Causal phenomena

Fault movement on sea floor, accompanied by an earthquake.
A landslide occurring underwater or above the sea, then plunging into the water.
Volcanic activity either underwater or near the shore.

General characteristics

Tsunami waves are barely perceptible in deep water and may measure 160 km between wave crests
May consist of ten or more wave crests
Move up to 800 km per hour in deep water of ocean, diminishing in speed as the wave approaches shore
May strike shore in crashing waves or may innundate the land
Flooding effect depends on shape of shoreline and tides

Predictability

Tsunami Warning System in Pacific monitors seismic activity and declares watches and warnings. Waves generated by local earthquakes may strike nearby shores within minutes and warnings to public may not be possible.

Factors contributing to vulnerability

Location of settlements in low lying coastal regions
Lack of tsunami resistant buildings
Lack of timely warning systems and evacuation plans
Unawareness of public to destructive forces of tsunamis

Typical adverse effects

Physical damage - The force of water can raze everything in its path but the majority of damage to structure and infrastructure results from flooding. Withdrawal of the wave from shore scours out sediment and can collapse ports and buildings and batter boats.
Casualties and public health - Deaths occur principally by drowning and injuries from battering by debris.
Water supply - Contamination by salt water and debris or sewage may make clean drinking water unavailable.
Crops and food supplies - Harvests, food stocks, livestock farm implements and fishing boats may be lost. Land may be rendered infertile due to salt water incursion.

Possible risk reduction measures

Protection of buildings along coast, houses on stilts
Building barriers such as breakwaters

Specific preparedness measures

Hazard mapping, planning evacuation routes
Establish warning systems
Community education

Typical post-disaster needs

Warning and evacuation; search and rescue; medical assistance; conduct disaster assessment, provide food, water and shelter

Impact assessment tools

Aerial surveys of coastal areas, damage surveys, evaluation of warning systems and evacuation plans.