A ridge is a geological feature that features a continuous elevational crest for some distance. Ridges are usually termed hills or mountains as well, depending on size. There are several main types of ridges:
- Dendritic ridge: In a typical plateau terrain, the stream drainage valleys will leave intervening ridges. These are by far the most common ridges. These ridges usually represent slightly harder rock, but not always -- they're often simply due to the fact that there were larger joint spaces where the valleys formed, or other chance occurrences. This type of ridge is generally somewhat random in orientation, often changing direction frequently, often with knobs at intervals on the ridge top.
- Stratigraphic ridge: In places such as the Ridge-and-valley Appalachians, very long, very even, very straight ridges are formed due to the fact that they're the uneroded remaining edges of the more resistant strata that were folded laterally. Similar ridges have formed in places such as the Black Hills, where the ridges form concentric circles around the igneous core. Sometimes these ridges are called "hogback ridges".
- Oceanic spreading ridge: In tectonic spreading zones around the world, such as at the Mid-Atlantic Ridge, the volcanic activity forming new plate boundary forms volcanic ridges at the spreading zone. Isostatic settling and erosion gradually reduce the elevations moving away from the zone.
- Crater ridges: Large meteorite strikes typically form large craters bordered by circular ridges.
- Volcanic caldera ridges: Large volcanoes often leave collapsed central calderas that are bordered by circular ridges.
- Thrust fault ridges: Thrust faults often form escarpments. Sometimes the tops of the escarpments form not plateaus, but slope back so that the edges of the escarpments form ridges.
- Dune ridges: In areas of large-scale dune activity, certain types of dunes result in sand ridges.