Mount Gambier Volcanic Complex State Heritage Area
LocationThe Mount Gambier Volcanic Complex consists of a series of craters and other volcanic features on the southern edge of the city of Mount Gambier, approximately 480 kilometres south-east of Adelaide. The boundaries of this State Heritage Area protect the sides and rim of the craters that form the Blue Lake, Leg of Mutton Lake, Valley Lake and Browne Lake. Also included in the designated area is the associated volcanic feature known as the Devil's Punchbowl. View Public Notice (300Kb PDF). Significance
The declaration of the Mount Gambier Volcanic Complex State Heritage Area, on 11 June 1992, recognises the region's geological significance as south-eastern Australia's most recent site of volcanic activity. The designation also acknowledges the area's historic role as a major tourist destination since the 1880s. This geological complex represents the final phase of volcanic activity that occurred approximately 4 000 years ago (carbon-dating). When these eruptions took place the area's shallow water table caused steam to rapidly accumulate, resulting in explosive volcanism that created characteristic craters (maars) as well as steam vents or blowholes. The largest of these (the Blue Lake) is recognised as one of the best-preserved examples of this type of crater in the world. This crater-lake complex is an important geological site for teaching about, and continuing scientific research into, volcanic activity in Australia.
The volcanic upheaval also exposed the region's water table, filling the craters and producing the four lakes that have become well-known tourist attractions and centres for local recreational activities. The town's water supply is drawn from the famous Blue Lake, named for the cobalt-blue colour of the water between November to March each year. Two hectares, near the Leg of Mutton Lake, are historically significant as the site of a tree nursery established in 1876. Pinus radiata, which now dominates forestry in the south-east, was first cultivated from this site in the 1870s. Mount Gambier is a designated South Australian Geological Monument. GeologyThe most obvious features of this geological complex are a series of volcanic craters, some of which bottom below the water table and so contain lakes. These crater lakes are the result of explosive volcanic activity and a build-up of ejected material - not calderas (formed by the collapse of rock), as often described. Carbon-14 dating and palaeomagnetic results agree that the eruptions at Mount Gambier occurred as late as 4 000 to 4 300 years ago, making it possibly the youngest volcanic feature on mainland Australia.
Initial eruptions occurred at the present sites of the Tenison College Oval and the Leg of Mutton Lake crater. Small, low, open explosion craters (maars) were produced, covering the countryside with ash and small pea-shaped droplets of solidified lava (lapilli). Lava flowed from fissures near the present-day Browne Lake and from a vent near what is now Leg of Mutton Lake. A scoria cone, now partly exposed in the crater walls west of Browne Lake, completed the first stage of eruptions. Activity ceased temporarily, allowing time for lava flows to cool and crystallise. The next period of volcanic activity took place on a much larger scale. During the dormant years, ground water percolated into the underground channels and mixed with the hot and possibly molten lava at depth. The resultant explosions caused the large craters that are obvious today, containing Blue, Valley and Browne Lakes. During these later eruptions many large blocks, known as 'bombs' and potentially weighing many tonnes, were thrown out of the craters. One of the best examples can still be seen in the road cutting on the north-west corner of the intersection of Crouch and Gwendoline Streets.
The Leg of Mutton crater was a late stage feature, while lava fountaining in Browne Lake was the last magmatic event. Volcanic activity ended with steam venting through blowholes, such as those at the Devil's Punchbowl and the Blowhole in Boandik Terrace. Active volcanism within the entire complex is believed to have lasted over a period of two to three centuries. The largest and most famous of the crater lakes is the Blue Lake, named for the cobalt blue colour of the water during certain months (November to March). Popular theories suggest that the colour is due to the fluorescing properties of large organic molecules that are washed from the limestone strata each year. The information above has been adapted from the Register Assessment Report (Heritage Branch files). Additional information about the Mount Gambier Volcanic Complex is available in the Earth Resources Information Sheet M14, Volcanoes of the Mount Gambier Area (Office of Minerals and Energy Resources South Australia, July 2001). HistoryThe oral history of the Boandik people of south-eastern South Australia includes a story that suggests their ancestors witnessed volcanic activity in the Mount Gambier area. The Craitbul story tells of a giant ancestor, who made an oven to cook for his wife and family, at what is now Mount Muirhead. The groaning voice of a bird spirit warned them of evil spirits and so they fled to another site (Mount Schank) where they built another oven. Once more they were frightened off by the threat of the evil spirit and moved on to another place (Mount Gambier), where they again built their oven. One day water rose and the fire went out (the Blue Lake). They dug other ovens, but each time water rose, putting out the fires. This occurred four times, so Craitbul and his family finally settled in a cave on the side of the peak.
The Lakes area was one of the first sites of Colonial pastoral settlement in the south-east. Stephen Henty, bringing stock from Portland Victoria in 1841, built a hut on the rise near Browne Lake and constructed stockyards that covered part of the dried lake bed. In 1862 Father Julian Tenison Woods published his much-acclaimed first book, Geological Observations in South Australia, which included an analysis of the volcanic regions of Mount Gambier and Mount Schank. His pioneer writings are recognised as the first systematic examinations of South Australia's geology.
In 1876 a tree nursery was established at Leg of Mutton Lake. Two hectares of the crater's area were fenced off and a stone cottage was erected for the first nurseryman, Charles Beale. His job was the care of the Mount Gambier Forest Reserve that covered most of the mountain area. Trial plantings of exotic and native trees were carried out in the area for many years. By 1881 plantings were made annually and consisted of eucalypts from all Australian regions. European hardwoods were also planted, as was a range of softwoods, principally European and North American pine species. It is significant that Pinus radiata, which now dominates forestry in the region, was first introduced to the Leg of Mutton plantation in the 1870s. Cultivation and planting methods were developed there, giving this nursery a legitimate claim as the beginnings of the timber industry of south-eastern Australia. The Mount Gambier area, in particular the Blue Lake, has been an appealing tourist destination for South Australians and Victorians since the 1880s. Features of Mount Gambier Volcanic Complex State Heritage AreaNatural Features
The Mount Gambier Volcanic Complex State Heritage Area is predominantly a series of volcanic cones enclosing four crater lakes - Blue, Browne, Valley and Leg of Mutton Lakes. It also encompasses the blowhole at the Devil's Punchbowl. The Blue Lake is the most unique and spectacular feature of the region and one of the south-east's major tourist drawcards. It is renowned for its intense blue colour over the summer months. As well as differing physically and chemically from the other lakes, Blue Lake is in an almost pristine condition due to its protection as the town water supply. Its banks support the only original vegetation of the craters. Browne, Valley and Leg of Mutton Lakes form a recreational reserve, with parklands and facilities such as barbecues and toilets. Numerous lookouts and walks provide pleasant views of the crater complex. Built Heritage
The Mount Gambier Volcanic Complex contains many individual buildings and places that contribute to its heritage significance. The remains of the Nurseryman's Cottage (1876) at Leg of Mutton Lake, lookouts (such as the 1936 Potters Point and the 1937 RSL Lookout), numerous walks and many recreational structures are all noteworthy. The most significant historic features however, are the four State Heritage Places entered in the South Australian Heritage Register: |
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