Differential Weathering

Monuments to weathering

Masses of rock do not weather uniformly. Take a moment to look back at the photo of Shiprock, New Mexico, in Figure 1.

Figure 1 – Volcanic neck Shiprock, New Mexico, is a volcanic neck that stands about 520 meters (1700 feet) high. It consists of igneous rock that crystallized in the vent of a volcano that has long since been

The durable volcanic neck protrudes high above the surrounding terrain. A glance at the chapter-opening photo of Joshua Tree National Park shows an additional example of this phenomenon, called differential weathering.

The results vary in scale from the rough, uneven surface of the marble headstone in to the boldly sculpted exposures of bedrock in New Mexico’s Bisti Badlands (Figure 2).

Figure 2 – Monuments to weathering This example of differential weathering is in New Mexico’s Bisti Badlands. When weathering accentuates differences in rocks, spectacular landforms are sometimes created.

Differential weathering and subsequent erosion are responsible for creating many unusual, often spectacular rock formations and landforms. Many factors influence the different rates of rock weathering. Among the most important are variations in rock composition. More resistant rock protrudes as ridges or pinnacles, or as steeper cliffs on an irregular hillside (see Figure 3).

Figure 3 – Shale crumbles easily This image was taken in the Grand Canyon. Hikers soon notice that the trail is usually gentler when layers of shale are encountered.

The number and spacing of joints can also be a significant factor (see Figure 4).

Figure 4 – The formation of rounded boulders Spheroidal weathering of extensively jointed rock.

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