As waves pass around Islands and other land masses they refract. Their shape and size alters as energy is dissipated when it passes around the land mass. This causes a convergence of long shore current or drift on the sheltered lee side of the island, where sand or sediment can build up, eventually forming a spit or sand bar. When this spit or sand bar connects the island to another land mass, it is known as a Tombolo.
Where a Tombolo connects an island to another landmass, it is known as a Tied Island.
It is also possible to have clusters of Tombolos where several islands are tied together by Tombolos.
The picture below shows an example of a Tombolo (picture source wikipedia).
To gain permission to log this Earthcache you must email the answers to the following questions to the cache owner. Please do not post your answers on line, however you are most welcome to post photos of the area on line if you wish to.
At GZ, you are standing next to a large geological feature that protrudes vertically from the tombolo, which connects South Bruny Island and North Bruny Island.
1. a. What is that feature? would it be a separate island if the sand spit didn't exist?
1.b. Estimate the height of the feature. If you can access it then you can use your GPS to estimate its height.
2. a. Looking out at Adventure Bay and beyond to Storm Bay (to the east of the Tombolo), what are the sea conditions (wave size, wave direction, any visible current)?
2. b. How do you think these conditions might affect the Tombolo?
Finally, take a look at the sand or sediment that has built up on the beach on either side of the Tombolo.
3. a. Does the sand or sediment on each side of the Tombolo look the same or different?
3. b. Describe your answer in terms of where you think the sand or sediment came from and how it came to be part of the Tombolo and why it is either the same or different on either side of the Tombolo.
I hope that you will learn a little about Tombolos in general and this Tombolo in particular as you work to get your answers.
Please feel free to log your visit as soon as you have submitted your answers. I will respond confirming permission to log, or asking clarifying questions if I feel that you have not answered the questions correctly.