Can archival visual sources be used to quantify coastal change?: insights from the dynamic coastline of Ceredigion, west Wales

Along many coastlines worldwide, a variety of direct and indirect anthropogenic influences are influencing natural processes of coastal erosion and deposition.  Both traditional change reconstruction and monitoring techniques (e.g. repeat surveys) and increasingly sophisticated approaches (e.g. photogrammetry, LiDAR, drone imagery) require specialist knowledge and equipment, can be time consuming to apply, and may be restricted to assessing relatively recent changes over short timeframes (e.g. typically years to a few decades).  Here, we evaluate the potential for archival visual sources - maps, paintings, geological sketches, and historical photographs – to help document changes in the coastal environment of Ceredigion County, west Wales, over the past 100-150 years.  Two extant sites of geoscientist interest, both located within 20 km of Aberystwyth, were investigated: Harp Rock (Craig y Delyn), which represents the westward-dipping limb of a synclinal fold, and Monk’s Cave (Twll Twrw), which has essentially now developed into a coastal arch.  Egg Rock (Tŵr Gweno), a coastal stack which was previously located near to Monk’s Cave but has since disappeared, was also investigated.  All three sites were well-known tourist attractions in the late 1800s and early 1900s, and various maps, paintings, sketches and photographs help to provide both qualitative and quantifiable insights into the nature of coastal change, including the sequencing, rates, and timing of key changes, as well as volumes of mass loss.  For example, Harp Rock is retreating landward as sandstone strata of ~37 cm thickness are removed by wave action and mass movement; for every 1 m² of stratal loss, a mass of 858.4 kg is removed.  For Monk’s Cave, the average vertical erosion rate of the cave entrance is estimated to ~0.65 cm/yr over a timespan of 139 years.  Based on the last known photograph of Egg Rock (early 1900s), the total mass loss is approximated to be 197.70 t.  Collectively, the findings from these three sites provide insights into rates of Holocene shore platform development along this dynamic coastline.

Wider use of archival visual sources clearly has potential for complementing more technically sophisticated short-term change reconstruction and monitoring approaches.  Key challenges include sourcing well-dated, high-quality archival visual sources to enable establishment of robust timelines of change and the generation of quantitative data, and safely accessing potentially hazardous locations to enable new paintings, sketches, or photography.  If these challenges are surmounted, opportunities include enhanced potential for: i) providing quantified landscape change case studies for inclusion in school/university geoscience syllabi; ii) demonstrating the relevance of geoscience for local/regional natural and cultural heritage; and iii) enhancing public engagement with coastal geoscience (e.g. through citizen science projects or science-art collaborations).