| Into
the Fossil Cave:
Arriving at the Naracoorte Caves Conservation Park late one afternoon,
cave tours had been concluded for the day. Although we would have
to wait until the following day to see the underground wonders of this
place, we decided to have a look around the park above the surface.
I was finally at the Naracoorte Caves, which like the Rancho
La Brea Tar Pits of California, contain one of the largest, most unique
concentrations of Pleistocene vertebrate fossils in the world.
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| The
Naracoorte Caves Conservation Park Visitor Centre and Laboratory, opened
to the public in 1979. |
The following morning, it was time to take a tour of Victoria Fossil Cave.
I already had some idea of what I would see below, having had a first glimpse
of the cave's fossil chamber many years earlier in "The Rise of the
Mammals", the ninth episode of the 1979 BBC television series "Life
on Earth". In that classic documentary, I had watched naturalist
David Attenborough crawl his way into the fossil
chamber, shining a caver's lamp upon the bones of numerous marsupials
which had lain there since the Ice Ages. I couldn't have been more
than six years old when I first saw those images, but it had a highly influential
effect on me then, and still does today.
.
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| Formations
inside Victoria Fossil Cave. |
Victoria Fossil Cave is located about 1.5 km from the visitor centre.
As we slowly traveled the limestone corridors of the cave on a guided tour
over the course of an hour, the atmosphere became progressively cooler
and more humid. This is an active cave, which means that water still
flows through it. The cave contains many examples of speleothems
such as stalactites (formations that grow downward from the ceiling) and
stalagmites (formations that grow upward from the floor).
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| Another
area of the cave which bears many dripstone formations (speleothems). |
Some of the speleothems are still growing, but others became inactive long
ago. These formations are the result of thousands of years of mineral
deposition by water. As ground water seeps through the porous limestone
which lies beneath the Naracoorte area, it carries with it dissolved minerals
from the rock. Upon reaching the void which is the cave's interior,
the mineral-laden water may begin to drip from an already projecting surface
on the ceiling of the cave. A thin mineral coating then begins to
crystallize on that surface, and each successive water droplet adds yet
another, very thin coating of tiny crystals.
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| Some
of the rocks in this section of the cave have developed smooth coatings
through the long term dripping action of mineral-laden water. |
Over many millennia, this can produce quite large formations, especially
if the deposition rate is high, and occurs regularly. If this process
continues uninterrupted for a very long time, it can eventually build a
robust stone column of enormous size. However, most of the formations
within this particular cave are rather slender and are in the form of conical
spikes (stalactites and stalagmites).
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| The
surfaces of stalactites often have a corrugated texture which is a result
of the process by which they grew in a hanging position within a cave.
Stalactites have growth rings much like those of a tree, as can be seen
in a cross section (right) of this specimen. The rings are caused
by periodic variances in formation activity over thousands of years.
Speleothems are extremely dense and very heavy, being composed of many
tightly packed mineral crystals such as calcium carbonate. This particular
specimen began as two separate formations which eventually grew together
(note the smaller, secondary lobe). |
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