Glaciology and Cryosphere Quiz: 20 Questions & Answers

Correct answer: The ice mass deforms and flows under its own weight.

A glacier is a persistent ice body that flows under its own weight. Snow surviving summer is necessary for many glaciers to form, but persistence alone does not establish glacier flow. This question concerns an active glacier, not a detached remnant of stagnant glacier ice.

Correct answer: An ice cap covers a smaller land area.

NSIDC uses about 19,300 square miles (50,000 square kilometers) as the conventional dividing area: ice caps are smaller and ice sheets larger. Both consist of glacier ice and can flow outward from broad domes. The distinction is not fresh versus salt water or moving versus stationary ice.

Correct answer: Calving of glacier ice from a floating extension.

An ice shelf is a floating extension of glacier ice. When a large piece breaks away, the process is calving and the detached block is an iceberg. Floating in seawater does not make that block sea ice, which forms by freezing seawater.

Correct answer: Yes, because permafrost is defined by ground temperature and duration.

Permafrost is ground that stays at or below 32°F (0°C) for at least two consecutive years. It may be soil, sediment or rock, and it need not contain ice. Temperature history, rather than snow cover or latitude alone, determines whether the definition is met.

Correct answer: The active layer.

The active layer is the ground above permafrost that undergoes annual thawing and freezing. Its lower boundary can move as thaw depth changes. The seasonally thawed layer should not be confused with the ground that remains at or below freezing from year to year.

Correct answer: Sublimation, which contributes to ablation.

Sublimation changes solid ice directly into vapor. It removes mass and therefore contributes to ablation, the collective loss of snow and ice. Ablation is broader than melting: a glacier can lose mass even when the particular loss process produces no liquid runoff.

Correct answer: −15 inches (−38.1 cm) water equivalent.

Net balance is gain minus loss: 40 − 55 = −15 inches (−38.1 cm) water equivalent. The negative sign means net mass loss. Water equivalent puts snow and ice on a common mass-per-area basis; it is not necessarily the measured drop in the ice surface.

Correct answer: It becomes smaller.

With the stated pattern and unchanged outline, a higher equilibrium line leaves less glacier area above the line and more below it. The line marks zero annual surface balance locally. It does not mean that the whole glacier has zero total mass balance.

Correct answer: Internal deformation of the solid ice under stress.

Glacier ice can deform slowly under sustained stress, a process called creep. Basal sliding is another possible source of motion, but it is not required for internal deformation. Ice need not melt into liquid water before a glacier can flow.

Correct answer: The front is retreating while the glacier ice continues to flow downhill.

The snout is a boundary, not a fixed parcel of ice. It can retreat when ice is removed at the front faster than flow supplies it, even as individual ice parcels move downhill. Terminus position and ice velocity therefore describe different aspects of glacier behavior.

Correct answer: No; ice discharge and other non-surface losses can outweigh the surface gain.

Surface mass balance accounts for surface gains and losses, not the full glacier budget. Ice lost through calving and other non-surface exchanges must also be considered. Positive surface balance can coexist with total mass loss if those additional losses are larger.

Correct answer: Mass increased during the last interval, but remained below the starting amount.

The cumulative value rose from −45 to −40 inches, a gain of 5 inches (12.7 cm) water equivalent during the last interval. It is still below zero, so the earlier losses have not been fully recovered. A cumulative total and an interval change answer different questions.

Correct answer: The land ice, because it adds water mass not previously in the ocean.

Floating sea ice already displaces seawater, so its direct melt effect is much smaller than adding the same mass from land. It is not strictly zero: salinity and density differences produce a small effect. This comparison excludes indirect climate effects and changes in grounded-ice discharge.

Correct answer: Reduced restraint can let grounded ice flow into the ocean faster.

A shelf can provide back stress, often called buttressing, that restrains the glacier feeding it. Removing that restraint can accelerate grounded-ice discharge into the ocean. The response depends on the shelf and glacier geometry; every calving event does not cause the same acceleration.

Correct answer: 20 square miles (51.8 km²).

The 40% and 80% cells qualify, so extent is 10 + 10 = 20 square miles (51.8 km²). Weighting those cells by concentration instead gives an ice area of 12 square miles (31.1 km²). Neither extent nor area alone establishes ice thickness or volume.

Correct answer: B yields twice the water depth: 8 inches (20.32 cm) versus A’s 4 inches (10.16 cm).

Snow water equivalent measures stored water rather than snow depth alone. Multiplying depth by the stated density ratio gives A: 20 × 0.20 = 4 inches, and B: 20 × 0.40 = 8 inches. Equal snow depths can therefore represent different water stores.

Correct answer: More runoff may arrive early, leaving less snowmelt supply later in summer.

Dust can lower snow reflectivity and accelerate melting, shifting water release earlier. Equal starting snow-water storage does not guarantee equal seasonal availability, or even equal annual runoff after evaporation and other losses. The practical issue here is timing, not simply how deep the snow looks.

Correct answer: The trapped air can be younger than the enclosing ice, requiring separate age estimates.

Firn is compacted snow that has not yet become fully consolidated glacier ice. Air can diffuse through its connected pores before closure traps it. The resulting gas age can be younger than the enclosing ice age, so researchers account for that offset rather than assuming simultaneous formation.

Correct answer: Melting ground ice can leave the sediment structure to compact or collapse.

Ground ice can occupy substantial volume and support an ice-rich soil structure. When it melts, drainage and consolidation can cause settlement. This mechanism is much less relevant to nearly ice-free bedrock, although real infrastructure risk still depends on geology, drainage, foundations and other site conditions.

Correct answer: An unstable slope could send an avalanche into the lake and overtop the dam.

An avalanche entering a lake can generate waves that overtop and erode a moraine dam, potentially releasing water rapidly. Lake growth alone does not prove that failure will occur. Assessment also needs dam properties, water volume, possible triggers and downstream exposure.