The sea around Mallorca can change dramatically in a matter of minutes. On Monday, August 24, several coastal areas of the Spanish island were hit by a phenomenon known locally as a rissaga – a sudden oscillation of sea level that can make the water surge into harbors and waterfront streets, then retreat just as quickly.
The latest episode was reported in the ports of Alcúdia, Andratx and Sóller, as well as around Port Adriano. On neighboring Menorca, Spain’s national weather agency, AEMET, maintained an alert for possible sea-level oscillations of up to 1.2 meters at the port of Ciutadella.
Videos from Alcúdia showed seawater pushing into the waterfront, reaching areas around restaurants and the promenade. To anyone watching from shore, the movement can look remarkably similar to a small tsunami. But it isn’t a tsunami in the conventional sense.
A Tsunami Without an Earthquake
A rissaga is the Balearic Islands’ local name for what scientists call a meteotsunami – a tsunami-like wave generated by atmospheric disturbances rather than an earthquake beneath the ocean.
Unlike a conventional tsunami, which can be triggered by an undersea earthquake, landslide or volcanic eruption, a meteotsunami begins in the atmosphere.
Rapid changes in atmospheric pressure associated with weather systems can disturb the surface of the sea, generating a long wave that may initially be barely noticeable in the open water. Under the right conditions, however, the disturbance can become dramatically amplified as it approaches the coast.
Scientists have documented this process extensively in the Balearic Sea. Research led by scientists from Spain’s AEMET, the Balearic Islands University and other institutions has shown how traveling atmospheric pressure disturbances can interact with ocean waves and become amplified inside vulnerable bays and harbors.
The key is resonance. When the speed of an atmospheric disturbance is close to the speed at which the resulting ocean wave can travel, the two systems can reinforce one another. Once the wave reaches a harbor or inlet with the right shape and dimensions, another resonance effect can amplify the oscillation even further.
That is why a relatively subtle atmospheric disturbance can eventually produce a startling rise and fall in sea level.
Why the Balearic Islands Are So Vulnerable
The Balearic Islands are particularly well known for meteotsunamis because their geography provides several places where the phenomenon can be strongly amplified.
Ciutadella harbor on Menorca is perhaps the world’s most famous example. There, rissagas have occurred repeatedly, sometimes producing oscillations of less than a meter and sometimes generating much more destructive events.
A 2011 study of the Balearic Sea found that typical rissaga oscillations at Ciutadella are around 0.5 to 1 meter, with periods of roughly 10 minutes. Much larger events can occur, however, with exceptional episodes producing oscillations of several meters inside the harbor.
One of the most dramatic examples occurred on June 15, 2006. The event produced an estimated oscillation of around four meters in Ciutadella, according to eyewitness accounts and subsequent scientific studies. More than 35 boats sank and around 100 others were severely damaged.
The reason the effect can become so extreme has less to do with the size of the original wave than with what happens after it reaches the coast.
A bay or harbor can essentially act like a giant bathtub. If the incoming disturbance has the right timing and wavelength, the water can begin oscillating back and forth, with each movement reinforcing the next.
Why It Can Look So Sudden
One of the most unsettling characteristics of a rissaga is its speed. A harbor may appear perfectly normal, only for the water to begin retreating rapidly. Minutes later, the sea can rush back into the same area, flooding docks, promenades and waterfront businesses.
That apparent disappearance of the sea is one reason the phenomenon is sometimes mistaken for the first stage of a tsunami. But the physics are fundamentally different. A meteotsunami does not require the seafloor to move. Instead, the ocean is responding to disturbances in the atmosphere above it.
AEMET describes meteotsunamis as destructive ocean waves with tsunami-like characteristics but a meteorological origin.
Rapid atmospheric-pressure changes associated with fronts, gravity waves, squall lines and convective weather can generate the initial disturbance, which may then grow through resonance as it reaches suitable coastal environments.
The Mediterranean Has Seen Them Before
The phenomenon is not unique to Mallorca or Menorca. Meteotsunamis have been observed around the world, but some coastlines are particularly prone to them because of their geography and typical atmospheric conditions.
In the Balearic Islands, the phenomenon has become sufficiently familiar that Spain’s meteorological service operates a dedicated forecasting and warning system for rissagas.
Forecasting the precise size of an event remains difficult, however, because relatively small differences in the atmospheric disturbance can dramatically affect the final sea-level response inside a harbor.
That uncertainty is one of the reasons these events can be so dangerous. A relatively modest atmospheric pressure signal does not necessarily produce a modest rissaga.
What matters is whether its timing, direction and speed happen to match the natural response of a particular bay or harbor.
A Familiar Summer Hazard With a Strange Appearance
The Balearic Islands are not experiencing a conventional tsunami every time seawater suddenly floods a waterfront.
What residents and visitors are sometimes seeing is something much more localized – and, in the right setting, surprisingly powerful.
The latest Mallorca episode is another reminder that dangerous changes in the sea do not always begin beneath the sea.
Sometimes the trigger is hundreds or thousands of feet above it, moving through the atmosphere as an otherwise ordinary-looking weather disturbance.
And when the atmosphere and the ocean happen to fall into step, a quiet Mediterranean harbor can begin behaving like a giant wave machine.
Sources and Further Reading:
AEMET – Spanish State Meteorological Agency: Background on meteotsunamis, their atmospheric origins and the rissaga phenomenon in Spain.
Renault et al., Geophysical Research Letters: Scientific analysis of meteotsunami formation and amplification in the Balearic Sea, including the mechanisms behind major rissaga events at Ciutadella.
Natural Hazards: Research into forecasting Balearic meteotsunamis and analysis of the major June 2006 event.
Última Hora: Reporting on the August 24, 2026 rissaga events affecting Alcúdia, Andratx, Sóller and other parts of Mallorca, as well as the warning issued for Menorca.
