Death Valley is filled with countless examples of weathering. One way this process works significantly upon rocks is through joints (cracks or fractures in rock); joints speed up the process of weathering by allowing access to space within the rock for chemical and physical weathering to take place. An example of a rock with many joints and on-going physical weathering is pictured below.
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| The faint white coloring of salt along some of the joints in this rock (e.g. the white colored cracks in the shadowed portions of the rock towards the bottom right and bottom left of the photograph) are evidence of salt weathering, a typical kind of weathering in desert environments (click the photo to enlarge it). Photo credit: http://www.flickr.com/photos/7230309@N05/2657404804/ |
Physical weathering in dry places like Death Valley often takes the form of salt weathering because there is insufficient moisture to wash away the accumulation of salts. The effect of salt weathering on rock can lead to a specific form and process called cavernous weathering. Two types of cavernous weathering are displayed in the following pictures.
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The large, smooth, gaping, cave-like holes in this boulder are called Tafoni and they are the result of salt weathering. Photo credit: http://www.geog.le.ac.uk/staff/.
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The small but distinct holes on the side of this rock are good examples of Alveoli and are also the result of salt weathering. Photo credit: www.portervillecollege.edu/.
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Another form and process of weathering that we can find in Death Valley is that of case hardening. Case hardening is a term used to describe rocks that have outer shells that are more resistant to erosion than what is beneath that external shell. The picture below illustrates the concept nicely.
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| The two egg-shaped boulders in the center of the photograph are examples of case hardening. The resistant outer layer (called a weathering rind) developed a rock varnish, which made it less vulnerable to erosion than the parts beneath it. Photo credit: http://avtanski.net/images/var/boulders.jpg |
In addition to physical weathering there is also the process of chemical weathering occuring in Death Valley. Spheroidal forms such as the ones pictured below result from a type of chemical weathering called spheroidal weathering.
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| Spheroidal forms are produced when chemical weathering first begins on the corner of rocks. When this happens, the rock takes on a spheroidal shape. As erosion wears down the surrounding material, the rocks become exposed to the surface and we are left with a collection of boulders such as the ones in this picture. Photo credit: http://jennifercutler.com. |
In arid desert environments such as Death Valley, chemical weathering can profoundly effect granite by the process of biotite weathering.
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| This rock shows advanced erosion through biotite weathering, which is a specific type of chemical weathering process that involves oxidation. Biotite weathering has eroded the granite to such an extent that the surrounding ground has accumulated a large amount of small pieces of coarse granular sand. This granite sand (visible on the ground in the photograph) is called grus. Photo credit: http://portervillecollege.edu/ |
