Ike and Jimena continue their tour of Tasmania with a visit to Marakoopa Caves. This cave system is typical of subterranean karst (limestone) with speleothem’s such as the stalactites shown above.
Speleothem is the name given to a feature in a cave formed by minerals deposited by water. This happens when rain water absorbs carbon dioxide from the atmosphere and becomes a very weak carbonic acid. When this falls on the ground and infiltrates the soil it picks up more carbon from the organic matter. Now the pH is lower (therefore more acidic) as the water percolates into the limestone bedrock. Here it dissolves the limestone from the joints, bedding planes and fractures as it moves through, making the spaces wider, eventually forming caves. Water saturated with calcium bicarbonate continues to seep into the cave passages, and as it enters the cave environment the carbon dioxide is released from the liquid, leaving carbonate minerals to precipitate out of solution with each drop of seepage. The calcium carbonate builds up over time, at a rate of no more than 10cm per one thousand years, depending on seepage rate and the concentration of gases within the cave itself.
Stalagmites form from the bottom up, stalactites from the roof down. Columns are created where they join. The photograph below shows a cross section of a stalactite which was found in 1969 in a cave in Indiana, USA, already broken. The photographer has cut and polished the sample, which is actually two stalactites that have grown together. You can see slight variations in colour showing in the growth rings, these variations demonstrate small differences in the mineral content of the seeping ground water and cave atmosphere over the growth cycle:
The Marakoopa Caves are located in the Mole Creek Karst National Park, in central northern Tasmania.
Caves like these provide a unique ecosystem for the creatures that live there, and who could not live anywhere else. This phenomenon is called an ecological niche. Ike was interested to see what delights he would be missing:
Visitors have been coming into these caves for over a hundred years. Every piece of dirt trodden into a cave system, and every breath, changes the delicate chemical balance therein. Hair and skin cells shed by visitors are foreign to the environment. The installation of visitor infrastructure such as walkways, stairs and lighting also damage the system. Therefore, is it right that sites such as these are tourist destinations?
Tourism also brings revenue to the area, and guided tours serve to educate visitors. Therefore, the answer is not necessarily clear cut. Caves and associated speleothem features are non-renewable resources and need protection. Many exist that have yet to be discovered, and doubtless there are others which have been discovered, but which will not be opened to the public and subject to scientific research only. The Marakoopa Caves are managed carefully by the National Park authorities to minimise visitor impact.
These are the words from the plaque next to the installation by local sculptor Helmut Scwhabe:
The Tasmanian landscape, with all its flora and fauna, needed hundreds of millions of years to develop to what it was when Europeans first arrived. Over the last 200 years the philosophy that everything natural is a resource to be exploited has altered this ancient ecology.
This fossil may remind the visitor to Marakoopa Cave of the origin of limestone and the long ecological history of this island.Helmut Schwabe (Ulveston, Tasmania) Installed April 2002