Cave explorers have traversed what is now Australia’s deepest known cave.
A group of explorers Saturday discovered a 401-meter-deep cave, which they named Delta Variant, in Tasmania’s Niggly-Growling Swallet cave system in the Junee-Florentine karst region.
Its depth just surpassed its predecessor, the Niggly Cave, by about four meters.
With a descent that took 14 hours and many months to prepare, Delta Variant is causing a stir among explorers.
But it has a different kind of fascination for researchers like me who study the interaction between groundwater and rocks (including in the context of caves).
This helps us learn about natural processes and how the Earth’s climate has changed over millions of years.
A team of nine cavers from the Southern Tasmanian Caverneers discovered Australia’s deepest known cave on Saturday.
As exciting as Delta Variant is in an Australian context, it’s probably just a starter in the wider world of caves; the deepest known cave, located in Georgia, goes more than 1.4 miles into the earth.
So how exactly do these massive geological structures form beneath our feet?
Simply put, caves form when flowing water slowly dissolves rock over a long period of time. In particular, they form in certain geological formations called “karst” – including structures made of limestone, marble and dolomite.
Karst is made of tiny fossilized microorganisms, shell fragments, and other debris that have accumulated over millions of years.
Long after they perish, small sea creatures leave behind their “calcareous” shells of calcium carbonate.
Corals are also made of this material, as are other types of fauna with skeletons.
This calcareous sediment builds up into geological structures that are relatively soft.
As water trickles down through fissures in the rock, it constantly dissolves the rock to slowly form a cave system.
Unlike many harder igneous rocks (such as granite), calcareous rocks dissolve on contact with water that is naturally acidic.
When rain falls from the sky, it absorbs carbon dioxide from the atmosphere and soil along the way, making it acidic.
The more acidic the water, the faster the karst material will corrode.
So, as you can imagine, the formation of a cave can become quite complex: the specific composition of the karst, the acidity of the water, the degree of drainage and the overall geological environment are all factors that determine what kind of cave is located. will form.
In geology, there is a lot of spatial guesswork.
So being able to see how deep a cave formation goes is a bit like going into the deepest layers of a cake, where you may not find the same in all directions.
Stalagmites and stalactites
From a research perspective, caves are incredibly valuable because they contain cave deposits (or “spelethemes”) such as stalagmites and stalactites.
These are sometimes spiky things that point up from cave floors, hang from ceilings, or form beautiful stream rocks.
Cave deposits are formed by the passage of water. Like trees, they contain growth rings (or layers) that can be analysed.
They can also contain other chemical features that the water contains and reveal processes that took place at the time of formation.
While they may not seem like much, we can use these deposits to unravel past secrets about Earth’s climate.
And since they are a hallmark of rock-water interaction during cave formation, we expect to find them in most caves.
Descending deep into a cave system is no small feat. You can’t use your cellphone (because there’s no reception), it’s incredibly dark and you mostly rely on a guideline to find your way back out.
There can be many dead ends for explorers, so mapping space effectively takes time and great spatial exploration skills.
While cave systems are usually stable (shallow caves can theoretically collapse and form sinkholes, but this is very rare) – there is always risk.
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The unexpected geometry of caves means you can make tricky manoeuvres, twist and swing in all sorts of awkward ways as you rappel into the darkness.
While the air pressure doesn’t change dangerously as you descend, other gases such as methane, ammonia, and hydrogen sulfide can sometimes coalesce and create a choking hazard.
Despite all of the above, cave exploration is something that people continue to do, and it offers great benefits to researchers in various subfields of geology.
And while we’ve come a long way, there are always nooks and crannies we can’t get in – after all, people aren’t small. I’m sure there are small spaces, too small for us to explore, that culminate in much longer or larger systems than we’ve ever discovered.