Seafloor Lift Starts a Tsunami

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An undersea earthquake can suddenly lift a block of the ocean floor. The lifted floor pushes the water above it, starting a long wave that can travel across the ocean toward a coast.

In the picture

Raised seabed block: a section of ocean floor pushed upward
Swollen water surface: seawater lifted above the raised block
Long wave crest: a broad swell moving across the ocean surface
Small boat: a vessel riding on the ocean surface
Coastal town: low buildings at the shoreline in the wave’s path

Examples

Dropping a heavy stone into a bathtub makes ripples spread across the water.
Pushing up the bottom of a full water bottle makes the surface rise and spill.

Key takeaways

An undersea earthquake can move the seafloor and displace a large volume of water.
A tsunami travels as long, low waves in the open ocean and can rise near the shore.