TSUNAmi
A tsunami is a series of powerful ocean waves caused by a sudden movement of water, most often from a large earthquake. Tsunamis can travel long distances across the ocean and create dangerous flooding and strong currents when they reach shorelines, bays, and waterways.
How This Affects Alameda County
While tsunami events are uncommon, Alameda County’s low-lying coastal and bayfront areas are vulnerable to strong currents, rapid water level changes, and localized flooding. Areas such as Alameda Island, shoreline communities, ports, marinas, and wetlands may be affected, especially during tsunamis generated by distant earthquakes. View this short clip to learn more about characteristics of What is a Tsunami?
Past earthquakes highlight tsunami events:
1906 San Francisco Earthquake – Caused a smaller, local tsunami, demonstrating that even local seismic activity poses a threat
1960 Chile Earthquake – Caused tsunami effects throughout the San Francisco Bay Area
1964 Alaska Earthquake – The most damaging tsunami event for the Bay, causing strong currents, flooding, evacuations, and damage to docks and infrastructure in Alameda
2006 Kuril Islands Earthquake – Produced minor tsunami impacts and strong currents, prompting precautionary evacuations
2011 Japan Earthquake – Generated a trans-Pacific tsunami that caused strong currents and localized flooding in Alameda County harbors and marshes
Tsunami Safety Tips
Before a Tsunami
- Sign up for ACAlert to receive emergency notifications
- Plan evacuation routes and identify higher ground
- Prepare emergency supplies and important documents
- Monitor weather forecasts
Warning Signs of a Possible Tsunami
There may not always be enough time for an official warning, so it is important that you understand natural warnings. If you observe any of the following signs near the coast or Bay shoreline, move away from the water immediately:
- Strong or long-lasting ground shaking
- Rapid or unusual changes in water level
- Water suddenly receding and exposing shoreline or bay bottom
- Loud ocean or roaring sounds
Note: Do not wait for an official alert if you notice these signs.
During a Tsunami
- Stay informed through alerts and official updates
- Follow evacuation instructions from local officials if directed
- Move to higher ground if you are in a flood-prone or low-lying area
- If a tsunami warning or advisory is issued while you are in a marina or near shore, secure your vessel if time allows, then leave the area and move to higher ground on land.
- Do not remain on docks, piers, or vessels tied in marinas, as strong currents can cause significant damage.
- If a tsunami warning or advisory is issued while you are already at sea when it is safe to do so, move to deeper water and avoid returning to ports, marinas, or harbors until officials lift the warning.
- Follow guidance from harbor masters, the U.S. Coast Guard, and local authorities
Learn more and access Tsunami Safety & Preparedness Tips
After a Tsunami
- Stay away from the coast until authorities say it is safe
- Avoid floodwater, debris, damaged buildings, and downed power lines
- Watch for aftershocks and additional waves
- Follow official emergency updates
- Check on others only if it is safe
Tsunami Alert and Warning (National Weather Service)
Understanding alerts help you take action at the right time.
Tsunami Advisory – Take Action and Move to a Safe Place: are issued when strong currents and hazardous conditions are expected
Tsunami Warning – Take Action and Move to a Safe Place: are issued when flooding and life-threatening conditions are possible or occurring
All Clear – No Threat: is an official notice that it is safe to return to coastal areas
Tsunami Resources
Alameda County | Tsunami Alert & Warning Terminology: A short clip explaining the language and terms used for official tsunami notifications
Alameda County | Tsunami Warning Signs: Offers a downloadable flyer on key tsunami warning sign indicators
Cal OES | Tsunami Preparedness Program: Access tsunami preparedness tips and recovery guidance
Statewide California Earthquake Center | Know Your Tsunami Zone: Check your commonly visited locations to identify whether they are situated in a tsunami hazard or evacuation zone
National Weather Service (NWS) | Tsunami Safety: Provides forecasts, alerts, and safety guidance
National Weather Service (NWS) | Weather Warnings: Learn about the ways you can receive NWS Weather Warnings
NOAA | National Tsunami Warning System: Provides the most recent updates on tsunami messaging