ADH        This restless world     posted on Sunday 19 February 2006

If you find this essay interesting, you may care to look at its partner ABC written earlier.  Just click on the link to go to that essay.  This one has taken its data from a New Scientist article dated 22 October 2005 issue number 2522.

On the evening of 31 October 1755 Lisbon was hit by a devastating earthquake.  This same quake demolished a mosque in Rabat in Morocco that the king aimed to be the highest in the world.  Whether the Creator wanted to put the monarch in his place or, if you believe as I do, that nature was just 'doing its thing', the effects were truly enormous.  That quake is reckoned to be the most devastating one in the history of Europe. Seismographs had not then been invented then, but from the impact it is now reckoned that the disturbance would have been Magnitude 8.7 on the Richter Scale.  That is about 30 time the intensity of the 1906 San Francisco quake.  Northern Italy, Switzerland and Finland, as well as Morocco felt the quake.

But the centre was not below Lisbon itself, but was at the  Ocean Gorringe Bank a a few  hundred kilometres out into the Atlantic.  The jolt triggered a huge seafloor avalanche and this seabed disturbance generated a series of tsunamis.  Within an hour three waves estimated to have been thirteen metres high surged up the River Tagus, burst through the sea wall and did enormous damage to the buildings that were still standing.  Many survivors of the earthquake were drowned by the torrent..  The death toll of the combined events is estimated to have been between 30 and 75 thousand people.  Not only Portugal, but southern Spain, Morocco, Madeira and the Azores suffered   Portugal is the best recorded city as it was at the hearty of the civilised world at that time.  Even the Caribbean recorded seven metre waves in the Lesser Antilles   There are no contemporary reports from the USA but models suggest that the east coast must have had waves of at least two metres high.  Tsunamis were reported in Newfoundland, Canada, France, Belgium, The Netherlands, Ireland , and the south coast of Wales and England.  A truly horrendous event.

The passing of the 250th anniversary  causes one to ponder "when is the next event?"  Before the anniversary of the Lisbon quake, the US National Oceanic  and Atmospheric Administration (NOAA) announced that they are setting up an Atlantic tsunami warning system similar to the one set up in the Pacific.  The system would consist of  five Deep-Ocean Assessment and Reporting Buoys (DARTs) to measure pressure changes.  Four of the buoys would be on the east coast of the US and one in mid-ocean.  Meanwhile the Canadian government has decided to buy a super-computer capable of modelling the threat to its coastline.  In Nigeria  scientists have called for the establishment of a tsunami early warning system.  The UK body Department of Environment Food and Rural Affairs (DEFRA) published a report that evaluated the threat to the UK.

The threat to the North Atlantic countries is much lower than to the states of the Pacific Rim, but that there is a threat is beyond any doubt.  The Lisbon example demonstrates the potential for a serious loss of life

There are a lot of other examples that demonstrate that nowhere on the globe is immune.  Melting ice caps due to global warming could cause a rebound of land as the enormous weight of the ice is released.  The mid-Atlantic Ridge that goes as far as Iceland is one of the tectonic plates' boundaries.  New Scientist prints a map of a large number of recent and not-so-recent events in the Atlantic basin

The 1755 earthquake had an intellectual impact in that it moved the subject from being considered to be Divine Retribution into a scientific study of the natural causes of such events.  But there is one piece of real estate that is certain to cause an enormous tsunami at some unspecified date in the future; it is the western flank of Cumbre Vieja, one of the Canary Islands.  The 500 cubic kilometres of rock is going to break off and plunge into the sea.  Two University of California workers estimate that if that piece of rock fell in one go, the water swell would bulge 900 metres high causing a wave of about seven to ten metres hitting the USA and Europe.  These waves are comparable with the waves that hit Asia on Boxing Day 2004.  It is suggested that local islands could be hit by waves up to 100 metres high.

If you found this topic interesting click on either of these links ABC and/or ABQ

Sleep tight!