Anahulu Cave
The spectacular Anahulu Cave is a limestone solution cave that has formed in the coral rock that covers the entire island of Tongatapu.
The coral island of Tongatapu sits on ancient volcanic rock on top of the Tonga ridge - the ridge along the edge of the Indo-Australian tectonic plate, being thrust upwards as the Pacific plate subducts underneath it. The island has been raised out of the sea by the action of changes in the sea level, and tilted towards the North and by more recent volcanic activity in the island chain where new volcanic activity is weighing down on the crust tilting the northern coast of Tongatapu gently into the sea and raising 10m high cliffs into the sea on the southern coast.
With the ancient coral limestone raised from the sea and exposed to the elements, solution caves can form from the action of rainwater, acidified by decomposing organic matter on the surface, seeping through cracks and opening them up to form caves. It is possible that the Anahulu Cave initially formed as a sea cave, but evidence found in the cave, in the form of stalactite and stalagmite formations, suggest that the cave has been above sea level for a considerable length of time.
The cave contains a number of enormous and dramatic speleothems (cave decorations) that can be closely examined and which are continuing to grow. As a visitor to the cave, you will be able to enter for a small fee of 15TOP (approx 7USD) and be guided about 50 metres down and into the cave, past beautiful rock formations, and to a deep freshwater pool that you can swim in and it is here where you will be expected to perform the required task in order to log this earthcache.
This Earthcache
In order to log this earthcache as found you need to visit the site and complete an educational task. The answer to the following question should be emailed to the cache owner by using the link at the top of the cache page. Do not include any spoilers to the answers in your online log. You will need to enter the cave and proceed down to the freshwater pool in order to complete this task.
Questions: The water level in the cave may rise and fall a small amount seasonally, but thinking on a geological time scale (thousands of years), can you find evidence of a major change of water level within the cave? If so, was this change a raising or lowering of water level, and in terms of cave formations (not colouring of the cave walls), what evidence can be seen that supports this conclusion?
Required Photos: Take some photos of speleothems (cave decorations) within the cave, or of yourself visiting the cave, and post them with your online log. This is a mandatory requirement.
You can log this earthcache as soon as you have emailed your answers to the above questions. Logs that do not follow such an email, or do not include at least one photo from the cave, will be deleted.
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First to learn something while swimming in the dark:
Cats&Dragons
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