Plate tectonics and powerful streams eroding into hillsides have been attributed with creating the steepness of mountain slopes.

Researchers studied images of over 15,000 landslides and found that small increases in slope angle above 30 degrees translated into large increases in landslide erosion as gravity overcame the strength of the bedrock.

The creation of landslides and mountainside angles was also recreated with sand. When pouring sand into a pile, similar angles are formed (about 35 degrees) and when material at the base of hill slopes is removed, landslides occur.