Questions: Glaciers and Glaciation: Formation, Flow, and Mass Balance

Question 1

A glacier's terminus has been retreating for 20 years. What is happening to the ice within the glacier?

• A. The ice is flowing back uphill toward the accumulation zone
• B. The ice is still flowing downhill, but melting at the front removes ice faster than flow brings it
• C. The ice has stopped moving completely
• D. The glacier is gaining more snow than it loses

Answer: (B)

Flow and terminus position are different things. A glacier with a negative mass balance keeps moving downhill, but its front shrinks back because ablation outpaces the ice supplied by flow.

Question 2

Explain how snow becomes glacial ice.

Model answer: Snow that survives the summer melt is buried by later snowfall. The weight of the overlying layers compacts it, and grains partly melt, refreeze, and recrystallize, pushing out air. The snow first becomes granular firn and then, after years to thousands of years depending on temperature and snowfall, dense glacial ice with only small trapped air bubbles.

This slow transformation is why glacial ice traps tiny samples of past air, which ice cores use to measure ancient atmospheric CO₂.

Question 3

Glacial till is a poorly sorted mixture of clay, sand, gravel, and boulders, while outwash deposited by meltwater streams is sorted and layered.

• T. True
• F. False

Answer: True

Ice carries and drops sediment of all sizes together, so till is unsorted. Meltwater streams sort sediment by size as their speed changes, so outwash shows sorting and layering.

Question 4

Parts of Scandinavia and the Hudson Bay region are still rising today, thousands of years after their ice sheets melted. Why?

• A. Volcanic activity is pushing the crust upward
• B. The weight of the ice sheets pressed the crust down, and the crust is still slowly rebounding toward isostatic balance
• C. Sea level in those regions is falling because of evaporation
• D. Plate collisions are building new mountains there

Answer: (B)

Ice sheets kilometers thick depressed the lithosphere into the mantle below. When the ice melted, the load was removed, but the mantle flows slowly, so the crust continues to rise. This is called glacial isostatic adjustment.