A tsunami is a wave caused by sudden displacements in the sea floor due to underwater earthquakes, landslides or volcanic eruptions. The speed at which a tsunami wave travels is dependent upon the depth at which the triggering event occurred; and as the tsunami moves from the open ocean to shallower waters, wave height increases.
When wave reaches the shore, it often arrives trough (the lowest part of the wave) first, drawing coastal waters out and exposing the ocean floor. The crest (the highest part of the wave) can arrive a short time after, inundating coastal areas with rushing seawater. Tsunami waves may be part of a “wave train,” a series of successive, destructive waves.
Click for links to Maui County Tsunami Evacuation Maps
Tsunami Watch vs. Tsunami Warning
What’s the difference between a tsunami “watch” and “warning”?
A Tsunami Watch is automatically declared by the Pacific Tsunami Warning Center for any earthquake magnitude 7.5 or larger (7.0 or larger in the Aleutian Islands) if the epicenter is in an area capable of generating a tsunami.
A Tsunami Warning is issued when tide-gauge stations near the earthquake epicenter report that a tsunami has been generated. A warning may be issued automatically if an earthquake powerful enough to create a tsunami occurs nearby.