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This is for the intrepid Melburnians who get out of the city, travelling the open spaces, winding up through the north past the more famous Hanging Rock, feeling the sun on their knees and the wind in their hair, exploring Major Mitchell’s old stomping ground, curious about the landscape therein. The wanderers, the dreamers, the scientists and artists. Here forth a note about the geology of the Coliban valley, in the Redesdale area, Victoria, Australia, that I wrote for the Redesdale and District Association:
A 400 Million Year Old Geological Tale
The landforms around Redesdale:
As far back as the expedition of Major Mitchell, the shape of the hills in this area were remarked upon for their flat table-top features, presiding over incised valleys and crumbling slopes pock-marked with giant granite boulders. The shape of the land here is a result of the slow erosion of rock and soil over the past million or so years. However, some of the rocks here are very much older than that.
Beginning at the bottom are the sedimentary rocks (mostly made up of clay and silt and sand, formed on an ancient sea floor, cemented into place some 450 million years ago, hundreds of millions of years before the world would see its first dinosaur) that form the foundation stone of much of Victoria. These are sometimes seen in road cuttings in the area and are typically grey to cream in colour, sometimes displaying their characteristic layered pattern. Pushing up through these like a bubble rising in water are the granites, which arrived around 100 million years later. Eventually they reached the end of their bubble like journey and solidified into the grey-coloured crystalline rocks you see poking up through the paddocks. In geological terms, the granites are ‘igneous rocks’ (as opposed to ‘sedimentary rocks’, like the previously mentioned sandstones).
The final arrival on the scene was the basalts (volcanic rock), which are, by comparison, mere infants, spewing out from nearby volcanic vents within the last few million years. They would have filled ancient valleys and streams carved into the granites and sandstones beneath, valleys which would later be known to geologists as ‘paleochannels’, and created a very flat volcanic plain. However, basalt is not very resistant to the weather. Soon after the volcanoes stopped flowing, Mother Nature would have started to carve new valleys and streams into the volcanic landscape, and much of the basalt would be eroded away. Once the water was through the basalt, it would start to erode away the more ancient rocks beneath, and the different way the different rocks erode can be seen in the different slope angles between the basalt hilltops and the granite slopes beneath. Some little sections of basalt remain, however, and these can be seen in their original flat lying glory, capping many of the hills in the region and creating perhaps the most striking geographical sight in the area.
(WARNING: may contain geological terms!)
Around the paddocks you will see large, grey coloured rocks that are generally rounded in shape. These are members of the rock unit known as the ‘Harcourt Granodiorite’ (‘granodiorite’ is a granitoid rock with more plagioclase feldspar than a typical granite, for the lay people, they’re typically just called ‘granite’). These erode in a characteristic ‘onion skin’ pattern, resulting in rounded boulders and curved sheet like portions that have peeled off the boulders. They also tend to form very coarse sand as they erode, typical of the river sand you see in the Coliban and Campaspe Rivers.
Also around some of the paddocks in the area you will find a paler creamy-pink rock that is in flatter and in more square/rectangular shapes. It has been used extensively in rock walls in the region. It looks a little bit like sandstone, but in actual fact, it too is a granitoid, in this case, a true granite. This is the Metcalfe Granite, and it is part of the same group of rocks to which the Harcourt Granodiorite belongs (and they are of similar age, around 350 million years old). This group of rocks is properly termed the “Harcourt Suite” and includes several regional variations of granite and granodiorite. The interesting thing about the Metcalfe Granite is that it contains many ‘leucocratic dykes’ (leucocratic – pale coloured, as opposed to melanocratic – dark coloured). These are internal zones that have more of the feldspar and quartz minerals and were like internal ‘channels’ when the rock was emplaced. They actually ‘flowed’ through the surrounding rock. As a result, they contain features that look like the layering of a sandstone, and this also explains their more blocky fracture pattern.
Granites (and granodiorites) are what are known as plutonic igneous rocks. They formed beneath the ground when their rise up from the inner earth ceased upon reaching a natural buoyancy level in the earth’s crust. They then solidified (‘crystallised’) and stayed there. In the local version’s case, this happened around 350 million years ago (for scale, the dinosaurs came onto the scene around 250 million years ago and were gone by 65 million years ago). Locally this meant that the granites rose up into the surrounding sedimentary rocks. Thus these are like blobs within the regionally-more-significant sedimentary rocks (sandstones, siltstones and the like). What this implies is that these granites you see today are seeing their first ever sunshine, having previously languished beneath the earth’s surface for most of their 350 million years of existence.
Atop many of the flat-topped hills of the area you will find crumbling reddish-brown rock with lots of holes in it (properly termed ‘vesicles’). This is basalt, and this is the rock that caps the hills and causes their shape. Basalt is a volcanic rock (think of lava flows in Hawaii). You are looking at the last remnants of huge volcanic eruptions that occurred over the last 4 or 5 million years. Victoria was a very active volcanic place in its recent geological history, and in some areas of south western Victoria, it is even possible that eruptions were still taking place when the first human inhabitants arrived some 40 thousand years ago.
A final, related point; a side note about the colours of rocks. Basalts are dark-grey to black when they are fresh. Granites are normally very pale grey, as are granodiorites (although they can have a range of colours from pinks to greys to blue-ish colours right up to reds and even some greens in places). Most of the pink to red to brown colours you see in these rocks are a result of erosion – “weathering”. The colour comes from the fact that all these rocks contain some minerals that have iron in them (basalt contains a lot of these minerals, granite hardly any). When those minerals weather they produce iron-rich minerals such as limonite and hematite. These are orange-red in colour and spread out and ‘stain’ the surrounding rocks. The effect can be quite pervasive, resulting in the colouration of entire rock pieces. In the case of basalt, the entire rock has had some degree of weathering, and so it is now a dark brown-red colour, having lost nearly all of its original fresh black. In the case of the local granite, the original rock is nearly white, however, the little bit of iron staining that has occurred has given these rocks their slightly pink hue. Indeed, a little bit of iron staining is exactly what gives some of these rocks their spectrum of colour, resulting in the beautiful pinks and creams that you see today.
You may have detected a skeptical vein in me whilst reading. I am skeptical. I am a scientist, it’s my job! Furthermore, I am a geologist who specializes in groundwater. I earn money through the planning and delivery of water (potable or construction water typically) to major projects. Part of that process is the exploration for water. Through a combination of looking at maps, on the ground reconnaissance, and clever things like geophysics, I decide where precisely to drill water wells. It is a scientific process, with a lot of learning along the way. You really do get better with experience, and for me anyway, my background in gold and nickel exploration has helped. I’ve been doing all these various exploration tasks for a several years now (about 6 in fact) and definitely I’ve improved. I know how drill rigs work and I have a decent idea of how (basically) to tease out from the local geology in a given area the better places to look for water (or gold, or nickel or whatever). Again, it relies on the collective knowledge from generations of geological science. Knowledge that I started to learn at university.
Enough about my scientific credentials already! Why I write this is that I am currently working on a project where we are trying to find enough groundwater for the construction of 100km of railway. Railway line construction requires a lot of water (about 800,000L per day every 10-15km of line in this case).
We’re working in a pastoral area, sheep and wheat country. The geology is pretty much granite through and through, and anyone who knows what that’s like will tell you that water is scarce. Surface water is practically non-existent and groundwater is hard to come by. This is nearly a desert. How do I know this specifically in this area? Because I have been talking to the local farmers. These guys have been breaking their backs for generations, eeking out the precious value this land will throw up to those who persevere. The one thing that determines success or otherwise more than anything is water. Stock need it to survive, and having no mains water system, a farmer’s house supply relies on it. Subsequently, the farmers invest a large amount of thought and effort into finding water. The country is pock-marked with drill holes and windmills. With this effort comes a culture of great interest in the techniques deployed to find that precious water.
From my discussions, the number one technique employed to find water here is water divining (“water witching” or “water dowsing”, depends where in the world you are). Before you sigh and stop reading, consider this: a water bore can cost more than $10,000 whether or not you actually find water. A farm would quickly go broke drilling holes if their success rate wasn’t too good. But then, hiring geological consultants such as myself is not cheap either, and materially adds to the cost.
What you need is a method of locating the holes yourself (or even getting a mate to do it for a few beers). Enter divining. You know who they are – they’re the ones with bent pieces of wire or Y-shaped sticks who wander about and find the “stream” and tell you where to drill. There is no scientific evidence for its efficacy whatsoever. Indeed there is scientific evidence that demonstrates that diviners have success rates no better than chance (for a good summary, I do recommend the Wiki page). This scientific ‘disproof’ has been around for at least half a century. Despite claims by practitioners to the contrary, we can probably consign water diving to the quack-bin and declare it bogus. Hocus pocus pseudoscience.
BUT, does it work “in the real world”? Given that so many still use it, even rely on it, what residual value might it poses for the farmers out here?
Well, my unscientific study of the local farmers deploying this unscientific technique suggests that it is valuable indeed. The process of divining has located many successful bores in this district (together with a largely unmentioned number of failed bores!). Any geologist will tell you that drilling completely at random will not give you a good success rate. To this end, drilling on “crossing streams” found by diviners is not random. There is a great deal of local land knowledge that is deployed when divining, thus narrowing the focus of the search. The divining really then just delivers a reason for siting the drill rig in a particular location. With limited resources at-hand, this is perhaps just what is needed – comfort in spending the money.
So how am I to react when confronted with several ‘divined locations’ (I can’t help but make the mistake of pronouncing it ‘divine locations’ here!)? This is difficult country to explore, and even I, the skilled geologist, have limited data. My locations are beset with large error margins. In fact I will plan for a certain failure rate given the known geology.
I decided to let them have the run of it for a while, as the divined spots had some features that made them acceptable exploration targets. One diviner, we’ll call him ‘Bruce’, comes with, it is said, a 100% success rate! (Forgive my skepticism, 100%?) I have spent the last week drilling his targets. So far, we’ve drilled four holes. The first one was an absolute gusher! More water than we hoped for. Even the farmer, lets call him ‘Barry’, said he’d never seen anything like it! Then the second came up with water too. Not as much, but adequate.
At this stage, I’m running through the stats in my head. This is getting like some sort of baseball or cricket statistic. Surely the ‘run’ must end soon. But then comes the third hole, better than the second. So Bruce is 3 from 3. Pretty good. Don’t worry, I’m not about to be ‘converted’.
The fourth hole comes. I press on, drilling deeper than I usually would. Barry is telling me I have to go deeper, Bruce is never wrong! Bare in mind, this is hard, dry granite. No water in that. But then, sure enough, there’s the water! This time though, it’s minimal; not enough for a bore. So how to call this? 3.5 out of 4?
It’s hard to explain this without saying that there was simply a network of water baring fractures in the granite that would have been found anyway. That would be the logical, geologically appropriate explanation. I happen believe this to be the case. We may even have been able to detect the fracture systems with the right geophysics. And then, we might have drilled proper ‘geological holes’. But, like Bruce the diviner might agree (perhaps not) how will I ever know? We can’t drill everywhere, and geophysics for this kind of exploration is costly in both time and money with limited chance of improving the success rate.
So, what is the upshot of this? Well, I have spent a week drilling holes and conversing with Barry. We get on well and he has been helpful above and beyond the call. It has been a pleasure. What about the divining? Well, Barry wouldn’t let me drill anywhere that didn’t come approved by Bruce anyway. So, the upshot is that we have a happy landholder, and a happy geologist drilling good water bores (the task for which I am paid). Everyone’s a winner, except, perhaps, science. I come out of this a little miffed that I couldn’t show Barry a better way. But then I’m not from round here. It seems that local knowledge has beaten science in this round. Next time, I will have better data, and a better story. I hope.
I still don’t believe that we wouldn’t have found the water without Bruce though!!
There are a few dramatic climate-change related videos going round at the moment, frequently going after the shock factor. Whilst the shock factor is not always effective, this one below I think is very good, because it has a cognitive component – linking polar bears with your behaviour. No longer are they stuck on a melting iceberg, and this delivers a nice little way of thinking about your carbon footprint:
North western Australia. A marsh landscape. A place to be filled and developed. It is hard to describe the feelings I had here. Best put, I felt a sense of impending loss. A creek flows through the marshes and the fish and kangaroos go about their business. The hum of nature is barely perceptable. One day, this will be filled with sand and a giant industrial facility will take it’s place. It will never look like this again. Progress, progress, progress. Unavoidable. How then to reconcile what’s lost? I am still to decide.
We have a lawn at home, and we only water it on our water-restricted watering days (except very occasionally by hand if its a 40+ degree day). It keeps the garden cooler, and we assumed it was also a good carbon sink. Well, it is a good carbon sink, but it seems that all the grooming efforts eliminate that or worse: http://www.physorg.com/news183129874.html
I know that ours is only a garden lawn, and this study focussed on public parks, but some of the results must be transferrable – we mow our lawn and only a month or so ago we applied some fertiliser for the summer. We use an electric mower, so that probably helps as it is only drawing baseload from the power station (which is of the super-green, brown-coal-fired type!) – arguably better than an inefficient 2-stroke mower. But it calls into question the "greenness" of the backyard lawn, which does after all take up a considerable portion of the garden.
So, what do you do?
You could replace it with synthetic turf, but that would have all sorts of issues relating to its manufacture. Or you could replace it with gravel and the odd plant, but that would not have the cooling effect and would have even less carbon storage capacity. Perhaps its best to keep the lawn and not fertilise and mow less. Its a tricky area in a climate where everyone wants to do their bit.
As always with these issues, there is more than one aspect. Here we balance CO2 emissions against water security. Where we live, water is scarce and resources are stretched. Electricity generation produces tonnes of CO2. But it will be water that gets us first. Increasing population demands greater water supply. In an area at least 50% supplied by groundwater, much of which is "fossil water", it is obvious that a limit will be reached. What is worse, increasing water demand forces government to install desalination plants, further increasing electricity demand. A vicious cycle is established. SO, ultimately water demand reduction could have a double benefit – reduce the need to enhance supply and reduce expanding electricity demands.
Where does this leave the lawn? Well I guess it means replace it with a garden bed full of drought friendly plants that require little water. Either way, it reminds us that reducing water use is one of the best things you can do for the environment. Still, that lawn is a nice thing to have…