Latitude -28.397743, Longitude 153.271551
Located in the Northern Rivers Region of NSW, nearest town Murwillumbah
Source: National Parks and Wildlife Service and others
Captain James Cook named Mount Warning but it is known by the local aboriginal people as Wollumbin and considered by them as a sacred place. It is at the heart of the Wollumbin National Park which is one of "The Gondwana Rainforests of Australia World Heritage areas", that was inscribed on the World Heritage List in 1986.
Mt Warning is the remnant central plug of the Tweed shield volcano also known as the 'Tweed Caldera' and is one of the largest and best examples of an erosion caldera in the world, notable for its size, age and landforms that represent all three stages of the erosion of shield volcanoes: the planeze, residual and skeletal stages. Planeze means one of a series of triangular facets facing outward from a conical volcanic peak and separated by radiating streams which run down the flanks of the cone. A caldera is a bowl shaped depression caused by the collapse or erosion of a volcanic cone.
In its prime, the crater rim stood two kilometres tall with lava flows sprawled across more than 7000 sq. km. Erosion has stripped away almost a kilometre of softer material from Mt Warning's crown to expose the tough, crystalline rocks - trachy-andesite, rhyolite and syenite - that plugged the volcano's magma chamber. When active, the volcano secreted lava on to an ancient landscape composed of part of the eastern edge of the Clarence Moreton Basin and erosion has since cut right through the shield in places, exposing the older rocks of this basin. Most of the volcanic material was extruded from a central vent located at Mt Warning, as well as other lesser vents. This took place over a period of 3 million years via separate eruptions occurring between dormant intervals. The eruptions occurred in three phases, an initial extrusion of basalt, then a more volatile stage where acid material, mainly rhyolites, were thrown out sometimes explosively, from the vents, rhyolites, volcanic 'glass', agglomerates and tuffs were included in this group and a final gentler extrusion of basalt.
The caldera of the Mt Warning shield volcano has eroded over 23 million years and has a diameter of over 40kms, making it the biggest erosion caldera in the southern hemisphere and one of the largest calderas on earth.
The landform is the result of the different erosion rates of the two main rock types of basalt and rhyolite. The more erodable basalts which formed the bulk of the original shield volcano have been extensively worn. This has isolated the less erosive central vent of the original volcano, that is now Mt Warning, from the rest of its shield. It is encircled by the McPherson, Tweed, Nightcap and Koonyum Ranges which largely consist of the more erosion resistant rhyolite with areas of basalt on plateaus, foothills and lowland basins.
On the escarpment plateau, the basalt rock weathers to form krasnozems which are highly weathered red-clayey soils. The basalt on the slopes produce prairie soils which are brown to grey in colour and less acidic than krasnozems. Both are moderately fertile and tend to support rainforest and wet sclerophyll vegetation. Conversely, the rhyolites of the escarpment weather to produce less fertile yellow podzolic soils and support drier eucalypt vegetation types.
Deep gorges have been worn in the rhyolites where streams plunge over the cliffs at Purlingbrook, Minyon, and Tuntable Falls.
Undercutting of rock faces occurs beneath rhyolite cliffs especially where the rhyolite has covered a less resistant layer of tuff. Bushrangers Caves at the head of the Numinbah Valley is a good example as well as the base of Protester falls (see photo). There is well developed columnar structure of the grey to pink rhyolite at Minyon Falls.
The Wollumbin National Park is 12km south-west of Murwillumbah, off Kyogle Road.
Out of respect for Aboriginal law and culture, the Aboriginal people ask that you consider choosing not to climb Wollumbin-Mount Warning. If you do climb, be aware that it is a steep 9-km return trip, with a challenging final rock scramble. The return trip can take 4-5 hours, so be sure to leave enough time to get back before sunset.
In winter months it is not advisable to undertake the walk after 12 noon. Near the top you'll find a chain to help you up the last of the climb.
No overnight stays are permitted in the park, car-based and caravan camping are available at a privately run caravan park in the area.
More information can be obtained from the local National Parks and Wildlife office at 1/135 Main St Murwillumbah. Phone: 02 6670 8600