Here's why:

* Formation: Arêtes are sharp, narrow ridges that form between two cirques (bowl-shaped depressions carved by glaciers).

* Erosion Process: Glaciers erode the surrounding rock by plucking (lifting out pieces of rock) and abrasion (grinding and scraping). This erosion process creates the steep walls of the cirques and leaves the narrow ridge, the arête, standing between them.

In summary, arêtes are not formed by deposition of material, but by the erosive power of glaciers.