Glaciers often form parallel scratches and grooves in bedrock because glaciers move.

Here's why:

* Glaciers are massive rivers of ice: They flow slowly but relentlessly under the force of gravity.

* Embedded rocks and debris: As the glacier moves, it carries rocks and debris within its ice. These act like sandpaper.

* Scouring action: The embedded rocks scrape against the bedrock as the glacier moves, creating parallel scratches and grooves.

These scratches and grooves are called glacial striations. They provide valuable clues about the direction and movement of past glaciers.