People living on the low-lying shores of the Bristol Channel and Severn estuary began their day like any other on January 30 1607. The weather was calm. The sky was bright.
Author
- Simon Haslett
Pro Vice-Chancellor and Professor of Physical Geography, Bath Spa University; Swansea University
Then, suddenly, the sea rose without warning. Water came racing inland, tearing across fields and villages, sweeping away the homes, livestock and people in its path.
By the end of the day, thousands of acres were underwater. As many as 2,000 people may have died. It was, quite possibly, the deadliest sudden natural disaster to hit Britain in 500 years.
More than four centuries later, the flood of 1607 still raises a troubling question. What, exactly, caused it?
Most early explanations blamed an exceptional storm. But when my colleague and I began examining the historical evidence more closely in 2002, we became less certain that this was the full picture. For one, eyewitness accounts tell a more unsettling story.
The flood struck on January 30 1607 - or January 20 1606, according to the old Julian calendar , which was still in use at that time. The flood affected coastal communities across south Wales, Somerset, Gloucestershire and Devon, inundating some areas several miles inland. People at the time were no strangers to storms or high tides - but this was different.
Churches were inundated. Entire villages vanished. Vast stretches of farmland were ruined by saltwater, leaving communities facing hunger as well as grief. Memorial plaques in local churches and parish documents still mark the scale of the catastrophe.
Much of what we know about how the event unfolded comes from chapbooks, which were cheaply printed pamphlets sold in the early 17th century. These accounts describe not just the damage, but the terrifying speed and character of the water itself.
One such pamphlet, God's Warning to His People of England , describes a calm morning suddenly interrupted by what witnesses saw approaching from the sea:
Upon Tuesday 20 January 1606 there happened such an overflowing of waters … the like never in the memory of man hath been seen or heard of. For about nine of the morning, many of the inhabitants of these countreys … perceive afar off huge and mighty hilles of water tombling over one another, in such sort as if the greatest mountains in the world had overwhelmed the lowe villages or marshy grounds.
Our interest in the event arose from reading that account. It gives a specific time for the inundation - around nine in the morning - and emphasises the fair weather and sudden arrival of the floodwaters.
From a geographer's perspective, this description is striking. Sudden onset, wave-like forms and an absence of storm conditions are not typical of storm surges. To us, the language was reminiscent of eyewitness accounts of tsunamis elsewhere in the world. This suggested a tsunami origin for the flood should be evaluated.
Until the early 2000s, few researchers seriously questioned the storm-surge explanation. But as we revisited the historical sources, we began to ask whether the physical landscape might also preserve clues to what happened in 1607. If an extreme marine inundation had struck the coast at that time, it may have left geological evidence behind.
In several locations around the estuary, we identified a suite of features with a chronological link to the early 17th century: the erosion of two spurs of land that previously jutted out into the estuary, the removal of almost all fringing salt marsh deposits, and the occurrence of sand layers in otherwise muddy deposits
These features point to a high-energy event. The question was what kind?
Testing the theory
To explore this further, we undertook a programme of fieldwork in 2004. We examined sand layers and noted signatures of tsunami impact such as coastal erosion, and analysed the movement of large boulders along the shoreline. Boulder transport is particularly useful, as it allows estimates of the wave heights needed to move them.
Some fieldwork was filmed for a BBC documentary broadcast in April 2005, which featured other colleagues too. It included an argument for a storm, but also another suggesting it isn't fanciful to consider that an offshore earthquake provided the trigger.
Our results were published in 2007 , coincidentally the 400th anniversary of the flood. In parallel, colleagues published a compelling model supporting a storm surge. The scientific debate, rather than being resolved, intensified.
An updating of wave heights based on boulder data using refined formula was published in 2021 , suggesting a minimum tsunami wave height of 4.2 metres is required to explain the coastal features - whereas, according to the calculations, storm waves of over 16 metres would be required. This is perhaps unlikely within the relatively sheltered Severn estuary.
The low-lying coasts around the Bristol Channel remain vulnerable to flooding. Storm surges occur regularly, though usually with more limited effects. Climate change is now increasing the risk through rising sea levels and more intense weather systems.
Tsunamis, by contrast, are rare. A report by the UK government's Department for Environment, Food & Rural Affairs found it unlikely that the 1607 flood may have been caused by one. However, it also noted that offshore southwest Britain is among the more credible locations for a future tsunami, triggered by seismic activity or submarine landslides.
This distinction matters. Storm surges can usually be forecast. Tsunamis may arrive with little or no warning.
Scholarly and public interest in the flood has not waned. In November 2024, a Channel 5 documentary brought together several strands of recent research, concluding that the jury is still out on the flood's cause.
That uncertainty should not be seen as a failure. Evaluating competing explanations is essential when trying to understand extreme events in the past - especially when those events have implications for present-day risk.
Whether the flood of 1607 was driven by storm winds, unusual tides or waves generated far offshore, its lesson is clear. Coastal societies ignore rare disasters at their peril.
The sea has come in before. And it will do so again.
Simon Haslett does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
