Environment: ‘The likelihood of a tsunami happening in Britain’…

EXPERT EVIDENCE

From the desk of MD

IT WAS BOXING DAY, 26 December 2004: 30-metre-high waves; more than a quarter of a million people dead. Tsunamis are amongst the most destructive forces known to mankind: they can arrive without warning devastating entire regions. Until 2004, most of us in Britain probably didn’t know what a tsunami was – and it is likely that people still think we need concern ourselves little with these freak events.

This view, however, has been challenged by professors Simon Haslett, of the University of Wales, Newport, and Ted Bryant, from Woollongong University in Australia. They believe they have uncovered a catalogue of great British floods over the past 1,000 years that could only have been caused by tsunamis – a catalogue they say that should make us reconsider how vulnerable our shores really are to these “killer waves”.

If correct, their discovery would have major implications for the safety of coastal communities in the UK: we don’t have a tsunami warning system for our coastline and we barely even recognise that tsunamis might pose a threat. Haslett and Bryant want that perception to change, hence their desire to go public with their research. For example, the public did get a chance to assess the risk when the professors laid out their ideas in Britain’s Forgotten Floods, a BBC2 Timewatch documentary, screened in October and presented by Vanessa Collingridge.

Controversially, their theory builds on research six years ago that looked again at the historic British Channel Flood. In 1607, a wall of water swept up the channel, destroying everything in its path and claiming thousands of lives. Until recently, this had always been explained as a massive storm surge – water forced towards the shore by the winds swirling around an area of low pressure. When these combine with high tides, the resulting water level can be raised by three metres or more – enough to cause severe coastal flooding.

However, the professors claim that contemporary reports and physical evidence from the period back up their view that the flood was caused not by a massive storm surge but by a British tsunami. They now say, too, that they have found more examples of tsunamis affecting our coastline.

We already know that Britain can be affected by tsunamis: one hit our shores in 1755, when a massive earthquake reduced Lisbon in Portugal to smoke and rubble. The quake sent a wave charging across the Atlantic and into the English Channel, travelling as fast as a modern aeroplane and hurling giant slabs of rock from the sea bed far up the beach at Lamorna Cove in Cornwall. But the professors say that wasn’t a unique event; in fact, they claim we have experienced an array of tsunamis, and, for the past 300 years, they have struck once every century.

Their argument rests on four key floods, stretching back more than a millennium. Their earliest evidence comes from a flood in Mounts Bay in Cornwall, which was devastated by the sea in 1014. With only scant detail in the written record (William of Malmesbury mentions “overwhelming waves”), the professors had to rely on soil samples, coring deep down through the layers of peat and sand on Marizion Marsh, a little inland.

Using techniques such as radio carbon dating, Haslett and Bryant analysed the cores of earth, looking for micro-fossils from organisms usually only found far out to sea. These, plus a deep layer of sand carried inland from the coast, shore up their case for a medieval tsunami, which they believe was caused by a comet plunging into the North Atlantic, sending out giant waves that hit Britain from Cumbria to Cornwall, causing widespread flooding along the west coast.

Certainly, there are records of floods along the coast from that time, but other experts contend that the evidence does not stack up. Any comet, they argue, would have left a giant crater 20 to 30 times the diameter of the comet – and there just isn’t the evidence on the ocean floor to support the theory put forward by professors Haslett and Bryant.

However, Haslett and Bryant have three other tsunamis in their armoury: in 1580, an earthquake with a magnitude of 5.8 hit Kent. Contemporary accounts talk of ships grounding on the sea floor and widespread panic on both sides of the Channel. Whilst most academics put this down to a normal process called “seiching”, Haslett and Bryant argue the waves and flooding were due to a tsunami, triggered by the earthquake causing an undersea landslide.

In 1884, they claim the “Great British Earthquake”, with its epicentre in Essex, triggered a giant wave that swamped Mersea Island and surrounding areas, leaving a signature layer of sand in the soil profile. Again, the sand layer dates from this time, but Professor Bill McGuire, from University College London, claims that this is far more likely to be the result of the water sloshing on shore as the Earth’s crust deformed with the shock of the quake.

Most surreal of all, however, is the so-called “meteo-tsunami” that hit the south coast of Britain on 20 July, 1929. On an otherwise peaceful summer’s day, a squall line moved up the Channel at 40mph – taking with it what newspapers described as a “tidal wave”. In a fatal storm that lasted barely three minutes, a 16-year old boy fishing in Folkestone was carried off by a four-metre wave. At the same time, just off the beach in Hastings, a woman in a small boat was hit by a wave more than six metres high. Neither of them survived.

Meteo-tsunamis are caused by sharp differences in pressure creating the giant waves. An onlooker wouldn’t know if they were caused by a squall or an earthquake: the end result is just as terrifying. But while these tsunami-like waves are hugely powerful and can cause serious flooding, they are relatively short-lived. Whether they can really be deemed as tsunamis is a matter of debate.

Whether or not we go along with the research produced by Haslett and Bryant, until we get a tsunami alert system in place, it seems wise in paying heed to their warning.

 

 

 

© Mark Dowe 2008: all rights protected

mark.dowe@googlemail.com

The writer is a management accountant by profession, also holding an M.Sc in Geography and campaigns on behalf of WWF (Scotland).

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