The Landforms of Oregon EarthCache
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An Earthcache near the intersection of the North and South sections of the 804 trail. Best parking for this Earthcache is at Smelt Sands or you can use the parking lot at the Yachats State Park.
Coastal erosion is the wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, or drainage (see also beach evolution). Waves, generated by storms, wind, or fast moving motor craft, cause coastal erosion, which may take the form of long-term losses of sediment and rocks, or merely the temporary redistribution of coastal sediments; erosion in one location may result in accretion nearby.
The hardness or ‘erodibility’ of sea-facing rocks is controlled by the rock strength and the presence of fissures, fractures, and beds of non-cohesive materials such as silt and fine sand. The rate at which cliff fall debris is removed from the foreshore depends on the power of the waves crossing the beach. This energy must reach a critical level to remove material from the debris lobe. Debris lobes can be very persistent and can take many years to completely disappear. Beaches dissipate wave energy on the foreshore and provide a measure of protection to the adjoining land. The stability of the foreshore, or its resistance to lowering. Once stable, the foreshore should widen and become more effective at dissipating the wave energy, so that fewer and less powerful waves reach beyond it. The provision of updrift material coming onto the foreshore beneath the cliff helps ensure a stable beach. The adjacent bathymetry, or configuration of the seafloor, controls the wave energy arriving at the coast, and can have an important influence on the rate of cliff erosion. Shoals and bars offer protection from wave erosion by causing storm waves to break and dissipate their energy before reaching the shore. Given the dynamic nature of the seafloor, changes in the location of shoals and bars may cause the locus of beach or cliff erosion to change position along the shore. Coastal erosion has been greatly affected by the rising sea levels globally. There has been great measures of incresed coastal erosion on the Eastern seaboard of the United States.
Your location is on an ancient, rocky beach that was originally formed by wave erosion before the last ice age when the sea level was higher than it is presently. Now the rocks are being ended by wave action for the second time, producing massive boulders and sculptured forms. Most of the dark colored rocks that you see at this end of the trail are basalt. Much of the basalt is mixed with a combination of sandstone and siltstone, rocks formed by sedimentary deposits. At the north end of the trail is sandstone known to geologists as the Yaquina Formation, which may be as much as 25,000,000 years old. The exposed, weathered sandstone often appears as rust colored, rough spheres. Short, sandy “pocket” beaches found in the rocky beach are where the waves have eroded a fracture in the rocks.
To claim credit for this Earthcache you will need to email the answers for the following three questions to the cache owner. Failure to properly email answers may result in your log being deleted.
Question 1: The study of erosion and sediment redistribution is called ___________ _____________.?
Question 2: Where the waves have eroded fractures... why is this happening at this particular location?
Question 3: What is the Smelt Sands beach just to the north of this location know for?
Question 4: Estimate the height of the dune at this location.br />
Although Pictures are not necessary to log this cache... we hope you will post pictures of the nearby location on this cache page for the enjoyment of others.
RESOURCES : Wikipedia, Geology books
Additional Hints
(Decrypt)
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