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Logging Requirements: To log this earthcache, send an email or message to the cache owner with answers to the following questions. Do NOT include in your log either the answers (even if encrypted) or photos of the boulder or tree.
1. Name two ways that plants can cause biological weathering.
2. How far (in feet) did the boulder drop? In other words, how far are the tree roots above the current top of the boulder?
3. This tree grew from a seedling with a single root approximately 1/8 inch in diameter. Estimate the current diameter of the middle root exposed at the base of the tree trunk.
4. Which side of the tree did the boulder fall from, mainly right or mainly left? How do you know? Important information: Lichens (mostly light-colored, flat, crusty plant-like organisms which “hug” the rock tightly) are the first living things to grow on newly exposed rock. Mosses (dark green, softer, thicker plants) can only begin to grow on rockafter lichens are well established.
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At ground zero you will be standing across the creek from a solitary boulder which has been deposited at the edge of the water. How did it get there? A common means of rocks arriving in streambeds is by being washed downstream during floods. But this boulder is far too large to have been moved by the amount of water that might fill this tiny creek.
Looking around for another source of large rocks, you may notice the small cliff behind the boulder. The outcrop making up the cliff appears to be “solid as a rock.” But look at the large tree near the top that has its roots embedded deeply into the mountainside. Now you have found the source of the large boulder!
In the geologic process known as biological weathering, solid rock is slowly broken apart due to the pressure created by plant roots forcing their way into tiny cracks in the rock and then growing. As the roots become larger and larger, they can exert enough pressure to force the crack farther and farther open. In addition, organic acids produced by the living roots begin to eat away at the chemical makeup of the rock, weakening the rock still more, until a large rock can be cracked completely through.
In time, this piece of the rock was forced apart from the main outcrop. When rock material is moved from its original location, the term erosion is used. In the case of this outcrop, the downward force of gravity eventually pulled the loosened boulder away from the cliff, and the boulder dropped into the streambed.
Rock is constantly changing and moving. There’s no such thing as “solid as a rock!”
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http://geology.about.com/od/glossaryofgeology/g/deforgweathering.htm
http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1124303183&topicorder=5&maxto=6
http://www.ehow.com/facts_7459716_gravity-cause-erosion_.html
http://www.thinktrees.org/my_folders/Envirothon_Forestry_Resources_2010/FROM_ROCK_TO_TREE.pdf
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USFS rules state that geocaching is not permitted within Bent Creek Experimental Forest. Under a special use permit geocaches are permitted at The North Carolina Arboretum when placed and maintained by Arboretum staff only. Please refrain from adding additional caches.
The North Carolina Arboretum was established in 1986, and features a 434-acre public garden with over 10 miles of hiking and biking trails. For more information on fees and policies, visit our website at www.ncarboretum.org.