Tsunami natural warning signs

What to look for when the ground stops shaking

NOAA operates two Tsunami Warning Centers that monitor earthquakes and issue alerts around the clock. For distant tsunamis, those generated by earthquakes hundreds or thousands of miles away, the warning system usually has enough time to issue alerts before the waves arrive. For local tsunamis, those generated by a nearby earthquake, the waves can reach shore in minutes. Official alerts may not arrive before the water does.

NOAA and FEMA's Ready.gov identify three natural warning signs that a tsunami may be coming. None of them require a phone or a siren.

A strong or long earthquake. NOAA says any earthquake lasting 20 seconds or more, or strong enough to make it difficult to stand, should be treated as a potential tsunami trigger on any coast. The shaking itself is the warning. You do not need to confirm the magnitude before acting.

A loud roar from the ocean. A faint rumbling that grows louder, compared by some observers to a train or low-flying jet, can indicate an incoming wave. If you hear this after a coastal earthquake, move immediately.

Rapid and unusual water behavior. Water receding suddenly and exposing the sea floor is the most dramatic natural warning. It is also widely misunderstood as a curiosity rather than a signal to run. It means the water is being pulled back to build up the incoming wave. A rapid, unusual rise in water level is equally dangerous. Either change, following a coastal earthquake, means evacuate now.

Walk or run, avoid driving, avoid river valleys

NOAA's guidance is to walk or run to ground at least 100 feet above sea level, or at least one mile inland, immediately after observing any natural warning sign. If you cannot reach that distance, go to the fourth floor or higher of a sturdy building. Every floor of elevation you gain is meaningful.

Do not drive unless you are certain you can reach high ground without creating a traffic jam. Ready.gov advises keeping roads clear for emergency vehicles. A car stuck in traffic can become a trap when the water arrives faster than expected. Walking is often faster than driving during coastal emergencies when roads are congested.

Avoid river valleys and low-lying areas along rivers that empty into the sea. Tsunamis travel upstream along rivers and can inundate areas well inland from the coast if a river valley provides a path. Move perpendicular to the shore, not along it.

Do not return to the coast until officials issue an all-clear. NOAA states that the first wave may not be the largest. A series of waves can continue for hours, at irregular intervals, sometimes 12 hours or longer. The interval between waves can be long enough for people to mistakenly believe the danger has passed.

Sirens, Wireless Emergency Alerts, and NOAA radio

When time permits, official tsunami alerts arrive through several channels: Wireless Emergency Alerts pushed to cell phones in the affected area, NOAA Weather Radio, outdoor sirens in designated tsunami hazard zones, television and radio broadcasts, and in some areas, door-to-door contact by emergency responders.

For local tsunamis triggered by nearby earthquakes, NOAA states that there will not be time for an official warning. The earthquake is your only warning. If you are on the coast and experience a strong or long earthquake, do not wait for a siren or a phone alert. Begin moving to high ground immediately.

Tsunami hazard zones and evacuation routes are marked with blue-and-white signs in many coastal communities. These signs show the nearest safe direction and elevation. If you spend time in a coastal area, noting the nearest tsunami evacuation sign before you need it takes about ten seconds.