Mount Gambier (volcano)
Mount Gambier is a maar
A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Moselle...

 complex in South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...

 associated with the Newer Volcanics Province
Newer Volcanics Province
The Newer Volcanics Province is a complex of volcanic centres formed by the East Australia hotspot across south-eastern Australia. It has an area of 6,000 square miles with over 400 vents and contains the youngest volcanoes in Australia...

. It contains four lake-filled maars called Blue Lake
Blue Lake (South Australia)
The Blue Lake in Mount Gambier, South Australia is a large monomictic lake located in an extinct volcanic maar associated with the Mount Gambier maar complex. It is one of four crater lakes on Mount Gambier...

, Valley Lake, Leg of Mutton Lake, and Brownes Lake. It is one of Australia's youngest volcanoes which formed about 5,600 years ago.

"Ash from the Mt Gambier area has been dated at about 4,700 years old and about 1,400 years old, indicating that the vents were certainly active at these times, though possibly for a considerable period before and after."

Mount Gambier is thought to have formed by a mantle plume
Mantle plume
A mantle plume is a hypothetical thermal diapir of abnormally hot rock that nucleates at the core-mantle boundary and rises through the Earth's mantle. Such plumes were invoked in 1971 to explain volcanic regions that were not thought to be explicable by the then-new theory of plate tectonics. Some...

 centre called the East Australia hotspot
East Australia hotspot
The East Australia hotspot is a volcanic hotspot that forces magma up at weak spots in the Indo-Australian Plate to form volcanoes in Eastern Australia. There have been no eruptions in Australia during historic times. It does not produce a single chain of volcanoes like the Hawaiian Islands...

 which may currently lie offshore.

This area is part of the UNESCO-endorsed Kanawinka Geopark
Kanawinka Geopark
The Kanawinka Geopark, named for Kanawinka, “Land of Tomorrow”, is situated along a structurally controlling geological fault of the same name that extends from the Narracoorte Caves in South Australia into Western Victoria, before disappearing offshore at Portland...


Of the original four lakes found within the calderas, only two remain. The Leg of Mutton Lake (named for the outline of its shoreline) became permanently dry in the 1960s. Brownes Lake suffered a similar fate in the late 1980s. Both these lakes were quite shallow; their demise is attributed to the lowering of the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...

 as a result of many years of land drainage to secure farmland.

The rural city of Mount Gambier
Mount Gambier, South Australia
Mount Gambier is the largest regional city in South Australia located approximately 450 kilometres south of the capital Adelaide and just 17 kilometres from the Victorian border....

partially surrounds the maar complex.
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