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A tsunami-like phenomenon in St Paul's Bay
18th June 2019
The sea level changes observed last Tuesday early morning at St. Paul’s bay could
have appeared like a mini tsunami, but in reality have no relation at all to seismic
activity. Such sea level fluctuations occur as a series of lows and highs repeating
cycles every few minutes. The water retreated and uncovered the seabed underneath
the boats. It returned back and rose higher than the adjacent side quay. Theses
dramatic sea level changes occurred over a matter of a few minutes, appearing much
like a tsunami. They are a most remarkable feature in the sea level signals observed
in the Maltese Islands occurring as an expression of a coastal seiche, known by local
fishermen as the ‘milgħuba’ (from the verb in Maltese ‘lagħab’, as a connotation to
the play of the anomalous sea level movement). This phenomenon is triggered from
the atmosphere and is commonly referred by scientists as a meteo-tsunami.
In the early hours of the day a train of atmospheric gravity waves hit the Maltese
Islands from the East; their impact on the sea is like a big sea hammer hitting
repeatedly the sea surface and producing long period waves in the open sea areas.
When these waves reach the coast they cause the water bodies in embayments like
St. Paul’s Bay to resonate, leading to amplified sea level excursions closer to
Real-time monitoring stations forming part of the national observing system run
by the Physical Oceanography Research Group at the Dept. of Geosciences of the
University of Malta have captured this phenomenon. The atmospheric waves were
particularly coherent and intense, starting at around 2:30 am local time, and
protruding for a stretch of around three hours.
Sea level measured in PortoMaso showed a slight seiching response, but the
rubberstamp inside the embayments is definitely much more amplified. The same
phenomenon must have also occurred in the sister embayment inside Mellieha Bay
which is known to oscillate in antiphase with St. Paul’s Bay as two connected
Sea level excursions in Mellieha Bay exceeding 1m have been measured in the past.
Owners are advised to avoid leaving vehicles on the quay in St. Paul’s Bay...
the oscillating water was repeatedly brimming over the quay. Just a few
centimeters higher and the high sea level could have well penetrated the vehicles.