How did glaciers shape the valleys and mountains of the Rocky Mountains?

Glaciers have played a transformative role in shaping the dramatic landscape of the Rocky Mountains, primarily through intense erosion during multiple periods of glaciation.12

As valley glaciers moved through the mountains, they drastically reshaped existing V-shaped river valleys into characteristic U-shaped valleys by scouring the bedrock along the valley floors and lower sidewalls. This process also sharpened the surrounding terrain:34
* Cirques and Tarns: Glaciers carved amphitheatre-shaped hollows known as cirques into the mountainsides. When these basins were over-deepened and later filled with water, they formed mountain lakes called tarns.34
* Arêtes and Horns: The headward erosion of multiple cirques narrowed the divides between parallel valleys into jagged, knife-edged ridges called arêtes. Where several cirques met around a single mountain, they left behind sharp, steep-sided peaks known as horns.34

Additionally, glaciers left behind distinct deposits, such as looping moraines that mark the extent of past ice coverage, further defining the rugged alpine scenery observed today.14