Experts probe 'mini tsunami'

[ianvr]

Cape Town - A mini tsunami may be the reason for the sudden rise and fall of the sea level along the West Coast over the last few days.

The National Sea Rescue Institute (NSRI) received reports that the sea level in Hout Bay, St Helena Bay, Saldanha Bay and Lambert's Bay changed suddenly three times on Thursday.

In Hout Bay, the water level first fell by a metre and then rose again by the same amount in the space of 20 minutes.

Factories were damaged by the high waves in St Helena Bay.

The NSRI called in the help of Geoff Brundrit, a retired professor of the University of Cape Town's Oceanography Department, to help investigate the phenomenon.

Seismic activity

Brundrit said the readings of a hydrographic monitor in Walvis Bay indicated seismic activity in the Atlantic Ocean, which could cause a tsunami.

Volunteers at the NSRI office in Mykonos also reported a phenomenon known as Proxigean Tide, which can lead to flooding.

Experts expect the next tide of this nature on December 12.

NSRI spokesperson Craig Lambinon said they were waiting to receive the readings on the hydrographic monitors in Luderitz, Port Nolloth and Saldanha Bay to see whether those monitors gave similar results to the Walvis Bay and Simon's Town hydrographic monitors.

"We are also waiting to hear from Ascension Island, St Helena Island and Rio de Janeiro to find out whether they have experienced similar circumstances.

"No one has been injured or killed. We have not been informed of any major damage but we believe that what was experienced on the West Coast on Thursday was a mini tsunami," Lambinon said.

Southern, Eastern Cape affected

There is also a possibility that the mini tsunami could affect beaches in the Southern and Eastern Cape, Tisha Steyn reported.

"There was abnormal movement in the water on Saturday," Ray Farnham said on Sunday.

"If you don't specifically look at it, you won't see it. There was a warning that the water level would be different to that given in the tide table, but it's nothing serious."

For example, if it was supposed to be low tide at 12:00, it was low tide but there were fluctuations.

"There were also larger swells, as if a large ship was travelling past, but we were unable to determine what caused it.

"No damage occurred."

The heads of the NSRI stations in Witsand, Stillbaai, Mossel Bay and Wilderness did not notice anything unusual.

 

[Laura]

Weird. Wonder if there was a landslide under water somewhere in the Atlantic?

 

[Erna]

Mmmm, interesting.

The onslaught from the sea in KwaZulu Natal in March 2007 was also hectic. Here's some gallery shots of that damage.

http://blog.ecr.co.za/newswatch/?m=200703

When we were there end of last year there were still trucks driving out sand to fill up the beaches again. That one was caused by the alignment of the moon, sun and earth. It's a relatively unknown fact that the most dangerous seas are around South Africa, because of freak waves, of which 80% occur around the SA coast, because of the warm Agulhas current coming down on the Eastern side of Africa and colliding with the cold Benguela current from the Atlantic ocean. Most people think that the seas around Cape point are the most dangerous, hence the name "Cape of Storms", but the most dangerous stretch of sea is on the Eastern coast from St. Lucia all the way down to Mosselbay. Sailors wait for 3 days of good weather before they attempt that stretch.

The ocean is full of mysteries. When I did my sailing course in Durban end of last year, they started the course with lots of fear mongering. On the one video they showed us about freak waves, a survivor said he was standing on deck looking at the moon on the water, when something came between him and the moon. It was a freak wave. Scientists are still not in agreement about what exactly causes freak waves.

The guy who owned the Sailing School, who has been training sailors for 27 years, told us that one of the best kept maritime secrets of our time is that a vessel disappears off radar around the world, never to be seen again, at a rate of about once a day. Don't know about that one though...

Another big wave filmed by someone in April 2007:

http://www.metacafe.com/watch/529018/50m_tsunami_wave_frightens_villagers_off_south_africa_coast_apri/

 

[Pierre]

Mmmm, interesting.

The onslaught from the sea in KwaZulu Natal in March 2007 was also hectic. Here's some gallery shots of that damage.

http://blog.ecr.co.za/newswatch/?m=200703

When we were there end of last year there were still trucks driving out sand to fill up the beaches again. That one was caused by the alignment of the moon, sun and earth. It's a relatively unknown fact that the most dangerous seas are around South Africa, because of freak waves, of which 80% occur around the SA coast, because of the warm Agulhas current coming down on the Eastern side of Africa and colliding with the cold Benguela current from the Atlantic ocean. Most people think that the seas around Cape point are the most dangerous, hence the name "Cape of Storms", but the most dangerous stretch of sea is on the Eastern coast from St. Lucia all the way down to Mosselbay. Sailors wait for 3 days of good weather before they attempt that stretch.

The ocean is full of mysteries. When I did my sailing course in Durban end of last year, they started the course with lots of fear mongering. On the one video they showed us about freak waves, a survivor said he was standing on deck looking at the moon on the water, when something came between him and the moon. It was a freak wave. Scientists are still not in agreement about what exactly causes freak waves.

The guy who owned the Sailing School, who has been training sailors for 27 years, told us that one of the best kept maritime secrets of our time is that a vessel disappears off radar around the world, never to be seen again, at a rate of about once a day. Don't know about that one though...

Another big wave filmed by someone in April 2007:

http://www.metacafe.com/watch/529018/50m_tsunami_wave_frightens_villagers_off_south_africa_coast_apri/

Freak waves and tsunami waves are not exactly the same. They have different origins and different shapes.

Freak waves usually come from an accumulation of waves, a "resonance" dynamics leads those kind of waves.

The eastern coast of South Africa is indeed notorious for those kind of waves because there are strong currents with different temperatures and direction mixing and also because the dominant wind direction is usually opposite to the main current direction.

Those freak waves can reach 30 meters and now the ESR2 satellites allows to see and measure such phenomena.

But then tsunami waves are usually triggered by underwater phenomena like landslides, earthquakes or volcanic eruptions, their shape is quite different from freak waves. Usually tsunami waves are not very high but they are quite long and voluminous, they generate long lasting sea level changes, like the tsunami wave that hit Indonesia in 2004

 

[Erna]

and also because the dominant wind direction is usually opposite to the main current direction.

Oh yeh, of course, I think that's the largest contributor to this phenomenon.