Conservation of rock art in Western Australia
Video | Updated 2 years ago
Dr Ian MacLeod, Executive Director of Collections Management & Conservation
WA has a vast collection of rock art that depicts elements of indigenous cultural activity for more than 40,000 years. How can we ensure survival of the images that are being impacted by microbiological decay, micro-nutrients and the movement of moisture through the rock substrates?
Thank you Theresa It's really interesting that I have just recently come back for four months at The Getty conservation institute in Los Angeles and in the United States they never in any public event acknowledge the first owners of the land and so and meeting some of the first people at an exhibition in L.A. where Barbara Streisand was and DKNY turned up blah blah blah. It was very very much L.A. and they did finger food I got two fingers worth of food for the whole evening but one of the things was one of the local Indian said I wish I lived in Australia cause than at least we will be acknowledged so there you go that's something that least in WA we can do right.
So what I want to do today is just give you a quick run trough of some of the rock art science the different times of rock art that surround in WA and give you a bit of a feel for what some of the processes of deterioration are all about and how I as a, you know, boring chemist went around solving the problems and if any of you know where Bolgart is it's up near Northam and John Clark who used to be the museum rock art conservator had tried this is a big Kangaroo. In case you can't see it but the big kangaroo was all covered with lichen and the lichen was destroying the granite and the end the engravings and so he reckoned, right well lichen needs zinc "maybe we just give it a lot of zinc" and so he tried zinc sulphate zinc fluoride, zinc this, zinc that it really didn't matter so we used the cheapest thing of all zinc sulphate and just painting a little bit of zinc sulphate on the rock surface killed the lichen in a bio-friendly environmentally friendly fashion and so it meant that the image was preserved and so it was several years later when I went to Wave Rock and I saw this unusual patination of the rock and here you can see it in more details and of course it's the zinc because for occupational health and safety you just stop people going "OH I wonder where the e-AHH....is" and falling over and killing themselves and making a real mess down below at least is easy for FESA when bodies are dropped at the bottom of the cliff to pick them up.
But anyway I looked at it and here is the flaw lines this is where all the lichen has been killed off from the corrosion of when rain does occasionally comes to Hayden and the galvanized iron fence posts and the galvanized matched crows. So zinc corrosion products are generally water soluble and so it went and killed off the lichen on the rock and so it's always the case of too much of something is not good for you. So it's a bit like San Paul said to Timothy take a little wine for those stomach’s sake, and thine often infirmities and yet if you drink a bottle a night you will end up getting cirrhosis of the liver. So you got to find the balance and in conservation of the natural environment and working on shipwrecks and on rock art science it's a matter of finding that delicate balance point between in subtle intervention or changing the environment so much that a new problem suddenly emerges nearby up in the Wheatbelt you've got, here are some examples of typical images that you might find.
These are concentric ochre circles deep inside a granite cave and this is how the granite does block weathering. And you just want to make sure that if you camping just look at the cap edging of the rocks because it is inadvisable on a frosty night to camp to close to those edges because all of the sudden they can just go thump...and if you want to know what is like to have five and half tonnes of block drop on you in the middle of the night, I will recommend you camp there, but in this case here are the hand stencils and all throughout this cave. And I mean that's popa hand, mama hand and baby's hand and those hand stencils you know were made. You chew up the kaolin or either the clay there's there put your hand there and than just go Phhhurrrrppt!!! And blow the biggest longest raspberry you can and you leave you imprint there and when is properly cared for in the environment inside the shelter some of these hand prints in this cave have been dated at more than 8,500 years old, and so what nice subtle way of saying I was here.
Our current methods of saying I was here are either building monstrous buildings on St Georges terrace in the hope it might be there in 60 years time so I think they knew the better part and of course. Here you've got a snake and a goanna joined in together. And the person who started me off in rock art is this man John Clark and that was me, yeah before I got old and lost my beard and mustache. And this is the rest of the team and obviously working in conjunction with indigenous elders who take you to the site because it's their country you working and walking on their land and so you need to be guided by their experience and understanding of the spirituality of the sites. And up if you go to Kew, hands up those who've been to Kew... Good! Good. West Australians it's magic country up at Kew and up at Walga Rock there are whole series of images painted in the shelter here, this is original vegetation that's obviously original vegetation but one of the problems there was the there are a lot of inherit fugitive that is reactive pigments like kaolinite the white clay calcite, calcium carbonate which are very prone to acid dissolution and being lost.
Now everyone normally says on archaeological sites look out for bird shit, I mean sorry avian guano, but it's basically bird shit and the birds would roost up here and then occasionally it would rain and the water would wash the poo down. And so these are basically poop lines from birds quite naturally occurring, but one was amazing was the Ochre pigments near the rock art there. It's really quite very, very, fine paintings but you can see these areas are where little bits of the granite. There you can see it less active spalling but this is where the solution weathering of the granite gets in and changes the minerals under the surface, the hydration changes and than the new minerals underneath that little rocks they just go Budoing! And blast the surface off and so that's what's happening in there. But one of the curious thing was that right under the bird shit lines for one of another word these white pigments were incredibly well preserved and everyone had said initially "yo got to get rid of the birds" you... you poison them!
People said "the best way to manage the rock art on this site is kill the birds" well if you are a Kestrel or a Sparrow Hawk or a Falcon, I mean life it's tough in the Murchinson and to have a rock art conservative getting around with a gun, a 22 trying to shoot you or something is not nice! So we said no let's just understand what's going on and in fact what it was was that acidic phosphates from the avian guano reacted with calcium carbonate to give you a different calcium mineral calcium pyrophosphate and the bicarbonate just washed away and here you can see the surface PH of different parts of the rock and right near the avian guano flow the surface Ph in about 4.75 which is acidic enough to get this reactions so what did we do?
With our mates in CSIRO we went and got.. I went to the zoo and got modern poo from the same type of birds because the composition of poo varies enormously from bird to bird just as it does from human to human depending on your diet. And so what we did we replicated a reacting the old guano or modern guano with the modern minerals and we were able to reproduce and get the same minerals turning up in a little accelerated experiment as the rock had gone and produced. And so we really are sure that this was the mechanism of preservation and so the answer to that treatment was live the birds alone live the rock alone. And in fact the best thing that we had to do was in the area in front of the cave we modeled the amount of moisture that was coming in when during cyclonic rains, and we just planted native plants that will grow to a specific height and we bought tanks and trickle fed them for five years and then they grew up and now the whole front of Walga rock is naturally protected from cyclonic rains so you wont get any washing away of the rock art because we planted native species that have very low evaporation and transpiration through their leaves the moisture balance was modeled the micro climate of the cave was modeled the chemistry was understood.
And so our intervention on that site was planting some trees and so but if you don't know what's going on you can make mistakes and the Kaolinite the aluminum hydroxide silicate went with the bird guano to a calcium hydroxide silicate and another different aluminum one and so it went from being very subject to rapid expansion and falling off to be a very stable mineral so people were amazed they said and you got twenty four thousand dollars from a AIATSIS in Canberra to study the reaction of avian guano?
Yeah where's the sense in that? At least we can tell people if you've got bird poop on the site just check your reactions. If we go and move up the coast and up into the Kimberly this is a view I took from the helicopter window in the wet season and this is the Napier Ranges it's dead flat on either side why because this used to be the sea bed and in an ancient time this was in fact a coral reef so if you want to know, if you don't like diving and you want to know about the structure of a coral reef just fly or drive up to Derby, go out to the Napier Ranges and walk around, and you never run out of air, never get the bends and you get to see some of the most magic country side in WA. And naturally areas like this show shelter would have been cut in by waves into the reef structure and so Aboriginal people for roughly 28,000 years had been painting images up here and this is a highly sophisticated method of holding our senses up against the rock surface. Which means you get a machete and you find a little sapling and you just go: "whack, whack" and cut a pole and then "chck, chck", cut a little chisel point in the top and then just bend it down put you're thermocouple up the top and then gently release it and it goes "kiss sound" and kisses the rock art art surface.
And it is fully reversible, totally green, literally green and it's a nice way to do things One of the things everyone said was: "Oh, everything will be happening in the wet season, nothing happens in the dry". Well, that's a load of cobblers it's all happening in different ways in the wet and in other ways in the dry and what we've found was: in the dry season the amount of moisture coming in varies, you can get little moist fronts and then what happens is that all of a sudden "shwooomp" these desiccated rock surfaces go "slurping noise" "wahrgh, water hahaha, oh, oh that was good" - and as a result: all of a sudden desiccated surfaces become hydrated and therefore, the pigments bonded to that desiccated rock surface suddenly swell and change their profile, and then can go "ping, ping, ping" and fall off.
So we were able in fact to pickup night time heating form some of these surfaces. Now the amount of cooling you normally get depends on the so called "Skyview" factor: the amount of radiative bits of sky that the long wave radiation can see the more of the sky that you can see, the faster you will cool.
That's why at home if you've got a carport your car never has dew on it because the amount of sky that the car can see is small and therefore the rate at which it will cool is small and so therefore corrosion on your car deterioration of your paint is minimised because you've got a low Skyview factor.
Do not put you car in a lockup garage in the winter unless you want accelerated decay but that's another story, you can ask me about that later.
Audience: "What date was that Done?". Ian: "What this?", Audience: "yes".
This work, we were up here this photo was taken in 1992. What we found was that sometimes there was night time heating and I looked at the results because I love plotting things. And sometimes the rate was faster and slower so what we did was multiply the relative humidity by the absolute vapor pressure of water at that temperature to find the real partial pressure of water, the number of millimeters of mercury water pressure there.
We found that the rate of cooling and heating was dependent on the vapor pressure of water. So as we plotted the rate against vapor pressure of water "Boom", there was a result. The reason why we were getting night time heating of 0.032 degrees per hour not much but measurable was because a moist front happen to be passing through the Kimberly at the time and the rock went "sluurrrp" and as it condense the moisture on the rock surface the water gave off its later heated condensation and surface increased in temperature, so I mean talk about sensitive you might think that chemists are non sensitive non caring people that just destroy the environment, I tell you what I'm with proper data loggers and really good thermocouple we are very sensitive.
And there's my colleague Phil Haydock looking a bit tired I think and that three fingers in the air means it's the third roll of film you make it a register of it and there's Phil attaching one of the sensor climbing up on a little ladder but when you have to carry everything in or chopper it in you become very adapt at, if necessary climbing on each other shoulders to go an attach sensors up in the roof of caves but the advantage of it is, we know what's going on now and so there you can see thermocouples right against the rocks surface and the RH probe taped to the top of the trip stick and there you can see an image partially covered with calcium carbonate because these are limestone cliffs and as solution weathers but here is a nice crocodile and there's a a Wandjina and it's in fact this white pigment of the Wandjina is a calcium magnesium carbonate that's got three magnesiums and one calcium in it, it's very unusual and guess where?
It's found in WA and that mineral Huntite has been traded as far north as northern Queensland that has come from a Kimberly mineral site and I mean it's a long way to walk to get the white pigment, but what happens is this pigment when the relative humidity gets over 56% its normally lying there hmm...I am a pigment humidity comes and the pigment swells and becomes bigger and fatter and absorbs multiple layers of and this two dimensional pigment becomes three dimensional and so the Wandjina goes from being flat to fully engorged and alive and shortly after "thunderstorm sound" the rains come because the Wandjina spirit is the spirit that brings the rains in the wet season and the life and the hope of new, new everything to the Kimberly.
And of course you can say well it's just a chemical reaction of the Huntite pigment swelling as the moist fronts come in as a harbinger of the wet season, or you can say that's real power there, and one of the simple ways of protecting these re painted images from cattle is wack a barbwire fence in front of it, because animals when you're a cow, you imagine being a cow or a bull and you got an itchy back you know, it's a little bit hard to get the back of your hoof up and or if you got two itchy points, you get two legs up and you fall down flat in your face and so therefore that's why cattle always go and rub their backs or their bottoms against nice rocks in the cave.
Well if the cave happens to be an Aboriginal rock art site the images can get seriously abraded and because there was still cattle on the station that hadn't been cleared the simplest form of site protection was just wack up a fence and that stopped the physical abrasion of the painting and these images had been re painted just four or five years before this photograph was taken in 1990 and there was a lot of controversy cause is up near Mount Barnett at the time and someone said "the Aboriginal people are destroying this ancient rock art images, this is desecration, it should be stopped, they don't know what they doing".
The person making that noise was trying to sell his station at the time and promoting the value of this ancient rock art images on his land so of course he had a commercial interest in it but our analysis of some of the layers in these cave paintings and sites show us that they have been repainted 10, 20, 30 times over maybe 15/25,000 years. It is all part of the all symbolism of the spiritual power of the site calling the elders to go and re paint them and re vitalize them, it's the world's oldest living culture and we living right in the heart of it.
If we only look and so up in the Mitchell plateau you've got lots of Wandjinas and you can see tale of big Kangaroo and you can see the areas where the Huntite pigment has been coming away and one of the reasons this gray black material in there was the calcium oxalate mineral hyoo-uh-lahyt spelled Whewellite and it was there as a result of biological activity. Plants are not like dogs, I have the walk my sister's dog the other morning at 6 o'clock Mt Henry bridge so it drops stuff, you have your plastic bag and you pick it up but with plant do we know do we know what plants do with their stuff? They left over stuff? No we don't! Why? Because it's normally hidden and you can't see the minerals because they go back into the ground.
But in a rock art site with plants living on top of you where do the plants metabolites go? Out down onto the rock surfaces and so oxalates which are inherently toxic to plants the plants go " oooh I didn't want to" and they get rid of them and the oxalates react with the calcium carbonate pigment and form a very stable calcium oxalate.
Now you might say well look what you should do, you should get rid of the stuff because it's not original but what was the most extraordinary chemistry up in the Kimberly in these sand stone country was the rate of which these reactions happened you got what it's chemically called isomorphic, yeah isomorphic replicas of the original painted surface but so the huntite very reactive calcium magnesium carbonate turned into totally unreactive calcium oxalate and retained the image! WOOOW I mean that's I mean everywhere in Europe the caves in Spain in France problems with nephantidis tomb in Egypt and so on.
You've got oxalate destroying images Kimberly different story some of these sites the rate of evaporation the rate of reaction everything was just absolutely perfect to get preservation of these painted images and although we haven't done any dating of these images because the elders said it is culturally inappropriate we don't want them dated so we didn't because they know it was their ancestors who painted them and so therefore we know that, good enough for us! I mean who wants to know?
I mean what's the difference if this is 28,000 years old and this is 32,000 years old, does it make it anymore significant, culturally, spiritually? No! Doesn't matter a woot! However for archaeologists who like, really like dating things they were able to dig up some charcoal in the site which they were given permission to and they got dates of 28 to 32,000 years and so what you looking at is the oldest evidence of human decoration and response and cultural expression in an art form that's known in the world and where is it? In WA. And what do we do with it? We are looking after it.
And so there's one of the elders but look at this site you know look at all the white Wandjinas all over the place and all the different designs and than you can see lots of data logging and why did I know to get into micro meteorology and that was cause I used to work at Murdoch before museum days and I met there my first micro meteorologist professor Tom Lyons and he taught me all about microclimates and suburbs and vegetation and how you can alter water balance and energy balance so I got one of his students on when I got money for a grant and so we began to study the micro meteorology of this rock art sites. And as a result we actually understand what's going on and more importantly we have been able to model the energy balance on these rock arts sites and predict temperatures and heating and cooling profiles for when we're not there.
So we know what stresses the rock art is going under therefore, we can go back periodically and monitor it. Then we have a better idea of how to manage these things in the future, when I'm no longer in the Museum because I'll be gone in a few years I mean, we all have to go. But the rock art you want to make sure that it has the best chance of living on so that's why we work the way we do.
Now slipping along into the Burrup this is so called climbing man panel and these are men climbing up the trees of life and with animals there to support them and one the things it was a lot of the stuff was been said that, oh the emissions from the woodside gas plant aren't, sorry correct that, the emissions from a significant industrial complex in the area were causing irreversible damage to the rock art and I said well what's the PH like, what's the surfaces like and every question I asked I got the classic aquatic zoological response ba..ba..ba.. ba..ba...ba..dont know I said well let's find out so we did and this is the image that you will see people against industry showing and they will say massive pollution you know in the Barrup caused by industrial plants and it is smoking and it does look sort of scary but this is a flair tower when you are processing gas and oil there is a very nasty toxic biologically produced materials. The safest way is to kill those nasty chemicals by burning them so when you get a build up of these nasty gases they just get vented through the top of the tower and woooshh all gone safe and sound so not a problem. So next time you see a flair tower don't think nasty nasty say thank you Mr flair tower from stopping me breathing in those nasty toxic compounds that nature has made.
And here this is me down below while you might ask am I wearing a shade over my neck and that's because it's very hot out there and I am very prone to sun stroke and I don't like vomiting for 24 hrs on a three day field trip as I done in the past, so anyway this is in a obviously in a close proximity to Woodside plant so we decided to find out what's going on so we took samples of the yeast, molds and fungis over set areas on the rock surfaces and wack them into ice backets which we will then take back and keep cold and fly down to Perth. And you can see it's hot it's sweaty, look at the veins sticking out on the pause yeah, temperature 25 is in the middle of the night, 55 degrees in the shade is when you are doing your measurement in the middle of the day.
It's hot and if you accidentally squat down in your shorts and the back of your legs hits the rocks in the sun the temperatures can be 60, 65 enough to cook an egg and you quickly move but we took our samples and being a chemist I measured the surface chloride and then measured the surface PH and in the Burrup instead of being a painted image what you've got is these weathered gabbro and granophyre rocks have got a natural red brown crust on them so the rock art is made by engraving that crust away and showing up the lighter colour of the parent rock and so then as the rock ages the brightness, if you like that engraving gradually diminishes with time.
And so you need to be at a surface at the right time of day with the right amount of breaking light coming in to see a lot of the images but never the less they're there and they're real and you might say that's a funny form of subtle intervention painting a number three on a rock, and that's because the rocks that we're doing measurements on in this museum compound were relocated rocks from 25-30 years ago during the first stage of development up there when the idea was, well, you want to save the rock art you just grab it and put it in a compound put a fence around it and it would be kept safe. And so we were checking how are the museum rocks preforming and one of the other thing was I went and washed rocks I mean, you might say you are seriously sick who on earth would want to wash rocks? I did because I wanted to know what is on the surface of the rocks because we've got bug counts, we've got PH, we've got chloride, but what else is there?
So we would go and collect standards amounts of water from reaction with various rocks surfaces and analyze them by Ion chromatography inductively coupled plasma mass spec, info low concentration of metals and we've got some data together and to make sure that we got some reference material we went way way out into the Dampier Archipelago to remote islands well away from where the winds will blow any industrial emission and took samples of PH chloride, rock surfaces bag counts and everything. And this is up in Mermaid sound and look it's if you ever get the chance go it is just simply beautiful country and, and so PH is balanced in part the acid from the metabolites is balanced out by the sea born salts because as the wind comes in it blows salty air over the rocks surfaces. And as salt water concentrates it becomes more alkaline and so it acts as a natural balancing effect to biological decay.
What we found was very nice correlation between the main PH of the rocks and the amount of chloride so low piv chloride it was a more alkaline surface and you can see the PHs we getting some of them in some area relatively acidic and that's because of the biological activity and the reason why you have this different same slop 0.02 .021, .023 .024.
Look at those art correlation co efficiency I mean non read data, I mean this is natural environmental data with our squared value greater than 0.98, it's simply brilliant you can't argue with that the reason why you have these parallel lines different intersects is. You seeing different rocks surfaces all the rocks don't have the same weathered surface they have different mineralogies and therefore they would be reacting in different ways to the different population of yeast, mold and fungi on them so if anyone says it's all the same don't you believe it the rocks in the Burrup is basically different as all of you see I've got the advantage like in a pulpit you can see everyone in a congregation and it is seriously scary first time I preached never again did I slouch in the pew.
But anyway if you look after the talk at all of you you'll see you are very different all basically the same bits put together but wonderfully different, well so it is with the rocks and that's why the way in which they weather and the acidity they build up it's all depend on their past history and we were literally staggered sorry this is a bit bright to read these numbers but you've got PHs basically round about vinegar level on the surface of these rocks. Some of this ancient rock engravings, this engraving is been dated to about 22,000 years, you can just still make it up, it's very weathered and so it's holly boop we have a really major problem but no when I looked at the PH at one of these remote control sites we have very similar values why? Because euro your little boing boing your little ding that goes boing cross the rocks had been booping and peeing on that engraving and so the yeast mold and fungi they didn't care whether the nitrates and urea and so on came from an industrial pollution or from nature. They just said ho ho ho ho gluurp love this it was just like fertilizing your loan with some supadupa products from bunnings or something and all of the sudden it goes from brown to green.
And well same thing happened with rocks so what we found was that the most acidic surfaces could be close to the industrial plant or could be miles away and in the miles away ones it was the natural material coming from the natural animals that was causing the local increase nutrients so it's not as simple as you make out and what we found was, if we look at the the number of bacteria here 600 no 60,000 of them 50,000 and the PH as the number of bacteria increased the acidity of the rock surface increased and again in the parallel lines reflect the different geology of the rocks surfaces so we knew that the acidity was coming not from SOX not from NOX pollution it was coming from naturally occurring yeast mold and fungi. And the night before I was doing a lot of measurements, there's a beautiful kangaroo engraving on one of the rocks in the Burrup Pat Vinnicombe said to me just care for my rocks would you and then the next morning she died and so that's why I'm a bit passionate about the Burrup because I've got to do the work that Pat had done years ago in documenting the rock art I've got to make sure that her legacy lives on so Rest Her Soul In Peace.
And we found there was a direct relationships between the log of the bacteria and the amount of nitrate so doesn't matter what the source of nitrate is whether it's natural or from pollution or whatever, the more nitrate on the surfaces the more bags and therefore the more acid and you can look here at the different surfaces of the rocks and you can see that some are much more friable other have different mineralogy and so therefore the reactivity of the surfaces varies enormously. But what is amazing is if you come up here and put little gold micro electrodes on the surface and measure the resistivity between underneath the crust and that even on a stinky and hot day when it might be 55 the rock surface is still moist enough to keep yeast, mold and fungi alive and active up to three o'clock in the afternoon. And so it's always the micro environment those bugs, they've been around for millions of years and they not going to sit on the top of the rock in the middle of the day!
They are not dumb they just go, I know where I hide excuse me we wait for the night fellows then will do our stuff and so again that's the PH with the nitrate and here is where we found the nitrate concentrations highest around Withnell Bay but also right up here there is some also very high nitrate concentrations and what was interesting was we there is not essential solphure dioxide from the industrial plants but there are some sulphates, extra sulphates coming onto some the rock surfaces and we thought, Where from? Well out there on West intercourse Island you can just see there was a little oil rig just floating around off there, but that's where they load their big ships and the iron ore ships burn cheap bunker fuel and it's dirty, mukky sticky oil, which is high in sulfur and we were able to pick up in a rock surface analysis the difference between where the wind had blown the fuel.
The exhaust from the iron ore ships and where it hadn't and that's the reason why I was dumb enough to go and wash the rocks and then analyze them because you never know what you going to find and so that's the results with the sulphates and this shows you what happens when an engraving is left facing up towards the sky instead of in a vertical position, when you facing up you say, ok hit me so the sun comes,whack, and then the wind comes, whack, and then when it rains it comes where if you are on a nice vertical surface which you were originally ah, you suffer much less deterioration, so was as a result of our work we said these rocks need to be re oriented so what have they done? They reoriented them back into their original aspect and the rate of deterioration has really slowed down. Simple.
And what we were able to do was by going back a different season you're there in the winter and that was in the summer in February and in August in spring time what we were able to show on the same rock was that there are natural seasonal variations in acidity and it's all to do with the availability of moisture and so and it's all part of the natural environment in the Burrup. And no one knew that before we went out there because no mad chemists were available and so what we were able to see was that in some areas where there was a on various rocks there was sometimes a decrease in acidity following the rain and that's because the rain washed the micro nutrients of the rock surface so no nutrients biological activity down acidity goes back to be more neutral and look at this for reproducibility.
Three different rock surfaces with PH profiles on them so, many people say how reproducible is your data it's very reproducible and there you can see the engraving of that's a tail of a Dugong and so what we found was it's all very sensitive to moisture level we are up there in the summer and one of my darling colleagues went and said to me ok Ian in you go into St George's Cathedral just pray for rain I said, it doesn't work like that you can't sort of try and trick god into giving you optimal research conditions doesn't work, and he said "Just try it" and so three days later all of the sudden out of the middle of nowhere this unexpected thunderstorm came through, so we sort of race back and went down and re sampled the rocks and re measured PH and re measured this and that and as a result we found that don't worry about this ups and downs but the main thing to know is that in some areas wet like here this is the number of used mold counts before the rain.
It was a 144 less than 24 hours afterwards the number of yeast, mold, and fungi counts had gone up to 402. This site was sheltered and didn't get any rain, they got lots of rain and this one up at King Bay right up on the edge of the peninsula got plenty of rain and this in the summer but it was not too much rain to wash off the nutrients, but it was enough to basically double the biological activity. So water is one the critical factors in controlling biodeterioration of rock surfaces in the Burrup and so my colleague Warren Fish was there Mann Silkfin and this is Pearson Cove just around the corner is the site of much of this beautiful rock art, and so part of the government's work I have set up helps set up the Burrup rock art monitoring committee. So we've got weather stations all through out the Burrup and a reference point down at Mardie station and (question from the public: they've taken them away) oh, they have alright, yeah, well we set them up anyway and we did the monitoring and one of the problems you have in rock art science in different part of WA is ignorance and in this site up in the wheat belt you have land rights for whites etc, you can read it and so what we did, we used nice combination of cocktails of solvents and removed the graffiti and rubbed dirt back into the rocks surface to remove the residue of the paint and as John Clark said, the best protection for a rock art site is been more than 500mt for a 4WD access track isolation is the best protection but also if you do get graffiti on a site get rid of it, because it only encourages people to do it again and that ladies and gentlemen is the end of my little travel log of rock art.
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