PINNACLES - ENIGMAS IN STONE
In the Pinnacles Desert, right in the heart of Nambung National Park, thousands of huge limestone pillars rise out of a stark landscape of yellow sand. In places they reach up to three and a half metres tall. Some are jagged, sharp-edged columns, rising to a point, while others resemble tombstones.
They are part of the Tamala Limestone, the geologically young formation of remnant sand hills that occurs over an extensive part of the west coast. However the Pinnacles are quite extraordinary and give rise to a unique and beautiful landscape.
The Tamala Limestone is one of the most recent deposits in the Perth Basin. It consists essentially of sand dunes which have been cemented into hard limestone by rainwater percolating through them and redepositing dissolved calcium carbonate within the core of the dune to form limestone.
Just like today’s sand hills, these old sand hills were covered in vegetation. The humus layer made the rainwater slightly acidic and this dissolved calcium carbonate at or near the surface. Roots of the larger plants provided conduits for this water to percolate down and this resulted in redeposition of the calcium carbonate around the (possibly dead) root system. There is evidence that bushfires denuded the dunes allowing strong winds, so prevalent in this area, to blow away the loose sand leaving the columns of cemented calcium carbonate (limestone) exposed.
“Despite their spectacular and widespread occurrence in this region, little if any scientific research has been dedicated to understanding how and when the pinnacles formed. Nearly all geological aspects related to their formation are controversial…”
- geologist Paul Hearty, 2006
“…as sand hills are such a common feature on our planet I find it curious that pinnacles are so relatively rare. Perhaps the above explanation of their formation has been oversimplified and some more unusual and subtle process has taken place. The Pinnacles are an outstanding example of this phenomenon and as such remain somewhat enigmatic.”
- geologist Peter Lane, 2004
The Pinnacles Desert is accessed via Pinnacles Drive and is approximately 17km SSE of Cervantes.
PLEASE NOTE: Fees apply to enter Nambung National Park.
The Pinnacles Desert Discovery Centre is open daily (for 7 hours) except on Christmas day. The park can be accessed outside of these hours, with payment made during the day, but overnight camping is not permitted.
Apart from visiting the Discovery Centre and enjoying the view from the Pinnacles View Lookout (which are both wheelchair accessible), you can walk through the Pinnacles Desert on the Desert View Walk (a 1.2km loop) and/or drive through on a 4km one-way loop.
To log this cache you need to
A. Answer the following questions:-
1. At the entrance to the Pinnacles Desert Discovery Centre are some charred posts with Aboriginal words inscribed on them. According to the sign, what is the meaning of the words on the post closest to the sign?
2. According to the above theory of pinnacle formation, what was it that caused the calcium carbonate near the surface to dissolve?
3. According to the sign at The Pinnacles View Lookout (at the given co-ords), after pinnacles have been exposed by shifting sands, what further process do they undergo?
B. Post a photograph of your visit to the area (but please don’t include any of the signs).
Please email your answers for part A to us so we can give you the OK to claim a find, then you can log it and upload your photo.