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
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
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
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.
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
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
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
(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
IAVCEI Canberra 1993 excursion guide. Australian geological Survey
Knutson, J., and Brown, M.C., 1989, Monaro, Snowy Mountains and South Coast,
R.W., (ed.), Intraplate volcanism in eastern Australia and New Zealand:
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
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
Townsville, EGRU Contribution 56, p. 60-61.
Roach, I.C., McQueen, K.G., and Brown, M.C., 1994, Physical and petrological
basaltic eruption sites in Monaro Volcanic Province, southeastern New South
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,