Meteotsunamis Explained: Atmospheric Tsunamis, Rissaga Events & Sudden Ocean Recession

What Are Meteotsunamis?

A meteotsunami is a tsunami-like wave caused by the atmosphere instead of by an earthquake,
volcanic eruption, landslide, or major seafloor displacement.

The word combines meteorological and tsunami. Meteotsunamis can produce rapid
water-level changes, strong currents, harbor surges, coastal flooding, and sudden withdrawal of the sea.

Common Meteotsunami Signs

• water suddenly rises or falls in a harbor;
• the sea rapidly pulls away from shore;
• currents suddenly strengthen in a marina, bay, or channel;
• boats surge against docks or moorings;
• flooding appears without a local earthquake warning;
• a fast-moving storm line or pressure jump passes nearby.

Atmospheric Tsunamis vs Earthquake Tsunamis

Meteotsunamis are sometimes called atmospheric tsunamis because they behave like small or moderate
tsunami waves in certain coastal settings. However, their origin is completely different.

• Earthquake tsunamis begin when the seafloor suddenly displaces a large volume of water.
• Meteotsunamis begin when atmospheric pressure, wind, or storm disturbances push on the sea surface.

Both can create long waves, harbor oscillations, coastal flooding, and dangerous currents. But meteotsunamis are
part of the ocean-atmosphere system, while seismic tsunamis belong mainly to geological hazards.

How Do Meteotsunamis Form?

Meteotsunamis form when a moving atmospheric disturbance transfers energy into the water. If the disturbance travels
at the right speed and direction, the ocean response can grow into a long wave. If that wave enters a resonant harbor,
bay, lake, or coastline, it can amplify dramatically.

The Basic Meteotsunami Recipe

1. Atmospheric disturbance: a pressure jump, squall line, thunderstorm, derecho, or gravity wave moves over water.
2. Energy transfer: the atmosphere pushes or pulls on the sea surface.
3. Wave generation: a long wave begins moving through the water.
4. Speed matching: the atmospheric disturbance and water wave reinforce each other.
5. Coastal amplification: bays, harbors, shelves, or lake geometry increase the wave height.
6. Impact: water suddenly rises, falls, floods, withdraws, or creates strong currents.

Pressure Jumps & Atmospheric Forcing

A pressure jump is a rapid change in air pressure. When a pressure jump moves across a body of water,
it can slightly depress or lift the sea surface. Usually this effect is small. But if the disturbance moves at the right
speed, the ocean can respond strongly.

Atmospheric Triggers

• Squall lines: organized bands of thunderstorms.
• Derechos: fast-moving windstorms that can cross large regions.
• Thunderstorm pressure waves: sudden pressure disturbances produced by convective storms.
• Atmospheric gravity waves: waves moving through stable layers of air.
• Cold fronts: rapid weather changes that can force water-level oscillations.
• Strong wind shifts: abrupt changes in wind stress over the water surface.

Harbor Resonance: Why Some Meteotsunamis Become Dangerous

Harbor resonance happens when incoming wave energy matches the natural oscillation period of a harbor,
bay, lake, fjord, or enclosed coastline. The water begins to slosh back and forth, sometimes increasing in amplitude.

This is why a meteotsunami may be barely noticeable along one stretch of coast but destructive inside a nearby harbor.
The local shape of the coast can magnify the same incoming wave.

Places That Can Amplify Meteotsunamis

• narrow bays;
• long harbors;
• marinas and ports;
• semi-enclosed seas;
• large lakes;
• continental shelves;
• fjords and inlets.

Sudden Ocean Recession & Drawdown

One of the strangest meteotsunami signs is sudden ocean recession, also called drawdown,
drawback, or rapid sea withdrawal. Water may pull away from the shoreline, exposing seabed, rocks,
sandbars, harbor floors, or reefs before returning quickly.

Many people associate sudden sea withdrawal only with earthquake tsunamis, but meteotsunamis and harbor oscillations
can also cause rapid water-level fall and return.

Why Water Suddenly Recedes During Meteotsunamis

• the first phase of the wave may be a trough instead of a crest;
• harbor resonance may temporarily drain water from one side of a basin;
• pressure forcing may displace water away from shore;
• oscillations can repeatedly expose and reflood the shoreline.

Rissaga: The Mediterranean Name for Meteotsunamis

Rissaga is a regional name used especially in the western Mediterranean, including the Balearic Islands,
for meteotsunami-like harbor oscillations. These events can cause sudden water-level changes, damaging currents,
and rapid flooding in ports and marinas.

Rissaga events are important because they show how local geography, atmospheric waves, and harbor resonance can repeatedly
combine in the same region.

Typical Rissaga Features

• rapid water-level rise and fall;
• harbor surges;
• boats breaking moorings;
• strong currents inside ports;
• association with atmospheric pressure waves;
• recurrence in known Mediterranean hotspots.

Great Lakes Meteotsunamis

Meteotsunamis are not limited to oceans. They also occur on large lakes, especially the Great Lakes,
where fast-moving storm systems, squall lines, and pressure jumps can generate sudden water-level oscillations.

The Great Lakes are especially important because many people do not expect tsunami-like waves on inland freshwater lakes.
But large lakes have enough size, depth, and fetch to support dangerous long-wave events.

Great Lakes Meteotsunami Hazards

• sudden water-level rise along beaches and piers;
• strong currents in harbors and channels;
• unexpected flooding in marinas;
• people swept from breakwaters;
• rapid water withdrawal followed by return flow.

Mediterranean Meteotsunamis

The Mediterranean Sea is one of the world’s best-known meteotsunami regions. Its enclosed shape,
complex coastlines, island harbors, and fast-moving atmospheric disturbances create favorable conditions for
tsunami-like oscillations.

Important Mediterranean Areas

• Balearic Islands: especially associated with rissaga events.
• Adriatic Sea: narrow geometry and basin resonance can amplify waves.
• Sicily and southern Italy: exposed to pressure-driven coastal oscillations.
• Greek coastlines: complex island and harbor geometry can enhance local effects.
• Western Mediterranean: repeated atmospheric wave setups can trigger harbor impacts.

Mediterranean meteotsunamis are often highly local. One harbor may experience damaging oscillations while nearby open coastlines see less dramatic effects.

Global Meteotsunami Hotspots

Meteotsunamis can occur anywhere the atmosphere, water depth, and coastline align correctly. However, several regions
appear repeatedly in scientific reports and historical case files.

• Balearic Islands: classic rissaga events.
• Adriatic Sea: enclosed-basin amplification.
• Great Lakes: storm-driven freshwater meteotsunamis.
• U.S. East Coast: pressure jumps and derechos can generate broad events.
• Japan: some bays are highly sensitive to resonance.
• Black Sea: basin-scale atmospheric disturbances can produce water-level oscillations.
• Argentina Atlantic coast: rare but dramatic beach impacts have been reported.

Meteotsunami Warnings: Can They Be Predicted?

Meteotsunami warning is difficult because these events depend on both weather and local water response.
Meteorologists may detect a dangerous pressure jump or squall line, but the strongest impacts often depend on
whether a specific harbor or coastline resonates with the incoming wave.

Warning Ingredients Forecasters Watch

• rapid atmospheric pressure jumps;
• fast-moving squall lines or derechos;
• strong thunderstorm outflows;
• matching speed between weather disturbance and long water waves;
• known resonant harbors or bays;
• water-level gauge spikes;
• radar signatures of fast storm lines.

Why Forecasting Is Hard

• small timing errors can change the impact location;
• local resonance can amplify one harbor but not another;
• pressure jumps may be narrow and fast-moving;
• events can unfold within minutes;
• many regions lack dense water-level monitoring.

Meteotsunami Comparison Table

Famous Meteotsunami Events

Meteotsunami Safety

• If the ocean or lake suddenly recedes, move away from the shoreline immediately.
• Do not walk onto exposed seabed, harbor floor, reefs, or sandbars.
• Stay away from piers, jetties, seawalls, marinas, and harbor entrances during unusual water movement.
• Watch for repeated surges; the first wave may not be the largest.
• Secure boats if water-level oscillations begin, but do not risk personal safety to protect property.
• Follow local weather, coastal flooding, high surf, and tsunami-related warnings.

FAQs About Meteotsunamis