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Thin rocky soil in road cutting on the Monaro Plain

The Monaro Plain

Located in the Snowy Mountains Region of NSW, nearest towns Bombala and Cooma

Source: Monaro Region, New South Wales G.Taylor and I.C.Roach

Source: The Native Grasslands of the Monaro Region New South Wales J.S.Benson

Source: Source: Wikipedia

Link to Detailed Map

The name Monaro has Aboriginal origins, meaning a high plateau or high plain. Because of the cold temperatures and lack of game it is likely that Aborigines did not stay year around in the higher parts of the Monaro. For the purpose of this document we will define the Monaro as covering the area from Bredbo to Delegate in the north south aspect and Cathcart to Berridale in an east west direction.

It is famously known as the treeless plain and many people think this is because it has been over grazed, but this is not the case. It was treeless when pioneers first came to the region. Lhotsky (1835) described the plains in the vicinity of Cooma "The scene all around was composed of undulating downs, long projected hills among them, covered with very few trees." The Monaro Plain is a classic case of how geology and weather affects land use. The soil in the region is thin, the temperatures are cold and the plain falls in a rain shadow area between the Eastern Escarpment and the Snowy Mountains.

Geology

The underlying rocks are mainly Palaeozoic Era sediments which have been folded, faulted and metamorphosed during the formation of the Lachlan Fold Belt. The Palaeozoic Era includes the periods Carboniferous (youngest), Devonian, Silurian and Ordovician (oldest). There are Ordovician flysch sequences (sedimentary rocks deposited in a deep marine environment) that host two significant regional metamorphic complexes.

Granitoid intrusions occurred in the late Silurian period (Berridale Batholith) to the early Devonian period (Bega Batholith). Late Devonian to early Carboniferous sediments overlay the earlier Palaeozoic Era rocks.

From about 58 to 43 million years ago (Eocene epoch) there was much basaltic lava field volcanism in the Monaro creating thick lava masses including interlocking lava shield and scoria cone volcanoes and some maars (shallow volcanoes created from groundwater coming in contact with lava/magma). This is known as the Monaro Volcanic Province and included about 65 volcanic eruption sites. The basalt has covered the pre-eruptive landscape and preserved it from weathering. It is thought that the basalt flows filled the existing valley systems leaving the older Palaeozoic era hills.

At Myalla Lake, (directly south of Cooma on the west side of Myalla Road) drilling has proved the basalt pile is 197m thick and is made up of about 22 individual flows. Seven of these are topped by weathered material up to 12.5m thick. This alternate basalt and weathered rock strata indicates that there were long periods of approximately 5 million years between lava flows.

The Monaro plain has an elevation of around 900 metres with the occasional hill or low range. Other than the Palaeozoic Era hills there are volcanic plugs such as Hudsons Peak 1,123m, (latitude -36.433333 and longitude 149.166667). Topped by a communications tower, Hudsons Peak is located at the end of the Peak Road which leads west from the Monaro Highway halfway between Cooma and Nimmitabel.

Surprisingly there are many high country lakes on the Monaro Plain. Some of these are caused by basalt flows cutting off headwater streams, an example is Arable Lake, located on the east side of Arable Road which leads off Kosciusko Road south west of Cooma. Others are caused by a wind erosion process known as deflation and occur mostly on the Monaro Range which runs in a north westerly aspect from Bemboka to Nimmitabel and on to Cooma. This range is made up of remnant eruptive sites linked by high standing lavas and is a dominant feature of the area.

In the last million and a half years during the Quaternary period, the area has continued to weather with most of the regolith (layer of old loose rocks covering base rock) consisting of alluvium (sediments, which has been eroded, reshaped by water in some form), colluvium (rock debris) or aeolianite (wind weathered sediments forming into rocks - lithification). Much of the regolith contains calcium carbonate (calcrete) which normally forms in areas of low rainfall. This indicates the rain shadow over the Monaro Plain must have been in place for many millions of years to allow for the development of thick calcrete profiles that occur in this region.

Getting There

The Monaro Plain is beautiful in its isolation, far horizons and swaying grasslands. The sight of the velvet dark blue sky immediately after sunset is awesome. There is accommodation in Cooma, Nimmitabel and Bombala but it is a good idea to book ahead as a wedding in town can take up many of the available beds. There are many other interesting sites in the Snowy region including; viewing platypus in the Bombala River; the historic Mill in Nimmitabel, wineries and Cooma Monaro Rail Motor rides. While you're in the area visit the spectacular Myanba Creek Gorge near Bombala; you will find information about it on this website.


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