Forest Geology Trail
The above coords are for the trailhead to the Forest Geology Trail with the "Talking Rock" Trail. This is where your adventure for this earthcache begins. Follow the "yellow" trail. I was in awe as I hiked along the trail and saw so much beauty while I listened to the seven "Talking Rocks" and read the signs about how the rocks relate to the soil, the forest, and us.
NOTE: At the waterfall, turn left and continue on the boardwalk. It makes a loop, so you will come back where you started.
Some of the things I learned were that:
(1) 25 million years ago the ocean covered this area with sharks and whales and how from all
this, limestone was formed. A beach was located somewhere near Raleigh;
(2) some rocks contain fossils, traces of ancient life -
like dinosaur footprints, ancient fishbones and other neat stuff;
(3) the ingredient of your cola that gives it its tangy taste is phosphate acid, made from
phosphate rocks; and
(4) how rocks influence our life today.
As you hike, you will find:
1) a rock that was formed over 300 million years ago;
2) the oldest rock located in this forest formed over 600 million years ago;
3) a waterfall;
4) running cedar and so much more.
What other interesting things did you find and/or see on the trail?
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Layers of Soil
On the trail, you will come to a display with a list of the layers of soil. Our group did not know what some of these were, so I am including definitions here.
DUFF is decaying leaves and branches covering a forest floor.
HUMUS is rich, highly decomposed organic matter mostly made from dead plants, crunched-up leaves, dead insects and twigs.
TOPSOIL is the upper, outermost layer of soil, usually the top 2 inches to 8 inches. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. The topsoil is relatively thin but it has most of the soil’s nutrients.
SUBSOIL is the soil lying immediately under the surface soil (topsoil). The subsoil may contain some broken down organic matter but it is mostly made of weathered rocks and clay minerals.
PARENT MATERIAL is the underlying geological material (generally bedrock or a superficial or drift deposit) in which soil horizons form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are often classified based upon their contents of consolidated or unconsolidated mineral material that has undergone some degree of physical or chemical weathering and the mode by which the materials were most recently transported.
ROCKS are the solid mineral material forming part of the surface of the earth, exposed on the surface or underlying the soil or oceans.
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Weathering
The difference between weathering and erosion is that weathering occurs with no movement of the rock; whereas erosion does involve the movement of rocks and minerals.
Two types of weathering:
1. MECHANICAL WEATHERING involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure.
It takes place when rocks are broken down without any change in the chemical nature of the rocks. The rocks are essentially torn apart by physical force, rather than by chemical breakdown.
The most common type of mechanical weathering is the constant freezing, and thawing of water. In liquid form, water is able to penetrate the many holes, joints, and fissures within a rock. As the temperature drops below 32 ° F, this water freezes. As water freezes, it expands, becoming about 10% larger than it was in liquid form. The result is that the holes and cracks in rocks are pushed outward. Even the strongest rocks are no match for this force.
Temperature changes also effect mechanical weathering. As temperatures heat up, the rocks themselves expand somewhat. As the temperatures cool down, rocks contract slightly. The effect can be the weakening of the rock itself.
Plant roots can make a crack in the rock and as time passes it gets longer and cuts more into the rock until the rock eventurally breaks. It can also split rocks apart as they grow which causes pressure.
2. CHEMICAL WEATHERING is the direct effect of atmospheric chemicals or biologically produced chemicals also known as biological weathering in the breakdown of rocks, soils and minerals.
Chemical weathering takes place in almost all types of rocks. Smaller rocks are more susceptible, however, because they have a greater amount of surface area. Chemical reactions break down the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces. Chemical weathering is much more common in locations where there is a lot of water. This is because water is important to many of the chemical reactions that can take place. Warmer temperatures are also more friendly to chemical weathering.
Chemical weathering is any type of weathering that is caused by living organisms. Plants create an acid that breaks the rock down and use its minerals for nutrients.
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Both types of weathering occur together, and each tends to accelerate the other.
The materials left over after the rock breaks down combined with organic material creates soil. The mineral content of the soil is determined by the parent material, thus a soil derived from a single rock type can often be deficient in one of more minerals for good fertility, while a soil weathered from a mix of rock types (as in glacial, aeolian or alluvial sediments) often makes more fertile soil.
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