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| Layers of ash and scoria form a tuff wall characteristic of maar craters. |
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Tower Hill is an inactive volcano beside the Warrnambool to Port Fairy Road. Tower Hill contains a 'maar' crater formed at least 30,000 years ago when hot magma came into contact with ground water resulting in violent explosions and a distinctive, flat-bottomed crater.
The first event at Tower Hill was a massive explosion when a lava column rising through the crust towards the surface came into contact with ground water; the water turned to steam, expanded violently and blew out the ground above hurling rocks, scoria and ash into the air.
Subsequent explosions ejected more ash and scoria; some blew over the surrounding country, but much of the material settled in layers around the crater rim forming a landform known as a tuff ring. The wide crater formed this way is known as a "maar" crater defined as a broad, shallow, flat-floored crater caused by hot magma coming in contact with ground water.
A maar usually fills with water forming a shallow crater lake. At Tower Hill subsequent activity, less violent than the first phase, generated several small cones of scoria and coarse volcanic fragments which are now surrounded by a shallow crater lake.
During the nineteenth century Tower Hill was treated as nothing special; much of the original vegetation was cleared and the slopes used for grazing, cropping or growing vegetables. In 1892 Tower Hill was declared as Victoria's first National Park but regulations were not enforced; grazing, cropping, timber cutting and burning, quarrying and rubbish dumping continued and by 1950 the islands within the crater and the crater walls were bare, pests were common, and little wildlife remained.
Tower Hill was declared a State Game Reserve in 1961 in the hope that the original condition of the crater and slopes could be restored. By then the slopes had been so seriously denuded for so long that nothing of the original vegetation remained so restoration relied on a painting by Eugene von Guerard done in 1855 and so detailed that plant species could be recognised. Identity of other species could be inferred from the habitat. Replanting of selected species continued until nearly 250,000 had been planted by 1981. Removal of introduced non-native plants and weeds has been an ongoing project. Restoration of tree fern gullies will proceed once the specialised habitat requirements of the ferns can be met. Native birds and animals have returned to the area naturally or have been deliberately introduced.
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