Mole Creek karst caves & geology

A limestone country beneath the dolerite

Twenty-five minutes west of Deloraine the Meander Valley changes rock. The dolerite of the Tiers gives way to Ordovician limestone, laid down as a tropical sea floor roughly 450 million years ago and lifted, folded and dissolved ever since. The result is the Mole Creek Karst, a belt about 30 kilometres long holding more than 300 known caves, dozens of sinkholes, disappearing streams and springs, and the Mole Creek Karst National Park that protects the best of them.

Two caves are open to the public with guided tours: Marakoopa, with its glow-worm chamber and underground rivers, and King Solomons, a dry, compact cave dense with formations. The rest of the system is a conservation reserve where entry needs a permit and caving experience. This sheet covers what you can see on the tours, the geology under your feet, and why the sinkholes in the paddocks matter as much as the caves themselves.

Show caves at Mole Creek Karst National Park

Cave	Character	Tour length	Temperature	Steps
Marakoopa — Underground Rivers & Glow-worms	Wet cave, two streams, large glow-worm display	45 min	9 °C year round	~120, gentle
Marakoopa — Great Cathedral	Upper chambers, flowstone, high domes	60 min	9 °C	~360, steep
King Solomons	Dry cave, calcite shawls, helictites, sparkling crystal	45 min	9 °C	~180, tight

Subterranean hydrology: where the creeks go

Karst drainage is the thing to understand before anything else. Rain falling on the limestone does not run off; it sinks. Surface creeks flow for a few hundred metres, then vanish into a swallet, travel underground through solution passages, and re-emerge kilometres away as springs. Mole Creek itself behaves this way: parts of its bed are dry in summer while the water moves beneath them.

Marakoopa is the clearest demonstration. Two streams run through the cave, the Marakoopa Creek and a tributary, cutting the lower passages and depositing the sediment that the glow-worms depend on. Dye tracing by Tasmanian cavers has linked sinks in the Mole Creek valley to springs that emerge days later and several kilometres away. The practical consequence is that anything spilled on the surface, from diesel to dairy effluent, is in the cave system within hours.

Rock

Ordovician Gordon Group limestone, bedded, folded, heavily jointed.

Cave temperature

9 °C, stable within a degree all year. Bring a jumper in January.

Humidity

Close to 100% in the wet caves. Camera lenses fog on entry.

Recharge

Rainfall on the Tiers above, plus the sinking creeks of the valley floor.

Flood risk

Marakoopa tours are suspended when the underground rivers rise after heavy rain.

Glow-worms: Arachnocampa tasmaniensis

The glow-worm chamber at Marakoopa holds the largest display of Arachnocampa tasmaniensis in any Australian public cave. The animal is not a worm but the larva of a fungus gnat, endemic to Tasmania. Each larva spins a silk hammock on the cave ceiling, hangs up to 30 sticky threads below it, and glows blue-green from its tail to lure midges and mayflies rising off the stream. The hungrier the larva, the brighter it glows.

They need three things, all supplied by the cave's hydrology: a ceiling surface that stays damp, still air so the threads do not tangle, and a stream below to breed the insects they eat. The colony's density tracks the stream's flow. Dry years thin the display. The guides turn off every light for the viewing, and the rule is absolute: no torches, no phone screens, no flash. Light pollution causes the larvae to retract their threads and stop feeding, and the colony can take weeks to recover from a single camera flash.

Formations: how the stone grows

Every formation in the caves is calcium carbonate, dissolved from the limestone by rainwater carrying carbon dioxide, then redeposited drop by drop where that water meets cave air. The rate is slow. A centimetre of stalactite can take a century; the large columns in King Solomons are tens of thousands of years old.

Speleothem field key for the Mole Creek show caves

Formation	How it forms	Where to see it
Stalactite	Drip water deposits calcite as it hangs from the ceiling. Starts as a hollow straw.	Both caves; straws in Marakoopa upper chambers
Stalagmite	The splash of the same drip builds a mound on the floor.	King Solomons main chamber
Column	A stalactite and stalagmite that have joined.	King Solomons
Shawl / curtain	Water running down a sloping ceiling leaves a thin, folded sheet.	King Solomons, often banded and translucent
Flowstone	Sheets of calcite laid over walls and floors by thin films of water.	Marakoopa Great Cathedral
Helictite	Twisting, gravity-defying growth driven by capillary pressure.	King Solomons, in the crystal alcoves
Rimstone pool	Calcite dams built at the edges of slow-flowing pools.	Marakoopa lower stream passage

Formations stop growing when touched. Skin oil seals the surface and the calcite will not bond to it, which is why the tour paths are railed and why guides ask you to keep hands in pockets through the narrow sections.

Karst sinkholes and conservation

Drive the back roads between Mole Creek and Chudleigh and you will see depressions in the paddocks, some the size of a tennis court, some big enough to swallow a tractor. These are dolines, or sinkholes, where the limestone roof of a passage has collapsed or the soil has been washed down into the cave below. They are the lungs and drains of the karst. Water, air, leaf litter and animal life all move between surface and cave through them, and most of the known caves were first entered via a sinkhole.

They are also the most abused feature of the landscape. For a century sinkholes were the farm rubbish tip, filled with car bodies, fencing wire, chemical drums and dead stock. Every one of those tips drains straight into the cave streams and from there into the springs that feed the Mersey. The Mole Creek Karst National Park, declared in 1996, protects only a scatter of small reserves, so most of the karst, and most of the sinkholes, remain on private land.

The conservation work is therefore slow and local: the Mole Creek Caving Club and landholder groups clearing historic tip sites, fencing sinkholes against stock, and planting buffer vegetation. The Trust's part is small. We fund a sinkhole survey every second year and keep the valley's sinkhole register with the club. If you own karst land in the valley and want a doline assessed, write to curator@deloraine.org.

Visiting

Getting there

Mole Creek is 25 km west of Deloraine on the B12. Marakoopa is signed from Mayberry Road; King Solomons is on Liena Road. Both are about 10 minutes beyond the village.

Bookings

Tours are run by Tasmania Parks and Wildlife and sell out in January and over Easter. Book ahead.

Wear

Closed shoes with grip and a warm layer. The paths are wet and 9 °C is cold after an hour.

Pair it with

The Alum Cliffs lookout on the way back, or the craft trail through Chudleigh and Deloraine.

Wild caves

Entry to the undeveloped caves requires a permit and a caving club. The Trust does not organise wild caving trips.