Volcanic History.
The area of western Victoria and south-eastern South Australia traversed by the Volcanoes Discovery Trail is known as the Newer Volcanic Province. There are a number of other Volcanic Provinces in far north Queensland. The Newer Volcanic Province includes six sites of international significance and 14 of national significance, and is Australia's most extensive volcanic province. It features almost 400 individual points of eruption, most of which took place between 4.5 million and 2 million years ago.
Various lava flows spread evenly across the existing plains, followed valleys, flowed under water, and in some cases forced upwards into rough, stony hills called tumuli, or steeper scoria cones. In particular, the volcanic activity immediately around this Earthcache site took place a mere 8000 years ago. Even more recently, the last eruption in the Newer Volcanic Province took place at Mount Shank (see What a Blast!!, by Derringer, GCDE45), not far from Mount Gambier, in South Australia only 5400 years ago. Australian volcanologists and seismologists now agree that such young ages imply the possibility of further activity. They also say that at present there are few of the tell-tale signs of renewed activity, such as tremors, earthquakes or hot springs.
Human Significance.
Many of these eruptions were witnessed by the indigenous peoples of the area, who have lived here for up to 45,000 years, and feature prominently in their stories of the dreamtime. Aboriginal people also made use of the stones from the lava flow to construct channels linking the wetlands, weirs, fish-traps, wind breaks and stone huts. Excellent examples of these, created by the Gunditjmara people, can be found around Lake Condah (about 19km SW near Mount Eccles)) in particular. Later, during the 1870s and 80s, European settlers used the volcanic stone cleared from the land to construct dry stone walls in order to grow crops and introduce stock. Many examples of these walls can be found surrounding Camperdown on the Dry Stone Walls Heritage Trail.
Harmans’ Valley and Surrounds.
At the posted coordinates you are overlooking Harman’s Valley, with Mount Napier, the youngest volcano in Victoria, visible about 10km away. Mount Napier is a composite volcano comprising a broad lava shield topped by a central scoria cone. It rises 150m above the surrounding plains to an elevation of 440m. It is the highest point on the Western District Plains of Victoria. A spectacular lava fountain several hundred metres high erupted from a lava lake in Mt Napier's crater about 8,000 years ago. The lava rose from a depth of over 30km and its temperature was about 1200 degrees Celsius. It flowed in four directions, and the westerly flow, down Harman's Valley before you, extends for around 24km. Spectacular lava blisters, or tumuli, formed near the western extremity of this flow nearly 6km away. The flows also formed the Byaduk caves, a series of collapsed and intact lava tubes about 3km away. Try to imagine how the valley below you would have appeared when Mount Napier was erupting, with a river of lava slowly flowing past. The lava, heat, smoke, fumes and ash would have created a truly hellish scene. The information signs here today will help you to understand the processes involved and how the present-day landscape was formed.
Recent Controversy
This spot hit the news in mid-2015 when the local landowner "flattened" a significant part of the lava flow. He claimed that his predecessor had crushed most of the lava flow 10 years earlier. See https://www.theage.com.au/national/victoria/protests-erupt-over-crushing-of-36000yearold-volcanic-lava-flow-in-harmans-valley-20160718-gq87do.html for details. We like to think of this as our Earthcache having been muggled!
This is what the valley before you used to look like, in November 2008.
How do you claim this EarthCache?
To log this Earthcache, you will have to answer a few simple questions and, optionally, take a photo. Do not include your answers in your online logs. Visit the posted coordinates, where you will find a series of signs explaining the origins of Mount Napier and the Harman Valley lava flow. As you study the information provided in these signs, try to relate it to the scenery before you. Then, email your answers to the following questions to us using the link on our profile page. Do not include your answers in your online logs.
1. During the formation of Mount Napier, how long might individual lava flows have lasted? How long would the final lava shield have taken to build up?
2. How have scientists estimated the date of the lava flows?
3. Why would local aboriginal people have been in little danger from the lava flow down Harman’s Valley?
4. One sign shows a view from this spot 8000 years ago. How many numbered volcanic features are shown on this diagram?
Finally, we'd love you to take a photo from this spot of yourself and your GPS with Harman’s Valley and Mount Napier in the background. Upload this photo with your log, and don't forget to send your answers separately. Logs for which we don't receive answers will be deleted.
This is the tenth in our Vulcan series of caches along the Volcanoes Discovery Trail. Brochures describing the Trail can be obtained at the Colac, Hamilton, Port Fairy, Portland, Warrnambool, Tower Hill or Penshurst Visitor Information Centres in Victoria, and Millicent or Mt Gambier in South Australia. Penshurst is also the home of the Volcanoes Discovery Centre.
Other maccamob caches on the Trail are:
Ready To Rock (Red Rock, a nested maar)
A Leurid View (Mount Leura, a nested maar)
Puddle Jumper (Mount Noorat, a complex scoria cone with an entire circular crater as its main feature)
Rouse About (Mount Rouse, a massive accumulation of scoria, with lava flows dating about 1.8 million years ago)
Tumultuous (unique Lava Tumuli up to 10m high and 20m diameter, and located less than 6km from the Earthcache site)
Peking Market Place (Byaduk Caves, the most extensive and accessible lava caves and tubes in Australia, located less that 3km away)
Vol-Au-Vent (Mount Napier, a breached scoria cone about 10km away and the major source of the lava features around this earthcache)
Big Rock Candy Mountain (Giant Rock, the remnant of a Tertiary volcanic plug which has been dated at 250 million years old)
”What A Blast” (by Derringer, at Mount Shank), “Elemental Forces – Earth” (by Derringer, at Mount Eccles), “Centenary” (by Team Piggy, at Mount Gambier) and “Towering Inferno” (by Alex, at Tower Hill) are some of the other caches along the Trail.
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