What develops as glaciers move over a ridge or cliff?

The correct answer is that crevasses develop as glaciers move over a ridge or cliff. As a glacier flows, it deforms and may encounter obstacles such as ridges or cliffs. The movement of the glacier causes stress and strain, leading to the formation of deep cracks or fractures in the ice, known as crevasses. These structures are indicative of the dynamic processes at work within glaciers, as they adapt to changes in topography.

In contrast, moraines are accumulations of debris and sediment that are left behind as glaciers advance or retreat, which means they form as a result of glacial activity but are not directly caused by the glacier moving over a ridge. Tarns are small mountain lakes formed in depressions left by glaciers, and cirques are amphitheater-like valleys created by the erosion of a glacier at the head of a valley. Both tarns and cirques are the end products of glacial processes rather than directly related to the movement of glaciers over ridges.