Tsunamis Explained
Landslide tsunamis form when massive volumes of rock, sediment, ice or volcanic material suddenly collapse into water or slide beneath it. Unlike many earthquake tsunamis, landslide tsunamis are often local, fast-arriving and capable of producing extreme wave heights in fjords, lakes, bays and coastal regions.
What Is a Landslide Tsunami?
A landslide tsunami is a tsunami generated by the sudden movement of land, rock, sediment or ice into a body of water. The collapsing mass rapidly displaces water, creating waves that can strike nearby shorelines within seconds or minutes.
These events can occur in oceans, fjords, reservoirs, lakes and enclosed bays. Because the source is often close to shore, warning time is usually much shorter than for distant earthquake tsunamis.
How Do Landslide Tsunamis Form?
- A slope becomes unstable because of earthquakes, erosion, volcanic activity, heavy rainfall, glacier retreat or long-term weakening.
- A large mass of rock, sediment, soil, ice or volcanic material collapses suddenly.
- The landslide enters water or moves underwater along the seafloor.
- The displaced water forms one or more tsunami waves.
- Waves radiate outward and can amplify inside narrow bays, lakes or fjords.
- Nearby coastlines may be hit within minutes, sometimes before any official warning is possible.
Main Types of Landslide Tsunamis
Submarine Landslide Tsunamis
These occur when underwater sediment suddenly fails and slides down the continental slope, displacing seawater from below.
- Continental slope failure
- Submarine canyons
- Sediment collapse
- Earthquake-triggered slides
Coastal Rockslide Tsunamis
Large cliffs, mountainsides or unstable coastal slopes can collapse directly into the ocean, fjords or lakes.
- Rock avalanches
- Fjord waves
- Cliff collapse
- Bay amplification
Glacier and Ice-Collapse Tsunamis
Glacier calving, ice avalanches and collapsing ice-covered slopes can generate dangerous local waves in polar and alpine waters.
- Glacier calving
- Ice avalanches
- Proglacial lakes
- Retreating glaciers
Volcanic Flank-Collapse Tsunamis
Volcanoes can generate landslide tsunamis when unstable flanks collapse into the sea or into crater lakes.
- Volcanic island collapse
- Debris avalanches
- Caldera lakes
- Sector collapse
Where Do Landslide Tsunamis Happen?
Landslide tsunamis are most likely in places where steep slopes meet deep water. Narrow fjords, volcanic islands, glaciated coastlines, reservoirs and submarine canyon systems are especially vulnerable.
- Alaska fjords
- Norwegian fjords
- Greenland and Arctic coastlines
- Volcanic islands
- Steep-sided lakes and reservoirs
- Continental margins with unstable sediment
- Coastal cliffs weakened by erosion
Why Landslide Tsunamis Can Be So Extreme
Landslide tsunamis can produce enormous local wave heights because the moving mass may enter the water all at once and transfer energy very efficiently. In narrow fjords or enclosed bays, wave energy can be trapped, reflected and amplified.
This is why some landslide tsunamis produce extreme run-up heights near the source, even if they do not travel across entire ocean basins like major earthquake tsunamis.
Landslide Tsunamis vs. Earthquake Tsunamis
| Feature | Landslide Tsunami | Earthquake Tsunami |
|---|---|---|
| Main trigger | Rock, sediment, soil or ice collapse | Sudden seafloor displacement |
| Warning time | Often seconds to minutes | Minutes to hours |
| Typical range | Usually local or regional | Can cross entire oceans |
| Extreme height | Very high near the source | Usually lower offshore, grows near coast |
| Common locations | Fjords, lakes, bays, volcanic islands | Subduction zones and ocean trenches |
Warning Signs of a Landslide Tsunami
Landslide tsunamis can arrive very quickly, so natural warning signs matter.
- Sudden cliff collapse or rockfall into water
- Loud rumbling, cracking or roaring from a slope
- Strong local earthquake near steep coastal terrain
- Unusual waves in a fjord, lake, bay or harbor
- Rapid water withdrawal or sudden water rise
- Visible slope movement, landslide scars or falling debris
If you see a large landslide enter water, hear a major slope collapse, or feel strong shaking near the coast, move immediately to higher ground.
Famous Landslide Tsunamis
| Event | Location | Cause | Why It Matters |
|---|---|---|---|
| Lituya Bay, 1958 | Alaska | Earthquake-triggered rockslide | Produced the highest known tsunami run-up, about 524 meters. |
| Vajont Dam, 1963 | Italy | Mountain slope collapse into reservoir | Generated a catastrophic wave that overtopped the dam. |
| Storegga Slide | Norwegian Sea | Massive submarine landslide | Generated a prehistoric tsunami that struck North Atlantic coastlines. |
| Taan Fiord, 2015 | Alaska | Mountain landslide into fjord | Produced a major local tsunami in a glaciated landscape. |
| Anak Krakatau, 2018 | Indonesia | Volcanic flank collapse | Generated a deadly tsunami with little warning. |
What Makes a Coast Vulnerable?
- Steep unstable slopes above water
- Deep water close to shore
- Fjords, bays or lakes that focus wave energy
- Recent glacier retreat exposing unstable rock
- Volcanic islands with weak flanks
- Submarine sediments overloaded by rapid deposition
- Coastal erosion weakening cliffs
Related Guides
Frequently Asked Questions
Are landslide tsunamis real tsunamis?
Yes. A tsunami is defined by the sudden displacement of a large volume of water. Landslides, rock avalanches, submarine slope failures and glacier collapses can all generate true tsunamis.
Can landslide tsunamis happen in lakes?
Yes. Landslide tsunamis can happen in lakes, reservoirs and fjords when a large mass collapses into the water or slides beneath the surface.
Why are landslide tsunamis so dangerous?
They are dangerous because they often occur close to shore and may arrive within seconds or minutes, leaving little time for official warnings or evacuation.
Can earthquakes trigger landslide tsunamis?
Yes. Earthquakes can destabilize slopes and trigger underwater landslides or rock avalanches into water, producing landslide-generated tsunamis.
Are landslide tsunamis usually local?
Most landslide tsunamis are local or regional, but very large submarine landslides can affect coastlines across wider areas.
