One Cornwall tsunami, in 1755, was larger than most and devastated a lot of the south coast, including swamping St Michael’s Mount and the Marazion and Penzance areas. This is well documented in old documents and media from the time.
The Cornwall Tsunami in 1755 was caused by an earthquake in Lisbon, causing a three metre high tsunami at about 2pm on 1 November 1755. From the time the earthquake hit Lisbon, it took four hours for the tsunami wave to reach Cornwall. It didn’t just affect Cornwall, but the whole of the UK south coast, even being noticeable in London.
The tsunami generated three very large tsunami waves. One giant wave at St Michael’s Mount was noticed when the sea suddenly receded – after 10 minutes the sea came rushing back as a wall of water. At Newlyn the sea rose 10′ in height, as it did in St Ives and Hayle too.
One writer at the time said the Cornwall tsunami caused “great loss of life and property occurred upon the coasts of Cornwall”
A tsunami wave doesn’t work like a normal wave; a normal wave doesn’t have the force behind it pushing outwards relentlessly. A tsunami wave rises up to great height as it approaches land because the water becomes shallower, once it’s run out of water and is crossing land it can still continue inland for some considerable distance, depending on the speed and height of the wave – and how many other waves are pushing it from behind.
Other Cornwall Tsunamis
One other Cornwall tsunami occurred in March 709AD, and a large tsunami at St Michael’s Mount recorded in 1099, but there’s been a tiny one that was captured on video in 2011. At that time, there was either a small landslide, or maybe an unusual meteo-tsunami, that caused a tidal surge affecting the coastline from Cornwall to Hampshire on the morning of Monday 27 June 2011,. Reports were received of rivers changing direction and fish leaping out of water. A National Trust Guide at St Michael’s Mount reported that “People’s hair stood on end”.
In 1765 Rev Borlase wrote extensively of another tsunami in the area of Mount’s Bay, on 28 July 1765.
Cornwall 2011 Tsunami Video
Now the worry is not “if”, but “when” another large tsunami would strike the coast – and what can be done to plan for it.