The Ballroom "Te Ana Ru" EarthCache

The above co-ords will take you to the entrance of one of Auckland's largest volcanic relict abrasion caves - Te Ana Ru, also known as "The Ballroom".

The Waitakere Ranges are the remnants of what originally formed the eastern slope of the giant Waitakere Volcano, which lay 20 km offshore and is now heavily eroded. The ranges dominate the western skyline of the Auckland isthmus.

The Oligocene Waitakere Volcano began life as an under sea volcano, erupting from the sea floor between 22-15 million years ago. Over the next 7 million years it gradually grew until it formed a large volcanic island, 50 km in diameter and 3000m in height.

Approximately 16 million years ago, two lines of smaller volcanoes erupted on the Waitakere Volcano’s eastern flank. These eruptions left behind large lava bombs, lava flows and domes of andesite lava, which can be seen in the cliffs, headlands and the bays of Auckland’s west coast.

Today there are nine abrasion caves still visible at the western part of the area along the coastline near Whatipu. The caves developed in a volcanic conglomerate along a North East - South West orientation, trending joint planes and fault lines. Abrasion was the main process responsible for the caves formation.

The development of the caves was controlled by lithology and tectonics of the volcanic rocks, especially by the fault bunches and was related to the zones of the loosened (less resistant for erosion) conglomerates. The rock, in which the caves were formed, consists of a volcanic formation, mainly shallow marine andesite breccia, andesite tuff, conglomerate, sandstone and siltstone and a mixture of gravel and sand left behind by the underwater lahars.

The caves are situated at the same level along the cliff wall. The smaller caves were formed along the bedding planes, while the other, larger caves developed in the fault zones. The looser rock formation near the fault planes encouraged this abrasion effect.

In recent times, a one kilometre wide sand flat has appeared between the caves and the Tasman Sea. The rapid acceleration of the coastal sand flat mostly occurred when a huge volume of sand was slowly being moved northward up the coast by sea currents. In the last 50 years, the sand flat has become stabilized and the sea never reaches the cliffs. As a consequence of this, the caves can be regarded as relict abrasion caves.

The Big Cave or “Te Ana Ru” has the largest and most spectacular entrance of these caves, at 18m wide and 8m high. A large, approximately 3500m³ abrasion chamber extends far beyond the entrance. The length of the cave, including the lowering and narrowing of the last 10m, is 56m. In the entrance area of the cave, a large amount of sand accumulated in the form of partly consolidated dunes. The dark dune sand has also invaded part of the large chamber.

This cave has its own history, it served as a shelter for early maori. In the late 1870's and up until 1922, the cave was used by the local timber-mill workers for social events and even had a dance floor, which was also called The Ballroom. Today the wooden kauri floor lies several metres below the intruding sands.

The caves are located within the Whatipu Scientific Reserve owned by the Department of Conservation and managed on behalf by the Auckland Regional Council. It is located approximately 1 hrs drive from downtown Auckland. To access the caves, cross the small bridge from the car park, and walk past the information shelter. Take the track on the right towards the Gibbons Track trailhead until you reach a track junction. Then follow the sign-posted Caves track on the left. It should take less than 15 minutes walking at a leisurely pace to reach the caves from here.

The listed co-ordinates will take you to the general area in front of the entrance of Te Ana Ru. Please feel free to explore all the other caves and tracks in this area. There is an ARC camp site at the end of this track at Pararaha.

While in the area, why not grab the nearby cache of GC1A2X2 Cutter Dog.

Please take care while exploring the caves, a good torch and hard hat is advised. Enjoy your visit here and respect the fragile environment. Finally, please practice Cache In Trash Out.