Clues from last year’s Sulawesi tsunami shed light on the South Wales’ 1607 flood


This week BBC Four are showing again The Killer Wave of 1607, a Timewatch documentary about Professor Simon Haslett’s research into the catastrophic flood that was, with an estimated 2000 fatalities, the worst natural disaster in history to have hit mainland Britain, and now last year’s tragic tsunami on the Indonesian island of Sulawesi provides a new insight on its possible cause..

Simon Haslett with his co-author Dr Ted Bryant

A Professor of Physical Geography, and Pro Vice-Chancellor at the University of Wales and the University of Wales Trinity Saint David, in 2003, he published, with his Australian co-author and tsunami-expert Dr Ted Bryant, the theory that the 1607 flood in the Bristol Channel was caused not by a storm but by a tsunami inundating the coasts of south Wales, Devon, Somerset, and Gloucestershire.

In south Wales, the Gwent Levels either side of Newport were particularly badly affected, as was Cardiff, and in Carmarthenshire, an entire village was swept away.

The flood occurred in the morning of 30th January 1607 and some contemporary accounts state that the weather was “fayre and brightly spred” and that “mighty hilles of water” sped across the coastal plains surrounding the Severn Estuary causing death and destruction to the inhabitants which, alongside other evidence, we suggested describes a tsunami rather than a storm.

Speaking about the documentary, Professor Haslett said:

"Ted and I filmed the Timewatch documentary in the summer of 2004 and, at the time, we were very careful to explain what a tsunami was and how one is triggered, as the word tsunami itself was not well-known back then. However, by the time the documentary was broadcast in April 2005, following the Boxing Day tsunami of 2004, the world was all too aware of what a tsunami is and the devastation one can cause.”

After the Boxing Day tsunami, governments around the world commissioned tsunami risk assessments and the DEFRA Report of 2005, which cited Professor Haslett and Dr Bryant’s research, concluded that southwest Britain is the most likely part of the UK to experience a tsunami. Since then, unfortunately, the terrible Japanese tsunami of 2011 and the smaller Solomon Islands tsunami of 2013 have reinforced the risk posed by tsunami to coastal inhabitants worldwide.

Since they made Killer Wave of 1607, Profesor Haslett and Dr Bryant have gone on to publish in scientific journals further evidence that they collected from their fieldwork around the Bristol Chanel:

"Reading the clues left in the landscape, our field evidence suggests the wave exceeded 6m (18ft) high in the inner Severn Estuary and in places penetrated several kilometres inland.

"Also, although there is no certain record for an earthquake being felt that day, the period seems to have been relatively seismically active, with two earthquakes being felt in the Bristol Channel region in the weeks and months following the flood. One of the earthquakes was strong enough to cause the water in a lake in Devon to slosh back and forth; a phenomenon known as seiching.

"However, an earthquake may not necessarily be the direct cause of a tsunami in the Bristol Channel, but that a tremor may be enough to trigger an undersea landslide off the continental shelf that might then be capable of creating a tsunami.”

"One of the main criticisms of our research when it was broadcast, in the wake of the widespread impacts of the 2004 Indian Ocean tsunami, was why would a theorised tsunami in 1607 only affect the coasts of the Bristol Channel? The Sulawesi tsunami in Indonesia that occurred on 28th September 2018 now gives us some clues as to why that might be possible.”

"The Sulawesi tsunami was generated by a powerful 7.5 magnitude earthquake on the seafloor, but this earthquake resulted in the sea-bed moving sideways and not vertically as is usually needed to generate a tsunami. Indeed, the Indonesian authorities issued a tsunami warning but then cancelled it around half-an-hour later!”

"Nevertheless, tsunami waves over 2m high crashed into the coastal town of Palu leading to over 4000 fatalities. The reason for the unexpected high tsunami waves at Palu is now considered to be due to the fact that the town lies at the end of narrow bay which amplified the tsunami wave as it travelled up it. This is exactly the explanation that Ted and I presented in connection with the 1607 flood in the funnel-shaped Bristol Channel, so this recent event in Indonesia may give us clues to the historic event in south Wales.”

As their research widened, it became clear that the British Isles has experienced a number of tsunami throughout history, which led to their second Timewatch documentary Britain’s Forgotten Floods broadcast in 2008.

Now in 2019, their research continues to offer the reminder that tsunami, although very rare occurrences in the UK, do occur over time and very occasionally cause devastation and loss of life.

The Killer Wave of 1607 is to be shown again on BBC Four at 11.10pm on Tuesday 14th May 2019.

Copy of a simply black-and-white illustration from a 1607 account of the great floods. People climb trees to stay above the water; a church spire and roof sticks out above the flood; a baby floats past in a crib.

Further Information

Rebecca Davies

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