Calcite connections EarthCache

To get to Buchan from Melbourne follow the Princes Highway to Bairnsdale and proceed to Nowa Nowa via Bruthen and take the turn off to Buchan on the left. If approaching from the east follow the Princes Highway to Nowa Nowa and proceed to Bairnsdale via Bruthen and take the turn off to Buchan on the right.

The caves reserve is part of the Victorian National Parks system and is managed by local rangers who also look after the western half of nearby Snowy River National Park. National Parks are special protected places so please obey all signs and requests from rangers and be sure not to take specimens or feed the kangaroos.

European settlers came to Buchan in the 1800's and the township is one of the oldest in Victoria. One of the attractions of the Buchan Valley was the rich soils developed over extensive areas of limestone. Limestone caves were soon discovered across the region but it wasn't until early in the 20th century that extremely beautiful show caves were discovered, developed and public tours commenced.

Apart from the fertile agricultural land of the Buchan River Valley the area also yielded limestone to be cut for dimension stone and for use in the making of cement and agricultural lime.

Limestone is defined as a rock containing more than 50% calcium carbonate although many limestones, including those at Buchan, often contain more than 90% calcium carbonate. Buchan limestones are formed from the calcium carbonate skeletons of marine animals and plants that lived in a shallow sea about 380 million years ago during the Devonian Period. Many of the Buchan limestone beds are lime muds and fossils are hard to see but fossils are scattered throughout the rocks and include numerous species of brachiopods, bivalves, gastropods, nautiloids and corals.

Over time many hundreds of metres of lime muds, sands and gravels accumulated on the floor of this sea, packed down and slowly became limestone rock. Around 350 million years ago tectonic forces folded and faulted these rocks and lifted them up to become part of the mainland of Australia where they have remained. About 60 million years ago erosion began to expose the limestone rocks and form the Buchan Valley.

Limestone is an unusual rock because the carbonate minerals that it is composed of are easily dissolved in weak acid and are soft and easily abraided. As rain falls, it collects carbon dioxide from the air forming carbonic acid. All rainfall is naturally slightly acidic because of the formation of this weak acid. In most landscapes, including limestone ones, cracks in the rocks allow water to seep in. However, in limestone the water in these cracks slowly dissolves the walls away making the cracks wider and wider. This process began in the Buchan Valley about 40 million years ago and in the area around the Buchan Caves Reserve about 20 million years ago.

Eventually, as the cracks widen and open up in all directions some join up and water begins to flow from one part of the landscape to another through the newly forming caves in the rocks. As water moves it tumbles rock fragments around and further enlarges the caves through abrasion.

Erosion in the river valley lowers the landscape and the water table drops, following the river level down. When this happens the water table that once filled the caves no longer does and the open spaces begin to have calcium carbonate rich waters drip off the roof and trickle down the walls. This may have begun happening in some of the Buchan Reserve Caves about 10 million years ago.

Calcium carbonate saturated water dripping and trickling into the caves is responsible for building all the amazing structures - called speleothems - we see in the Buchan Caves and many other caves all around the world. Each time water drips or trickles it leaves behind tiny amounts of calcium carbonate, usually as the mineral calcite, building up dripstones, flowstones and other curiously shaped structures.

Dripstones include the well known stalactites [they are on the ceiling, holding on tight], stalagmites [they are on the floor growing upwards, one day the might reach the ceiling] as well as straws, the hollow, fragile beginnings of stalactites and columns or pillar - the structures that form when stalactites and a stalagmites join. In the Royal Cave 'Font of the Gods' chamber excellent examples of these can be seen.

Flowstones include both sheets of carbonate deposited by water flowing in a film across rock and shawl-like structures developed from water dripping and trickling down inclined ceilings. There are excellent shawls to be seen in the Fairy Cave.

To find out more about cave and speleothem formation processes read the information on display in the Buchan Caves Reserve Visitor Information Centre [Free entry] or take a tour of the Fairy Cave or Royal Cave or both at Buchan [Entry fees apply - you may even meet GeoGeckoEd] or go to http://www.amonline.net.au/geoscience/earth/caves.htm

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