40 Acre Rock Swirl Holes EarthCache
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Located in 40 Acre Park. Please be careful when hiking in the area as there are sheer drop offs from the rock in places and areas are open for hunting.
Visitors please do not step into the shallow pools on 40 Acre Rock. They contain very fragile, globally endangered plants that are listed by the US Fish and Wildlife Service as federally-endangered, which means they are in danger of becoming extinct. These plants are very small, hard to see unless blooming, and extremely fragile.
A rock Swirl hole, aka Pothole, is formed when sand, pebbles and small rocks are spun around on bedrock by river currents or wind. As they spin they work like sandpaper and slowly start to grind away the softer rock. The result looks familiar to a pot hole. Once they are started they can vary in size from small to very large depending on the size of the bedrock and the amount of time the river current/wind is strong enough to push the rocks.
The action of the rocks swirling around in the pothole literally just "drills" down into the bedrock. In the process the stones and pebbles wear away at themselves as well as the bedrock until they are small enough to get out of the hole and they are replaced by other pebbles until the hole fills in or a stone breaks through the downstream side of the pothole.
Geologists recognize two kinds of potholes in bedrock channels -- vertical and lateral.
Vertical potholes formed on rock surfaces that were at one time part of the rock floor. These potholes are now exposed because that portion of the rock has been raised above the active river. Vertical potholes can be several meters deep and across. Viewed from the top, they are almost round and plunge nearly vertically into the rock. If you clear the hole of its accumulated debris, you might see at the bottom spoon like depressions separated from each other by water-smoothed ridges.
The second kind, lateral potholes, tell very different stories. These potholes cut into the rocky sides of channels or into sides of rocks that stuck out of the channel as mini-islands. Lateral potholes appear lopsided, having rounded down-stream ends and narrowing upstream ends, somewhat resembling the shell of a garden snail. This asymmetry tells the direction of former flow.
Lateral potholes commonly have an overhanging part and have shallow, simple basins, in contrast to the complex chambers of vertical potholes. Lateral potholes, once considered remains of broken vertical potholes, formed near the river's surface, where rock, water and air meet, instead of at the river bottom.
Swirl Holes are formed on top of 40 Acre Rock not by rivers but by wind and rain water. Pebbles or rocks will get trapped in a small hole and high winds will cause them to "drill" into the rock much like a river current would.
To log this cache you must:
#1 - What is the depth of the swirl hole located at the posted coordinates. Use the deepest edge.
#2 - What type of swirl hole is the one at posted coordinates? (Vertical or Lateral)
#3 - What is the elevation of this swirl hole?
#4 - What is the length of the swirl hole at the posted coordinates?
#5 - What type of swirl hole is located at Stage 2?
#6 - What type of swirl hole is located at Stage 3?
Please email answers through my profile. Thanks!
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