A 4WD vehicle is not required to get here but may be needed elsewhere in the area. Please check road conditions before heading off to this site.
Read this information first. Then after retrieving the nearby traditional cache take a rest at the coords on the way back down from your climb. Look at Walgahna from here to answer the Earthcache questions below.
The local indigenous name for Walga Rock is Walgahna. It is 5km around the base and 1.5km long, making it the second largest monolith in Australia. It looks a bit like a mini-Uluru but does not similarly dominate the landscape.
Walgahna is composed of post-tectonic granite and is one of the many whalebacks scattered throughout the Yilgarn Craton. The rocks in this area are thought to be approx. 2.5 billion years old. There is evidence here of both weathering and erosion.
Weathering is a destructive process. It refers to the breakdown in situ of a substance where as erosion refers to the carrying away of material. Both are natural processes and have been fundamental in the shaping of the Australian landscape over geological timescales.
Chemical weathering involves a chemical change in at least some of the minerals within a rock. Mechanical weathering involves physically decomposing rock into fragments without changing the chemical make-up of the minerals within it. Weathering is a surface or near-surface process and no movement is involved.
As soon as a rock particle (loosened by one of the two weathering processes) moves it is called erosion or mass wasting. Mass wasting is simply movement down slope due to gravity. It is called erosion if the rock particle is moved by a flowing agent such as air, water or ice.
Most rocks have natural cracks. The geometry of the cracks depends on the minerals that make up the rock and any bedding or layering structures present. Homogenous rocks such as granites develop rectangular joints and the rock mass weathers to form massive tors.
During weathering some horizontal joints are also formed when load pressure is decreased causing sheets of granite to peel off. This is the beginning of “onion skin” weathering. The Bungle Bungles, Uluru and Walgahna are fine examples of this process.
The mechanical weathering here has resulted from the process of contraction and expansion. This process is caused by expansion and contraction of the surface because of extreme seasonal and diurnal temperatures in this inland arid climate.
Rocks heated during the day will cool at night. The rate of cooling is greater on the outside of a rock than at its core. This differential also contributes to “onion skin” weathering in homogenous rocks such as Walgahna. You can see very large slabs of granite in the process of ‘peeling off’ the main rock form.
You may log this Earthcache straight away but then please email your answers to the questions to the CO. We will contact you ONLY if your answers need extra work. Logs with no answers sent will be deleted.
The answers can be found by observation, reading the provided information and a bit of thinking. Please do not post your answers in your log.Photos of you in the area are most welcome but no spoilers please.
Q1. What is your current elevation on your navigation device?
Q2. What evidence can you see that weathering is taking its toll on Walgahna?
Q3. You can see a triangular rock that looks like a cheese-wedge. Describe how you think it was formed.
Q4. Which of these processes describes how the cheese-wedge arrived at its current position?
A - chemical weathering
B - mechanical weathering
C - mass wasting
D- erosion
Q5. What evidence can you see that indicates water has had an impact on Walgahna?
Remember to take only photos and leave no trace of your time here. We hope you enjoy your visit to this area showing geological processes in action. 