The mechanical weathering process that results in the enlargement of fractures and their extension deeper into large boulders and bedrock is frost wedging.

Here's how it works:

1. Water seeps into cracks: Water enters cracks and crevices in rocks.

2. Freezing: When temperatures drop below freezing, the water inside the cracks expands as it freezes into ice.

3. Expansion and pressure: The expansion of ice exerts significant pressure on the surrounding rock.

4. Crack widening: This pressure widens the existing cracks and can also create new ones.

5. Repeated cycles: As temperatures fluctuate, the freezing and thawing cycles repeat, progressively enlarging the cracks and pushing them deeper into the rock.

Over time, frost wedging can break down large boulders and even bedrock into smaller pieces, contributing to the overall weathering process.