s Ross Ice Shelf and Filchner-Ronne Ice Shelf.
Ice shelves are found in Antarctica and the Arctic, including Greenland, Northern Canada, and the Russian Arctic. Their thickness ranges from about 100 to 1,000 meters (330–3,280 feet). Their movement is driven mainly by the pressure of grounded ice behind them, which pushes ice from the grounding line toward the seaward front. The front typically advances for years or decades between major calving events, where large chunks of ice suddenly break away. Snow piling up on the surface and melting from the underside also affect the shelf’s mass balance, and ice can sometimes accumulate on the bottom as well.
Climate change has caused visible shifts in the cryosphere, including shrinking sea ice and ice sheets and the disruption of ice shelves. Over recent decades, scientists have observed steady declines in ice shelf size due to melting, calving, and the complete collapse of some shelves. Well-studied examples include the Thwaites Ice Shelf, Larsen Ice Shelf, and Filchner–Ronne Ice Shelf in Antarctica, as well as the Ellesmere Ice Shelf in the Arctic.
- type
- Geophysical feature
- location
- Antarctica and the Arctic (Greenland, Northern Canada, Russian Arctic)
- largest_examples
- Ross Ice Shelf and Filchner-Ronne Ice Shelf (Antarctica)
- key_processes
- Gravity-driven flow, calving, basal melt, snow accumulation
- climate_impact
- Observed decreases in extent through melt, calving, and complete disintegration
Lore & Background
Ice shelves are thick plates of ice formed continuously by glaciers, floating atop an ocean. They act as brakes for glaciers, moderating the amount of melting on the glaciers' surfaces. The movement of ice shelves is principally driven by gravity-induced pressure from the grounded ice, continually moving ice from the grounding line to the seaward front. Snow accumulation on the upper surface and melting from the lower surface are important to the mass balance of an ice shelf, and ice may also accrete onto the underside.
Reader's Guide
Ice shelves are significant because they serve as critical regulators of glacier flow and ice discharge into the ocean. When ice shelves are removed, glaciers increase in speed due to meltwater percolation or a reduction of braking forces, potentially dumping more ice into the ocean than they gather as snow. In recent decades, glaciologists have observed consistent decreases in ice shelf extent through melt, calving, and complete disintegration of some shelves, with well-studied examples including the Thwaites Ice Shelf, Larsen Ice Shelf, Filchner–Ronne Ice Shelf in Antarctica, and the Ellesmere Ice Shelf in the Arctic. The effects of climate change are visible in these disruptions to the cryosphere.
Did You Know?
- At least 1/9 of an ice shelf's floating ice is above the ocean surface, depending on air bubbles in the glacial ice.
Frequently Asked Questions
Who is Ice shelf?
Ice shelf is a vast platform of glacial ice that floats on top of ocean water, fed by one or more upstream glaciers. It exists in coastal zones where the ice is too thin to push aside the denser seawater, so it simply rides on the surface instead.
What are Ice shelf's powers/role?
Ice shelf acts as a floating buttress that slows the gravity-driven flow of the glaciers behind it, keeping them from surging into the sea. It also continuously sheds ice through calving at its front edge and loses mass to warm water melting its underside.
How does Ice shelf's story end?
Ice shelf can undergo complete disintegration when basal melting, accelerated calving, and structural weakening combine to break it apart. Several major shelves have already shrunk dramatically or collapsed in recent decades, removing their hold on upstream glaciers.
Why is Ice shelf important?
Ice shelf serves as a critical brake on grounded glaciers, preventing them from flowing into the ocean at uncontrolled rates. Without this floating barrier, the ice behind it would accelerate, delivering far more meltwater to the sea and raising global sea levels.
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