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Solutional Caves
Solutional caves are the most frequently occurring caves and such caves form in rock that is soluble, such as limestone, but can also form in other rocks, including chalk, dolomite, marble, salt, and gypsum. Rock is dissolved by natural acid in groundwater that seeps through bedding-planes, faults, joints etc. Over geological epochs cracks expand to become caves or cave systems.
The largest and most abundant solutional caves are located in limestone. Limestone dissolves under the action of rainwater and groundwater charged with H2CO3 (carbonic acid) and naturally occurring organic acids. The dissolution process produces a distinctive landform known as karst, characterized by sinkholes, and underground drainage. Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation. These include flowstones, stalactites, stalagmites, helictites, soda straws and columns. These secondary mineral deposits in caves are called speleothems.
The portions of a solutional cave that are below the water table or the local level of the groundwater will be flooded.
A Legendary Place
Lake Te Anau is New Zealand's second largest lake. According to Maori legend, this large body of water was created by an unfaithful wife's deception.
According to the legend, the Maori chief Te Horo discovered a sacred spring and asked his wife not to reveal to anyone else its existence. When he departed on a journey, however, she showed it to her lover.
As soon as the lover's face was reflected in the water, a raging torrent burst out, drowning the village and forming Lake Te Anau.
Rediscovery of the Caves
In the mid 20th century, the Te Ana-au Caves were known only as a place of legend. Maori folklore told of a cave filled with swirling water. Early European explorers also spoke of underground caves in the area.
Over time, however, the location of the caves became lost in history. A local tour operator, named Lawson Burrows, was so intrigued by the tales that he spent three years searching for the legendary spring. In 1948 he found a spring gushing out of the hills along the edge of Lake Te Anau.
He slipped into the cold water, squeezed through the rocky entrance and surfaced inside the dark cave. Above his head he was stunned to see thousands of glittering glowworms.
Te Ana-au "Swirling Water" Caves
Located on the western shores of Late Te Anau, the Te Ana-au Caves are part of a 6.7km, four-level limestone labyrinth known as the Aurora Caves system.
The Te Ana-au Caves, at the lower level of the caves system, are very young in geological terms, only about 12000 years old. The limestone and sandstone that they carve through, on the contrary, is ancient - up to 35 million years old. The upper levels of the cave system are much older, but these parts are not easily accessible, and are not the subject of this earthcache.
Unlike many dry cave systems, the Te Ana-au Caves are still increasing in size. The river that flows through the caves is mildly acidic, which helps the water dissolve the rock and create passages, accelerating the erosion process.
The acidity of the water flowing through the caves is produced from carbon dioxide originating from the humus (forest floor) high above the caves.
This Earthcache
In order to log this earthcache, you will need to visit the solutional "karst" cave located at the published coordinates and perform the tasks listed below. Answers are to be emailed to the cache owner, and not included in your online log.
Throughout the caves, you will see clear examples of the chemical and erosional processes present. The tasks required to be completed for this earthcache will take you inside the caves where you will need to observe and describe formations and processes. All of the tasks can be completed at the site, but you may need to perform some additional research after your visit, based on your observations within the caves. Whatever the case may be, you must visit the caves in order to log this earthcache.
No photos may be taken within the caves, and no samples may be collected from them.
1. These caves cut through layers of limestone and sandstone. Identify the limestone and sandstone and describe the two types of rock in terms of colour and formation (eg layer thickness).
2. Which of these two rock types - sandstone and limestone - is eroded faster in the Te Ana-au Caves?
3. What can be often seen in the water as evidence of the chemical nature of the water and the erosion process (an information panel in the whirlpool chamber may help)?
4. What is the name of the river that passes through the Te Ana-au Caves?
5. Describe the nature of any speleothems (cave decorations) you observe within these caves.
6. (Optional) Please take a photo outside the cave entrance, including your GPS unit and the stream and/or the cave entrance. Do not take any photos inside the cave as this is not allowed. You should upload this photo with your online log - don't email it to the cache owner.
You can log this cache as soon as you have emailed your answers, 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, if you want a reply, please include your email address. Any problems with your answers we'll be in touch.
Access to the Caves
Unless you have a boat and can get a permit from the Dept of Conservation to visit the area, it is likely you will need to pay to be taken across the lake to the caves. At time of publishing, the costs are $70 per adult and $22 per child.
While there are steps within the cave, most people should be fine. Some bending is required at the cave entrance due to a low ceiling, but otherwise the cave itself would qualify for around a 2 star terrain rating.
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