The picture above shows a glacier in eastern Greenland, in the world’s largest national park, flowing from mountains at the top of Jameson Land (at the top of the picture) toward the lowlands of Kong Oskar Fjord (just out of the picture at the bottom).

The yellow arrow from the letter C is pointing at a geological feature. What is that feature?

Question

The picture above shows a glacier in eastern Greenland, in the world’s largest national park, flowing from mountains at the top of Jameson Land (at the top of the picture) toward the lowlands of Kong Oskar Fjord (just out of the picture at the bottom).
 
The yellow arrow from the letter C is pointing at a geological feature. What is that feature?

BlackTom AI · Accepted Answer

Moraines are ridges of unsorted glacial debris (till) deposited at the margins or terminus of a glacier, so the feature at C is a moraine produced when the glacier stopped or retreated and left a pile of transported rock and sediment.

1) Relevant knowledge points and concepts
- Glacier zones: accumulation zone (upper part where snowfall adds mass) and ablation zone (lower part where melting, sublimation and calving remove mass).
- Mass balance: glaciers retreat when ablation exceeds accumulation (more melting or less snowfall).
- Moraines: terminal/recessional moraines form at the snout when debris is dumped as the glacier stalls or retreats; lateral moraines form along the valley sides where debris accumulates.

2) Step-by-step reasoning
- The arrow points to a sinuous, raised, dark ridge at the glacier margin/valley floor — morphology typical of a deposited ridge of mixed rock debris, not a carved bedrock ridge.
- Aretes are sharp bedrock ridges formed between two cirques; they are narrow, knife-like, and lie above glacier valleys, not as a low ridge of loose sediment beside the glacier.
- The presence of a ridge at the former glacier margin indicates deposition during retreat, consistent with a moraine.

3) Calculations
- No numerical calculations are required; reasoning is morphological and process-based.

4) Why the correct answer is correct
- The correct answer names a moraine and correctly links retreat to increased melting in the ablation zone and/or decreased snowfall in the accumulation zone — this is the standard explanation for negative glacier mass balance and moraine formation during retreat.

5) Why other options are incorrect
- Options that swap “ablation” and “accumulation” describe physically inconsistent causes (melting occurs in the ablation zone, not the accumulation zone).
- The arete options are wrong because an arete is a bedrock ridge carved by ice, not a deposited ridge of till.
- The “dirty ring” option is a joke and not a geological explanation.

6) Conclusion
- Therefore the feature is a moraine left behind when the glacier retreated because of increased melting in the ablation zone and/or decreased snowfall in the accumulation zone, matching the provided correct answer.

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