Is Gower at danger from a possible future Tsunami? An incredible question at first glance, but local history proves that the entire coastline along the Bristol Channel is at risk from such natural disasters.
Not too many centuries ago, the shoreline of Swansea Bay lay as far as five miles out from its current location. 19th Century oyster dredgers still referred to certain portions of the bay as 'Grove Island' or 'Green Grounds' and trawler men spoke of seeing ancient homesteads beneath their sea craft. An extensive forest, known as Coed Arian or Silver Wood once stretched from the foreshore at Mumbles to Kenfig Burrows (the remains of which can still be viewed along certain parts of Swansea Bay) and a bridle path is also known to have existed between Penrice Castle and Margam Abbey along what is now a stretch of the Bristol Channel. From the depths of this area of sea, local fishermen have dragged the remains of numerous animals, including stag antlers, elk and wild ox horns and wild boar tusks. Human artefacts dredged from "Green Grounds" include an immense tablet of stone bearing cement includes and chisel marks and numerous horseshoes. The former is believed to have been part of a farm house owned by the Angel family. This particular family owned much of Mumbles, including the stretch known as "Green Grounds" that have now been lost to the sea. Whilst the encroachment of the sea on "Green Grounds" had been a recognised gradual process, the loss of the complete area to the sea from one great Tsunami at 9a.m. on 20th January 1607 (the later amendment of what is today's modern calendar would now make that date as January 30th 1607) could not have been foreseen.
On this date, it is believed that an active fault line in the sea off Southern Ireland triggered the collapse of tens of cubic kilometres of sand from the edge of a continental shelf into an abyss. It has been calculated that the speed of the descent would have been in the region of 500km an hour. This monumental activity created a wave of awesome magnitude, estimated at being 4 metres high as it past Worm's Head and entered into the Bristol Channel. Squeezed between the English coastline and that of the Gower Peninsula, the wave increased in height by a further two metres. By squeezing the wave between these two coastlines, the Tsunami also increased in speed to nearly 50km per hour. This sheer wall of water crashed into the Gower Coast, invading the peninsula landscape to a depth of over 3km. The devastation was enormous with a total loss of life running to over two thousand along a total of 570 km of coastline, including that of Gower. Many areas hit by the Tsunami did not recover from this onslaught of water, Grove Island and its "Green Grounds" being one of the landscapes permanent casualties that would never resurface from the sea as the wave finally settled.
Of course, such overnight devastation has left a wake of folklore and superstition, as well as historical fact. Crymlyn Pool, located in the burrows a little to the east of the current City of Swansea is worth noting in this respect. It was believed that beneath this lake stood the original town of Swansea. During calm weather, when the surface of the water here was still, the chimneys and even the church steeple of old Swansea could be seen at the bottom of the lake. On quiet nights, the bells of this drowned church could also sometimes be heard chiming from the depths of the lake. Legend also held that if any person standing facing the lake was sprayed by the water by an oncoming wind then they would be dragged by an invisible force down into the submerged town. Of course, much of this lake has now been drained, converting both the area and its title into a bog.
Returning from the world of legend, the geographical fault which give rise to the 1607 Tsunami is still active and has generated an earthquake measuring Richter 4 within the last few decades adding a foreboding response to the opening question of this article; Is Gower at danger from a possible future Tsunami?
Green Grounds, Mumbles
