Why is a tsunami hard to notice in the open ocean?
Tsunami waves can be hard for ships to notice because they travel rapidly with very long wavelengths but may have small height in the open ocean.
Formation process and geographic mechanism
Sudden displacement of the seafloor by an earthquake, landslide or volcanic event transfers energy through the whole water column. In deep water the wave can span hundreds of kilometers and travel hundreds of kilometers per hour, with many minutes between crests. Unlike wind waves it moves great depth, not only the surface. Not every submarine earthquake generates a tsunami; vertical displacement and source geometry matter.
Spatial outcomes, measurement and management
Approaching shore, shallower water slows the wave, shortens wavelength and converts energy into greater water level and strong current. Water does not always withdraw first, and the first wave may not be largest. Official alerts, natural strong-long earthquake warning and evacuation routes all matter. People should move inland or uphill rather than watch from the coast.