Yes, a tsunami is possible when two oceanic plates collide.
Understanding Plate Collisions and Tsunamis
Tsunamis are powerful ocean waves most often caused by large-scale disturbances on the seafloor, such as earthquakes. One of the primary triggers for these devastating waves is the interaction of Earth's tectonic plates.
According to scientific understanding, most large tsunamis occur at convergent plate boundaries where two tectonic plates are crashing into each other. When two oceanic plates collide, one is typically forced underneath the other in a process called subduction. As referenced, "As the two plates collide one plate is forced down underneath the other. As this happens the leading edge of the top plate snags on the bottom plate and pressure starts to build."
This 'snagging' and build-up of pressure is crucial. When this pressure is suddenly released – often in the form of a powerful underwater earthquake – the seafloor can be abruptly uplifted or dropped. This vertical displacement of the seafloor displaces the entire water column above it, generating the initial wave pulse that can evolve into a destructive tsunami.
How an Oceanic Plate Collision Can Lead to a Tsunami
- Collision and Subduction: Two oceanic plates converge, and the denser or faster-moving plate slides beneath the other.
- Plate Locking: The leading edge of the overriding plate gets stuck or 'snags' on the subducting plate due to friction.
- Pressure Build-up: As the subducting plate continues its slow descent, the overriding plate is forced to deform and bend upwards, accumulating immense stress and energy.
- Earthquake: The built-up stress exceeds the strength of the rocks, causing the locked plates to rupture. This sudden slip is a large earthquake.
- Seafloor Displacement: The earthquake causes the seafloor along the rupture zone to abruptly move vertically (up or down).
- Tsunami Generation: The sudden vertical displacement of the seafloor displaces the overlying water, generating the initial tsunami wave that propagates across the ocean.
Convergent Plate Boundaries and Tsunami Risk
Convergent boundaries, especially those involving subduction zones (like where oceanic plates collide, forming trenches and volcanic arcs), are particularly prone to the large, shallow earthquakes that can trigger tsunamis. These zones are often referred to as megathrust zones.
| Plate Boundary Type | Description | Tsunami Risk |
|---|---|---|
| Convergent (Subduction) | Plates collide; one slides beneath the other. | High |
| Divergent | Plates move apart. | Low |
| Transform | Plates slide past each other horizontally. | Low to Moderate (depending on associated deformation) |
The collision of two oceanic plates creates a subduction zone environment highly conducive to the powerful earthquakes needed to generate significant tsunamis.
Examples
Famous examples of tsunamis generated by earthquakes at oceanic-oceanic convergent boundaries or similar subduction zones include:
- The 2011 Tohoku earthquake off the coast of Japan (Pacific Plate subducting beneath the Okhotsk Plate, partially oceanic/continental)
- The 2004 Indian Ocean tsunami (Indian Plate subducting beneath the Burma Plate, primarily oceanic)
These events underscore the significant tsunami threat posed by underwater earthquakes at these types of plate boundaries.
