Climate Change & Coastal Archaeology
by Ellie Graham
Climate change is affecting all aspects of the environment with increasing severity. Some of the worst manifestations are still avoidable depending on our behaviour if we reduce our greenhouse gas emissions, but other impacts are already ‘locked in’, including sea level rise. The coast will therefore experience some of the most severe effects of climate change with accelerated erosion, increased storm surge and coastal flooding. A national assessment of coastal erosion in Scotland, Dynamic Coast, (Dynamic Coast 2022) has identified that more of the coast will experience erosion at a faster rate due to climate change, under all emissions scenarios (Rennie et al. 2021a). This Scotland-wide picture is being refined to a local scale in a handful of locations around the coast, mapping the vegetation edge to define the changing coast (Rennie et al. 2021b). This is a far more precise proxy for the coast edge than the high water mark of spring tides (MHWS) which was used for the national scale analysis, but is much more difficult to map accurately.
Skara Brae is one of the most iconic sites in Scotland, one of the country’s biggest tourist attractions and one which is most well-known for its coastal location and vulnerability to erosion, having first been revealed by a storm in 1850 and now protected by a sea wall in front of the prehistoric village. It is also one of the case study locations where the refined coastal erosion assessment is being applied, with regular monitoring through biennial programmes of terrestrial laser scanning and analysis of coastal change rates and future risk (Rennie et al. 2021c).
Climate change impacts to heritage have also been assessed nationally; Historic Environment Scotland have carried out the first stage of a climate change risk assessment for the properties in their care, which looked at a range of natural hazards, including coastal flooding and coastal erosion (Harkin et al. 2018). Historic Environment Scotland have also produced a Guide to Climate Change Impacts, which emphasises the threat to heritage on the coast (Harkin et al. 2019).
Many hundreds of other sites are both threatened by climate-driven coastal change and deemed archaeologically significant, containing valuable scientific evidence and potential knowledge but are falling into the sea. The information they contain about past societies and environmental changes is being eroded by the rising tides. The Scotland’s Coastal Heritage at Risk Project (SCHARP) undertaken by the SCAPE Trust from 2012 to 2016 gathered and analysed updated condition information contributed by local coastal communities and volunteers, many of whom were Archaeology Shetland members. This national review of coastal heritage produced a prioritised list of 145 sites which are significant and vulnerable but are often not fully understood (Hambly 2016).
Drone surveys and Coastal Erosion
New research aims to harness the potential of drone technology to apply detailed, high-resolution coastal erosion analysis and vulnerability assessment to some of these identified high-priority sites, and places that are less renowned but are, in their own way, equally valuable.
Drone surveys and aerial photography of some of these sites which were highlighted by the SCHARP project and by local communities as being worthy of further attention will be used to create detailed 3-dimensional models of the sites as a baseline for future monitoring. This can also be used to map the vegetation edge and define the current location of the dynamic coastline as the basis for vulnerability assessments for these sites. Building upon these records with future surveys will also offer the opportunity to observe climate change impacts at site scale and in high resolution.
Drones offer the opportunity to rapidly and cost-effectively - but accurately - record a wider range of sites than only those highest profile places such as Skara Brae, and study climate driven changes at places where such intensive programmes of monitoring aren’t feasible.
These are places we know are vulnerable, containing archaeologically significant remains, and sites that are valued by the local community, but are not yet fully understood. They contain rich potential information and new knowledge that we are in danger of losing before we get the chance to understand it.
Shetland’s Vulnerable Coastal Heritage
Shetland’s long, indented and geologically variable coastline is the setting for many of these sites, from the sandy bays to dramatic exposed beaches, towering cliffs to low rocky promontories. The sites are equally varied, and are found from north to south, and east to west.
From the west coast in Bannaminn where piles of stonework and patches of charcoal-rich soil in the coastal section hint at structures that are in danger of being lost before we get the opportunity to learn about them, to Fugla Ness broch near Toft ferry terminal facing Yell across the sound, on a north-facing but generally sheltered stretch of coastline. Sitting on a low rocky cliff, the arc of wall on its seaward side is being lost to erosion. In Busta Voe, it’s post-medieval industrial archaeology that’s under threat, where a lime kiln is perched on the coast edge. Channerwick broch on the east facing coast of the south mainland sits in the corner of a sandy bay, already half sectioned by the sea to give a slice through the middle of the prehistoric tower; although it was investigated and thoroughly recorded in a joint project by SCAPE and Archaeology Shetland in 2015, it remains exposed and vulnerable (SCAPE 2015).
Some of these sites have been partially investigated, others we don’t yet know anything about. Although drone survey can record the site and landscape in detail and can inform our understanding of future vulnerability to coastal change, simply monitoring sites as they are lost to erosion would represent a missed opportunity. Exposure by natural processes gives us a chance to learn from these sites through the process of loss. Therefore, this research includes small-scale investigation at a selection of sites which aren’t yet fully understood, which are very vulnerable to damage by erosion, and which have potential to add new archaeological knowledge and improve understanding of past coastal change – and which are valued by the local community.
Over a long weekend in August, three eroding sites were rapidly investigated, selected for their potential, the urgency of the threat they face and the interest of Archaeology Shetland members. From Whalsies Ayre on Burra in the south, to the beach at Hillswick and north to Yell’s Gossabrough beach, hints of Shetland’s history from the Neolithic to the 19th century were investigated and recorded in fragile eroding coastlines.
The steep slope of the beach profile at Hillswick, the sheer vertical faces cut through the soft sediments at the back of the beach, and the modern rubble dumped over the coast edge as an ad hoc coastal defence all attest to the dynamic, high-energy environment, and the threat from erosion. As with many sites, the archaeological records here started with reports of finds (Canmore ID 468). High-status Iron Age artefacts were recovered from the beach in the 19th century; bone combs, prehistoric pottery, and bone implements contained in a midden deposit, fuelling speculation of a broch sited here, in what would be an eminently suitable location. However, subsequent surveys through the 20th century alternately failed to locate anything at this spot (it wasn’t found by the Ordnance Survey visit in 1969) or located the site and added new information to the record, when Noel Fojut noted shell, bones, charcoal and Iron Age pottery in 1980. The Coastal Zone Assessment Survey saw nothing of this date (Moore & Wilson 1998) and SCAPE’s first survey visit in 2015 didn’t find anything prehistoric here but flagged an eroding stone structure in the coast edge (SCAPE 2018a). It exemplifies the typical story of intertidal deposits that come and go; erosion, exposure, destruction - or concealment by newly deposited beach sediment. Epitomising the adage that absence of evidence isn’t evidence of absence, the records are also an illustration of why regular monitoring visits to vulnerable coastal sites are always useful to check their condition.
Archaeology Shetland investigated the structure eroding out of the coast edge in 2016, cleaning the section, recording the building, and recovering pottery which suggested a post-medieval date (SCAPE 2018a), possibly associated with the local fishing industry, or related to the nearby Stenness Fishing Station. However, in late 2020 and just in front of the later structure, Kevin Thompson again spotted the elusive prehistoric deposits in the intertidal beach; midden containing bone, shell and charcoal, a possible orthostat, hinting at a structure buried beneath beach sediment, and most strikingly, a lot of fire cracked stone strewn across the south end of the bay.
We had a single day to revisit and rescue what we could, so after clearing the
beach sediment and rubble from a strip of the sloping beach, a narrow strip of
brightly coloured midden rich in charcoal and peat ash was revealed at the top of
the slope. Enough survived to yield an assemblage of Middle to Late Iron Age pottery and animal bone, though intrusive plastics and other modern material attested to recent disturbance, the erosion damage also evident in the midden’s truncated seaward edge and the disturbed stratigraphy.
In front of this narrow surviving strip of Iron Age midden, the sandy shore below was very mixed by the action of the sea, beach sands and gravels interspersed with darker brown clays which still contained flecks of charcoal, probably the remnants of an occupation deposit but unfortunately too disturbed and contaminated to yield much archaeological information. The putative orthostat that had suggested a structure seems to have been its last surviving remnant. At its base, a smaller slab set on edge on the same alignment might be a packing stone inserted into a cut to support the larger structural stone, and reinforces the interpretation it was a deliberately erected orthostat, but little else survives. It appears that the large stone might have acted as a scour pit, focusing the action of the waves on this area and eroding out any sediments around it, down to the construction levels and base of the cut in which it was set.
This might have been the last opportunity to investigate the elusive site which has intermittently been visible for around 150 years, and our last chance to record and recover what’s there. It was certainly a day of surprises; despite its close proximity to the much later fishing-related structure, this was much earlier and unrelated, although located almost directly beneath its walls; so little intact archaeological deposits were left, yet they yielded a rich and diagnostic assemblage of pottery, and we were just in time to record what survives. However, the lesson from this beach over the past century is the importance of maintaining a monitoring presence on coastlines and sites such as this, so it shouldn’t be written off just yet.
The north coast of east Burra is completely different from the dramatic and exposed bay at Hillswick. The low boggy landscape slopes gently down to the coastline and shallow waters, the coast edge itself is just a low step from the grassy covered marshy hinterland to the stony foreshore. Sheltered on three sides, by West Burra, Trondra directly opposite, and the South Mainland just around the corner, the generally tranquil conditions here are illustrated by the number of mussel farms and fish farms in the surrounding waters. However, the archaeological sites themselves are the markers of erosion and sea level rise. Stone structures in the hinterland are visible as low raised banks with occasional large stones protruding through the grass, but some lie right on the coast edge, and the wall lines continue as stone alignments on the shore, the remains of walls where the associated deposits have been washed away as the structures have been submerged by rising seas. Clearly, they weren’t built to straddle the coast edge, but they’re now intertidal as indicators of past coastal change.
One particular site has been on the archaeological radar ever since the first Coastal Zone Assessment Survey of the area in 1998 highlighted it as actively eroding (Moore & Wilson 2001). With long bowed walls and a curved gable, it was originally interpreted as a possible Norse long house while recent visits by SCAPE and Archaeology Shetland have monitored the erosion. Pottery recovered from the eroding section and the beach in front of the site has indicated dates from the Bronze Age to the Hanseatic periods, reflecting this multiperiod landscape (SCAPE 2018b).
Taking advantage of the section which had been cut through the structure by the rising seas, we straightened the coast edge to give a vertical face across the walls and interior deposits, while a small test pit targeted the approximate centre of the building.
Our decision to focus on this particular stretch of the coastline was soon validated by the recovery of a large sherd of beautifully decorated pottery which was protruding from the eroded section in a discrete dense area of bright orange deposit.
Removing the deposits from the coast edge layer by layer revealed that this was a dense deposit of peat ash and burnt material, which had already been partly lost to erosion. Our work gave us a chance to properly excavate the deposits in sequence and gave us stratigraphic control over samples and the rich assemblage of finds: worked stone tools and further sherds of decorated pottery. We also recovered samples of the peat ash- and charcoal-rich hearth deposits, and the associated compacted clay floor layers.
Analysis of the samples of the burnt ashy deposit and floor layers is ongoing, but the pottery has been examined by Jenny Murray. Many of the sherds are decorated, but it’s the piece that Steve found first, hanging out of the section that’s garnered the most excitement. It’s now been confirmed as rare Shetland Beaker, one of the few from domestic sites, alongside Ness of Gruting (Canmore ID 227, Sumburgh Airport (Canmore ID 556), and Scord of Brouster (Canmore ID 405) and possibly Stanydale Temple (Canmore ID 387) to produce Beaker pottery in Shetland, dating this site to the late 3rd millennium BC (Jenny Murray, pers. comm.).
We didn’t have time to fully excavate the walls, but the burnt material was next to what appeared to be an external wall. On the assumption that this was the building’s hearth it would be an unusual position. It might hint at a period of remodelling and reorganisation of the internal space, or possibly represent a secondary hearth such as that seen at Ness of Gruting (Canmore ID 227). Alternatively, rather than an in-situ hearth, this might be a discrete spread of burnt material and ash adjacent to a wall as recorded at the Pund of Burland (Canmore ID 600) on nearby Trondra. Ness of Gruting also used peat ash as the fill of a double faced wall (Scholma-Mason 2018), so we may have encountered a similar use of burnt material in the structure here.
Meanwhile, the test pit at the centre of the building (which had actually been positioned in the hope of locating the hearth in the middle of the house) just kept getting deeper. Beneath the turf was a thick deposit of angular gravel which resembled quarry waste, which we’d also encountered in the coastal section. We suspect this might indicate deposition by a large storm event, dumping material across the building after it had fallen out of use. A layer of rubble below this was removed to reveal a wall running roughly east-west, and – eventually – an ashy layer, possibly related to occupation of the building. However, at this depth the deposits were below the MHWS, very soft and waterlogged.
Beneath the occupation deposits in the interior, under the structure and continuing onto the beach, and forming the surface of the intertidal shore was a brown clay deposit flecked with occasional charcoal. Although waterlogged and now lower than the modern MHSW, it appears to be the original ground surface upon which the building had been constructed. Although it pre-dates the building, the charcoal indicates human activity in the landscape at this time.
This building turned out to be much earlier than anticipated, and has already produced some exciting results. We’ll know more and hopefully get some more refined dates from the analysis of the samples, but already this has shown that the structure is interesting and deserves further investigation to resolve some of the unanswered questions and as a priority to rescue information from the rising sea.
Complimenting the detail of the small-scale work on the coastal section and test pit on this one structure, a drone survey of the entire headland will produce a digital elevation model, which will help to examine the extensive prehistoric landscape of houses and boundaries, as well as providing the basis for mapping the coastline here and analysis of the future erosion threat.
At the other end of the Shetland archipelago, the sandy sweep of Gossabrough Beach in Yell is backed by sand dunes, but the sheer sandy cliff at the back of the beach and overhanging lumps of turf show that this coastline is vulnerable and eroding. The ruined Ha’ sits at the corner of the bay, now roofless but still imposing, having latterly functioned as a local shop, supplied by the Earl of Zetland, then became a family home until the 1970s.
A local with deep family roots on the island, and family connections to the Ha’, first spotted a box formed of flat stone slabs eroding out of the sand dune in spring 2022. The urgency of the situation and vulnerability of the site was clear, but the exact nature of the feature was not; the first thought was a funerary cist, but no human remains were seen in the area - so the fieldwork in August was an opportunity to investigate, characterise the site and make a decision about further work in the future.
By this point, one of the sides of the box had collapsed, showing that even a few summer months could cause damage in such a vulnerable landscape. Closer examination showed that it had not originally been a single box but had a central vertical slab which acted as a divider forming two smaller adjoining cubbyhole-type boxes. However, the broad, thin sandstone slabs immediately proved to be roofing tiles, with peg holes for holding them in position. Such tiles were quarried only from Aithsness, Bressay in a quarry that operated from c.1600 to the mid-19th century (Ian Tait, pers. comm.) so clearly this was no prehistoric funerary cist. Presumably they had originally formed the roof of the Ha’ and been put to secondary use in the construction of this box, most likely in the late 19th or early 20th century.
Cleaning the section also showed the cut through the
sand dune, proving that the box had been dug into the
dune from above, though small cobbles on one side
suggested that it might have been dug into or adjacent
to a naust of which only ephemeral traces remained.
Although clearly neither funerary nor prehistoric, the exact function of this small structure remains uncertain. The presence of the shop nearby led to suggestions of cold underground storage, basic refrigeration in an area that didn’t have electricity. Alternatively, but more dramatically, a smuggler’s hiding place for contraband and alcohol was suggested. Finally, more prosaically, it may have been a post-socket for a strainer in a post and wire fence, which would have needed extra support in the sand (Ian Tait, pers. comm.). In some ways, although much later in date than expected, and not funerary, it’s more exciting, as a unique feature without any parallels (as far as we know) and still mysterious as to its function.
While we were on the beach we also took the opportunity to record a more common, but very interesting site; the former peat stack in front of the Ha’, which had been exposed in section by erosion. The bands of alternating processed peat interleaved with layers of clean windblown sand were clearly visible in the section, and a marker of past storm events where the wind had deposited sand on the stacked peat. Although prosaic, this little piece of Shetland history exemplifies the issue; prehistoric peat which formed in the landscape, cut thousands of years later to be burned as fuel, releasing carbon back into the atmosphere and contributing to the problem of climate change, only to be re-exposed by climate driven erosion and sea level rise, where the alternate black and white banding form markers of past storm events and can act as a proxy for past climate change.
All of these sites in their own way contribute to our understanding of Shetland’s history, past landscapes and climate change. Each was revealed by climate-driven loss and yielded information which would otherwise have been lost to those processes. They demonstrate the real and urgent need to monitor known sites and keep an eye on the coast for future exposures. Local information and regular updates are central to responding to the threat; SCAPE’s app and website are a portal through which you can explore vulnerable coastal archaeological sites and contribute valuable information about this precious heritage that will help inform future research and management (SCAPE 2020).
To learn more about the effect of climate change on heritage, visit the DigIt! article, 'How Drones are Helping to Save Scotland's Coastal Archaeology'.
Canmore (2021). Available online https://canmore.org.uk/ Accessed 02/10/2022
Dynamic Coast, 2021. Dynamic Coast https://www.dynamiccoast.com/. Accessed 02/10/2022
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Rennie, A.F., Hansom, J.D., Hurst, M.D., Muir, F.M.E, Naylor, L.A., Dunkley, R.A. & MacDonell, C.J. (2021c). Dynamic Coast Adaptation and Resilience Options at the Bay of Skaill. Crew Report, available online https://www.dynamiccoast.com/files/dc2/_DC2_WS4_BayOfSkaill_FINAL.pdf
SCAPE (2015). Channerwick Broch. https://scapetrust.org/channerwick-broch/
SCAPE (2018a). West Ayre, Hillswick. https://scapetrust.org/sites-at-risk/site/5473
SCAPE (2018b). Whalsies Ayre. https://scapetrust.org/sites-at-risk/site/6970
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SCAPE (2020) The SCAPE Trust https://scapetrust.org/
Past In Depth articles can be found in the Archive.