The high level of seawater that flooded Msida’s main square on Thursday was not caused by the tide but is a phenomenon described by experts as an “atmospheric tsunami”.

Technically known as seiche, or milgħuba in Maltese, the phenomenon is not uncommon and could take place both in good or bad weather, according to Aldo Drago, head of the University’s physical oceanography unit. A large volume of seawater flooded the Msida parking area near the Workers’ Monument in a matter of minutes at about 4pm on Thursday.

Readers from Birżebbuġa and Marsascala also sent in their photos and eyewitness accounts of the same phenomenon happening in their areas.

Prof. Drago said the seiche was caused by atmospheric gravity waves.

“It’s not related to bad weather but to very specific atmospheric conditions and even when these are in place, it’s not a given that it will happen,” he explained.

If the conditions are ideal, the open sea will oscillate, creating special signals known as long period waves that are very similar to a tsunami wave, according to Prof. Drago.

But seiche waves are much smaller and tsunami waves are caused by tectonic activity, such as an earthquake.

Seiche waves are caused by a fluctuation of atmospheric pressure that makes open sea waves resonate with those of the bay.

“It happens when the energy in the open sea matches the signal in bays and enhances the waves.

“The water retreats and floods successively for several times, exposing the seabed,” Prof. Drago said.

Like other Mediterranean countries, the tide in Malta is very low. Trieste in Italy is the only exception where the tide is high.

Prof. Drago said the seiche was enhanced when it coincided with the high tide but insisted that both were completely different.

Msida’s main square flooded on Thursday. Photo: Matthew Mirabelli