Tsunamis: revealing the abyss of the deep

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WITH the thousands killed in last week’s tsunami in Japan and in southeast Asia in 2004, it should surprise no one to learn that since 1945, more people have died from tsunamis than earthquakes. 

The ancient city of Salamis in Cyprus was destroyed by a violent earthquake and tsunamis in 76AD  [Credit: Cyprus Mail]

And while most tsunamis form along the 40,000 kilometre Ring of Fire in the Pacific Ocean, which displays intense seismic and volcanic activity, the Mediterranean region with its own seismic movement is by no means immune. 

Of course the size of Mediterranean tsunamis is not the same as those in the Pacific and Indian Oceans because of differences in the morphology of the seabed and the intensity of the quakes. Due to the shorter distances in the Mediterranean, tsunamis hit the coasts much faster despite travelling at lower speeds because the sea is not that deep. 

The first recorded tsunami in the Mediterranean took place in the region of Syria in 2000BC, while the oldest in Greece is the one that destroyed the Persian fleet in Potidea, Chalkidiki, in 479BC. 

Another significant tsunami was the one that hit Alexandria in July 365AD, killing 50,000 people. 

It was caused by an 8.2 magnitude earthquake and was described by historian Ammianus Marcellinus: 

“The waters pulled away so that in the abyss of the deep thus revealed, men saw many kinds of sea-creatures stuck fast in the slime; and vast mountains and deep valleys, which Nature, the creator had hidden in the unplumbed depths … first saw the beams of the sun. Many people thinking the worst might be over ventured into the shallow waters to gather stranded fish.” 

But the sea returned. 

“The roaring sea, resenting, as it were, this forced retreat, rose its turn … dashed mightily upon islands and broad stretches of the mainland, and levelled innumerable buildings … the great mass of waters, returning when it was least expected, killed many thousands of men by drowning,” Mercellinus wrote. 

Another large tsunami that hit the Mediterranean had been formed by the collapse of the caldera in Santorini after the volcano erupted in 1600BC. This tsunami is considered the cause of the destruction of the Minoan civilisation since it struck the northern coast of Crete. 

The last large tsunami that struck in the Aegean Sea was created by the Santorini quake in 1956 when the wave that reached the east side of Amorgos was estimated to be some 25-metres tall. The most recent is the one that followed the Turkey earthquake in August 1999 with the seismic wave affecting the coastal areas of Marmara. 

Cyprus is located in the second most seismic zone on our planet, which records some 15 per cent of the earthquake activity worldwide. The zone extends from the Atlantic Ocean to the Pacific Ocean through Italy, Greece, Turkey, Iran and India. 

Almost all cities and many settlements in Cyprus have been destroyed in the past by strong temblors. According to historical data, Cyprus was hit by 16 destructive earthquakes between 26BC and 1896, when instruments to record seismic activity were introduced. 

The most destructive quakes happened in 15BC when Paphos was levelled, and 76AD when Salamina, Kitium and Paphos were destroyed. The latter is considered the strongest quake to ever hit the island. 

Salamina and Paphos were destroyed again in 332AD and 342AD respectively. 

Since 1896AD, 400 temblors have been recorded in various areas in Cyprus with 14 causing damage. 

Most of the quakes in the greater area around Cyprus are undersea and could create tsunamis, and there exist historical accounts and convincing geological signs that the Cypriot coasts have been struck by such waves in the past. 

Ogerius Panis and Marchisius Scriba describe one such tsunami that struck Cyprus in 1222AD. 

“… the sea rose from the quake and dashed to the shore; huge volumes of seawater, large as mountains, flooded the coast, demolishing buildings and filling the villages with fish. Paphos, they say, suffered the most … the harbour dried and the city was flooded by the sea; the city and the castle were destroyed and the residents disappeared …” 

Apart from the accounts, there are also many strong geological indications regarding tsunamis that struck the island. 

When they hit the coasts, tsunamis carry with them material from the seabed like sand, shells, microscopic ostracea, seaweed etc, which are dumped in the areas they flood. 

The nature of these materials, the way they are deposited, mixed and distributed can lead to conclusions regarding their origin. 

Along the southwest coast of Paphos — starting north of the city and extending at a 40-kilometre distance to the south of the Akamas peninsula – there are deposits of boulders with sand and gravel, which do not fit in with the geological environment of the coastline. 

The boulders are found either individually or in groups five to 10 metres above sea level and weigh several tonnes. 

They have angular edges and relatively fresh signs of detachment that lead to the conclusion they were deposited at the site relatively recently. 

The areas between the boulders and the coastline are stripped of sediment. They have a rough surface and display the characteristic signs of erosion. Only the huge thrusting force of tsunami could have carried the huge boulders and deposit them on the coast at a time when no human means could do that. 

Similar deposits, possibly from a tsunami, can also be found in other areas of Cyprus like Cape Kormakitis, Karpasia, Cape Greco, Cape Pyla and elsewhere. 

There is no doubt strong earthquakes will hit the area in the future and that is why informing and preparing the public properly is imperative. 

The financial and social effects of a destructive earthquake will be such that it will cause dramatic changes to the lives of everyone affected. 

Tsunami risks should be assessed through a detailed study of the geological and historical evidence and data to determine the frequency and intensity with which the waves struck Cyprus, as well as their correlation with earthquakes and particular quake-prone areas. 

Public education is of special importance and those living on coastal areas should be instructed to head inland the minute an earthquake strikes. 

Putting in place tsunami warning systems through the installation of seismograph networks and tide measuring systems would be a useful tool for experts and the authorities. 

Source: Cyprus Mail [March 20, 2011]

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