"The Hole in the Rock" (Northland)
A cache by funkymunkyzone Hidden: 1/27/2009
Size:  (Not chosen) Difficulty: Terrain: (1 is easiest, 5 is hardest)
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| "The Hole in the Rock" |
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"The Hole in the Rock" is located off the northern coast of the
North Island of New Zealand. It is a popular tourist attraction in
the Bay of Islands region and can be found just off the northen tip
of Cape Brett.
The island was named "Piercy Island" by Captain James Cook, in
honour of one of the Lords of the Admiralty, but is also known as
"Motukokako" Island as it was named by early the Maori inhabitants
of the area.
The island is mostly barren, more of a rock than an island, and
its only inhabitants are gannets and other sea birds that use the
island as a nesting site.
The famous cave was created over centuries by the actions of
wave and wind against the rock causing erosion and fractures in the
rock that over time formed a cave all the way through from one side
of the island to the other.
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The Sea Cave
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More than half of the world's population live in coastal regions
so it should come as no surprise that coastal features provide a
source of recreation and a point of interest and inquiry as to
origins and formation. The coastline is an area of constant change
and development by forces much more powerful and unstoppable than
our own, and considerably faster than a lot of other geological
processes.
A sea cave, or littoral cave, is a type of cave primarily formed
by wave action from the sea and the primary process of cave
development is by erosion over time. Sea caves are found throughout
the world along forming along coastlines and presented as relict
caves on former coastlines.
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In order to form a sea cave, the wave action of the sea
typically acts upon a weakness in the rock, such as a natural fault
or bedding plane between two layers of rock. The driving force
behind the formation of the littoral cave is erosion, which, while
acting on the whole coastline, will yield more erosion activity
around the area of weakness, slowly tearing out a depression which
will eventually form an enclosed cave.
As the depression forms, the wave action is increased due to the
dynamics of the confined space, by both direct action and grinding
from rock particles borne by the waves. Adding to the hydraulic
power of the wave action is the abrasive force of the rock and sand
particles.
Most sea caves exhibit rough and rocky walls, indicating a
violent rock fracturing erosion process as opposed to smooth
surfaces that would tend to suggest a consistent flowing motion of
the water rather than that of turblent waves crashing.
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The Future
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History tells us that the future does not look good for "The
Hole in the Rock". It will eventually erode to a point where the
ceiling will collapse and the outer side of the cave will probably
become a stack or a stump, before it too eventually erodes into the
sea. This process will likely take many more centuries or millenia,
so there should be plenty of time yet to visit "The Hole in the
Rock".
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More About Motukokako
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The northern part of Piercy Island (Motukokako) presents a well
exposed example of a skarn containing babingtonite and ilvaite.
Large crystals (3-5mm in size) of babingtonite occur in a lead-zinc
skarn in tertiary limestone with associated ilvaite, garnet,
hedenburgite, epidote and axinite.
This represents New Zealand's best ilvaite exposure, with the
best of three babingtonite occurrences. This is classified as a
site of international geological importance. It is also classified
as a highly vulnerable site, with the major hazard being identified
as the over-collecting of minerals.
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This Earthcache
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In order to log a 'find' on this earthcache, you will need to
visit the published coordinates, take a photo of yourself and GPS
(the GPS must be clearly visible in the photo) and answer some
questions as below. The terrain rating of this cache is 5 because
access is by water only - either by private craft, tour or kayak if
the weather is good - in any case special equipment is most
definitely required!
Questions/Tasks:
1. Approximately how wide at sea level is the cave?
2. Approximately how tall is the cave from sea level?
3. Approximately how long is the cave?
4. What orientation, in relation to true north, is the cave
(to the nearest 10 degrees)?
5. Take a photo with "The Hole in the Rock" in the
background clearly showing yourself and your GPS - upload
this with your online log.
The questions above will require you to make estimates of
the cave dimensions. You are unlikely to find them on the internet
and they will probably not be part of any commentary, should you be
visiting by way of a boat tour. The orientation of the cave can be
estimated by using your GPS to mark waypoints outside each
entrance, or by using a compass.
Email the answers to questions 1 through 4 to the cache owner.
Do not post these answers in your online log. Your photo should be
uploaded with the online log.
No need to wait for confirmation email, go ahead and log online,
but be warned - any logs that do not include the photo showing GPS
as specified, and any that are not accompanied by an email with the
correct answers, will be deleted.
Happy (and Safe) Earthcaching!
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kiwicouple
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1 user(s) watching this cache.
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