While walking or cycling along the Merri, Moonee Ponds or Darebin Creeks you may notice remnant vegetation, indigenous plantings, constructed wetlands and the animal life of the creek corridors. But there is an underlying element to this - these creek valleys contain many millions of years of history and secrets.
Over 400 million years ago the sea covering this part of Victoria receded. It left behind a layer of yellowish marine siltstone and sandstone rocks. Around 65 million years ago non-marine sediments left a sandy layer behind.
Over time the Merri, Moonee Ponds and Darebin Creeks developed and eroded paths through these sediments to form their ancestral valleys.
Then, starting around 50 million years ago, volcanoes began erupting. This happened not just in northern Melbourne but right across western Victoria. A vast basalt plain, the Victorian Volcanic Plain, formed.
North of Melbourne, lava poured from Hayes Hill (about 5km east of Donnybrook) and Mt Fraser (near Beveridge). It flowed on an epic journey along the ancestral valleys of the Merri and Darebin Creeks and into the valley of the Yarra River nearly as far as the Central Business District Melbourne.
What the volcanoes left behind...
The modern day Merri, Moonee Ponds and Darebin Creeks were formed over many years, by incising through the lava surface. One of the many sites of geological interest along the Merri valley is the rocky cliff face on the eastern side of Merri Creek visible from the shared path in Clifton Hill (shown below). Primary school students explored the site in 2007 as part of Northern Nature Creek Connections program funded by the Natural Heritage Trust.
The cliff face is a sculptural revelation. Its tall, cracked (or jointed) basalt columns, formed by cooling lava, are clearly visible and the weathering evident in the rocky riffles mid-stream where columns have collapsed and tumbled into the stream. Some of the vertical fractures at the top of the cliff appear to be leaning, forming an amazing radial pattern. Find out more about this site.
You don’t have to be a primary school student to explore the fascinating secrets of the creek valleys! Next time you’re in the area see what you can observe in the rocky escarpment features along the way.
Find out more about the geology of Merri Creek. Find out more about the geology of Darebin Creek.
Click here for information on the geology of Melbourne, including Darebin Creek, Merri Creek and Moonee Ponds Creek.