This is an Earthcache. There is no physical container at the posted coordinates, but rather a geological lesson for you to explore. Please review the information on the cache page, then make your way to Ground Zero to make your observations and answer the three questions below. Email your answers to the cache owner by clicking the "message this owner" button above, and once complete, you can log this cache.
Thanks and happy caching!
QUESTIONS
1. Is there any potholing present at the base of the falls?
2. Describe the stratum at the base of the falls. Are there any signs of undercutting?
3. Are attrition and abrasion present? Don't forget to look downstream!
(Optional) Post a picture of yourself at GZ during your visit.
Welcome to Elakala Falls, one of the more hidden waterfalls at Blackwater Falls State Park. Just a short drive away from the main falls, this impressive water feature flows along Shay's Run and provides excellent photo opportunities all year long. The trail to GZ is gradual, with the final 200 feet being steep and rocky. Most observations can be made from the footbridge above the falls, but to really enjoy the full geological lesson here, you'll want to make your way to the foot of the falls. This earthcache explores the geological significance of this location and challenges you to think critically about the evolution of this beautiful West Virginia location.
The Geology of a Waterfall
The caprock model of waterfall formation states that the river courses over resistant bedrock, erosion happens slowly and is dominated by impacts of water-borne sediment on the rock, while downstream the erosion occurs more rapidly. As the watercourse increases its velocity at the edge of the waterfall, it may pluck material from the riverbed, if the bed is fractured or otherwise more erodible. Hydraulic jets and hydraulic jumps at the toe of a fall can generate large forces to erode the bed, especially when forces are amplified by water-borne sediment. Horseshoe-shaped falls focus the erosion to a central point, also enhancing riverbed change below a waterfall.
A process known as "potholing" involves local erosion of a potentially deep hole in bedrock due to turbulent whirlpools spinning stones around on the bed, drilling it out. Sand and stones carried by the watercourse, therefore, increase 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 1.5 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 in the gorge downstream.
Streams can 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. However, a study of waterfalls systematics reported that waterfalls can be wider or narrower above or below a falls, so almost anything is possible given the right geological and hydrological setting. Waterfalls normally form in rocky areas 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 lead to the formation of waterfalls.
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