Monaro Volcanic Province, New South Wales, Australia

Location: 35S, 15E

The Monaro Volcanic Province in southeastern New South Wales, Australia. The province covers an area of 4200 square km. At least 630 cubic km of lava and pyroclasts were erupted during the 20 million-year long history (57.5 - 34.0 million years ago) of the province. Erosion has cut deeply into the volcanic rocks. In some areas 300 to 600 feet (100-200 m) of material has been removed from the top of the volcanic province. This photo shows the Brothers volcanic plugs. The plugs are about 600 feet (200 m) higher than the road. A terrace is at the base of North Brother (left side of photo). The Brothers are one of the most prominent landmarks in the Monaro Volcanic Province. All photographs by Ian Roach except where noted.

The province is characterized by broad volcanic plains separated by flat-topped hills made of stacks of lava flows and round-topped hills centered on volcanic plugs. Gently dipping lava flows make this flat-topped hill in the Maclaughlin River valley.

The Brothers are excellent examples of the round-topped hills produced by deep weathering of volcanic plugs. Photograph by K.G. McQueen.

More than 65 vents have been recognized in the province. Most of these vents are volcanic plugs. The plug in the photo is near "The Peak". Note truck for scale.

Most of the volcanic province is made of lava flows. This photo shows a quarry that cuts into a lava flow. The deeply weathered surface is typical at Monaro. Deep weathering has produced bauxite, an aluminum-rich layer, on the surface of some flows.

Entablature, columnar joints in a lava flow, is preserved in The Peak. Columns are up to 1.6 feet (40 cm) wide and over 3 feet (1 m) long. Mantle xenoliths up to 4 in (10 cm) across are found in the lava.

Pillow basalt (upper half of photo) indicate that some lava flows advanced into water. The light colored layer is lake sediments. The presence of lake sediments indicate a reasonable pause between the eruption that formed hyaloclastite and the emplacement of the pillow lava. The reddish-layered deposit in front of the volcanologist is hyaloclastite, a type of pyroclastic rock that from when lava and water interact. Photograph by K.G. McQueen.

Red Cliff maar formed by the explosive interaction of magma and shallow groundwater. This photo shows a volcanologist studying the layers of basaltic tuff in the maar. Pieces of fossilized wood in the layers indicate a cool, wet climate in the geologic past for the area of Australia.

Volcanic bombs indicate an explosive origin for Red Cliff maar.

The tectonic setting of volcanism in eastern Australia is not simple. Older volcanics, like Monaro, are probably associated with rifting of the continent and upwelling mantle asthenosphere. Younger volcanic fields (less than 10 million years) may be related to a hot spot.

Special thanks to Dr. Ian Roach for providing the photographs for this page. Click here for more information about Dr. Roach's regolith science short course. Also, check out The Cooperative Research Center for Landscape Environments and Mineral Exploration. Additional information about Monaro and other volcanoes is available on the CARS homepage.

Click here for more photos of the Monaro Volcanic Province.

Sources of Information:

Brown, M.C., McQueen, K.C., and Taylor, G., 1992, A core through the Monaro basalt: Bega (BMR) no. 7: Australian Journal of Earth Science, v. 39, p. 555-559.

Brown, M.C., McQueen, K.G., Roach, I.C., and Taylor, G., 1993, Monaro Volcanic Province. IAVCEI Canberra 1993 excursion guide. Australian geological Survey Organisation, Record 1993/61.

Knutson, J., and Brown, M.C., 1989, Monaro, Snowy Mountains and South Coast, in Johnson, R.W., (ed.), Intraplate volcanism in eastern Australia and New Zealand: Cambridge University Press, Melbourne, p. 130-131.

O'Reilly, S.Y., and Zhang, Ming, 1995, Geochemical characteristics of lava-field basalts from eastern Australia and inferred sources: connections with the subcontinental lithospheric mantle?: Contributions to Mineralogy and petrology, v. 121, p. 148-170.

Roach, I.C., 1996, The formation of the Monaro Volcanic Province, southeastern NSW, Australia, in Whitehead, P.W., (ed.), Conference abstracts Long Lava Flows: James Cook University, Townsville, EGRU Contribution 56, p. 60-61.

Roach, I.C., McQueen, K.G., and Brown, M.C., 1994, Physical and petrological characteristics of basaltic eruption sites in Monaro Volcanic Province, southeastern New South Wales, Australia: AGSO Journal of Australian Geology & Geophysics, v. 15, p. 381-394.

Taylor, G., Eggleton, R.A., Holzhauer, C.C., Maconachie, L.A., Gordon, M., Brown, M.C., and McQueen, K.C., 1992, Cool climate lateritic and bauxitic weathering: Journal of Petrology, v. 100, p. 669-677.

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