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Monitoring Rock Art Decay: Archival Image Analysis of Petroglyphs on Murujuga, Western Australia


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This paper considers the effects of industrialisation upon one of the world’s most significant rock art sites, Murujuga (Burrup Peninsula), located in north-west Western Australia. Photographs of 26 petroglyphs taken prior to or early in the industrialisation of the area were compared with recent photographs to assess whether the presence of industry is accelerating degradation. Fifty per cent of the petroglyphs showed indications of changes, and two showed substantial damage. The bulk of the changes can be attributed directly to industrial activity in the area which commenced in the 1960s. All changed petroglyphs, with two exceptions, were in relative proximity to industry. A reduction in industrial emissions is considered essential if damage to the rock art is to be limited and this iconic cultural place is to remain largely intact for future generations.
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Monitoring Rock Art Decay: Archival Image
Analysis of Petroglyphs on Murujuga, Western
Benjamin W. Smith, John L. Black, Kenneth J. Mulvaney & Stéphane Hœrlé
To cite this article: Benjamin W. Smith, John L. Black, Kenneth J. Mulvaney & Stéphane
Hœrlé (2022): Monitoring Rock Art Decay: Archival Image Analysis of Petroglyphs on
Murujuga, Western Australia, Conservation and Management of Archaeological Sites, DOI:
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Monitoring Rock Art Decay: Archival Image Analysis of
Petroglyphs on Murujuga, Western Australia
Benjamin W. Smith
, John L. Black
, Kenneth J. Mulvaney
and Stéphane Hœrlé
Centre for Rock Art Research + Management, University of Western Australia, Perth, WA, Australia;
Art Research Institute, GAES, University of the Witwatersrand, Johannesburg, South Africa;
PACEA, Université de Bordeaux, Pessac, France
This paper considers the eects of industrialisation upon one of the
world’s most signicant rock art sites, Murujuga (Burrup Peninsula),
located in north-west Western Australia. Photographs of 26 petro-
glyphs taken prior to or early in the industrialisation of the area were
compared with recent photographs to assess whether the presence
of industry is accelerating degradation. Fifty per cent of the petro-
glyphs showed indications of changes, and two showed substantial
damage. The bulk of the changes can be attributed directly to
industrial activity in the area which commenced in the 1960s. All
changed petroglyphs, with two exceptions, were in relative proxi-
mity to industry. A reduction in industrial emissions is considered
essential if damage to the rock art is to be limited and this iconic
cultural place is to remain largely intact for future generations.
Petroglyphs; Indigenous art;
industrial emissions;
Murujuga; Burrup Peninsula;
photographic comparison
In the north-west corner of Western Australia lies a narrow land mass, about 30 kilometres
long and 6 kilometres wide, that is covered in a jumbled mass of red/black/brown
weathered rocks piled upon each other to create steep, largely treeless, hills overlooking
the Indian Ocean. This place was called Dampier Island by European settlers and named
Burrup Peninsula in 1979, but traditional owners call it Murujuga, meaning ‘hipbone
sticking out’. The location has special Aboriginal signicance as a Dreaming place,
a Law place and a landscape with a sorry history of colonial period massacres (Gara
1983) and ancestral dispossession (Owen 2016; Chapple n.d.). The rock art within the area
is specically treasured and comprises rock engravings or petroglyphs.
Murujuga has one of the world’s largest concentrations of rock art, with more than
one million images. It is also among the oldest, with strong evidence that the long series
of changing image styles and evolving fauna extends back at least 50,000 years (Mulvaney
2011a, 2013, 2015; McDonald 2015). The rock art contains some of the earliest known
images of the human face, complex geometric designs, extinct animals including the fat-
tailed kangaroo and thylacine and it depicts an evolving change in fauna both before and
CONTACT Benjamin W. Smith
© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License
(, which permits non-commercial re-use, distribution, and reproduction in any med-
ium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.
after the glacial maximum. An application for World Heritage Listing for the area is well
advanced (DBCA 2021).
A large section of Murujuga contains massive industries, including iron ore export
infrastructure, a large sea-salt evaporation area, a natural gas processing plant, gas
liquication trains, an ammonia fertiliser plant, and an ammonium nitrate facility.
Together with the associated shipping facilities, this area is one of the largest bulk export
ports in Australia. The development of industry since the 1960s has resulted in the
physical destruction of hundreds of cultural features, and thousands of individual petro-
glyphs (Bednarik 2006a; Mulvaney 2011b; González Zarandona 2020). As well as the
massive carbon emissions that have drawn widespread environmentalist condemnation
(350 Boorloo Perth 2021), this industry releases annually thousands of tons of nitrogen
oxides, sulphur oxides and ammonia, and hundreds of tons of ammonium nitrate particles
( The nitrogenous substances
stimulate adventitious microbial growth, which produce organic acids that can dissolve
the rock surfaces upon which the rock art is engraved (MacLeod 2005). Nitrogen and
sulphur oxides also combine with rain and dew to form highly caustic acids that are
similarly able to dissolve the rock surfaces (Bednarik 2009; Black, MacLeod, and Smith
2017; Gadd 2017; Smith et al. 2022).
Almost everyone today concedes that industry should never have been placed on
Murujuga and that other less culturally and environmentally signicant locations should
have been utilised (González Zarandona 2020). However, decades on from the decision to
locate industry here, and with tens of billions of dollars invested in infrastructure, we are
stuck with an uncomfortable cohabitation of exceptional Indigenous heritage among
entrenched industrial capitalism.
State governments have been successively compromised in their role as protector of
the area’s heritage and as a promoter for sustainable development. The Western Australia
State Government has funded the infrastructure upon which the industry is reliant, it has
guaranteed industrial loans, and it has put in place some of the weakest and most poorly
regulated pollution control measures in the developed world (Smith et al. 2022, p. 11). The
state government’s development agency still advertises the area as a ‘well-established
strategic industrial estate with vacant land for strategic industry’(https://developmentwa. New industrial devel-
opments are currently in the process of gaining approval. Murujuga has become one of
the world’s most contested landscapes; a test-case as to whether Australia will take the
hard actions needed to deliver on its commitments to emissions reductions and
a sustainable future. We have demonstrated elsewhere that pollution will damage the
rock surfaces and the petroglyphs of Murujuga (Black, MacLeod, and Smith 2017; Smith
et al. 2022).
As part of a series of independently funded studies into the impacts of industry on
Murujuga rock art, in this paper we examine observable changes to a group of
petroglyphs by comparing archival and recent photographs. This is the initial report
of a long-term project that will monitor the extent to which signs of industrial
impact are visible on the rock art at Murujuga. First, we provide background infor-
mation on Murujuga rocks, petroglyph creation, and the ways industry can damage
the rock art.
Murujuga Rocks and Petroglyph Creation
The rocks on Murujuga are extremely hard igneous types that crystallised under extremely
high temperatures and pressures some 3.75 billion years ago (Donaldson 2011). The now
exposed large at surfaces on which the rock art sits were produced by tectonic forces
and temperature changes over aeons. The weathering process of the rocks is described by
Smith et al. (2022). Newly broken blue/grey rock faces degrade extremely slowly, produ-
cing an orange/yellow coloured weathering rind with a thickness of 5–10 mm over around
30,000 years (Pillans and Field 2013). The outer surface of the weathering rind has a crust
or patina providing the dark reddish-brown colouring to the exterior appearance of the
blocks. In addition, there are both dull and glazed veneers across the rock surface. These
thin (1–200 µm), hard outer accretions, known as desert or rock varnish are
a ferromanganese crust partly formed by a biomineralization process, where specialised
bacteria and micro-fungi concentrate, 50–300 times, manganese and iron from environ-
mental dust to form a sheath for protection against the low moisture, high radiation, and
temperatures of the rock surfaces (Dorn 2020). The iron and manganese-rich outer
sheaths from the microorganisms are incorporated with clay from dust into the rock
varnish when the organisms die. Fossils from bacteria and fungi have been observed in
the varnish of rocks collected from the Pilbara region of Western Australia of which
Murujuga is part (Flood, Allen, and Longazo 2003). These rock varnish-forming organisms
remain dormant for most of their lives, becoming active only when conditions are
suciently moist. Consequently, the rock varnish forms at an incredibly slow rate of 1–
10 µm in 1000 years (Liu and Broecker 2000; Dorn 2009). The rock art is created by
breaking through the rock varnish and into the exposed underlying pale weathering
rind, which results in a colour and contour contrast.
How Murujuga Rock Art Can Be Damaged by Industry
There are three main ways that Murujuga rock art can be directly damaged by industry.
The rst is mechanical removal and damage during land clearance for industrial plants,
roads, pipelines, power lines, water, sewerage, and storage areas. This damage is readily
visible and, since the enactment of the Aboriginal Heritage Act in 1972, has been formally
recorded at its time of original impact. Based on land area covered by industry, survey
records and landscape features, it is estimated that some 10,000 petroglyphs have been
destroyed or moved from their sacred location (although see Bednarik 2002, 2006b). José
Antonio González Zarandona (2020) has characterised this as ‘landscape iconoclasm’, the
intentional act to dishonour an entire belief system and supersede Western economic
values above Indigenous living spiritual values. He argues that the scarred industrial
landscape of Murujuga, bulldozed for decades by industry, intentionally stamps visual
conrmation that there are ‘victors and vanquished’ in this landscape (González
Zarandona 2020, 210–17).
The second form of damage is that caused by the chemicals emitted by industry, in
particular the deposition of acidic dust. When combined with water, these acids cause the
dissolution of the manganese and iron compounds in the rock surface and, as these
compounds erode away, the rock varnish and patina become increasingly fragmented,
exposing the weathering rind and therefore appearing increasingly lighter in colour (Black,
MacLeod, and Smith 2017). Eventually, high acid concentrations will completely dissolve the
outer veneer as was found by Bednarik (1979) in locations with extensive bird droppings
and as is still observable today. Nitrogen emitted by industry also stimulates the growth of
adventitious organisms that produce large quantities of organic acids (MacLeod 2005),
further eroding the outer hard crust (Gadd 2017). Some of these organisms are visible in
the form of lichens, algae, and other discolourations of the surface. Increased porosity of the
rock varnish and patina after exposure to acids will facilitate the passage of acidic com-
pounds and sea salts into the surface veneer/weathering rind interface and this process will
weaken the bonds holding the outer hard crust to the rock. Crystallisation of nitrates,
sulphates, and sea salts upon drying at this interface may lead to the visible aking o
and breaking down of the rock surface (Oguchi and Yu 2021; Pillans and Field 2013).
The nal form of damage is the collateral damage from an increased unsympathetic
human presence in the landscape. The desecration is seen in rock scratching from o-road
vehicles and grati, broken rocks from inappropriate trampling, theft of rocks with
petroglyphs, rock splitting and discolouration from non-traditional burning practices,
damage from feral animals, and non-native plant infestations. Indirectly, the cultural
and heritage values of the rock art are impacted by the noise, heat, and smell of industry
as well as by the damage to the physical and spiritual fabric of the landscape and its
A photographic analysis was undertaken by comparing images from archival photo-
graphic collections dated from the early 1960s to early 1980s, when petrochemical
industrialisation commenced, with more recent photographs taken over the last decades
to 2021. Our analysis aimed to observe dierences over time in rock aking, spalling,
scratching, and erosion. We were less concerned about the colour changes because, in
many cases of the older images, the colour had been distorted considerably either by
degradation of the original lm or through the digitisation process. Lightening and
darkening of surfaces are potentially amenable to analysis because sucient images
exist with black and white scales to allow valid comparison. Nonetheless, we are aware
that the angle of the sun at the time of the photograph can shift the colour and surface
texture appearance of the rock panel and petroglyph.
Archival Photographs
To allow for meaningful comparative analysis of changes through time, we began our
work by digitising a series of archival photographic collections of petroglyphs and also
brought together sets of more recent images that were either born-digital or were already
digitised by others. The oldest photographic images of Murujuga rock art date back to the
1960s and 1970s when the iron export facilities, salt evaporation ponds, roads, and ports
were being constructed. We used more than 800 photographs from the collection of the
Archaeological Section and the Department of Aboriginal Sites, both now held at the
Western Australian Museum. These included images taken by Patricia Vinnicombe, Robert
Bevacqua, Warwick Dix, Peter Randolph, and Bruce Wright. We also analysed a set of
images taken by Fulgenzio Leonardo (Enzo) Virili while working as a project engineer for
Dampier Salt between 1970 and 1976 and that have been donated to the Western
Australian Museum. We gained access to a number of important early private collections
of photographs and slides. There was a partial collection of images (42) taken by Robert
Bednarik between 1967 and 1970 when he worked as a project manager for an engineer-
ing rm based in Dampier and, in his spare time, recorded rock art. Bednarik holds his
recordings in his private collection. Unfortunately, we were not able to digitise all of this
important collection. There is a signicant archival collection of Murujuga recordings
made between 1974 and 1977 by the French archaeologist Michel Lorblanchet. We
were able to access the sections of these recordings that have been made public but
did not access the large collection of his materials held at the Australian Institute of
Aboriginal and Torres Strait Islander Studies in Canberra. We were able to utilise the
private collection of Sylvia Hallam, the pioneer Western Australian archaeologist based at
the University of Western Australia. Hallam never undertook formal research at Murujuga,
but she made private visits to the site in the late 1970s. A collection of 74 Hallam slides
were provided to the project by the Honourable Robin Chapple.
These early collections of rock art images from Murujuga are extremely valuable
because they show the rock art in its original state prior to the introduction of heavy
polluting industry. The early iron and salt export facilities from the 1960s and 1970s, while
bringing limited pollution from shipping, did not themselves introduce major issues from
acidic pollution. The highly signicant acidic pollution emissions only started in the 1980s
with the processing of the natural gas and then the proliferation of associated facilities
built to utilise the by-products of gas processing.
Selection of Archival Photographs for Analysis
More than a thousand photographs from the archival collections were examined to select
the most suitable sites for our detailed photographic analysis. The rst stage of this
project concentrated solely on the oldest available archival collections. It was of prime
importance to select a set of sites for which there were multiple ‘early’ and high-quality
photographs. ‘Early’ for this project was dened as dating to the 1960s and 1970s. There
are very few photographs of Murujuga that are older than this, and the few that exist are
mostly landscape shots, rather than images of petroglyphs. It was important to choose
images where the date of photography was known, at least approximately. We were not
concerned if it could only be ascertained that an image was taken in the ‘early’ or ‘mid’
1970s. This was sucient for our purposes to place it within a known phase of industrial
development. The exact location of the petroglyph was also necessary as we sought to
compare sites that were both closer and further away from industrial areas.
The second stage of the project was to identify petroglyphs for detailed analysis. This
project only focused on petroglyphs on the peninsula and did not include sites on the
surrounding islands. In selecting sites for analysis, we sought a sample that covered a wide
spread of the Murujuga landscape, both comparatively close and far from industry and that
had sucient photographic coverage from the 1960s and 1970s to allow for comparative
study. A sampling area was chosen near to the gas processing plants south of Withnell Bay
and that has been heavily exposed to industrial emissions since the mid-1980s. Another area
was chosen near to the Yara International ammonia fertiliser and ammonium nitrate plants
and that has been more exposed to emissions since 2006 and 2017, respectively. A nal area
was chosen in the southern part of the peninsula, further from the industrial plants, but that
has been exposed to varied aspects of the salt-working industry since the 1970s. Every
petroglyph in these areas with long spans of photographic coverage from the 1970s to the
present was selected. The nal overall sample contained 26 petroglyphs (see Figure 1); of
these 10 were on gabbro, 15 on granophyre and 1 on dolerite rock types. An extensive and
varied set of older images was amassed for each selected petroglyph.
Recent Images of Selected Petroglyphs
More recent images of the selected petroglyphs were then sought. This task was consider-
ably more cumbersome than it sounds because most of the site names, even broader
locality names, have changed over time and the bulk of the images had to be found via
Figure 1. Map of Murujuga showing the approximate locations and rock type of the analysed
petroglyphs. Green circles are monitoring sites on gabbro rock, red circles are monitoring sites on
granophyre rock, the yellow circle is a monitoring site on dolerite rock.
manual visual browsing through the thousands of digital images stored in the more recent
collections. Images of all selected sites taken in the 1980s, 1990s and 2000s were then
added to the site les for comparative purposes. Images of Murujuga rock art taken post
petrochemical industrialisation are far more extensive than older images. The Centre of
Rock Art Research + Management (CRAR+M) of the University of Western Australia contains
tens of thousands of images taken over the last 15 years by Professor Jo McDonald and her
team which included Rio Tinto colleagues. This collection provided many high-quality
recent images for the photographic analysis. Other recent collections used were the
Dr Ian MacLeod Private Collection and the Robin Chapple Private Collection. Additional
photographs were provided for selected sites by Drs Benjamin Smith, Mike Donaldson and
Ken Mulvaney (it should be noted that both Donaldson and Mulvaney have also donated
many tens of thousands of images to the CRAR+M collection). We then returned to every
one of the 26 selected sites in July 2021 to take a full set of contemporary images.
Image Analysis
The early archival photographs of these 26 sites were edited using Adobe Photoshop. This
work adjusted the brightness, contrast, exposure and levels of RGB channels to bring
maximum clarity and visibility to the images under study. We also produced a set of colour-
calibrated and standardised images, as far as was possible, for the purposes of comparison.
These enhanced and standardised images were subsequently used alongside the original
images. There was therefore no loss of image information, only the creation of varied sets
of images, each with their own uses for optical analytic purposes. All versions of images
from a single site were stored together in digital folders and these have been retained for
future analyses, including for petroglyphs not able to be analysed here.
The nal stage of the work involved the use of pairs of images (old and new) for
comparison on large format, high-resolution screens. Identied dierences between
images included cracks, aking, spalling, scratching, lightening or darkening of the sur-
face, lichens and other visible biological changes, and any removal or shifting of adjacent
rocks. The work did not include colour spectral change analysis since the archival images
were photographed with dierent types of lm, and then digitised using dierent digital
processes which has greatly impacted replicating the original colour. We were, however,
able to see when a surface had signicantly lightened or darkened. For the purpose of
analysis, each rock was divided into zones and magnied to the highest level possible
before pixilation and then compared side-by-side. Multiple old and new images, taken
from dierent angles, were used to ensure that all details were observed and compared.
Every crack, ake, lichen, and other analysed aspect was examined at maximum magni-
cation to see if it had expanded or been altered in any visible way. Where possible,
changes in the surrounding rocks and hillsides were also recorded. All visible changes, no
matter how small, were noted.
The ndings from the analysis of the 26 engraved rocks (Figure 1) show a number of
changes, some prominent, others relatively minor. We present these changes now by
category. It is important to understand that the rock art of Murujuga has only been subject
to acidic pollution for about four decades and the extent of acidic industrial pollution has
tripled over recent decades (Smith et al. 2022). Any change in visible condition within this
relatively short timeframe will indicate an alarming rate of rock decay and a cause for
grave concern about the long-term preservation of the art.
Petroglyphs Showing Flaking and Major Change
Two of the 26 petroglyphs show extensive evidence of aking and major observable
Petroglyph #16
An image of a sh, the petroglyph located towards the southern end of the peninsula shows
radical aking of the outer crust (Figure 2). In 1974, there was a relatively fresh aking scar at
the centre right, two areas of minor abrasion over the top right quartile of the sh, and a few
minor scratch scars spread across the surface. A recent photograph taken by this project in
2021 clearly indicates radical condition change. The scars that were visible in 1974 are still
visible but have patinated and are less visually prominent. Importantly, more than 30 areas of
surface veneer now display new aking, exposing the weathering rind that was not visible in
the 1974 photograph. The aking is both over and beside the sh petroglyph. A photograph
taken by Ken Mulvaney in 2009 shows the full extent of aking seen in the 2021 image. This
Figure 2. Petroglyph #16. Extensive flaking is visible around and over this fish petroglyph that was not
evident in the 1970s. Left a scanned slide by the Aboriginal Sites Department 1974. Right is a born
digital image by B.W. Smith 2021. The red arrows show flaking of the rock varnish not evident in the
1974 image. Note that the top right corner of the rock is concealed by shadow in the 1974 image.
means that this aking occurred rapidly between 1974 and 2009 but has since slowed,
perhaps stopped. The rock is located towards the base of a steep hillside and is immediately
adjacent to a gravel road. Other rocks in the immediate vicinity show similar aking, although
not as extensive. For 30 or so years, beginning in the early-1970s this road was used by open-
topped haulage trucks to transport salt to the ship-loading jetty on Mistaken Island. In 2003,
the truck haulage along this stretch of road was replaced by an automated conveyor-belt
system that continues to be used today. The aking seems to date to the period of the road
haulage. The most probable explanation is that the aking was caused by salt that had fallen
or blown o the trucks, onto the road, and which was then thrown up as road dust onto the
rocks of the lower hillside on which this petroglyph is located.
Petroglyph #1
Petroglyph #1 shows clear evidence of increasing blackening of the surface through
recent decades (Figure 3). This blackening goes against the ndings at our other sites,
which, if any colour change was noted, showed lightening through time, supporting the
ndings of Black and Diey (2016). The blackening of this particular surface is occurring
both over and around the petroglyph. Early photographs taken in 1981 and 1987 show no
visible blackening on the surface. A 2009 photograph by Robin Chapple shows early
evidence of blackening but without the intensity seen in 2019 and today. This panel is
630 m away from one of the larger Karratha Gas Plant ares and is in one of the areas most
exposed to industrial pollution. The blackening of this surface is therefore highly likely to
relate to industrial activity and needs to be properly investigated. It is important to note
that the most recent photographs since 2019 also provide evidence that the rock varnish
is starting to break down in the blackened area. There are distinctive and new lighter
orange marks immediately above and to the right of the head of the petroglyph caused
by a breakdown of the surface crust (Figure 4).
Petroglyphs Becoming Lighter
Nine of the analysed petroglyphs provide indications that they are becoming lighter
(#2, #5, #6, #9, #16, #17, #21, #22, #24). Denitive evidence of colour change is
Figure 3. Petroglyph #1. This site is located close to industry. It is showing increasing evidence of
blackening through time. In all three images, scales allowed for black and white calibration and
therefore confidence in the observed blackening. Left is a scanned slide by P. Vinnicombe 1981. Centre
is a born digital image by R. Chapple. Right is a born digital image by B.W. Smith 2021. Culturally
sensitive image blacked out by request of Murujuga Aboriginal Corporation.
dicult because the earlier comparative photographs up until the 1980s were taken
on colour slide lm. These older colour slides, particularly many that were taken
using Agfa lm, have discoloured signicantly becoming more purple, blue, and dark
(e.g. Figure 11, left). This change has sometimes been exacerbated in the digitisation
of the original slide. As an example, we provide an image taken by the Aboriginal
Sites Department in 1973 of petroglyph #22 that has been digitised on a Nikon
CoolScan, alongside a standard digital image taken with a Nikon D3100 camera in
2021 (Figure 5). The immediate impression is that petroglyph #22 is now much
lighter and redder, with less contrast between the petroglyph and rock surface.
However, some of this impression may be a product of the discolouration of the
original slide. Whether all of this impression is a product of the discolouration of the
older image seems unlikely, but it requires further study for us to be certain.
A second example (Figure 6) on a nearby rock, petroglyph #21, seems to be
a more clear-cut example of becoming lighter.
In one fortunate example (petroglyph #17) we have a long series of early images, with
photographs in each decade from the 1970s to the present. This allows a clearer observa-
tion of colour change through time. In this case, it is apparent that the rock art and
surrounding rock surface has lightened and that at least part of the colour change evident
from early slides is a genuine colour change on the rock. Unfortunately, this rock cannot
be illustrated due to Indigenous cultural protocols.
Figure 4. Petroglyph #1. Left image shows proximity of location to industrial emissions towers. Red
circle in right image highlights area in which the darker rock varnish is starting to break down. Left
image by B.W. Smith 2021. Right image by K. Mulvaney 2019. Both born digital. Culturally sensitive
image blacked out by request of Murujuga Aboriginal Corporation.
Petroglyphs Showing Mechanical Damage
Petroglyph #26
One petroglyph (#26) shows substantial mechanical damage from being moved. Two
scars are now evident on the upper surface that were not present when this rock was
Figure 5. Petroglyph #22. Left image is a scan of slide by the Aboriginal Sites Department 1973. Right
is a born digital image by B.W. Smith 2021. No colour adjustment.
Figure 6. Petroglyph #21. An example of probable lightening. Left image is a scan of a slide by
P. Vinnicombe 1988. Right is a born digital image by B.W. Smith 2021. No colour adjustment.
photographed in its original location in 1979 (Figure 7). This petroglyph was moved
during the original construction phase of the Karratha Gas Plant. It was mechanically
lifted onto a truck, moved, and placed alongside hundreds of other salvaged rocks in
a controversial holding enclosure near to Hearson Cove, known to locals as the ‘rock art
prison’. The ‘prison’ has now been dismantled and this rock art has been relocated, under
the supervision of Murujuga Aboriginal Corporation, to a culturally appropriate hillside
location that is not disclosed to the public.
Petroglyph #11
Petroglyph #11, a kangaroo, shows a precisely square abrasion at the centre of the top
back line in all photographs since 1991. This abrasion was not visible in an early image
from 1970 (Figure 8, left). The mark remains visible today. The purpose or cause of the
mark is not clear, but it was human-made either by mechanical or chemical abrasion.
Petroglyphs Showing Other Forms of Human Interference
Petroglyph #2
At petroglyph #2, four small unengraved rocks that were leaning up against the engraved
block have been removed since 1980 (not shown for cultural reasons). These were
partially obscuring (and presumably protecting) the lower left-hand corner of this large
Figure 7. Petroglyph #26. New scarring visible made during physical relocation of rock due to
industrial development. Left image is a scan of slide by P. Vinnicombe 1979. Right is a born digital
image by R. Chapple 2008. Culturally sensitive image blacked out by request of Murujuga Aboriginal
geometrically engraved block. It seems most likely that this removal was done by some-
body photographing the rock. The cultural signicance of these four rocks is unknown,
but it should not be assumed that they had no signicance. The shifting of rocks in this
manner, without permission, is deemed unacceptable by the Murujuga Aboriginal
Petroglyph #7
An early 1970s photograph of petroglyph #7 shows white lines and marks above the top
of the image (Figure 9). These marks are either chalk lines or, more likely, residue from
someone making a silicone peel of this petroglyph for the purposes of casting. Silicone
peel casting destroys the dating potential of a petroglyph and is not permitted in most
countries today. The white marks were not observable in images from 1991 and are not
visible at the site in 2021. Whatever the cause of this residue, it has now been eroded from
the surface.
Petroglyphs Showing Apparent Natural Changes
Petroglyph #13
Early 1970s photographs of petroglyph #13 show two distinct white spots in the lower
portion of the panel. These spots remained evident in a 1996 photograph, but were not
Figure 8. Petroglyph #11. Images show the appearance of square abrasion in the centre of the
backline of this macropod after 1970 (marked by a red arrow). Left image is a scan of slide by
Aboriginal Sites Department 1970. Right is a born digital image by Mulvaney 2013.
Figure 9. White chemical residue around the top of petroglyph #7 (indicated by red arrows). Image is
a scan of a slide by S. Hallam late 1970s.
visible in 2004 and subsequent images. Observation of the site in 2021 found that similar
white spots were still evident, but in new locations on the surface. High-power on-site
investigation revealed that these were minute desiccated spider webs and so do not
represent any material damage to the surface.
Petroglyph #8
Petroglyph #8 had a dark mark across the back and legs of the fourth bird to the right in
a 1988 photograph, which appeared to fade over time (Figure 10). However, closer
examination of the site reveals that the mark is a natural shadow due to an undulation
in the rock surface and the intensity of the apparent mark changes with the angle of the
sun. There has been no condition change at this site.
Figure 10. Petroglyph #8. Images provide the incorrect impression of a dark mark that is fading
(indicated by red arrows). Left image is a scan of slide by P. Vinnicombe 1988. Right is a born digital
image by B.W. Smith 2021.
These two examples emphasise the importance of careful on-site inspection to cross-
check the ndings from archival image analysis, and the worth of matching time of day
and photograph angle.
Petroglyphs Showing Signs of Re-Patination
Petroglyph #16
Petroglyph #16 (see Figure 2) shows signs of probable re-patination over a period of
approximately 50 years. The colour distinction between the background rock and the scar
to the lower middle right of the rock has diminished between 1974 and 2021. Similarly, the
contrast between the petroglyph and other marks on the rock in the 1974 photograph is less
visible in the most recent photograph. Additional investigations will be required to conrm
the apparent colour change with matched angle of sunlight at the time of the photograph.
Petroglyph #9
Petroglyph #9 (Figure 11) shows an emu petroglyph from the southern section of the
peninsula. Despite being a discoloured digitised slide, the left image from 1970 shows
Figure 11. Petroglyph #9. Various lines around and below the head of an engraved bird (indicated by
red arrows) are less visible today than in the past, suggesting re-patination. Left image is a scan of
a slide by Aboriginal Sites Department 1970. Right is a born digital image by B.W. Smith 2021.
a highly visible scar on the top of the rock and several visible lines running downwards
from the top and around the head and neck of the bird. While the lines are still visible, they
have become less pronounced over time, suggesting that some re-patination has occurred.
Petroglyphs Showing No Changes
For 13 out of our sampled 26 petroglyphs there was no evidence of a visible change over
time from the early archival photographs to the most recent images (#3, #4, #8, #10, #12,
#13, #14, #15, #18, #19, #20, #23, #25).
A comparison of observable physical changes to rocks containing petroglyphs from pre-
and early-industrialisation (mid-1960s), to more recent times, is seen as one way of
assessing whether the presence of industry on Murujuga has accelerated the weathering
process of the rock art. In searching for petroglyphs that had archival photographs
extending over multiple decades, we were aware that it would likely be the larger,
more well-known, more accessible petroglyphs and those surveyed due to the presence
of industry that would be included for assessment. These sites are likely to be the more
visited locations and will inevitably be the places that show greatest evidence of visitor
damage. However, most of the damage to petroglyphs that we have recorded through
the photographic record appears to have been caused not by visitors, but by changing
physical conditions, likely a consequence of industrial activities.
Two rocks of the 26 petroglyphs examined were shown to have major, and likely
irreversible, changes that have already damaged the petroglyphs on those rocks. Both
rocks are in close proximity to industry. Petroglyph #16 is near the solar sea-salt haulage
path, while petroglyph #1 is approximately 630 m from one of the larger petrochemical
industrial ares. Acidity of rock surfaces in this area has increased over a thousandfold
following industrialisation (Black, MacLeod, and Smith 2017; MacLeod and Fish 2021).
There are eight potential examples (petroglyphs #2, #5, #6, #9, #16, #21, #22, #24) and one
denite (petroglyph #17) example of petroglyph panels turning lighter over time, as is
predicted with increases in rock surface acidity (Black, MacLeod, and Smith 2017). Of
these, seven out of nine are close to industry. Petroglyph #26 has scars from being
physically relocated during an industrial expansion. Thus, the petroglyphs showing the
greatest damage are those most directly impacted by the major industrial complexes.
Eect of Salt
Examination of the rocks surrounding the damaged sh image (petroglyph #16), show
clearly that many other rocks at a similar elevation and near to the salt haulage road have
evidence of surface spalling (Figure 12). A few metres up the hillside, the spalling reduces
and on the upper section of the slope, there is no visible spalling on the rocks despite the
geology being identical.
Sea salt spray has been known for centuries to cause weathering and deterioration to
stone buildings, monuments, natural rocks, and other engineered masonry structures
(Oguchi and Yu 2021). The mechanisms by which salt damages these structures are now
well understood (La Russa et al. 2013; Oguchi and Yu 2021). Liquid salt water penetrates
the structures through pores in the surface. The salt water does relatively little damage
provided it remains in liquid form. However, damage occurs when the water evaporates
allowing salt crystals to form. Water enters the rock through pores and, when the rock is
subsequently heated, the water then evaporates through these same pores. This leaves
behind the salt in the form of crystals within the rock pores. As these crystals expand, this
creates pressures within the rock that exceed its tensile strength, causing cracks and
ssures to develop through time until eventually the rock surface layer exfoliates. The
warm and dry climate of Murujuga is an exacerbating factor for this weathering process.
Damage to petroglyph #16, where large sections of the surface crust have exfoliated,
suggests that the increased salt levels are causing the comparatively weak bonds
between the veneer and the weathering rind to break down, causing signicant aking
and erosion into the weathering rind. This rock remains a cause for concern although the
photographic evidence suggests that the immediate industrial threat to this petroglyph
has diminished since the installation of the salt conveyor belt (Figure 12).
Degradation Due to Increased Acidity
There are eight potential and one diagnostic example of lightening in the colour of rocks
examined. In other countries, there are examples of petroglyph panels becoming lighter due
to dust settling on the rock and becoming bonded into the rock surface (Kloor 2008). We have
examined all of the eight surfaces, and this is not the cause of change at Murujuga. We have
strong evidence that this colour change is caused by acids that are changing the chemical
composition of the rock varnish and surface patina (Smith et al. 2022). Many thousands of tons
of nitrogen dioxide and sulphur dioxide are released from industrial processing facilities and to
Figure 12. Petroglyph #16. Fish at lower left. Similar spalling visible on adjacent rocks at the same
height. Notice proximity to the salt haulage road and conveyor belt. Image is a born digital image by
B.W. Smith 2021.
a much lesser extent shipping, into the Murujuga airshed annually (Smith et al. 2022). Around
35% of nitrogen dioxide released is deposited on the Murujuga rocks (Woodside 2019). These
dry acids react with water from light rain and dew to form strong nitric and sulphuric acids.
These acids, along with increases in organic acids produced by microbial growth stimulated by
industrial discharged nitrogen, have resulted in a marked increase in the acidity of the rock
surfaces, particularly near the natural gas processing facilities. Rock surface pH in this region of
Murujuga has been shown to fall below 4.0 in 2017 (MacLeod and Fish 2021). Natural acidity of
the rock surfaces prior to industrialisation was near neutral (Bednarik 2002). The increase in the
acidity of the rock surface causes the darker iron and manganese oxides and hydroxides in the
rock varnish to dissolve, as well as etching into the weathering patina, making the rock surfaces
lighter and redder in colour as the iron compounds become dominantly ferrous oxide before
being completely dissolved (Black, MacLeod, and Smith 2017). Given the level of increased
acidity, the probable lightening of eight surfaces is not surprising and is a cause for concern.
Nevertheless, this suspected colour change identied on several petroglyphs requires verica-
tion of the cause through detailed microscopic and chemical analyses of the rock veneers
across the rock surfaces. As the project has been reliant on photographic images, it will also be
important to rule out potential natural factors such as the angle of the sun, time of day and
time of year, as well as surface moisture at the time at which the photograph was taken.
Other Damage
The unusual blackening of petroglyph #1 could have a number of causes. It could be soot
blackening from the smoke of the industrial gas ares (Figure 13), or it may be the residue of
a microbial explosion caused by the industrial nitrogen-rich deposit. Whichever, this requires
further investigation and, most alarmingly, it seems to be causing destabilisation of the rock
Two rocks have evidence of mechanical damage, one caused by the physical relocation
of the rock to clear land for industry (petroglyph #26; Figure 7) and the other by
intentional human-directed actions (petroglyph #11; Figure 8). Whilst there were no
incidences of grati or vandalism in the selected sample, there are incidences of this at
Murujuga (Figure 14), especially around the industrial areas and these are increasing as
more outsiders come to work in and/or visit the area. Disrespectful behaviour towards
Indigenous heritage in these areas is evident from the shooting at and removal of heritage
protection signage, the intentional toppling of standing stones and the driving of o-road
vehicles over and through sites of great Indigenous cultural signicance.
There was evidence of re-patination on the rocks associated with petroglyphs #16 (Figure 2)
and #9 (Figure 11). Neither of these two petroglyphs are in close proximity to those industries
producing acidic pollution. They are both in the southern section of the peninsula. To our
knowledge, rock surface acidity has not been measured on rocks associated with these
petroglyphs. Assuming the pH of the rock surfaces in this area is near neutral or slightly
alkaline as in the pre-industrial environment, it may be possible to observe some slight re-
patination over 50 years. On stable surfaces in desert environments re-patination has been
recorded at a rate of 1–10 µm in 1000 years (Liu and Broecker 2000; Dorn 2009). If we took the
Figure 13. Black smoke from the natural gas flaring towers. Image by R. Chapple 2017.
Figure 14. Graffiti near industry at Murujuga. Image by R. Chapple 2005.
higher end of this rate and assumed it to be growing in Murujuga at the rate of 10 µm in 1000
years, re-patination of 0.5 µm would be possible in 50 years and likely be visible.
This comparison of pre- and early industrialisation photographs of 26 petroglyphs on
Murujuga with recent photographs was undertaken as one means of assessing whether the
presence of industry is accelerating degradation of one of the world’s most signicant rock art
galleries. The analysis showed that only 13 of the rocks are showing no indication of change,
with 2 showing evidence of re-patination (petroglyphs #9 and #16). This means that half the
petroglyphs examined are showing either diagnostic or potential symptoms of damage. The
majority of these changes appear to be caused by industrial activity in the area. All petroglyphs
showing alteration, with the exception of the probable silicone peel and the abraded square,
are within close proximity to industrial activities. The silicone peel and the abraded square
were likely the product of past research activities rather than intentional vandalism. However, 5
(#3, #4, #18, #23, #25) of the 15 that show no change were also within close proximity to
industry. Interestingly, most of these were on more elevated and vertical surfaces. It may be
that vertical surfaces are more protected from the eects of industrial pollution than surfaces
on which airborne substances can accumulate more easily. Ongoing assessment of these
petroglyphs is needed to identify whether changes that are not yet visible will emerge.
We intend to record through photography our analysed petroglyphs sites every 10 years. As
this image database grows, it will provide a vital resource to map the impact of industrial
pollution and other factors on the rock art of Murujuga. The work reported here is a start to this
long-term study. As we digitise a larger section of the early recordings of rock art from
Murujuga, we hope to add additional sites to the list of those included in this analysis. Our
intention is to provide long-term support to the Murujuga Aboriginal Corporation in its eorts
to protect the Indigenous heritage of the area.
Reporting these observations now is at an important moment in time because there is
signicant pressure on industries worldwide to reduce their industrial emissions. If emissions
are reduced swiftly at Murujuga, the evidence presented in this paper suggests that damage to
the rock art may be limited and this extraordinary place can remain largely intact for future
The authors thank Natalia Podhajska for her work on analysing changes in the archival images and the
Murujuga Aboriginal Corporation for their support. We thank two anonymous reviewers whose recom-
mendations improved the paper. We thank the Honorable Robin Chapple and Drs Ian MacLeod and Mike
Donaldson for the photographs they provided. We are grateful for the institutional support that we
receive from the Centre for Rock Art Research + Management in the School of Social Sciences at the
University of Western Australia and the large photographic library developed by Professor Jo McDonald.
The authors are committed to conducting research that inicts no new damage to the rock art,
archaeology, environments, living cultural values, and viewsheds of Murujuga. This publication is
produced as a part of the Murujuga Rock Art Conservation Project. The views expressed in this paper
are our own and may not reect the views of those who have supported our research.
Disclosure statement
No potential conict of interest was reported by the authors.
This project was partly funded by the Gordon Darling Foundation and by ordinary citizens who gave
an amount in excess of AU$330,000 through crowdfunding. This extraordinary level of public
support shows the extent of public concern that exists on this topic. We thank each of the many
hundreds of people that supported this research.
Notes on contributors
Benjamin W. Smith (PhD) is Professor of World Rock Art in the School of Social Sciences at the
University of Western Australia. He is an archaeologist whose career has specialised in the study of
rock art, its interpretation and management. He has worked with rock art in many parts of the world
and is author of more than 60 academic publications on rock art. He is President of the ICOMOS
International Scientic Committee on Rock Art.
John L. Black (PhD) is a Research Management Consultant specialising in the management of large
programmes for the animal and veterinary industries. He worked in the CSIRO Division of Animal
Production for 23 years studying comparative physiology and nutrition across animal species and in
the development of computer simulation models before becoming Assistant Chief of the Division.
In recent years, he has been investigating, pro bono, the impacts of industrial emissions on
petroglyphs on Murujuga as an Honorary Research Fellow at the University of Western Australia.
Kenneth J. Mulvaney is an adjunct with the Centre for Rock Art Research + Management; he has
worked and lived on Murujuga since 2003 and was involved in the initial 1980s survey of the area
now occupied by the Karratha Gas Plant. Between 2000 and 2009 Ken was the President of the
Australian Rock Art Research Association. Ken’s book, Murujuga Marni, published in 2015, remains
the only substantive research tome on the Murujuga petroglyphs.
Stéphane Hœrlé is a researcher in material sciences. He is an honorary research fellow with PACEA
UMR 5199 CNRS (University of Bordeaux, France) and the Rock Art Research Institute (University of
the Witwatersrand, Johannesburg, South Africa). His research interests include the dynamics of rock
art site transformation through natural factors and human uses, with applications to the conserva-
tion and management of sites.
Benjamin W. Smith
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... Although our data clearly demonstrate that acidic rain has measurable effects on the varnish surface, including its colour and increased dissolution of Fe and Mn compounds, it should be stressed here that this does not necessarily mean that natural weathering of the petroglyphs is accelerated by anthropogenic pollution. Nevertheless, a recent analysis of photographs of twenty-six Murujuga petroglyphs from pre/early industrial development compared with recent photographs showed 50% changed over time, with the changes being attributed directly to industrial activity [49]. Modelling by Parsons and colleagues [50] shows that substantial deposition of nitrogen dioxide and nitric acid is concentrated over the industrial area of Murujuga, while deposition of sulphur dioxide is concentrated over the shipping lanes of the Murujuga coast, but extends to many locations containing rock art. ...
... With such a semi-actualistic experimental approach, it should be possible to reliably quantify the difference between the weathering rate of the rock varnish in contact with anthropogenically polluted and unpolluted natural rainwater under Murujuga climatic conditions. This statement is essentially in line with reliable and robust results obtained from other experimental studies with climate chambers to study weathering processes ( [33,34] and [49]). We thus hope to also encourage other researchers to design new experiments that study weathering of the rock varnish at Murujuga in order to obtain a more robust scientific understanding of the precise implications of industrial pollution. ...
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