This earthcache will bring you to the South River inside Ridgeview Park in Waynesboro, VA. This section of the river will only be available during regular park hours, typically from dawn to dusk daily.
The South River is one of the most popular trout fishing streams in the area. Unfortunately it is also very polluted due to the heavy industry that has existed along this section making it inadvisable to consume any fish other than newly stocked trout from the river. On the other hand recent environmental efforts have begun making gains in cleaning the river. Only time will tell if this river will ever be the same again, but it is encouraging to see efforts being made.
While worth noting, the purpose of this cache is not to bring attention to the environmental plight of the South River, but to showcase the unique way in which the river has eroded the rock in this area.
You will notice some unique rock features running across the river at ground zero. These features are made up of a metamorphic rock known as slate. Slate is a common stone that is formed as the sedimentary rock, shale (composed of sediment such as clay, silt and mud), is heated and pressurized into metamorphic rock. When shale is put under pressure with temperatures of a few hundred degrees the clay begins to revert back to the mica minerals from which they formed. Two things then happen: first, the rock grows very hard, and second, the rock gets a pronounced cleavage direction, so that it breaks along flat planes. This cleavage, called slaty cleavage, is not always in the same direction as the original sedimentary bedding planes, so any fossils originally in the rock are usually erased, but sometimes they survive in smeared or stretched form.
The pressure and heat that causes metamorphic rock to form can occur in a couple of different ways.
The first is contact metamorphism. This occurs when magma is injected into the surrounding solid rock. The resulting heat and pressure causes rocks to become more indurated and more coarsely crystalline. Contact metamorphism typically occurs in a more localized area with the changes becoming less pronounced as you move further away from the magma injection.
The second way is regional metamorphism or dynamic metamorphism. This occurs when large areas of rock are transformed simply by being at great depths below the Earth’s surface. These rocks are subjected to high temperatures and great pressure caused by the immense weight of the rock layers above. Horizontal tectonic movements create orogenic belts and cause high temperatures, pressures and deformation in the rocks these belts.
Typically all of this is hidden at great depths beneath the Earth’s surface, but in some areas rivers have eroded away the top layers to reveal these unique geological features. The South River is one such place, giving us a glimpse into the Earth’s past, allowing us to see how these rocks formed.
To log this earthcache, go to the fishing deck located at the posted coordinates and email me the answers to the following questions.
1. What type of metamorphism do you think caused these rocks to form?
2. How do you think these rocks ended up protruding from the water at an angle?
Congratulations to Fishercacher on the FTF!