South River Waterfall EarthCache
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Who doesn’t love a waterfall? Besides small cascades along streams, there are large and lovely waterfalls in each section of Shenandoah National Park. All are accessible from a parking place along Skyline Drive. But note that all involve a hike downhill—and, of course, the harder hike back up! All waterfalls are along blue-blazed, forested trails.
South River Falls access is located at mile post 62.8 along Skyline drive at the below parking coordinates. The hike is a 4.8-mile(900 ft. elevation change) moderately strenuous round trip hike from picnic area to observation point of the waterfall and then to base of falls. To return by a different route, take the fire road and AT back up to make a 4.8 mile circuit. I have listed way-points below with mileage markers to assist in your journey to the falls!
Waterfalls are commonly formed when a river is young. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens slowly, while downstream the erosion occurs more rapidly. As the watercourse increases its velocity at the edge of the waterfall, it plucks material from the riverbed. Whirlpools created in the turbulence as well as sand and stones carried by the watercourse increase the erosion capacity. This causes the waterfall to carve deeper into the bed and to recede upstream. Often over time, the waterfall will recede back to form a canyon or gorge downstream as it recedes upstream, and it will carve deeper into the ridge above it. The rate of retreat for a waterfall can be as high as one and half meters per year.
Often, the rock stratum just below the more resistant shelf will be of a softer type, meaning that undercutting due to splashback will occur here to form a shallow cave-like formation known as a rock shelter under and behind the waterfall. Eventually, the outcropping, more resistant cap rock will collapse under pressure to add blocks of rock to the base of the waterfall. These blocks of rock are then broken down into smaller boulders by attrition as they collide with each other, and they also erode the base of the waterfall by abrasion, creating a deep plunge pool or gorge.
Typical Erosion-Formed Waterfalls
Streams become wider and shallower just above waterfalls due to flowing over the rock shelf, and there is usually a deep area just below the waterfall because of the kinetic energy of the water hitting the bottom. Waterfalls normally form in a rocky area due to erosion. After a long period of being fully formed, the water falling off the ledge will retreat, causing a horizontal pit parallel to the waterfall wall. Eventually, as the pit grows deeper, the waterfall collapses to be replaced by a steeply sloping stretch of river bed. In addition to gradual processes such as erosion, earth movement caused by earthquakes or landslides or volcanoes can cause a differential in land heights which interfere with the natural course of a water flow, and result in waterfalls.
Lava Formed Waterfalls(non-erosion formed)
The waterfalls within Shenandoah National Park are formed by the erosion of a landscape that is underlain by a thick pile of ancient lava flows. The Catoctin Formation lava flows are stacked in a layered sequence that dips gently towards the east. These lava flows are comprised of erosion-resistant greenstone. As water passes over these ancient lava flows, it flows gently down the surface of one flow, then it cascades steeply as it tries to cut down through the thick erosion-resistant greenstone, and then, when it hits the surface of the underlying lava flow, it flows gently again. This forms a stair-step landscape, where the waterfall forms over the steps. The look of these cascading waterfalls can change drastically during different times of the year. The flow will be very little during times of drought and not be as spectacular as they are during and shortly after a heavy rain.
The Cache :
To claim this is an earthcache find, you must go to the posted coordinates and;
1 While it is not required, please take a photo with you and your GPSR with the falls in the background.
2 At Waypoint T2(N 38° 22.793 W 078° 29.998) What natural feature is prominent in this area that is referenced in the cache description and what direction are they dipping?
3 There are two major drops/stair-step that make up this waterfall overall height of 83 ft. Estimate the height of the second drop/stair-step to the slide into the plunge/drop pool at the base of the falls.
4 What is the depth and estimate width of the plunge/drop pool at the base of the falls. What makes this different from typical plunge/drop pools of more common waterfalls in other areas of the country and why?
Please send your answers via email.
Please remember that waterfalls take thousands of years to create and can also be very dangerous, especially in the areas closer to the falls that stay continuously wet, making them extremely slippery! Be safe....respectful of the area do not climb on the falls and view from a safe distance at designated viewing areas. Practice the "leave no trace policy".
Special Thanks to the Tim and Sally with Shenandoah National Park Service for their assistance and approval of this earthcache!
Sources:
Wikipedia
Geology Along Skyline Drive-Robert Badger
Sally Hurlbert-Resident Geologist Shenandoah National Park
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