Case Study Site 16 – St Michael’s Mount, Cornwall

Case Study Site 16 – St Michael’s Mount, Cornwall

1.         Location

St Michael’s Mount comprises a castle and other buildings on a small island located a short distance off the south Cornwall coast at Marazion in Mount’s Bay.  It is a fortified post-Medieval house built on the site of a former priory on a tidal inlet. 

2.         Why was the Case Study Site selected?

St Michael’s Mount is one of Cornwall’s most famous landmarks.  During the severe winter storms of 2013/14, the causeway leading from Marazion out to the Island was seriously damaged.  Risk are posed to the causeway in the future as a result of sea level rise and changes in weather patterns.  Between Long Rock and Wherry Town a well preserved fossil forest was uncovered during the storms in January and February 2014.  The increased scour and beach lowering with potential exposure and loss of heritage is a further issue at this location. 

3.         Summary of the Geology, Geomorphology & Coastal Processes

Most of this coastline lies within the Torbay and Tamar Groups of limestones, sandstones and slates of the late Devonian Period.  However, St Michael’s Mount is an outcrop of granite of which there are some outcrops also on the adjacent shoreline.  The almost continuously defended coastline in the vicinity of Marazion places some pressure on the shoreline and the hard defences mean that the Bay at this location is sensitive to sea level rise and the impacts of increased stormy weather.  The coastline is relatively sheltered from the dominant western Atlantic wave climate due to the sheltering effect of the Penwith Peninsula.  Although it receives less wave energy than the coastline to the east of Marazion, the Long Rock to Penzance harbour frontage still displays a sandy intertidal area in common with much of the high energy Cornish coast, and it does periodically receive large amounts of wave energy during storm events which originate from due south and the south-east (Royal Haskoning, 20111).  Mount’s Bay does have significant sediment accumulations compared with adjacent sections of the coast, but there has been a trend towards beach lowering observed.  This can lead to exposure of heritage sites on the sea bed and render the frontage more vulnerable to the impacts of coastal storms. 

4.         Risks to Heritage Assets along the Case Study Frontage

The storms of 2013/14 highlight the potential future risks to the causeway leading from the shore at Marazion out to St Michael’s Mount.  The instability of the western harbour arm at St Michael’s Mount has also been highlighted (Royal Haskoning, 20111).  The same winter storms also re-exposed evidence of the most extensive submerged forest in Cornwall on the coastline between Long Rock and Wherry Town; the site having been first photographed by Alexander Gibson in 1883.  This well-preserved 4,000 year old site includes sub-fossil tree trunks, rooted stumps and branches, as well as other material that have washed out of the early soil horizon.  Early accounts (Borlase, 17582) referred to local legends and tales concerning a forest extending out across Mount’s Bay. 

5.         How can historical Imagery inform heritage risk management?

St Michael’s Mount is one of the most painted subjects around the Cornish coast and artworks illustrate that, in physical terms, the Mount has remained relatively unchanged over time, although they do show us how the buildings were extended and altered over the last 200 years.  Most of the artworks also show the causeway extending out from the shore and visible at low water.  No illustrations have been found relating to the fossil forest, although it was referred to and illustrated in a geological cross section in 1827 (Boase, 18273).  The photographers, Gibson & Sons, produced photographs of part of the submerged forest which was exposed after storms in 1883 (Cornwall Conservation Group, 20144). 

Artworks and photographs can, therefore, highlight change in the vicinity of Mount’s Bay and St Michael’s Mount.  The impact of the recent storms and the exposure of the fossil forests over time, which have been illustrated through photographs, highlight the potential and increasing risks that this frontage is likely to face over the next century. 

6.         Key Issues – What can be learnt from this site?

In this location, although there are numerous artworks they do not provide any significant information about changing coastal risks.  Photographs of storm damage and exposure of the fossil forest highlight a potentially worsening situation for the frontage over the next decades. 

Figure 16.1: This copperplate engraving by S. & N. Buck (1734) shows the view of St. Michael’s Mount from the shore at High Water. Later artists (Figures 16.2- 16.5) tended to depict the Mount from this vantage point.

Private Collection.

Figure 16.2: William Daniell RA produced this detailed aquatint in 1825 and shows the scene at Low Water. The causeway, which provides the only access, is clearly visible.

Private Collection.

Figure 16.3: This fine lithograph was produced to mark the occasion of the visit of Queen Victoria and Prince Albert to the Mount in 1846. The landward end of the causeway can be seen on the left of the picture.

Private Collection.

Figure 16.4 ‘St. Michael’s Mount’ by Henry B. Wimbush. This watercolour (c.1895) shows thescene towards Low Water as the tide recedes to expose the causeway.

Image courtesy of Elford Fine Art of Tavistock.

Figure 16.5: ‘St. Michael’s Mount’ by Alfred Robert Quinton. Watercolour. C.1915.Quinton’s view provides a detailed, almost photographic, image of the Mount showing the full extent of the causeway.

Image courtesy of J. Salmon Limited of Sevenoaks.

Figure 16.6 and Figure 16.7 show the granite setts of the causeway before and after the severe storms of 2013/14.

7.         References

  1. Royal Haskoning, 2011.  ‘Cornwall and Isle of Scilly SMP2’.
  2. Borlase, W., 1758.  ‘The Natural History of Cornwall’.  W. Jackson (Printer).
  3. Boase, H. S., 1827.  ‘On the Sand-Banks of the Northern Shores of Mount’s Bay’.  Trans. Royal Geological Soc. of Cornwall. Vol. 3.
  4. Cornwall Conservation Group, 2014.  ‘Penzance’s 4,000 Year Old Fossil Forest’.  Press release.