St Michael's Mount 1830

Marazion Harbour looks a bit different today!

View from Start of Causeway; Chapel Rock on the right.

Ravaged by the Sea
Not a seaside haven.
Besides the effects on the coastline and construction on that coastline, the reason for that erosion and damage stems from immersion as a result of isostatic rebound, together with the combined effects of weather and driven sea level.

The Bay has seen many raging storms, but a handful may be considered to be Violent Storms, causing damage. Ignoring those tragic events that solely caused men to perish as they served onboard ships that were no match for the fury of sea and wind, this is a basic list of Violent Storms. It will be extended and expanded as and when I find details.

The Great Storm 26th November 1703; this was nature on a massive scale. Ships sunk, 15,000 people killed across the south, buildings damaged on a wide scale from Cornwall to the Isle of Wight. Massive damage to all windmills.
1717 storms
1766 storm damage to Penzance Quay
20th Jan 1817 Immense destruction accompanied by an abnormally high tide
1823 Violent Storm
22nd Nov 1824 reported in West Briton 26th Nov 1824
1848 Storms
26-27th December 1852 Destruction of the seafront and rail viaduct
1859, worst since 1823
February 1867 and the 25th March 1867
31st Jan 1868 severe storms washed away rail viaduct.
7th Oct 1880. Massive destruction called a Great Storm. Many fishermen suffer as a consequence and Charles Cambell Ross instigates an Appeal. Reported 21st Oct 1880 also 5th Nov 1880 in The Times.
8th March 1891 Great Blizzard massive destruction, isolation, 26 feet of snow, considerable loss of ships.
12th Nov 1915 Powerful Gale great damage
8th Dec 1934 High seas damage to new pool
7th March 1962. Ash Wednesday Storm.
October 1987 Hurricane Across the south from Cornwall to Kent; Gusts of wind reaching 100mph, damage, uprooted 15 million trees and killed 18 people. Cars were destroyed, roofs torn off buildings.
24 – 25th January 1990 storm winds
October 2000, a massive storm hit Britain from Cornwall to The Midlands. Gusts up to 93 mph, and massive damage and flooding.
26th October 2004 Monstrous seas

It will be helpful to tie these dates in with what has happened to the coastline.

Other Driven Sea Level mechanisms include wind powered sea surges, such as that on the East Coast (1953), Tsunami like waves or groups of waves from violent pressure submarine forces, Ocean driven broad tidal waves (generated by swell and wind in the Mid Atlantic), it can be accentuated by current or cumulative mass. Britain does experience earthquakes and any watershake that follows that will certainly affect driven sea level.

It has been suggested that the 1014 event was brought about by the impact of comet debris. The effects were sudden and dramatic, as well as very wide spread – even as far as the Netherlands. Affected were Cornwall, Hampshire, Kent and Sussex.

The two ‘Portugal’ earthquake tsunamis were 1.2 metres and 2.4 metres. The 1768 event ‘reached the top of the promenade wall’ on a calm day. Taking a high tide, that indicates a tsunami impact at 2 metres plus.

It is also considered that the increase in weight generated by the high tide actually can trigger earthquakes or submarine slips. This adds to the likelihood of coastal damage.
The worst case scenario is a Storm combined with a Strong South Easterly, on an Atlantic Sea Surge or Tide with a Tsunami, at a Spring High Tide. Thankfully the odds of that occurring are rather remote. But, a Southeasterly on a high tide is common enough. The once in 200 year event is an insurer’s myth. Such a basic event could happen the next day. 1847 came fairly close with an earthquake in May, the storm had happened earlier in the year. Similar situation in 1859. Of course I am ignoring the plausible Cumbre Vieja projected collapse and its effects. Due for eruption any day … so they say.

1014 Anglo-Saxon Chronicle ‘on the eve of St. Michael’s Day, came the great sea-flood, which spread wide over this land, and ran so far up as it never did before, overwhelming many towns, and an innumerable multitude of people’. The Bay was ‘inundated by a ‘mickle seaflood’ when many towns and people were drowned’. M G Healy describes organic deposits in Marazion Marsh, that lie behind the ‘coastal barrier’ that is dated to no later than AD 980 and overlain by a sand layer. Very much a pointer to that myckle seaflood.

1090 No cause noted, but no mention of storms.

1st November 1755 ‘Lisbon Earthquake’ Azores-Gibraltar Fracture Zone, Effects descibed in Penwith.

31st March 1761, Earthquake offshore Portugal, Reported by Borlase in Penzance, series of waves and purterbations.

23rd May 1847, Earthquake, near Isles of Scilly, all day. Waves up to 1.5m came ashore.

21st October 1859 offshore North Cornwall, Local sea disturbance

24th May 1960 Chile but registered marginally on the Newlyn Tide Gauge.

28th February 1969 Earthquake offshore Portugal, Heavy waves above normal at Newlyn

26th May 1975 Earthquake offshore Portugal, Disturbance measured at Newlyn.

The Times
‘23rd May 1847 a very extraordinary commotion of the sea took place in Mount’s Bay, which was observed by a great number of persons. About half-past 5 o’clock it made a rush on to the beach for 50 or 60 feet, and immediately receded to its natural position. This occurred a great many times up to half-past 8. The boats at Newlyn and Penzance were sometimes afloat, and then again almost dry; those that were at the moorings in Gwavaslake all showed their heads towards the shore, although the wind at the time was blowing very strong off the land. A schooner at anchor off this pier-head was noticed to go completely round several times’

Another aspect of 'sea level' is that current satellite measurements indicate a general rise of 1.7mm per year, due to ice melt. I will post a new thread on that subject.
Penzance is being lapped up at the present total rate of 3.4mm per year, so we have got another 1,800 years before the Bay is level with the Promenade.