A Small Sea Cave #1 (Auckland) EarthCache
A Small Sea Cave #1 (Auckland)
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Size: 
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A sea cave, also known as a littoral cave, is a type of cave formed primarily by the wave action of the sea.
The primary process involved is erosion. Sea caves are found throughout the world, actively forming along present coastlines and as relict sea caves on former coastlines. In places like Thailand's Phang Nga Bay, solutional caves have been flooded by the rising sea and are now subject to littoral erosion.
Littoral caves may be found in a wide variety of host rocks, ranging from sedimentary to metamorphic to igneous, but caves in the latter tend to be larger due to the greater strength of the host rock.
In order to form a sea cave, the host rock must first contain a zone of relative weakness. In metamorphic or igneous rock, this is typically either a fault as in the caves of the Channel Islands of California, or a dyke as in the large sea caves of Kauai, Hawaii’s Na Pali Coast. In sedimentary rocks, this may be a bedding-plane parting or a contact between layers of different hardness. The latter may also occur in igneous rocks, such as in the caves on Santa Cruz Island, California, where waves have attacked the contact between the andesitic basalt and the agglomerate.
The driving force in littoral cave development is wave action. Erosion is ongoing anywhere that waves batter rocky coasts, but where sea cliffs contain zones of weakness, rock is removed at a greater rate along these zones. As the sea reaches into the fissures thus formed, they begin to widen and deepen due to the tremendous force exerted within a confined space, not only by direct action of the surf and any rock particles that it bears, but also by compression of air within. Blowholes (partially submerged caves that eject large sprays of sea water as waves retreat and allow rapid re-expansion of air compressed within), attest to this process. Adding to the hydraulic power of the waves is the abrasive force of suspended sand and rock. Most sea-cave walls are irregular and chunky, reflecting an erosional process where the rock is fractured piece by piece.
The type of rock that is present in this area is Postglacial Alluvium, and doesnt change for roughly 5 Km's west of the cave, at which point it changes to Postglacial Alluvium and dune sand.An Expert informs me that this cave would of taken around 150,000 years to get to what it is today.
Best time to visit is low tide, though a few hours either side of high tide and you should be ok.
Tide times for Onehunga can be found here:Tides
To log this EarthCache, you must do the following and email us the results. You can go ahead and log your find, (ie. you don't need to wait for permission) but if we don’t think you have honestly completed the required tasks we will delete your log (after emailing you first of course):
1) Measure the mouth of the Cave, at ground level.
2)Measure the depth of the cave, from the mouth to the face, at ground level.
3)Take a photo of yourself with gps within 20 meters of ground zero, without the cave in the background.
Please email me this info, please DO NOT post it with your log.
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