Glaciology and Mountain Geography – Snow line in the Rocky Mountains (USA) Approximately at what elevation above mean sea level is the permanent snow line observed in the Rocky Mountains of the United States, considering continental climate conditions?

Introduction / Context:
The term snow line refers to the altitude above mean sea level where snow persists year-round, balancing accumulation and melt. Its height varies with latitude, continentality, and local climate. In mid-latitude continental ranges like the Rocky Mountains (USA), the snow line is substantially higher than in maritime ranges at the same latitude.

Given Data / Assumptions:

• Region: Rocky Mountains of the United States.
• Climatic type: predominantly continental (drier air, greater summer melt).
• Asked quantity: approximate altitude of the permanent snow line.

Concept / Approach:
Snow line elevation increases with decreasing latitude and with increasing continentality. Dry, sunny summers promote ablation, raising the equilibrium line altitude. In the mid-latitudes of the western USA, many glaciers and perennial snowfields cluster near or above about 3,000–3,500 m. Values around 6,000 m are unrealistic for the contiguous USA, and sea level snow lines occur only in polar regions.

Step-by-Step Solution:
Identify the target mountain system and its latitude: mid-latitudes with inland continental influences.Recall typical equilibrium line altitudes in the Rockies: near 3,000–3,500 m depending on aspect and region.Compare choices: 3 km is plausible; 6 km exceeds North America’s highest peaks; sea level applies only to polar coasts.Select the closest appropriate figure: 3 km above sea level.

Verification / Alternative check:
Topographic maps and glacier inventories show persistent summer snow and small glaciers primarily above ~3,000 m in Colorado’s Front Range and other Rocky subranges, confirming the order of magnitude.

Why Other Options Are Wrong:

• 6 km above sea level: beyond the summit elevations of the Rockies; physically impossible there.
• It is at sea level: occurs in Antarctica and parts of Greenland, not in the mid-latitude USA.
• None of the above: incorrect because ~3 km is a sound general approximation.

Common Pitfalls:
Confusing the winter snowline (seasonal) with the perennial snow line. Do not generalize maritime values (lower) to continental interiors (higher).

Final Answer:
3 km above sea level