Removal of vegetation. Down cutting by the river via abrasion by rocks and sand on the stream bottom. Abrasion rock fragments scrape the bedrock surface, much like coarse sandpaper. Glacial striations evidence of abrasion and movement. Moraines hill-like deposition that shows evidence of rock transport.
Air is a fluid, so wind behaves much like running water.
Naturally, the wind speed. Angle of repose. Water content in the soil. Vibrations from earthquakes. Wind speed and direction.