Granite tors form when magma cools and contracts below softer rock. Over time, erosion exposes the granite batholith and cracks form from contraction and pressure release. Freeze-thaw weathering from water in the cracks causes them to widen and break off scree. This leaves characteristic smooth, round edges and visible joints in the exposed tor. Dartmoor National Park in England has many popular granite tors for tourists to visit, such as Bowermans Nose, Black Tor, and Hay Tor.