The Whispering Wall is the retaining wall of the Barossa Reservoir. Built between 1899 and 1903, the dam was a revolutionary engineering feat for its day and attracted attention from all over the world, even making its way into the pages of the journal Scientific American. The dam was once the highest dam in Australia. Yetti Creek gorge is dammed with a concave concrete dam bending its back against the pressure many tons of water stacked up to twenty seven metres at the wall.
But what draws visitors to the Whispering Wall is its unique acoustic effects. Words whispered at one side of the wall can be clearly heard at the other side of the dam wall, almost 150 metres away. Children in particular love visiting the wall and testing its abilities. Voices were heard so clearly because of a parabola effect. The wall is one sector of a perfect circle, and soundwaves bounce in a series of straight jumps along it to the other end. So to our experiment. Does sound travel faster than the speed of your phone?
Stand at one of end of the dam and make a phone call to a friend at the other end of the dam. Listen to sounds from your friend with the phone and with your other ear and try to estimate the variation in the timing. The best sounds to use for your experiment are short sharp words like bop, stop, splat or zap. No need to shout. It is called the Whispering Wall. If you can hold the phone under your ear with your shoulder try a clap with your hands. Having a conversation will be difficult. Hear the echo? Sneaky is playing with your mind.
This same experiment can be done with thunder and lightning. The science is that the speed of sound through air is about 300 meters per second. The speed of light in air is about 300 million meters per second.
The Whispering Wall spans the dammed gorge of Yetti Creek. The headwaters of Yetti Creek are in the Barossa Goldfields. The Barossa Goldfield was discovered in 1868 and produced an estimated 3 tonnes of gold until activity ceased in the 1930s. Most production was alluvial gold from the base of Tertiary fluvial sediments and modern drainage channels. Small amounts of reef gold were also produced between 1894 and 1900 from quartz and haematite veins within underlying schist and gneiss which forms a basement inlier within younger Adelaidean rocks.
Sim's Rush. — Early in 1887 a fresh discovery of alluvial gold was made on sections Nos. 674 and 1103, near the junction of Spike Gully and Yetti Creek. The gold is found in ordinary alluvium, increasing in depth to the northward, and also the area previously worked between Yetti Creek and Spike Gully. It is impossible to state the amount of gold obtained from these diggings, owing to the reticence of the miners, and the owners of the property. The rocks of the neighbourhood are white kaolinized clay slates, quartzite sandstones, and metamorphic granite.
The question is whether the geology of the Yetti Creek gorge is the same on either side. The dam wall will provide access to both sides of the gorge. Let’s have a conversation about the geology. What rock types do you see? What rock types does your friend see? Do you see any gold?
Send your answers to logging tasks via the cache owner's profile. Post a fun photo with your log if you want. Squeaky hopes you have fun.