Kettle lakes are primarily formed from ice blocks calving off melting glaciers and digging holes. As glaciers advance and retreat, ice chunks can become isolated as they break off from the main body of the glacier. When these blocks of ice melt, they create depressions in the ground that can fill with water, forming kettle lakes.
To clarify the other options:
- The weight of glacier ice pressing down can create depressions, but that process typically leads to different landforms like basins rather than kettle lakes.
- Sinkholes forming from underground streams are unrelated to the glacier formation process.
- Glacier movement does indeed carve the landscape, but kettle lakes specifically result from the melting of isolated ice blocks rather than general scraping of the ground.
So, the correct answer to how kettle lakes are formed is the one about ice blocks calving off melting glaciers.