The Killer Wave of 1607

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Simon Haslett’s BBC Timewatch documentary on the “The Killer Wave of 1607” to be rebroadcast

Friday, 2 February, 2024

In 2005, Simon Haslett, Bath Spa University’s Professor of Physical Geography and Pro Vice-Chancellor (Partnership Strategy), starred in a BBC Timewatch documentary called The Killer Wave of 1607. This fascinating documentary is being rebroadcast on BBC 4 this evening and is also available on BBC iPlayer. 

At 9:00am on 30 January 1607, a massive wave devastated the counties of the Bristol Channel. It came without warning, sweeping all before it away. The flooding stretched inland as far as the Glastonbury Tor. Two hundred square miles of Somerset, Devon, Glamorganshire and Monmouthshire were affected and up to 2,000 people died. Yet for over 400 years, the killer wave of 1607 has almost been forgotten. Timewatch relives the terror and the human tragedy of 1607 and follows the research of Professor Simon Haslett, and his colleague, Australian Geologist Dr Ted Bryant, on a journey of discovery to determine if it was simply a freak storm, or in fact - a tsunami. 

To this day, 30 January 1607 remains the largest and most destructive flood in British history. Simon said:

“When I was young, I remember seeing in some books in the library woodcuts of the flood pictures of people stranded up on the top of high trees and roofs, and rabbits clinging to the backs of sheep as they were floating along. Very dramatic scenes which I've shown in my lectures to students for over 30 years now. These images are a good example of what a storm can do. 

“A lot of the commentators on the 1607 flood have put it down to a storm coming in, and as a child, you just accept what you're being told by the scientists and the historians. Attributing the flooding of 1607 to a storm makes sense. The area is famous for them.” 

On 13 December 1981, the sea defences along the Somerset coast were breached by a storm driven tidal surge and the lowlands behind them were inundated as they had been in 1607. As the wave swept through seaside villages during the night, it carried away cars and parts of houses. The lowlands of the Bristol Channel have always been prone to flooding. Much of the area is below high tide and has been protected by sea walls for 600 years. This weakness is exposed when heavy storms coincide with high tides, and this is exactly what happened in 1981.  

Simon and Ted interviewed locals affected by the storm in 1981 to get a better understanding about how that storm impacted the community in 1607, comparatively. This led them to look at the archives in churches in the area. The level of the 1607 flood is recorded in a number of churches on both sides of the Bristol Channel and there are eye-witness accounts in six different pamphlets that described these waves, with one reporting “mountainous waves, in lines like smoke as if the mountains were on fire. Into the view of sun, it seemed as if thousands of arrows had been shot forth all at one time”. After reading this account, Simon and Ted looked at each other and said “that’s not a storm. That's a description of a tsunami”.  

The very idea of a tsunami laying waste to the Bristol Channel goes against every assumption many make about Britain being geologically safe. The widely held view is that storms happen all the time but tsunamis never come anywhere near Britain. But in fact, they do. Some 7000 years ago, the entire east coast of Scotland was battered by a mega tsunami with 70 ft high waves. It was triggered by a gigantic landslide in Norway on an area off the continental shelf called Storegga. Billions of tons of sediment plunged from the shallows into the deep. The landslide is still visible in sonar surveys. And in 1755, an earthquake off the coast of Lisbon sent a series of tsunamis out into the Atlantic. The Southwest of Cornwall was hit by a three-meter-high wave.  

Simon and Ted set out to scour the coast of the Bristol Channel for evidence to support their theory. They analysed rock formations and sand deposits at Dunraven Bay in South Wales, analysing the size and shape of the boulders in order to estimate what height a tsunami would have to be in order to move the boulders up the hillside. Ted concluded that it would have taken a wave at least 20 meters high, over 60 feet. 

They also visited Rumney Wharf near Cardiff. In the 1980s there was a survey done that actually documented a sand layer within the mud deposits. It proposed that the sand layer was left behind by a massive surge of water from the sea around 400 years ago. Whatever force brought the sand there was an event of enormous power.  

Ted said:

“You try and track these deposits to the source. You look around you and there is no beach for miles so that is an indication that this stuff has been transported a considerable distance. To find something very fragile like this in this type of deposit, is an indication that we are dealing with tsunami flow.” 

In total, Simon and Ted took samples from five separate locations around the Bristol Channel, and at every site, they found sand or gravel deposits and all in a single layer. 

Ted also visited Sully Island, a small outcrop of rock just off Cardiff. It would have taken the full brunt of a tsunami moving up the Bristol Channel. Once again, big boulders seem to have been picked up and shoved against one another by a massive movement of the water and on the headland. The top layer of rock has been eroded away exactly the sort of thing a tsunami could do. 

However, Simon and Ted’s evidence can be challenged. On the microscopic level, however, Simon did make a breakthrough. Tiny spiral shells are typical of the species that grow in the shallow waters inside the Bristol Channel but these shells are only found at much greater depths out in the open ocean, over 50 miles away from where they were deposited along the Bristol Channel coast. 

Simon and Ted had assumed that their tsunami was triggered by a submarine landslide, but detailed surveys of the continental shelf around Great Britain reveal no evidence of a landslide. There next best hope is the possibility that an earthquake on its own could have triggered the tsunami. 

Roger Musson, Head of Seismic Hazard at the British Geological Survey, assessed the findings. He said:

“The big surprise is that the seabed off the Southwest tip of Ireland is far less stable than commonly imagined, and is the location of an ancient but massive fault line. We still have this old weakness in the crust here. And it's been suggested that this is exactly the sort of place where you could get an anomalously large earthquake happening.” 

This isn’t just an idle theory. On 8 February 1980, census recorded an earthquake from exactly this area. It was 4.5 on the Richter scale, not enough to lift the seafloor but violent enough to give fresh impetus to the tsunami theory. 

Roger continued:

“We know from geological grounds that the Bristol Channel is a likely site for getting an extra-large earthquake if we're going to get one anywhere around Britain. And we know from seismological evidence that we've actually had an earthquake there so there. It is a fault which is moving, it's active. So, the idea of putting a hypothetical large historical earthquake in the spot is not so fanciful.” 

With the historical accounts found in the pamphlets, coupled with the geological evidence they discovered meant that Simon and Ted had discovered a possible cause. The final piece of their tsunami theory was in place.  

Nineteen years on, Simon reflects on his theory and research work in the documentary. He said:

“Further analysis has shown that the 1607 flood was the worst historical natural disaster to occur on British soil. I am pleased that the research Dr Ted Bryant and myself undertook whilst I was Head of Geography at Bath Spa has shone a light on this exceptional event, bringing it into the public consciousness, and improving our understanding of natural hazards in Britain generally.

"Our theory that the flood may have been caused by a tsunami has generated much debate and stimulated further study by many students and researchers. Of interest, although there is no earthquake recorded on the day of the flood, is that historical documents have since shown early 1607 to have been a seismically active period with an earthquake being noted two weeks later and again in May affecting the region." 

The jury is out on this one but, tsunami or not, Simon and Ted’s documentary has generated lively debate for many years amongst university students, academics and geologists. 

The documentary will be rebroadcast on BBC 4 this evening. It is also available on catch up on BBC 2 via iPlayer.