Deep ravines are steep-sided valleys or depressions in the earth's surface. They can be formed by erosion, tectonic activity, or a combination of both. GULCHES, ABYSSES, COULEES, CHASMS, and GORGES are all types of deep ravines. GULCHES are narrow, steep-sided valleys with a stream running through them. ABYSSES are deep, steep-sided valleys with no water running through them. COULEES are long, winding, shallow valleys with a stream running through them. CHASMS are deep, narrow, steep-sided valleys with no water running through them. GORGES are deep, narrow, steep-sided valleys with a stream running through them. All of these deep ravines are characterized by their steep sides and depth.