The fine sediment that results from the crushing of rock under a glacier is called glacial flour.

Here's why:

* Glacial Erosion: Glaciers are incredibly powerful forces of erosion. Their immense weight and slow, grinding movement pulverize rocks into tiny particles.

* Fine Grain Size: Glacial flour is characterized by its exceptionally small particle size, often less than 0.0625 mm (0.0025 inches) in diameter. This makes it feel like a fine powder.

* Appearance: Glacial flour is typically light gray or white in color due to the presence of quartz and other light-colored minerals.

* Impact on Water: When glacial flour mixes with meltwater, it gives the water a milky, turquoise appearance. This is a distinctive feature of glacial lakes and rivers.

Let me know if you have any other questions!