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Erosional Landforms – The Arch EarthCache

Hidden : 10/19/2022
Difficulty:
2.5 out of 5
Terrain:
3.5 out of 5

Size: Size:   other (other)

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Geocache Description:


Erosional Landforms
Erosional landforms include headlands, bays, cliffs, caves, arches, stacks, stumps and wave-cut platforms. The process of erosion can create different landforms along the coastline.
 
Headlands and bays
Cliffs along the coastline do not erode at the same pace. A cliff is a steep rock face. When a stretch of coastline is formed from different types of rock, headlands and bays can form.
 
Erosional features such as wave-cut platforms and cliffs can be found on headlands, since they are more open to the waves. Bays are more sheltered with constructive waves which deposit sediment to form a beach.
 
Headlands are surrounded by water on three sides. Headlands are characterized by high,  breaking waves, rocky shores,  intense erosion and steep sea cliffs. Headlands are formed on discordant coastlines, where bands of rock of alternating resistance run perpendicular to the coast. Wave refraction occurs on headlands concentrating wave energy on them,so many other landforms, form on headlands. Joints in the headlands are eroded back to form caves which erode further to form arches. These gaps eventually collapse and leave tall stacks at the ends of the headlands. Eventually these too are eroded by the waves. Wave refraction disperses wave energy through the bay, and along with the sheltering effect of the headlands this protects bays from storms. This effect means that the waves reaching the shore in a bay are weaker than the waves reaching the headland and the bay is thus a safer place for water activities like surfing or swimming. Through the deposition of sediment within the bay and the erosion of the headlands, coastlines eventually straighten out then start the same process all over again.
 
Cliffs and wave-cut platforms
Cliffs are shaped through erosion and weathering. Softer rock erodes quickly and forms gentle sloping cliffs, whereas hard rock is more resistant and forms steep cliffs. A wave-cut platform is a wide gently-sloping rocky surface found at the foot of a cliff.
 
Caves, arches, stacks and stumps are erosional features that are commonly found on a headland.
  1. Cracks are formed in the headland through the erosional processes of hydraulic action and abrasion.
  2. As the waves continue to grind away at the crack, it begins to open up to form a cave.
  3. The cave becomes larger and eventually breaks through the headland to form an arch.
  4. The base of the arch continually becomes wider through further erosion, until its roof becomes too heavy and collapses into the sea. This leaves a stack (an isolated column of rock).
  5. The stack is undercut at the base until it collapses to form a stump.
 
A sea cave is a tunnel or passage in the rock at the foot of a cliff.
  • If the rock has a weak spot like a crack, the waves will attack by hydraulic action, compressed air and abrasion.
  • The crack gets larger and develops into a cave.
A sea arch is a passage that runs through a headland.
  • If the cave is deepened and enlarged by erosion, it may cut through to the other side of the headland to form a sea arch.
  • A sea arch may also form if two caves on opposite sides of a headland meet.
A sea stack is a pillar of rock that is cut off from the headland or cliff.
  • When the waves erode the base of the sea arch, they widen it.
  • Eventually the roof is unable to support itself and it collapses, the former tip of the headland cut off as a sea stack.
In many coast line areas sea caves, sea arches and sea stacks can all be seen close together.
 
To log this cache please message the CO with answers to the following questions.
 
Question 1.
At GZ look to the headland towards the South East.  What geological feature can you see in this headland?
 
Question 2
Explain in your own words how this feature has been formed.
 
Question 3
At GZ look down into the water towards the North East ( Bird Rock Island).  What geological features can you see immediately in front of Bird Rock ? 
 
Question 4
Explain in your own words how these geological features have been formed?
 
Question 5
What animal does the feature immediately in front of Bird Rock resemble.
 
Logging  Requirements
In your cache log please post a photograph of yourself or your GPS device or your cacher name on a card  looking towards the South East.
 
A Find can be logged immediately, but it may be deleted if answers to the questions are not submitted within a period, of 10 days.

 

Additional Hints (No hints available.)