World Geography20 Concepts & Facts

What Is a Crevasse and What Causes Deep Fractures in Glacial Ice?

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A crevasse is a deep, vertical or near-vertical fracture that opens in the brittle surface layer of an active glacier or ice sheet. Glacial ice exhibits a dual mechanical behavior depending on confining pressure, depth, and strain rates. While the deep mass of a glacier deforms plastically under high lithostatic overburden pressure and flows slowly like an extremely viscous solid, the uppermost layer—typically extending down thirty to fifty metres—remains cold, rigid, and brittle. When gravitational downhill flow subjects this upper zone to differential velocities, extensional stretching, or shear stresses exceeding the tensile strength of polycrystalline ice, the brittle crust ruptures into gaping chasms.

Structural glaciologists classify crevasses according to the specific stress fields that generate them. Transverse crevasses form perpendicular to the direction of ice flow, typically opening where a glacier accelerates over steep convex changes in the underlying valley slope. Longitudinal crevasses open parallel to ice flow where a confining valley widens, permitting the glacier to spread out laterally. Along the outer valley margins, frictional drag against rocky walls creates shear stress, spawning en échelon or marginal crevasses that slant obliquely up-glacier at forty-five-degree angles. At the uppermost headwall of a glacial cirque, a specialized gap known as a bergschrund develops where the actively moving glacier tears itself away from stagnant ice and snow clinging to the rock face.

Crevasses represent one of the most serious objective hazards in high-altitude mountaineering and polar exploration. During winter and spring, blowing snow frequently blankets these chasms with thin, fragile snow bridges called firn spans. These bridges conceal lethal drops beneath an apparently continuous snowfield, requiring mountaineering parties to travel roped together and carry technical extraction gear including ice axes, crampons, and crevasse rescue pulleys. In world-famous icefalls, such as the treacherous Khumbu Icefall on the South Col route of Mount Everest, intersecting crevasse systems fracture into towering, unstable ice pinnacles known as seracs. In modern glaciology, surface meltwater pooling in crevasses induces hydrofracturing, driving fissures deeper into ice shelves and accelerating glacial disintegration under warming climatic conditions.

Key Concepts & Self-Assessment20 Key Facts

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A crevasse is a deep, near-vertical crack that forms in the brittle upper layer of a glacier due to tensile or shear stress.

Glacial ice behaves as a brittle solid in its upper 30 to 50 metres, but deforms through plastic flow under greater hydrostatic pressure below.

Crevasses rarely extend deeper than 30 to 45 metres because the weight of surrounding ice forces deeper ice to deform plastically and squeeze fissures shut.

John Nye developed the theoretical mechanics of glacier slip-lines, explaining the mathematical limit of crevasse depth under plastic overburden pressure.

Transverse crevasses form perpendicular to flow where a glacier accelerates over convex breaks in valley floor slope.

Longitudinal crevasses open parallel to flow direction where a glacier exits a narrow gorge and spreads laterally into a wider valley.

Marginal or chevron crevasses develop along valley walls at roughly forty-five-degree angles pointing up-glacier due to lateral frictional drag.

A bergschrund is a distinct deep crevasse at the head of a cirque, separating actively moving glacier ice from stagnant ice frozen to the rock wall.

A randkluft differs from a bergschrund by forming between the glacier ice and the bare mountain rock face due to thermal radiation from rock.

#10

Seracs are massive, unstable pinnacles of glacial ice created where intersecting transverse and longitudinal crevasses cut the ice into isolated blocks.

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Icefalls are heavily fractured zones of a glacier characterized by steep gradients, dense crevasse networks, and collapsing seracs, such as the Khumbu Icefall.

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Snow bridges, formed by wind-drifted snow over crevasse lips, hide deep fractures and present major fall hazards to mountaineers and polar travelers.

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In India, the Himalayan Mountaineering Institute (HMI, Darjeeling) and Nehru Institute of Mountaineering (NIM, Uttarkashi) teach technical crevasse rescue techniques.

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The Indo-Tibetan Border Police (ITBP) and Indian Army maintain specialized crevasse navigation protocols during high-altitude patrols in Ladakh and Sikkim.

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Operation Meghdoot on the Siachen Glacier requires Indian armed forces to negotiate treacherous crevasse fields across the Saltoro Ridge.

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The Defence Geoinformatics Research Establishment (DGRE, Chandigarh, under DRDO) monitors glacier crevasses and snowpack hazards in the Himalayas.

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Hydrofracturing occurs when surface meltwater fills a crevasse, using hydraulic pressure to drive the fracture through the full thickness of an ice shelf.

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Rapid collapse of Antarctic ice shelves, including the Larsen B shelf in 2002, was accelerated by widespread surface crevasse hydrofracturing.

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Crevasse rescue protocols rely on roped-team travel, mechanical advantage pulley systems (such as the 3:1 Z-pulley rig), and snow picket anchors.

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In structural glaciology, crevasse patterns serve as natural strain markers revealing velocity gradients and stress orientations across ice sheets.

Subject Specialist Commentary

Analytical perspective & practical exam advice from the Master10 academic board

Educator's Insight

A crevasse is a surface crack in moving glacial ice. Why do crevasses stop forming below thirty to fifty metres? The answer lies in ice physics. In the upper zone, ice is rigid and snaps when pulled by tension. But below fifty metres, the immense weight of overlying ice generates intense confining pressure. Under this pressure, ice stops fracturing and instead flows like modeling clay, sealing shut any crack trying to open.

In competitive exams like UPSC and State PSCs, a frequent exam trap is confusing a bergschrund with standard crevasses. A bergschrund is the gaping fissure opening at the glacier's head where moving ice pulls away from the static cirque wall, whereas seracs are isolated ice towers formed by intersecting fractures. Use the mnemonic 'Brittle Above, Plastic Below' to remember that brittle crevasses only penetrate the upper thirty to fifty metres, while underlying hydrostatic pressure forces ice into plastic, fracture-free deformation.

What Is a Crevasse and What Causes Deep Fractures in Glacial Ice?

Key Concepts & Self-Assessment20 Key Facts

Subject Specialist Commentary

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