Did a tsunami crash on the Welsh coast over 400 years ago?

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In what is almost certainly Britain’s biggest natural disaster, more than 400 years ago, around 2,000 people were killed when a huge wave crashed into the Bristol Channel, drowning miles from South Wales.

But 412 years later, questions remain as to whether the Welsh coast was hit by an abnormal tsunami or by a powerful storm surge aided by inadequate flood defenses.

Either way, the overwhelming force that caused devastating destruction around the coastline swept away buildings, destroyed hundreds of livestock and even killed thousands.

Read more: Areas of Wales that would be underwater and lost by 2050 based on current climate trends

On January 30, 1607, around noon, the coasts of the Bristol Channel suffered unexpected floods which broke the coastal defenses in several places.

Low areas of Devon, Somerset, Gloucestershire and Wales have been inundated. The devastation was particularly severe on the Welsh side, stretching from Laugharne in Carmarthenshire above Chepstow in Monmouthshire.

Cardiff was particularly affected, with the destruction of the foundations of St Mary’s Church. Sainte-Marie Church was located at the southern end of what is now rue Sainte-Marie, from 1107 to 1620. After flood damage, it was abandoned in 1701 and later replaced at another location in 1843.




For centuries, those who survived called it an act of God, before modern scientific research began to determine whether it was Britain’s first recorded tsunami.

For a tsunami to occur, an earthquake must occur below the seabed. In the devastating Asian tsunami on Boxing Day 2004, an area of ​​1,200 km of the Indian tectonic plate was pushed up to 20 meters below the Burmese plate, raising the seabed several meters.

The energy released was the equivalent of 23,000 atomic bombs the size of Hiroshima, and on the coast of Sumatra, near the epicenter, waves could reach 10 meters high.

By comparison, contemporary accounts suggest that the damage caused by the Great Flood of 1607 was limited to Britain. But if it was a tsunami, places like Brittany, Spain, Portugal and western Ireland should have been affected as well, says author Mike Hall who revisited the disaster in this book The Severn Tsunami? The story of Britain’s biggest natural disaster.

Was it really a tsunami that swept across the Welsh coast?

Although the evidence is inconclusive, Hall believes the 1607 event was “probably” a storm surge rather than a tsunami.

Speaking to WalesOnline in 2013, the retired geography professor said: “There is no contemporary account to suggest that such a thing happened (beyond Britain).

“There are opinions that say it was basically a storm surge up the Bristol Channel, with the winds and tides combining in a way that is within the natural range of what could happen. .

“At first, the tsunami theory seemed very, very compelling, but there are things it doesn’t seem to explain.”

But Mr Hall, of Redwick, Monmouthshire, admits that the evidence that continues to support those who believe it was a tsunami comes from 17th century chronicles and other written sources that speak of a ‘day bright, sunny and cloudless “. Conditions very far removed from those one would associate with a storm.

Sooner or later the mix of high tides and severe storms traditionally blamed for flooding will recur – on average, they occur once every 500 to 1,000 years.

What if a 25-foot wall of water traveling at 30 mph were to strike again, would the consequences be just as devastating?



Around 2,000 people are believed to have drowned in what is arguably Britain’s biggest natural disaster

Mr Hall says the consequences would be “catastrophic” – but not on the scale of 1607.

He believes that the devastation was then, in part, linked to the weakening of the country’s maritime defenses following the dissolution of the monasteries by Henry VIII.

Historically, sea defenses were maintained by churches.

He added: “The dikes are maintained (now) and they are constantly monitored and trying to adjust them to allow for an expected rise in sea level.”

A 2002 research paper, following investigations by Professor Simon Haslett of the University of Bath Spa and Australian geologist Ted Bryant of the University of Wollongong, suggested that the flooding may have been caused by a tsunami, after the authors read eyewitness accounts in historical reports. which describes the flood.

The British Geological Survey has suggested that, as there is no evidence of a landslide off the continental shelf, a tsunami would most likely have been caused by an earthquake on a known unstable fault off the coast. southwest of Ireland, causing the seabed to move vertically.

However, due to the lack of evidence showing how the event impacted West Wales, Cornwall or southern Ireland – all of which were said to have been affected by a tsunami – it is widely believed that the mysterious flood was indeed caused by a storm surge.

What is a storm surge?

According to the Met Office, a storm surge is a change in sea level caused by a storm.

The main cause of a storm surge is the strong winds that push seawater towards the coast, causing it to accumulate there. The strong winds of the storm generate large waves above the tide which can damage the defenses against the sea or spread over them, increasing the risk of flooding. In the case of tropical storms (like hurricanes), there can also be a very large amount of rain which further increases the risk of flooding.

A recent example of a storm surge was in 1953 when a storm in the North Sea caused a storm surge that occurred at the same time as a large spring tide.

Although the storm and the tide were predicted in advance, the public warning systems were not very effective at the time and many people were not prepared for the flood. Over 2,500 people have been killed along the North Sea coast, including 307 in England and 19 in Scotland. In addition to the loss of life, the floods caused extensive damage to homes and businesses and destroyed large areas of farmland.

Following the storm surge of 1953, the British government invested significantly more in improving sea defenses, such as the Thames Barrier, and in effective warning systems.

What would be the impact if a similar surge occurred today?

In 2007, on the 400th anniversary of the Great Flood, Risk Management Solutions published a report suggesting that a similar event would now cause between £ 7 billion and £ 13 billion in damage.

Professor Simon Haslett, of the University of Wales, said 80% of those losses would occur in Bristol, Cardiff and Gloucester.

He believes the damage was caused by a tsunami, rather than high tides and severe storms.

The professor of physical geography said that descriptions in 17th-century brochures of “huge and mighty water hills” are more like a tsunami.

He maintains that there is evidence that the salt marshes were torn from the Severn Estuary in the early 17th century and that only a tsunami would have the power to erode the coastline in this way.

However, if climate trends continue as they are, it looks like it won’t take a tsunami to wipe out parts of Wales. A detailed map showing areas of Wales that would be underwater and lost by 2050 can be found here.



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In North Wales, experts say it could cut the A55, sweep away railways and swamp resorts by the end of this century. In the south, coastal areas and river valleys would be severely affected with the M4 submerged near the M4 Severn Bridge.

Large areas of Cardiff, Newport, Barry and Swansea would be left underwater. Almost all of the flat and low land between Cardiff and Newport and east of Newport would be under water.

Climate Central, a nonprofit news organization focused on climate science, has revealed the severity of this threat and produced a searchable map that you can adjust based on expected sea level rise.

According to the organization, coastal areas are expected to drop below sea level steadily over the next 30 years.

In 2019, a study predicted that the sea level would rise from 30 cm to 34 cm by 2050. However, so far, sea level rise has been much lower. After 2,000 years of little change, according to the US Environmental Protection Agency, sea level began to rise throughout the 20th century.

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