Weathering processes are often obvious in mountainous regions.
Weathering is one of the early processes of geological denudation -- that is, of the breaking down, removal and transport of rock materials. Evaluating the degree of weathering means assessing rock type and climate -- factors that help establish the rate and nature of the breakdown -- as well as the mechanism of the weathering itself. Mechanical and biological weathering involve physical and biological forces, respectively, wedging apart rock; chemical weathering takes the form of chemical reactions that dissolve or transform it.
Instructions
1. Consider your particular landscape's underlying geology. Certain kinds of rocks and rock structures are more vulnerable to weathering: For example, limestone is easily excavated by chemical dissolution as water seeps through its pores and the resulting cavities expose the rock to agents of mechanical weathering.
2. The high temperatures of warmer latitudes promote greater rates of chemical weathering.
Investigate the region's climate, which plays a significant role in weathering. Wetter areas provide more precipitation for all sorts of rock breakdown, and the higher temperatures of subtropical and tropical climates often result in higher rates of chemical weathering.
3. Signs of frost wedging are often prominent in boulders on high mountain reaches.
Look for evidence of frost wedging. This occurs when water seeps into rock pores and interstices, or gaps, and freezes, expanding as it forms ice. After melting, the water can penetrate further before freezing again. This repetitive cycle of freezing and thawing can exert tremendous cumulative pressure, prying rocks apart and even fully shattering them.
4. Salt wedging may be particularly prominent in dry climates.
Watch for the similar process of salt wedging, which sometimes is an important mode of weathering, especially in arid climates. In this case, water is evaporated through the interstices of rock, leaving behind salt crystals that had been suspended in the liquid. These salt structures can act the same way as ice, forcing apart sections of rock.
5. The famous granite walls of Yosemite show signs of exfoliation.
Keep an eye out for the unmistakable evidence of exfoliation. Exfoliation removes strips or plates of material from boulders, domes, platforms and other rock masses, the result of weathering upon contoured and concentric joints. This process may involve both chemical and mechanical weathering, but may be mainly due to releases of pressure on rocks thrust to Earth's surface or to extremes of temperature.
6. Chemical weathering can excavate cavities in limestone layers.
Identify signs of chemical weathering, which may work alone or in concert with mechanical forces. Along with the dissolution of carbonate rocks, these can include oxidation, such as the rusting of rock-faces high in iron content.
7. Mountaintop pines can weather rock with their penetrating roots.
Look for the relatively small-scale evidence of biological weathering. This can include the penetration of rock by plant roots -- often seen in trees situated on sheer rock surfaces. The presence of lichen, which can weaken rock by extracting nutrients and by repeatedly expanding and contracting, is another possible sign.
8. Evaluate the degree of weathering after searching for visual clues revealing these processes. A large, solid rock-face without many joints or cracks may be only in the beginning stages of mechanical weathering, at least from a visible angle. One heavily enervated by cavities or deeply rusted has likely been subject to chemical weathering for some time.
Tags: chemical weathering, mechanical weathering, biological weathering, chemical weathering, frost wedging
