In 1775, a massive tsunami created by the Great Lisbon tremor killed more than 10,000 people in Spain, Portugal and Morocco.
Now a major fault line in The Gulf of Cadiz – a magnet for British tourists and expats – is threatening to trigger a massive tremor that could unleash carnage on an even bigger scale.
Experts told Daily Star Online the massive shaker could send a barrage of 15-metre high tidal waves hurtling towards Spain, Portugal and Morocco – with coastal areas in the firing line.
Tens of thousands of lives could be at risk along their Atlantic coastlines, with waves of up to three meters expected to slam into southwest Britain.
A recent documentary claimed a tsunami of that magnitude could travel 20 miles inland – decimating a number of Spanish, Portuguese and Moroccan towns and cities.
Luis Matias, seismologist at the Dom Luiz Institute in Portugal, told Daily Star Online it’s a matter of figuring out when, not if, a devastating earthquake will strike.
He said: “In this region, we can only rely on the long‐term earthquake prediction.
“Geology and geophysics provide us with evidence on the average rate for large earthquakes in the area.
“Earth scientists were also able to identify several large faults in the area, each one able to generate a large earthquake and tsunami.
“The fact that the last one occurred in 1755 and that it takes more than 1000 years for that fault to reload again is not reassuring, because any other of the identified structures can be on the verge of rupturing generating a destructive earthquake and tsunami.”
The Gulf of Cadiz sits on a major tectonic boundary, the Azores-Gibraltar fault.
This means the region is vulnerable to earthquakes at sea, meaning huge tsunamis could be triggered at any time.
If La Gran Ola, or “The Great Wave”, were to hit, the Algarve and the western Atlantic coast from Cape. S Vicente to Nazaré in Portugal would be worst affected, according to Matias.
Meanwhile in Spain, the coastal regions of Huelva and Cadiz on the southwest Atlantic coast would be wiped out, he said.
Matias said the “worst case scenario” would be if the tsunami hit at the peak of summer – when millions of tourists are relaxing on beaches.
Thousands of terrified tourists would be forced to flee for their lives as 15-meter high waves came crashing towards to coastlines.
He said: “The tsunami risk is a seasonal risk, much like the fire risk, due to the large number of people exposed during the high season.
“The worst‐case scenario is a tsunami hitting on the summer, at 3pm, when the beaches are crowded with people.”
Speaking to Daily Star Online, Simon Day, of the Institute for Risk and Disaster Reduction at University College London, agreed that a repeat of the 1775 earthquake would have disastrous consequences.
He believes the frequency of giant offshore earthquakes in the region is “ambiguous” and therefore still up for debate.
Yet, should a 1775 magnitude strike again, he said Britain would not be immune to the threat and evacuations could be possible.
He said: “In 1775, anomalous waves and currents, and localised flooding were reported from Devon and Cornwall; quays were flooded and some arches beside the quays were damaged in Galway city in Ireland.
“Dry docks in Portsmouth harbour were affected water sloshing back and forth.