Question

why can crevasses in glaciers only be 50 meters deep?
a. plastic flow occurs below that depth.
b. glaciers cannot be thicker than 50 meters.
c. basal slip occurs below that depth.
d. surges prevent plastic flow below that depth.

Explanation:

Glaciers have brittle ice near the surface which cracks to form crevasses. Below about 50 meters, due to pressure, the ice undergoes plastic flow (deforms without cracking). Basal slip is related to glacier movement at the base. Glaciers can be thicker than 50 meters. Surges are rapid movements and not related to crevasse depth limitation in this context.

Answer:

A. Plastic flow occurs below that depth.