Umpherston Sinkhole EarthCache
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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.
HISTORY
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.
GEOLOGY
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.
Additional Hints
(No hints available.)