Holywell Beach on the North Coast of Cornwall is known for a small sea cave which houses a ‘holy well’. According to Mabel Quiller-Couch, in her 1894 book “Ancient Holy Wells of Cornwall” in 995 AD the bishop of Lindisfarne, Aldhun, was bringing the remains of saint Cuthbert back to Ireland. Blown off course in a gale, he was left stranded in Cornwall where he settled and built a church dedicated to St Cuthbert. After some years however, an oracle instructed Aldhun to return the relics of St Cuthbert to Durham. As he was leaving from Holywell Bay, the saint’s bones touched the side of the well, giving the spring its magical healing powers. In medieval times, many people flocked to this cave to seek out the healing powers of the spring.
I was in the area this week when the tide was low (at high tide the cave is completely flooded, so you have to check the tides!) and decided to bring out the fisheye lens and a tripod to take some long exposure pics. They came out all right. There are more colourful photos available online, but my suspicion is that these use artificial light and sometimes also some enthusiastic post-processing. By using the longest possible exposure time on my camera (Olympus OMD E-M1markII), a full minute, I was able to let enough light into the camera. This enabled me to use f/18, allowing great depth of field, and ISO200, meaning little noise.
The formations result from a rare (in Cornwall) limestone deposit in the roof of the cave. Slightly acidic rainwater percolates through this limestone, dissolving calcite and becoming enriched in calcium bicarbonate. When the water drips down the rocks, the process is reversed and calcite precipitates, especially in areas where the water moves a little, causing CO2 to gas off. This results in the dam-like rimstone (or gours) formations. The tiny ‘rice terrace’-like formations on the dams are called microgours. I’d like to go back one time to experiment more and also to take some macro photos of the microgours and colourful microbes.