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The Umpherston Sinkhole has ample parking and is accessible 24 hours a day free of charge. Make your way to the top of the sinkhole and read about the formation of this fascinating spot, all the information required to log this Earthcache can be found here.
The Umpherston Sinkhole is a popular tourist attraction in Mount Gambier. The area was named after James Umpherston who lived nearby and who initiated the beautification of the site in 1884. In 1887 the sinkhole, complete with splendid gardens, walk way and an island in the middle of the water was handed over to the public.
The beautiful gardens fell into disrepair during the middle of last century before restoration of the site began in 1976 by the Woods and Forests Department Social Club. Extensive replanting, staircases and greater facilities were built to form the magnificent site that exists today.
Umpherstone Sinkhole is situated within a large area known as the Limestone Coast, a region so named for the rich deposits of limestone in the ground. The expanse of limestone stretches for over 22,000 square kilometres in the southeast of South Australia and south west of Victoria and is responsible for the solution pipes found at Cape Bridgewater (see Petrified Forest?).
Limestone is composed almost entirely of calcium carbonate (CaCO3), a mineral which dissolves in the presence of acid. Rain and ground water can become mildly acidic when the water reacts with carbon dioxide in the air and soil. Over thousands of years this acidic water can dissolve substantial volumes of limestone, particularly where fractures in the limestone allow the acidic water to seep into the rock. Large sections of limestone may weaken or dislodge as a result of this, causing large sections to cave in. Some dramatic changes to the topography around Mount Gambier, such as Umpherston Sinkhole, are an example of this process.
How did the sink hole form? You’re going to tell me! To log this cache, email with the answers to the following questions. Obviously don’t post the answers in your log, we don’t want to spoil the discovery for others.
1. What caused the ground around Mount Gambier to be so rich in limestone?
2. What occurred at the site about 15 million years ago to begin the formation of the sinkhole?
3. The limestone begins to dissolve in two general locations, one horizontal and the other vertical. What are they?
4. What final event enabled the sinkhole to become visible at the surface?
5. What fraction of the sinkhole was filled with water in 1887?
6. As a final logging requirement, please post a photograph of yourself at the Umpherston Sinkhole. Photos from previous visits are acceptable.
When logging your visit I encourage you to note what your learnt or found interesting about the location.
I am obliged to delete logs that do not meet these requirements.
(No hints available.)