Location
Flinders Chase NP, Kangaroo Island SA
Rock
Granite (mica, quartz, feldspar)
Age
Cambro-Ordovician · ~500 Ma
Process
Tafoni on granite corestones
Status
Geological monument (GSA)
Overview
On a granite dome above the sea, huge boulders have been hollowed into shells, arches and beaks. Orange lichen coats their outer skins; inside, the hollows are clean and bright.
~500Ma
Age of the granite
20m
Largest cavities across
2sites
GSA geological monuments in Flinders Chase
Chapter 01
About 500 million years ago, when Kangaroo Island was part of Gondwana, magma cooled into the granite here: black mica, bluish quartz and pinkish feldspar. The boulders are corestones resting on a partly exposed granite dome.
Chapter 02
Salt-laden spray, wind and strong swings in temperature and humidity have carved some of the most striking tafoni known, with granite cavities up to 20 metres across.
Chapter 03
The golden-orange crust on the rocks is an extremely slow-growing lichen; grey and green lichens take over in less exposed spots. The Geological Society of Australia lists both Remarkable Rocks and nearby Cape du Couedic as geological monuments.
Chapter 04
Some boulders are now more air than stone. Where two hollows meet, or a hollow breaks through to the outside, the granite is left as a curved shell only centimetres thick, like a cracked egg.
Chapter 05
The 2019–20 bushfires burned through Flinders Chase National Park. The granite endured; the visitor boardwalk around the rocks was rebuilt after the fires.
How it forms
About 500 million years ago, molten rock cools slowly underground into granite.
Weathering along joints rounds the granite into boulders that sit on a dome.
Salt spray and damp shade attack the undersides; cavities grow into the boulders.
Cavities break through, leaving thin shells, arches and beaks of granite.
The lichen is a map. Where the orange ends, the rock is still moving.
The question
Undersides stay shaded and damp and collect salt, so they weather fastest. The sunlit tops dry quickly and are armoured by slow-growing lichen, so the boulders are eaten from underneath.
Tafoni on granite corestones
Deep time
~500 Ma
Granite
Magma cools into granite while Kangaroo Island is part of Gondwana.
Deep time
Corestones
Weathering separates the granite into rounded boulders on a dome.
Coastal era
Salt and wind
Southern Ocean spray hollows the boulders into tafoni.
2019–20
Fire
Bushfires sweep Flinders Chase; the site is later reopened.
Field record
Field data
IGMA simulation · move to heat
Rock Lab
Turn a 3D model of Remarkable Rocks with hand gestures, heat its surface with your fingertip and weather it through 250,000 years.
Enter the Rock LabReferences
Photography
Next case · 06
Where animals first walked on land