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The Three Sisters is a rock formation, formerly consisting of three stacks, on the coast of northern Taranaki. One of the sisters has recently been toppled and only the base remains, giving us an excellent example of how our coastline is constantly changing.
Stacks
A stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast. Stacks are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.
Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. A stack may collapse or be eroded, leaving a stump.
Stacks typically form in horizontally bedded sedimentary or volcanic rocks particularly on limestone cliffs, because of the medium resistance to erosion. A more resistant layer may form a capstone. Cliffs with weaker rock such as clay tend to slump and erode too quickly to form stacks, while harder rocks such as granite erode in different ways.
The sea attacks small cracks and opens them. The cracks then gradually get larger and turn into a small cave. When the cave wears right through the headland, an arch forms. Further erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast called a stack.
source: wikipedia
This Earthcache
The cliffs in front of you show evidence of the formation of new caves, which may result in the creation of new stacks and other interesting coastal features in the centuries and millenia to come. In fact, a new sister (not quite visible from this view point) is currently being formed.
To log a find on this earthcache you must visit the published coordinates during daylight. There you must:
1. Answer this question: How many sea caves can you count (from where you are standing) forming in the small island in front of you, and the cliff to the left (along the edge of the river estuary)?
2. Take a photo including yourself, your GPS, and The Three Sisters. Example photos are shown below. Do NOT give away the answer to the question above.
In order for your online log to be valid, you must send the answer to the question above to the cache owner and you must upload the photo, clearly showing your GPS, with your online log.
You can log this cache straight away after you have emailed your answers to the cache owner, no need to wait for confirmation. Please include the name of this earthcache in the email - you'd be surprised how many people forget. Also, when contacting us with answers, if you want a reply, please include your email address. Any problems with your answers we'll be in touch.
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