Exfoliation Weathering
The exfoliation, sheeting, or unloading is a physical weathering process.
For this process to occur several steps are required. It can happen with different rock types, but for this Earthcache, we will be concidering granites.
- Magma moves towards the crust but stops short. The magma forces open a cavitity that it fills. See the below image for the different structures that magma can create underground. The magma is under great pressures from both the forces from deep inside the Earth that force the magma towards the surface. The other pressure is from the overbearing rock layers from above the magma chambers.
- The magma slowly cools which is how granite can form the crystals it is composed of. The granite is still under high pressures.
- The overbearing rocks layers are eroded away. This exposes the once under ground mass of granite at the Earth's surface. As the overburden is eroded, the pressure is reduced in the granite.
- The release of the pressure causes the outer layers to expand or rebound more so than material farther from the surface. These expansions cause linear to curvilinear fractures or joints. Which can be thought of as like the layers of an onion.
- Other erosional processes cause the thin layers to brake down further. Such as freezeing and thawing of water, heating and cooling from the sun and chemical weathering.
- Also, it can increase spaces between individual mineral grains, or what is called particle disintegration. Particle disintegration happens along individual grain or crystal boundaries.
Logging Requirements.
When examining this piece of granite, please limit your touching of it. Excessive toughing will result in the Exfoliation process to be disturbed and future finders will not have a good experince here. Thank you.
Answer following questions.
1) Do you feel that Exfoliation Weathering is taking place on this specimen?
2) Look for the area that Exfoliation Weathering is taking place on this piece of granite. In your estimate, what percentage of the surface shows signs of Exfoliation Weathering.
3) How many types of granite are present on this specimen?
4) Describe all of them (color, crystal size)?
5) Post a photo near the posted coordinates. Your face doesn't need to be in the photo. A signature item or paper with your geocaching name on it can be used instead of your face.