Here's why:

* Ice: Glaciers are primarily made of ice, formed from compacted snow over long periods.

* Rocks and Soil: As glaciers move, they pick up rocks and soil from the mountainside, incorporating them into their flow.

* Slow Movement: Glaciers move very slowly, often just a few inches or feet per day, due to the weight of the ice and gravity.

Let me know if you have any other questions about glaciers!