Tombolos
Tombolos are coastal land formations that form to connect the mainland to an island. This can occur due to longshore drift, parallel to the shoreline, or wave refraction around the island. True tombolos are created as a result of wave refraction, and often one created by longshore drift or other processes is referred to as a spit.
"True" tombolos are formed by wave refraction. As waves near an island, they are slowed by the shallow water surrounding it. These waves then refract or “bend” around the island to the opposite side as they approach. The wave pattern created by this water movement causes a convergence of longshore drifting on the opposite side of the island. The beach sediments that are moving by lateral transport on the lee side of the island will accumulate there, conforming to the shape of the wave pattern. In other words, the waves sweep sediment together from both sides. Eventually, when enough sediment has built up, the beach shoreline, known as a spit, will connect with an island and form a tombolo. - Wikipedia
Panatahi Island
The tombolo that is forming at Panatahi Island, at the southern end of Karekare Beach, can be considered the result of two processes: The beach is itself is growing to meet the island in a process known as progradation, and wave refraction around the island is pulling the material deposited on the growing beach towards the island, accelerating the tombolo growth.
Until recently the island was separated from the mainland, but it is now possible to walk to the island at low tide due to the deposition of sand here.
This Earthcache
The published coordinates will take you to the south end of Karekare Beach, where the tombolo to Panatahi Island is forming. You will need to visit at mid-low tide to complete the tasks of this earthcache, and stay until low tide (really low tide, preferably) if you want to be able to walk to the island.
To claim a find on this earthcache, please complete the tasks outlined below. Answers to the questions should be emailed to the cache owner and not mentioned in your online log.
1. Visiting at mid-low tide, you can observe the wave action around Panatahi Island - describe the way the waves behave around the island.
2. In terms of the wave action, desribe any patterns/shapes in the sand, and relate this to how a tombolo forms.
3. Because tombolos, and their formation, are sensitive to weather patterns, please describe the weather and wind direction during your visit.
4. (Optional) Take a photo of yourself and/or your GPS with Panatahi Island in the background.
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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