Located 245km north of Perth, The Pinnacles Desert was the first planned stop on our quick trip up north.
We had landed at Perth International just after lunch-time, and naively thought that we would be well on our way and out of the city within in a couple of hours. Not so. (Read: “Australian Customs: A Different Experience”)
However, we made it through and picked up our hire-car. A monstrous Roo-kicking (I didn’t just say that, did I?) Holden SV6 Commodore… An automatic. How very American and nothing like the Toyota Corolla I was expecting. I’ve only ever driven manual transmissions before, so this was going to be interesting. But it turned out to be super-easy.. The biggest problem I had with it was when I returned home and back to my manual car – where I promptly forgot how to use a clutch pedal!
We arrived in Certvantes well after sunset, pushing our visit of the Nambung National Park to the next morning, after our quick visit to Lake Thetis and it’s Stromatolites.
Within the park itself, you can choose to either drive a 4km loop, or walk a 1.2km loop. You can of course do both if you so felt like it. We chose the “drive-about” option, and were met with this:
There are many legends that refer to the origins of this strange and wonderful landscape one of which is told by local Yued elder:
“Noongars knew this place, the Pinnacles Desert, as Werinitj Devil place, because of the sinking sands …the young men were told not to come here as they would disappear into the sand. But some did not listen to their elders, and when they got here they vanished into the dunes. The pinnacles are their fingertips, trying to grasp hold of something so they can drag themselves out of the sands.”
But, those who have read this blog before will know that I’ll be throwing a geological explanation at you too!
The Aeolians are coming:
Not to be confused with any UFOs, Aeolian describes the wind-blown origin of sediments, in this case the Tamala Limestone. Now, how on earth do you get a wind-blown limestone? Well this particular limestone was originally washed up as shell particles on the beach that were subsequently brought inland by the wind, along with minor amounts of “normal” quartz sands, forming large dunes.
Plants are key:
However, there are two arguments for the formation of these pinnacles (Not an uncommon thing in Geology!)
1) The first explanation suggests that during wet winters, rainwater would dissolve the calcite from the shelly component of the upper levels in the dunes, precipitating the calcite in the lower levels of the dunes as cement. Plants took hold on the surface producing a rich humus layer which in turn accelerates the leaching process. As the plant roots grow deeper, so the leaching process removes the calcium content in the nearby vicinity – resulting in a more quartz-rich environment. It is these quartz-rich areas that are less resistant to erosion. Basically they have “lost” their cementing component and have been more readily blown away. The result is towers of harder calcium-rich limestone: The Pinnacles.
2) The other interpretation for this environment is the belief that these pinnacles are actually fossilised tree stumps. An ancient forest was buried beneath sand during an intense storm; its organic acids produced on decaying would have dissolved the calcium-rich dunes. The calcium would have then re-cemented around the outside of the trunks of the trees as hard layers of calcrete. Over time the insides of the tree trunks would have filled up with more sand and calcrete, plus other plant detritus. Eventual erosion of the sand dunes would reveal these preserved fossil tree-trunks: The Pinnacles.
Personally – I vote for the first option.
I thought I could see shelly fragments and there is clear evidence of cross-bedding (a typical feature of wind-blown, aeolian deposits), which you won’t find in any tree, fossilised or not! If I had to compare these “fossil trees” with others I have seen, well – I’m not so convinced that the second theory should even exist!
These rocks are actually relatively young, having formed approximately 500,000 years ago during the Quaternary (1.8 million years ago – present day). Evidence at the site suggests that they were only uncovered after bush fires destroyed vegetation, which in turn allowed wind erosion to expose these pinnacles in the ground a mere 6000 years ago. They have been re-covered and uncovered again since then – perhaps only being finally revealed as recently as a couple of centuries ago.
It truly is an amazing place and well deserved of the description that there is nothing quite like it anywhere else in the world. Some of these natural monoliths reach up to 4m high!
They also apparently make great perches for Galahs – aka Rose-breasted Cockatoo!
Sources and Links: