Ridge

A ridge is a long, narrow, elevated geomorphologic landform, structural feature, or a combination of both separated from the surrounding terrain by steep sides. The sides of a ridge slope away from a narrow top, called the crest or ridgecrest, with the land dropping down on either side. If the crest is very narrow, it is also called a ridgeline.

Ridges can vary greatly in size. Their height above the surrounding land can be as small as less than a meter or as large as hundreds of meters. They can form in many ways, including through depositional processes, erosional forces, or tectonic movements, or a mix of these factors. Depending on their origin, ridges can be made of solid bedrock, loose sediment, lava, or even ice.

Ridges can exist on their own as independent features or as part of larger landscapes. Often, they can be divided into smaller parts based on their shape and structure. Understanding ridges helps scientists study the Earth’s surface and how it changes over time.

Classification

There isn't a single way to group or describe ridges, as they can be sorted based on how they were formed, how they look, what they are made of, or by using special data from satellites and other tools.

One way to classify ridges, used by soil experts in the United States, looks at the main natural process or setting that shaped the land. This method splits landforms, including ridges, into two big groups: Geomorphic Environments and Other Groupings, with 16 smaller groups in total. Ridges can appear in many of these smaller groups, such as those formed by wind, water, glaciers, volcanoes, or tectonic forces.

Aeolian ridge

An aeolian dune ridge is a ridge made of sand piled up by the wind. Sand dunes can be small hills or long ridges, ranging from less than a meter to many kilometers in length, and can be a few centimeters to over 150 meters tall. Very large dunes, called megadunes or draas, can have smaller dunes on top of them.

Coastal ridges

A beach ridge is a low, continuous ridge made of sand and other materials from the beach, formed by waves and currents. These ridges are found along shorelines, often in lines running parallel to the coast.

Erosional ridges

In areas where plateaus have been worn down by rivers, the valleys leave behind ridges in between. These ridges are very common and usually occur where the rock is slightly harder to erode, though sometimes it’s just by chance. They often change direction and can have rounded bumps on top.

Glacial ridges

Glacial movements can leave behind ridges called moraines and eskers. An arête is a thin ridge of rock shaped by glacial erosion.

Tectonic and Structural ridges

In areas where tectonic plates spread apart, volcanic activity creates new land and forms ridges, like at the Mid-Atlantic Ridge. Large asteroid impacts can also create circular ridges around the craters they form.

Volcanic and hydrothermal ridges

In volcanic areas, ridges can form from lava flows pushing up under a hardened surface, creating buckled shapes called tumuli. Large volcanoes often have craters or calderas with ridges around their edges. When volcanoes erupt under glaciers, they can create ridges made of volcanic ash called tindars.