Read the lesson below, visit the location, answer the following questions and send them to me by e-mail:
- In your own words, how does mechanical weathering work?
- Which type of mechanical weathering is most likely in action? Could more than one type affect these rocks?
- What type of mechanical weathering evidence are you observing on the rocks?
- Do the rocks near the tree line at the base of the hill appear to be part of the larger rocks near the parking area?
- With your "found it" log, include a photo of you or your group at the overlook. Optionally, you can take a photo of a personal item such as a geocoin or a piece of paper with your geocaching name.
If your answers are profoundly off, I’ll contact you. Otherwise, please log your find after you send an e-mail. In the e-mail, please indicate your geocaching name and include the names of other geocachers with you. Logs without accompanying answers sent will be deleted without notice. According to the guidelines, sending the answers is a requirement, not a request.
The Weathering Process
Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, water, and biological organisms. There are two main categories: mechanical and chemical. Some sources also include biological weathering, and biological factors typically contribute to the mechanical and chemical processes. This EarthCache though will focus on how mechanical weathering works.
Mechanical Weathering
Mechanical weathering is the physical breakdown of rocks by environmental factors. It makes big rocks into little ones, without changing their mineral or chemical composition.
There are four main types of mechanical weathering:
Frost Wedging – Most common in mountainous regions and occurs when water seeps into cracks in a rock and freezes, expanding and pushing the rock apart, possibly breaking off pieces. Typically takes multiple cycles of freezing and thawing.
Thermal Expansion – Basically this is expansion from the rock being heated and typically only the outer layer of a rock breaks off. Rocks do not absorb heat very well, so the outer layer heats up, causing expansion and then eventually breaks off while the inner portion remains cool.
Unloading – This type happens to igneous rocks and is also called sheeting or exfoliation. As the rock is exposed, it is released from the extreme pressure of being buried in the earth. Because of this pressure release, over time, the minerals expand and separate from the underlying rock, typically in sheets as seen below.
Abrasion – This is the most common type of mechanical weathering and occurs when rocks scrape against one another. An example of this could be glacial action where the glacier picks up rocks that eventually scrape with others, or wind action where the wind picks up bits of sand or other debris that impacts or scrapes against rock outcrops.
Observing Mechanical Weathering
One of the easiest ways to see the impact of mechanical weathering is by looking for joints. These are simply rock fractures along which no observable rock movement has occurred. When you see a joint in a rock, you are observing mechanical weathering in action.
Based on the surrounding terrain, gravity, and other factors, pieces of rock that have broken off from the “parent” rock can roll downhill or simply remain where they have split off. The weathering process then continues throughout though, eventually converting the rocks into sediments and soils.
FDR State Park
At 9,049 acres, Georgia’s largest state park is a hiker’s and backpacker’s haven. More than 40 miles of trails, including the popular 23-mile Pine Mountain Trail, wind through hardwood and pines, over creeks and past small waterfalls. Many visitors are surprised to find rolling mountains 80 miles southwest of Atlanta. Above King’s Gap is Dowdell’s Knob where President Franklin D. Roosevelt sometimes picnicked and pondered world affairs. A life-size sculpture of the president now welcomes visitors to the overlook.
Park Hours
7am – 10pm
Dowdell's Knob Hours
April–September 8 a.m.–8 p.m.
October–March 8 a.m.–5 p.m.
Fees and Passes: Daily $5 parking fee but annual passes are available.
While you're visiting Dowdell's Knob, make sure you also check out the other EarthCache: Chemical Weathering at Dowdell's Knob GC84QZR.
Sources
FDR State Park: gastateparks.org/FDRoosevelt
study.com/academy/lesson/mechanical-weathering-definition-process-types-examples.html
geography4kids.com/files/land_weathering.html
en.wikipedia.org/wiki/Weathering
Geology for Dummies by Alecia Spooner
Geology: A Self-Teaching Guide by Barbara Murck
Understanding Earth, 6th Edition by John Grotzinger and Tom Jordan