Location
Nambung National Park, WA
Rock
Tamala Limestone
Age
Pleistocene · formed ≈ 102 ka
Process
Karst dissolution
Status
Open · Pinnacles Desert
Overview
Thousands of limestone spires rise from yellow sand in the Nambung desert. In 2024 researchers finally put a date on them: most formed in a single wet pulse about 100,000 years ago.
102ka
U-Th/He age of pinnacle formation
5m
Maximum pinnacle height
5members
Units identified in the Tamala Limestone
Chapter 01
The Tamala Limestone is built from cemented coastal dunes. Rainwater carrying carbonic acid dissolved it from within; in the words of Curtin University's Milo Barham, the holes got so big that all that was left was the Pinnacles.
Chapter 02
Matej Lipar and Milo Barham dated goethite nodules that grew on the pinnacles, using the helium produced by uranium and thorium decay. Published in Science Advances, the result points to formation around 102,000 years ago, in a very wet period lasting several thousand years.
Chapter 03
Earlier mapping by Lipar and Webb divided the Tamala Limestone into five members spanning marine isotope stages 13 to 4. The intense karst that produced the pinnacle field falls between stages 7 and 4.
Chapter 04
As the landscape eroded, iron-rich goethite nodules grew on the pinnacles' surfaces. Those nodules became the clock: the helium locked inside them dates the moment the pillars formed.
Chapter 05
The desert is not finished. Dunes still drift across the site, burying some pillars and uncovering others, so the Pinnacles you see depend on the decade you visit.
How it forms
Shell-rich sand blows inland from the coast and piles into dunes.
Rainwater dissolves some of the shell and re-deposits it, cementing the dunes into limestone.
Acidic rainwater eats holes through the rock, like Swiss cheese, during a very wet period.
What resisted dissolution stands as pillars; wind strips the loose sand from around them.
A landscape made of absence: the pinnacles are simply what the rain did not take.
The question
Dissolution followed the weaker, more porous paths through the limestone and left the tougher parts standing. Exactly why particular spires survived while their neighbours dissolved is still an open question for researchers.
Karst dissolution
Deep time
MIS 13–4
Tamala Limestone
Five members of dune limestone build up over successive Pleistocene cycles.
~102 ka
The wet pulse
An intensely wet period lasting several thousand years dissolves the pinnacle field.
Since
Wind
Loose sand is blown away and the pillars emerge, then are re-buried and re-exposed.
2024
Dated
Lipar and Barham publish the U-Th/He age in Science Advances.
Field record
Field data
IGMA simulation · move to heat
Rock Lab
Turn a 3D model of The Pinnacles with hand gestures, heat its surface with your fingertip and weather it through 250,000 years.
Enter the Rock LabReferences
Photography
Next case · 05
Granite hollowed by the Southern Ocean