Latitude -35.623592, Longitude 148.683836
Located in the Snowy Mountains Region of NSW, nearest town Tumut
Source: Office of Environment & Heritage, National Parks and Wildlife service, Guide to New South Wales Karst and Caves.
The limestone at Cooleman Plain, in the Snowy Mountains Region of NSW, formed approximately 420 million years ago when it was thought to have collapsed into a marine caldera, the huge depression left by an explosive volcanic eruption. The large circular outcrop of limestone surrounded by mainly volcanic rock that remains today is evidence of this event.
A caldera is the result of a collapse that is triggered by the emptying of the magma chamber beneath a volcano, usually as a consequence of a large volcanic eruption. If enough magma is ejected, the emptied chamber is unable to support the weight of the volcanic edifice above it. A roughly circular fracture, a ring fault, then develops around the edge of the chamber. Ring faults serve as feeders for fault intrusions and are also known as ring dykes. Secondary volcanic vents may then form above the ring fracture. As the magma chamber empties, the centre of the volcano within the ring fracture begins to collapse. The collapse may occur as the result of a single cataclysmic eruption, or it may occur in stages as the result of a series of eruptions. The total area that collapses may be hundreds or thousands of square kilometres.
Cave and karst features first developed in the Cooleman limestone following its uplift above sea level (around 400 million years ago) before it was once again covered by the ocean and a layer of sedimentary rock. Upon lifting above sea level a second time, it took many millions of years of erosion to remove the sedimentary rocks overlying the limestone, re-exposing it some 65 million years ago. Most of the caves and features evident today have developed since the re-exposure, although some elements associated with the first land-forming phase 400 million years ago can also be distinguished.
Cooleman Plain Karst contains an outstanding collection of geologic features, including dry valleys, springs, stream sinks and more than 100 caves. It is commonly regarded as one of the most beautiful karst areas in NSW and can be viewed from the numerous walking tracks winding through the limestone gorges and over ridge tops, revealing striking rock formations, open limestone plains, springs, rivers, waterfalls and many caves.
Four of the main caves - Murrays, Barbers and the left and right Cooleman Caves- are predominantly horizontal and can be explored by torchlight. Though heavily souvenired (vandalised) in the 19th and 20th centuries, these and other caves at Cooleman Plain contain a wide range of cave formations created by the deposition of minerals (mainly calcite (speleothems)) and excellent examples of marine fossils are visible in many of the caves' bedrock walls. Speleothems are secondary mineral deposits formed in caves. The name covers formations such as: stalactites (roof down), stalagmites (ground up) and flowstone (usually located on the floor or walls of caves). Speleogens are pillar-like formations within caves that are created by the removal of bedrock, rather than as secondary deposits. Both Speleothems and Speleogens are in evidence in the Cooleman Plain Karst caves.
Nichols Gorge walk includes Cooleman and Murray caves: Clarke Gorge walk provides access to Barbers Cave and Cave Creek waterfall. The nearby lookout has excellent views to Cave Creek and spectacular limestone cliffs.
Blue Waterholes is the largest karst spring in Australia. The water in Blue Waterholes has a strong blue cast as a result of the minerals dissolved from the limestone. This colouring phenomenon is also visible at Jenolan Caves.
Clarke Gorge is accessed from Long Plain Road which leads off the Snowy Mountains Highway near Yarrangobilly Caves. The gorge is located at Blue Waterholes in the Kosciuszko National Park, where there is a car park, camping area, picnic tables, wood barbecues (bring your own firewood) and non-flush toilets. Long Plain Road is subject to closure between the June and October long weekends. This period may be brought forward or extended due to weather conditions. Check with the local NPWS office for more detailed road information.