Meteotsunamis – the ticking time bombs

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METEOTSUNAMI SITE: St Michael’s Mount is seen during the incoming tide. Note the causeway.

WE all know about tsunamis by earthquakes or other seismic activities. Their destructive capabilities were well documented in the devastation of Banda Aceh, Sumatera, Indonesia, on Dec 26, 2004. In Japanese, tsunami means a big wave in a harbour.

On a recent visit to my birthplace in West Cornwall in the UK, I learned of a strange happening that occurred there on June 27, 2011. Mount’s Bay is an iconic landmark and St Michael’s Mount is a pilgrimage place to visit for all tourists to Cornwall. This island is connected to the village of Marazion by a causeway, which at low tide allows people to walk to the island of St Michael’s Mount. The folklore of the island’s origin is not dissimilar to that of Mount Santubong.

It was whilst walking along that causeway in 2011 that pilgrims were suddenly drenched up to their knees in seawater. Just prior to this event, the water on the beaches each side of the causeway suddenly ebbed before a wave of water, out of the blue, hit them. Local people spoke of their hair standing on end and that they had been hit by a tsunami. There were no reported incidents of earthquakes or seismic activity in the area or beyond; yet other places along this 300km stretch of Cornish coastline reported similar incidents. Mount’s Bay in West Cornwall is similar in water depth, sea bed structure and in coastal plain shape to Damai Bay between Tanjung Sipang and Tanjung Po – both bays between two peninsulas.

With research, I discovered that the incident in West Cornwall coincided with a series of violent thunderstorms offshore in which updraughts of air can reach 120km per hour (kph) to be replaced by downdraughts of 50kph. The power of an ordinary thunderstorm, 1km wide, is equivalent in energy to 10 Hiroshima-type atom bombs.

This event was created by atmospheric disturbances that produced pressure-generated ocean waves, which became amplified as the seawater reached shallower depths nearer to the coastline, thus creating a meteotsunami. Reports of similar incidents have been recorded in Japan and China, along the Yellow Sea coastline. Meteotsunamis are infrequent and very local in nature, unlike seismic tsunamis with their global destruction forces.

There are many recorded instances in Japan and in the Mediterranean Sea of boats, moored in harbours, that were ripped away from their ropes and found themselves high and dry on the seabed as the water receded, only to be hit by the surge of water as the meteotsunami visited the harbours a few minutes later. Needless to say much damage was done.

It is conceivable that worldwide reports of small-scale tsunamis are not the result of earthquakes but due principally to sudden jumps in atmospheric pressure as occasioned by squalls and the passage of weather fronts. Anticyclonic (high pressure) conditions cause a lowering of sea level which can see the drainage of water off beaches in shallow water areas. Decreasing atmospheric pressure in the passage of a cyclone, sea level rises, combined with high speed onshore winds can produce an inundation in coastal areas.

The shape of a bay or coastal inlet together with seabed topography will affect the force and height of a meteotsunami wave. Some 99 per cent of the energy of such a tsunami is related to wind speeds and atmospheric pressure. Thus downdrafts from thunderstorms pump continuous energy into the sea which in turn, absorbing the atmospheric energy, leads to an increase in wave height as the waves enter shallower water in bays. Here, in Borneo, as has been found in Japan and China, the likely occurrences of meteotsunamis will be related to the general monsoon patterns, with largely northeasterly winds from November to April and southwesterly winds from May to October.

Unlike earthquake-generated tsunamis, meteotsunamis are unlikely to cause loss of life unless young children were playing in the sea when the tide suddenly ebbs leaving them on bare sand for a couple of minutes before a larger than normal wave hits the beach. Boat owners with vessels moored to harbour walls or piers be aware. Whilst evidence of such meteorological events has been recorded worldwide for many years, it is only relatively recently that meteotsunamis have been researched. It is a consolation to know that major meteotsunami events are exceptional in occurrence and, to date, have only been observed at a limited number of locations in the world’s seas. But, be warned if the sea suddenly ebbs and your hair stands on end through static electricity when there is an approaching thunderstorm, suspect that meteotsunamis have occurred along the coastlines.

Can anyone can recall such an event in Sarawak or Sabah?

DRY PATH: Visitors cross the causeway during low tide.