Geology of Mount Elephant, Scoria cones, stony rises and older basalt:
Mount Elephant is a steep sided volcanic scoria cone. It was formed about 20,000 years ago and is one of the highest volcanoes in Victoria, rising 240 metres above the surrounding plain. The area for several kilometres around consists of “stony rises” of more solid basalt of about the same age. This emerged from numerous vents and flowed in many directions as molten rivers of rock until they finally cooled. This dammed the old creek lines to form the numerous lakes in the district. There are similar areas of stony rises around the other volcanic cones in the district. In turn these stony rises sit on a much older basalt plain bordered by Melbourne, Ballarat, Warrnambool, and westwards to Coleraine. These plains formed at various times over the last 20 million years.
Mount Elephant is a site of National Significance and listed on the Register of the National Estate (AHC Database 22 July 2002). Characteristics of the mount include its conical form, steep sided, crater, and access to sections of the ejecta in the quarries. “It is the best example of a breached scoria cone in Victoria and possibly Australia”. (Rosengren 1994)
Types of basalt:
The cone of Mount Elephant consists of scoria, blocks and bombs of solid larva with common megacrysts of granite and olivine. There are occasional lumps of the limestone layer through which the larva erupted. Basalt as in the stony rises comes from the earth’s core at about 1800C and normally cools quite rapidly on the surface. It is normally quite dense and hard. Basalt is quarried for bluestone houses and bluemetal for concrete and railway line ballast. Scoria from mount Elephant has come as hot liquid through a layer of water or wet limestone. The steam made the solid rock frothy and the expanding steam threw it into the air, so it cooled with the bubbles inside, and is quite light. Occasionally some rocks were thrown out while spinning rapidly. The outer layer is basalt and shaped like a football with a point at each end. The centre is often hollow and lined with green crystals of olivine. These “volcanic bombs” can be from 2 to 20cm in diameter.
The scoria was used for a number of commercial purposes, including road surfaces and building materials. The reason it was useful was that it formed a solid foundation but was free-draining. It was easy to mine and crush to a suitable size and to transport.
There are two quarry scars on Mount Elephant. The one on the northern flank was used for railway ballast in about 1911 and has long since been disused. The large scar on the western flank consists of two quarries. The obvious one running up the slope was privately owned and is now terminated. There has been partial restoration of topsoil at the northern and southern ends, but the centre section has proved too unstable to cover. Trees were planted in 1985 at the base of the northern scar in an attempt to reduce the effect of the wind dislodging scoria from the cliff face. The second hidden quarry is below ground level at the base of the scar. It is owned by Corangamite Shire, and is still licensed but not operating. Modern quarrying techniques ensure that the slope is always manageable, the quarry is out of public view, one face is rehabilitated before another face is opened, and the quarry operator must hold the rehabilitation cost in a bond until the work is completed. These conditions did not apply at the time of these quarries. Various reports have suggested rehabilitation plans for these quarries, and these are being considered in the overall management plan of the Mount.
It is likely that since its eruption some 20,000 years ago, Mount Elephant has supported open woodland with a grassy understorey. A painting by Eugene von Guerard in 1857 showed scattered trees on the slopes , with apparently denser concentrations within the crater and around the base. A drawing of Mount Elephant also by von Guerard shows belts of stunted trees (probably manna gums, sheoaks, honeysuckles (Banksia marginata) and blackwoods on the stony rises at the base.
We can only guess that prior to pastoral settlement Mount Elephant was covered by “scoria cone woodland” (Commonwealth and Victorian RFA Steering Committee 2000). This vegetation type was dominated by manna gum, drooping sheoak, blackwood, banksias, sweet bursaria, and tree violet. The understorey consisted largely of native grasses (especially common tussock grass and wallaby grass) bracken, and a conspicuous herb layer including native peas and daisies. The proportions of each of these species would vary across the mountain depending on their exposure to soil, sun, rain and wind.
The effects of pastoral settlement were dramatic on the vegetation of the Mount. The removal of timber for yards, huts and firewood and grazing by sheep would have favoured the grasses (especially the introduced annual grasses) over the tree regrowth and the native herb flora. Vegetation diversity was quickly diminished across the plains also. The arrival of rabbits in the district probably caused the most drastic decline in native vegetation. A photograph by Gabriel Knight held at the State Library of Victoria, taken of the north-east peak in 1911, shows scattered adult trees each about 30 metres in height, with many scattered stumps and dying trees. There are thistles in the foreground, bare ground on the steeper slopes, and no young trees to be seen. Unfortunately since the devastating fires of 1944 and 1977 the only traces of trees are several charred logs.
It takes a keen eye to find traces of the original vegetation, however the different vegetation types can be easily seen. Shrubs of tree violet are surviving on the southern slope of the crater, and some charred logs of possibly drooping sheoak remain on the slopes of the north-east peak. Areas of native tussock (Poa sp.) and Danthonia sp. are on the north slope beside the access track to the crater. Introduced grasses include Phalaris and Yorkshire fog grass growing on the sheltered southern and eastern slopes. Annual ryegrass, wild oats, scotch and variegated thistle grow on the lower parts of the exposed northern slopes and along the access track from the highway.