Tsunami
Tsunamis pose a significant threat to coastal areas, causing loss of life and property damage. Tsunamis are primarily triggered by earthquakes but can also result from landslides, volcanic eruptions, or even meteor impacts. Their waves can vary in size and appearance. The largest surges may occur hours after the initial wave and can last 12 hours or more. Low-lying coastal areas face the highest risk, and in large coastal rivers, tsunamis may penetrate inland for over two miles. A sudden ocean drawdown can signal an incoming tsunami, but not all tsunamis provide this warning.
Given these risks, emergency preparedness is crucial. Having an emergency kit and a plan can be life-saving when the next tsunami strikes. An essential guide for earthquake and tsunami preparedness is Living on Shaky Ground. Published by the Redwood Coast Tsunami Work Group, this magazine provides valuable information on how to prepare, stay safe, and recover. It also outlines practical steps you can take now to protect lives, reduce injuries, and limit damage in the aftermath of an earthquake or tsunami.
Tsunami Hazard Map
The California Geological Survey has mapped Humboldt County's official Tsunami Hazard Areas. Map areas shaded in green are sufficiently high or inland to be safe in even the most extreme earthquake event. Map areas shaded in yellow indicate being at risk, especially for people closest to the beach or in low areas.
These maps show worst-case scenarios with an extra margin of safety, so communities are prepared for even the largest possible events. For the North Coast, this includes tsunamis from a magnitude 9 on the Cascadia fault, as well as smaller tsunamis from other sources. For most tsunamis, the water will not reach nearly as far inland.
The map boundaries are based on scientific inundation models but are extended slightly to make them practical for evacuation planning.
Significant Earthquake
After a significant earthquake, it’s best to always treat it as a potential tsunami warning. If you're on the beach or in a tsunami zone, head to higher ground, on foot, immediately - don’t wait for an alert!
Tsunami Alerts
The Tsunami Warning System is controlled by the National Tsunami Warning Center in Alaska. Alerts are sent automatically via Wireless Emergency Alert (WEA), when an earthquake of M 7.1 occurs in a coastal area.
Official tsunami warnings are broadcast through local radio and tv, marine radio, wireless emergency alerts, NOAA Weather Radio, and NOAA websites. They may also come through outdoor sirens, local officials, text message alerts, and telephone notifications. It’s important to know what the different alerts mean:
- Tsunami Warning - Take Action: A tsunami that may cause widespread flooding is expected or occurring. Dangerous coastal flooding and powerful currents are possible and may continue for several hours or days after initial arrival. Follow instructions from local officials. Evacuation is recommended. Move to high ground or inland (away from the water).
- Tsunami Advisory - Take Action: A tsunami with potential for strong currents or waves dangerous to those in or very near the water is expected or occurring. There may be flooding of beach and harbor areas. Stay out of the water and away from beaches and waterways. Follow instructions from local officials.
- Tsunami Watch - Be Prepared: A distant earthquake has occurred. A tsunami is possible. Stay tuned for more information. Be prepared to take action if necessary.
- Tsunami Information Statement - Relax: An earthquake has occurred, but there is no threat or it was very far away and the threat has not been determined. In most cases, there is no threat of a destructive tsunami.
Humboldt Alert
Humboldt Alert is an emergency notification sent out only after the appropriate agencies have confirmed with the Humboldt Sheriff’s Office of Emergency Services that there is a threat to public safety.
Earthquake Alerts
Early Earthquake Warning System alerts are sent automatically by the Governor’s Office of Emergency Services (Cal OES) via Wireless Emergency Alert (WEA), when an earthquake of M 5.0 or higher hits anywhere in California.
Learn more about Shake Alerts and download the MyShake App to get push notifications for earthquakes M 4.5+.
Near-Source Tsunamis
If you’re in an area where you feel the earthquake and it produces a tsunami, the ground shaking is your notification that a tsunami is potentially on the way. You may also observe an unusually large drawdown of water from the coast exposing the sea floor or even hear a loud roar.
For an event where you feel the earthquake, WALK out of the tsunami zone as soon as it is safe to move - don’t wait for an alert! Tsunami waves can arrive in as little as 10-15 minutes.
Do not enter or drive through tsunami hazard areas (including roads/highways in hazard areas) until officially informed it is safe to do so. Anticipate aftershocks.
Distance-Source Tsunamis
If the tsunami is generated in another location but is traveling towards your coastline, you may be notified by official alerts for a distant tsunami. This official warning can come from a Tsunami Warning Center in the form of messages on TV and radio, sirens, audio messages from airplanes and even door-to-door contact.
Natural and official warnings are equally important. Respond to whichever you hear or observe first!
Natural Warning Signs
- An earthquake that lasts for a long time - the longer the shaking, the more likely a tsunami could be on its way. The shaking could be weak or strong – the important signal is duration!
- A sudden change in the character of the ocean - a calm sea that suddenly becomes rough is a sign to move away from the beach.
- The ocean receding unusually far - this is a sign that the water will rush back in much faster and higher than you expect. Head inland or to higher ground as soon as you notice.
- A loud noise or roar from the ocean - this is an indication that the waves are building in size. Tsunami surges could arrive within minutes.
How do I know if an earthquake is big enough to cause a tsunami?
- If you are on the beach and feel an earthquake, no matter how small, move inland or to high ground immediately.
- If you are in a tsunami hazard zone and feel an earthquake that lasts a long time, evacuate as soon as it is safe to move. Not sure if the earthquake is long enough? When in doubt, DRILL IT OUT. Every earthquake is an opportunity to practice evacuating.
- GO ON FOOT. Roads and bridges may be damaged by strong ground shaking. Avoid downed power lines. If evacuation is impossible, go to the upper floor of a sturdy building or climb a tree — but only as a last resort.
- Sign up for Humboldt Alert emergency notifications.
- Create an emergency preparedness plan and plan how you would respond in the incident of a tsunami.
- Know the tsunami hazard zones in your community and how to get to safe areas.
- Recognize the natural warning signs of a tsunami—ground shaking, water receding unusually far, and/or a loud roar from the ocean—and make sure everyone in your family knows to immediately evacuate if they are in a hazard zone.
- Know how you may be notified if a tsunami warning is issued. Consider a NOAA Weather Radio with the Public Alert feature if you live or work in a tsunami hazard zone.
- If a tsunami warning is issued, get off the beach and tune in to your radio or television for further instructions on what to do.
- Identify family members or neighbors with special needs such as medications, special diets and wheelchairs.
- Identify an out-of-the area contact person to call who can relay information to other friends and family.
- Provide all family members with a current list of important contact telephone numbers.
- Determine where you might stay if your home cannot be occupied after an earthquake or tsunami.
- Ask about your children’s school or day care emergency response plans. Keep emergency release information current.
- Talk to your insurance agent about your coverage for earthquake and tsunami losses.
- Make copies of important documents such as identification, deeds, insurance policies and financial records in a secure, waterproof container. Include a household inventory of your belongings.
- Local agencies and partner organizations: Review the Earthquake and Tsunami Response Fact Sheet. The fact sheet is designed to provide information and guidance to help develop your own internal policies and procedures that protect personnel and will help maintain essential services during a local earthquake and tsunami response.
Organize Emergency Supplies
Everyone should have emergency supplies stored in accessible locations at home, at work, and in vehicles. Having emergency supplies readily available can reduce the impact of an earthquake or other emergency on you and your family.
You can choose what to put in each location:
- Under-Bed Bags hold shoes, a flashlight, and other items for when an earthquake happens while sleeping.
- Go-Bags or car kits contain supplies for about 3 days for when evacuation is needed.
- Home or work supplies are for sheltering in place for up to 2 weeks or for larger groups.
Learn more about preparing your emergency kits.
Minimize Financial Hardship
Help minimize your financial hardship by:
- Organizing Important Documents: Keep copies of documents for starting an insurance claim or applying for financial assistance in a go bag, along with ID, insurance policy, etc.
- Strengthening Your Property: Current building codes rarely require older buildings to be upgraded, but there are things that can be done. Visit Strengthen Your House to learn more.
- Considering Insurance Coverage: Homeowners and renters can protect themselves with earthquake insurance (a separate policy is required).
- Stay out of the tsunami hazard or evacuation zone until local officials tell you it is safe. The first wave may not be the last or the largest and the danger may last for hours or days.
- If there is earthquake damage, avoid fallen power lines and stay away from buildings, bridges and piers because heavy objects may fall from them during an aftershock.
- Follow your emergency plan.
After a Large Earthquake
For a large local earthquake, feeling ground shaking may be the only warning you will get that a tsunami is on its way. Use tsunami hazard maps and posted hazard zone signs to identify safe evacuation areas.
If you are at the Beach move to higher ground immediately–no matter how small the earthquake.
If you are in a tsunami hazard zone and the earthquake lasts a long time immediately gather your family members, grab your tsunami disaster kit, and W.A.L.K. to a safe area.
After a long-lasting Earthquake, remember to W.A.L.K.
- W - Watch for natural warning signs. Watch the ocean for sudden changes, receding unusually far, or a loud roar.
- A - Act quickly! Don't wait for an official alert, immediately move to higher ground.
- L - Leave on foot. Roads and bridges may be damaged, walk out of the tsunami hazard zone.
- K - Keep out. Stay out of the tsunami hazard zone until officials say it is safe to return.
If evacuation is impossible go to the upper floor of a sturdy building or climb a tree. This should only be a last resort.
DO NOT wait for an official warning. If you are NOT in a tsunami hazard zone, stay where you are. You are not at risk of a tsunami. Unnecessary evacuation will put you at risk and hamper the evacuation of people who really need to get away from danger.
- Stay out of the tsunami hazard or evacuation zone until local officials tell you it is safe. The cancellation of a tsunami warning does not mean the danger has passed.
- Stay away from areas that have been damaged for your own safety and so emergency responders can have full access.
- Stay out of any building that has earthquake or tsunami damage or has water around it until a professional or local official tells you it is safe to enter.
- Avoid fallen power lines or broken utility lines and report those that you see.
If Your Cannot Stay in Your Home
- Use your radio to find shelter locations.
- Bring your Grab and Go Bag with medications and personal information. Shelter space is limited.
- Check to find out what you can bring, including pets.
If Your Home Isn’t Damaged
Sheltering in place is the safest thing to do even if the power is out.
- Stay There!
- Do not use matches, lighters, or candles indoors.
- Never use a camp stove, gas lantern or heater, gas or charcoal grill, or gas generator indoors.
Be in Communication and Stay Informed
- Let people know you are okay. Text your out-of-area contact to tell them where you are. Stay off your phone to keep the lines open for emergency communications.
- Use your portable or car radio to find a station that is on the air and providing updates and safety advisories.
- Check on your neighbors.
Food and Water
- If the power is off, use refrigerated and frozen foods first. Food in the freezer may last several days.
- Use your stored water for drinking. You can also drink from water heaters, melted ice cubes, or canned vegetables. Don't drink water from swimming pools or hot tubs.
Document Damage
- Use your phone or camera to photograph anything you suspect may have been damaged.
- Contact your insurance agent right away to begin your claims process.
Verify Information
Rumors are rampant in the aftermath of a disaster. Verify Information from reputable sources before passing it on.
Be Prepared for a Tsunami
This video explains how to prepare for and respond to a tsunami. If you live, work, or play on the coast, be prepared and stay safe!
This video is produced by the National Weather Service.