Australia: The Land Where Time Began

A biography of the Australian continent 

Maar Lakes     see Volcanoes

A maar is a roughly circular, broad, flat-bottomed volcanic crater. It has steep inner walls, a low surrounding rim composed of rock material blown out by a gas and steam eruption. Of the 30 craters of this type found in Victoria most as centred near Colac and Camperdown, west of Geelong, and Tower Hill west of Warrnambool.

The formation of a maar begins with violent volcanic activity. Ahead of a rising column of lava there is a mass of superheated gas and steam from boiling groundwater. When the magma comes into contact with the groundwater an explosive gas eruption occurs. The pressure of the gases associated with the rising lava column and the pressure of the boiling groundwater steam blasts a vent, a pipe, through the covering rock. As the eruption continues the width of the vent increases into a broad crater. The rim of the crater is formed from tephra or tuff (pyroclastic rock).

Lake Keilambete, 1 of 3 maars near Terang, has been extensively studied. The other 2 near it have also been studied, Lake Bullen Merri and Lake Gnotuk. These 3 maars erupted through the Port Campbell Limestone.

Sources & Further reading

Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000