Karst Country series

Karst landscapes are unique because the limestone bedrock is literally dissolving away.

Limestone is a sedimentary rock with a mostly biological origin. It is formed either from old oceanic reefs or from the accumulation various shells (large and small). The common chemical composition of all these components (reefs and shells) is calcium carbonate (CaCO3). So limestone rock is mostly composed of CaCO3 although there often contaminants such as iron oxide, silica, and other clay sediments. CaCO3 is soluble in any slightly acidic water, such as rainwater, but it will also re-precipitate if solution acidity decreases or if solution concentration increases over a critical level. It is these chemical processes that produce limestone caves with their array of stalactites and stalagmites. Exposed limestone rock is usually a dull grey in appearance but pure CaCO3 mineral (called calcite) is white. So where weathering limestone has any re-precipitated calcite the colour changes dramatically to bright white or various shades of red, orange or pink due to the presence of iron oxides.

Percolating groundwater will dissolve limestone producing caves and as these underground cavities expand their roofs can collapse under gravity. If these collapses occur close to the ground surface then "sinkholes" can form and these will funnel further runoff water into the underground network. Thus the Karst landscape evolves. This can produce landscapes where there is little surface drainage with no classic streams, rivers and V-shape valleys (Mt Gambier is such a landscape). But mostly exposed limestone formations are limited in their areal extent so some surface hydrology exists. The underground streams can also suddenly re-emerge to the surface as springs.

Major streams can readily dissolve limestone outcrops producing some dramatic landforms such as those at London Bridge and the Blue Waterholes.

Karst country in Myopic Landscape paintings

London Bridge 1 and London Bridge 2 depict an interesting limestone outcrop undercut by the headwaters of the Queanbeyan River on Burra Creek, at Googong NSW.

Careys Cave is part of the Wee Jasper limestone outcrop.

Blue Waterholes

The Blues Waterholes paintings are of an area of the Kosciuszko National Park near the headwaters of the Murrumbidgee River.

The commentary on the Blue Waterholes series, a subset of the Karst Country series, provides more details on these painting.

Yarrangobilly River

Yarrangobilly Limestone defines the second major area of karst landscape in Kosciuszko National Park. The Yarrangobilly River flows through this limestone outcrop from where the Snowy Mountain Highway crosses it, south pass Yarrangobilly Caves. Yarrangobilly Caves is the main tourist attraction but the gorges cut through the dipping limestone strata by the Yarrangobilly River provide some spectacular scenery.

Harry Hill from Tumut has written extensively about the history of Kosciuszko National Park plus various published hiking guides. Harry has walked the Yarrangobilly River from the bridge to the caves. I have used 2 of his slides as the base for the two paintngs below.

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