What is weathering?

Weathering is the chemical alteration and physical breakdown of rock during exposure to the atmosphere, hydrosphere, and biosphere. As a result of weathering, the Earth is everywhere covered by an irregular blanker of loose rock debris or soil.

There are two types of weathering, both of which occur at Clark Creek.

First there is Chemical Weathering, that is the decomposition of rocks and minerals as chemical reactions transform them into new chemical combinations that are stable at or near the Earth's surface.

Some of the photos to the left from Clark Creek illustrate chemical weathering. In picture 1, oxidation has taken place. The outer (cream) layer formed from the inner (blue) layer as oxygen from the atmosphere caused the ferrous iron in the inner layer to change to ferric iron..In picture 2, you can see red splotches in the wall of sedimentary rock. The red areas are actually deposits of an iron oxide mineral called hematite.

The other type of weathering is Physical Weathering, that is the disintegration (physical breakup) of rocks. The two processes generally work hand in hand, and their effects are inseparably blended.

Plant roots (Picture 3) have grown into sedimentary rock and caused cracks to form. Ultimately, the wedging action of the roots may cause some of the wall to collapse, exposing the inner rock. This type of weathering was seen all over the Clark Creek area.

Below is an outline of the different processes involved in weathering.

I. PHYSICAL WEATHERING

A. Development of Joints

B. Crystal Growth

C. Frost Wedging

D. Effects of Heat (Spalls)

E. Plant Roots

II. CHEMICAL WEATHERING PROCESSES -

Named for the kind of chemical reaction taking place.

A. Hydrolysis

B. Leaching

C. Oxidation

D. Dissolution
 
 

III. FACTORS THAT INFLUENCE WEATHERING

A. Rock type and structure

B. Slope

C. Climate

D. Burrowing Animals

E. Time