1. Gravity: Gravity pulls everything downhill, including loose soil, rock, and water. This force is responsible for landslides, mudflows, and the slow, gradual erosion of slopes.

2. Water: Water is a powerful erosive force. It can move sediment, wear away rock, and carve out channels and valleys. This includes both surface water (rivers, streams, rain) and underground water (groundwater).

While these are the primary causes, other forces contribute to erosion:

* Wind: Wind can pick up and carry small particles of soil, sand, and rock, leading to wind erosion, especially in dry areas.

* Ice: Glaciers and ice sheets can carve out valleys and transport massive amounts of rock and sediment.

* Waves: Waves crashing against the shore can erode the coastline, creating cliffs and beaches.

* Human activity: Activities like deforestation, construction, and agriculture can accelerate erosion by disrupting natural processes and exposing soil to erosion.