Coolah Tops - Lava Cave? EarthCache

Coolah Tops National Park is a steep elevated basalt plateau that covers the junction of the eastern end of the Warrumbungle Range and the western limit of the Liverpool Range. Formed during the Tertiary Period (approximately 66 million to 2.6 million years ago), the plateau rises to 1200m ASL and is home to an abundance of wildlife and interesting geological features. Additionally, many tall open forests thrive in the area and the tallest silvertop stringybark on record is situated here. The park is also known for its very large grass trees that are believed to be around 300 years old.

BE PREPARED FOR SOME EXTREMES
Between 950 to 1000 mm of rain falls on Coolah Tops annually, with December to February the wettest periods. Temperatures range from -10°c (overnight minimum) to 16°c maximum in winter and 16 to 40°c in summer. Light snow falls occur most years with big dumps every 2 - 3 years. There are frequent frosts over the open parts of the forest in winter, but be prepared for cold weather anytime as temperatures can plummet suddenly, especially at night.

According to the U.S. Geological Survey website, the definition of a cave is:

“A natural opening in the ground extending beyond the zone of light and large enough to permit the entry of man. Occurring in a wide variety of rock types and caused by widely differing geological processes, caves range in size from single small rooms to interconnecting passages many miles long”

There are two main categories of caves; primary and secondary. Primary caves are caves that have been formed whilst the host rock is solidifying, such as a lava tube. Secondary caves are far more common, and are formed by erosion or carving of the host rock after it has solidified. Occasionally, erosion or tectonic movement can reshape primary caves.

The four most common types of cave are:

• Solution Caves. These are the most common caves and are formed when soluble rock such as limestone, gypsum or dolomite dissolve. Acidic water dissolves the rock, seeping through the bedding planes.
• Lava Caves. These are primary caves because they form at the same time as the surrounding rock. Sometimes lava flow creates a hollow tube, which results in the cave.
• Sea Caves. As the name suggests, these are formed by the waves and swell of the sea. They can be both over and under water.
• Glacier Caves. These caves are not formed in rock, but in glaciers.

Other, more uncommon types of caves include:

• Fracture caves. Formed when a soluble layer, such as gypsum, dissolves, causing the rocks around it to collapse.
• Talus caves. These unstable and dangerous caves are formed by the openings among large boulders that have fallen down into a random heap.
• Eolian caves. Commonly found in deserts, these caves can be very large and impressive. Fine sand or silt is blown against a rock face by the wind with a sandblasting effect creating the formations.
• Anchialine caves. These are usually found in coastal regions and contain a mixture of freshwater and salt water.

Coolah Tops is home to several caves that can be found at the base of an impressive 100m basalt cliff on the north-east side of Rocky Creek Gorge. One cave in particular, known as the 'Lava Cave', is the largest cave yet to be found in the Coolah area, and has been the topic of much discussion regarding its formation. At the very rear of this cave, there is a loooooong tunnel (which you will get to explore as part of this EarthCache!) that suggests a possible lava tube. However, features usually associated with lava tubes; a lining, flow features, clinkery floor and lava stalactites are absent, while the occurrence of both amygdaloidal and massive basalt in the caves indicate erosion has taken place. A 1979 study of the cave by Robert Armstrong Osborne of the University of Sydney resulted in the theory that the cave appears to have been formed by groundwater erosion of zeolite rich amygdaloidal basalt.

The Lava Cave track follows the base of the basalt cliff and is an amazing experience in itself. You will notice many unique rock formations and unusual colours on the cliff wall due to weathering and varying mineral content of the basalt. Basalt consists mainly of the mineral groups plagioclase, pyroxene, and magnetite. High concentrations of plagioclase and weathering can cause basalt to be light-coloured, whereas the iron found in pyroxene and magnetite gives basalt it's dark black appearance.

Coolah Tops National Park is located about 30km east of Coolah and is reached via The Forest Road. The Forest Road runs through the park providing access to all the main sites (there are lots of excellent camping locations available at many of these sites). Access is along dirt roads and care should be taken during or after wet weather as they can become slippery and boggy. 2wd is not advisable in adverse conditions.

Take note of the terrain rating!
This cave is an incredible location to visit, however it is a tough walk and can only be accessed by following a very steep and rocky unmarked track from The Pinnacle Lookout (bring your camera - the views are incredible!).
We do not recommend visiting this location during or after wet weather. Allow at least 4 hours return.

In order to log this EarthCache, you must visit the location and answer the following questions:

1. At the listed coordinates, stand at the entrance of the cave and estimate the height and width in metres.
2. As you stand at the entrance looking in, there is a small cave to your right with a distinct contrast of colouration in the surrounding basalt to the right-hand side of this small cave. What colours do you see, and what do you think has caused it?
3. Now time for some fun! Make your way to the rear of the cave where you will see a long tunnel that is 5 metres wide and 1.9 metres high. Using your torch, enter the tunnel and estimate the length in metres (you will need to go in a little distance in order to see the end as there are 2 bends. A mobile phone torch will not be strong enough unless you're brave enough to crawl to the very rear where there undoubtedly will be large hungry creatures!).
4. Examine this tunnel and try to find any evidence that it could be a lava tube? (look for lava stalactites, flow features, a lining, clinkery floor). With your findings, what category and type of cave do you believe the 'Lava Cave' is? There are several signs within Coolah Tops National Park that mention the 'Lava Cave'. Do you think it has been correctly named?
5. Optional - take a photo of you and/or your GPS in the cave.

Please then email, or send a message (through geocaching.com), your answers to the above questions. Feel free to log your find in anticipation - we'll let you know if there are any issues. Logs without the emailed answers may be deleted.