Porosity, the void space in rock, was conventionally thought to be produced when water flows through the rock, thus resulting in minerals chemically dissolving. Because mountain watershed provides large reservoirs of water, the new findings are relevant to water resource management throughout the U.S.
“It’s important to understand what is going on in the subsurface layer. It has enormous capacity to store water. In mountain landscapes, the saprolite may be the only thing keeping forests alive during times of drought,” says Cliff Riebe, an associate professor in UW’s Department of Geology and Geophysics. “This has been known for a while. What we don’t know is ‘How does the storage space get produced?’ Saprolite is difficult to access. You have to dig down under the soil. It’s rarely been studied. Understanding this layer between the soil and rock is important.”
Saprolite, which Riebe refers to as “rotten rock,” is the zone of weathered rock that retains the relative positions of mineral grains of the parent bedrock and lies between the layer of soil and harder rock underneath. As an example, Riebe says saprolite is much like the weathered granite found on the flat areas surrounding the hard granite of Vedauwoo.
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