Tsunamis

Tsunamis

Tsunami

Real-time Warning | Emergency preparation | Planning ahead | Tsunami Science Basics | Tracking and Forecasting | Case Study: March 2011 Tsunami | Tsunami Outlook for California

Latest NOAA Tsunami Warning Center Information

The box below contains the most recent report on earthquakes in the Pacific or Atlantic oceans made available by the NOAA Tsunami Center. Most earthquakes do not result in tsunamis, read the information to find out whether a tsunami is expected, which areas of the coast may be threatened and the timeline for the arrival of waves. DO NOT RELY ON THIS WEBSITE ALONE. Local radio or TV stations are your best source of information on tsunami warnings.


Tsunami Basics Animation This image shows the increasing height of a tsunami wave as it nears the coast and the resulting danger for coastal communities.
Tsunami Basics Animation An example of a tsunami evacuation strategy in one west coast town.
Tsunami Basics Animation Image by Regis Lachaume

An animation showing the slowing and increasing height of tsunami waves when nearing the coast.
DART Buoy
NDBC DART Buoy for measuring tsunami waves in the Pacific Ocean.
Japan Tsunami Model Map Image by NOAA Center for Tsunami Research

A model forecast map of the March 10th, 2011 tsunami wave heights across the Pacific.
Japan Tsunami Size in PacificAnimation by NOAA Center for Tsunami Research

Animation showing the predicted spread time and wave height following the 2011 earthquake offshore Japan. See YouTube video
Plot of Fort Point Water Depth - indicating tsunami Data from CeNCOOS Station, Plot by Bodega Marine Lab

Water pressure (indicating depth) plot for March 9-11th at Fort Point, CA (San Francisco). Data from the 9th and 10th show normal tidal cycles. The affect of the tsunami on water depth can be seen beginning at 8 AM on the 11th and continuing through the day. Click to enlarge the image.
Plot of Tiburon Water Depth - indicating tsunami Data from CeNCOOS Station, Plot by Romberg-Tiburon Lab

Water depth and pressure plot for March 11th at Tiburon, CA (San Francisco Bay). Data from early morning on the 11th show normal tidal cycles. The affect of the tsunami on water depth can be seen beginning the morning of the 11th and continuing through the day. Click to enlarge the image.
Japan Tsunami
A photo showing the inundation of a coastal community in Japan during the March 2011 tsunami.
Crescent City Harbor tsunami Photo provided by The Oregonian

An aerial photo showing damage to boats and docks just after the March 2011 tsunami hit Crescent City Harbor. Click to enlarge the image.
Plot of Tiburon Water Depth - indicating tsunami Photo by Tom Wadsworth (CeNCOOS)

A photo showing damage to boats and docks in the Santa Cruz Upper Harbor during the March 2011 tsunami. Click to enlarge the image.

Tsunami Emergency Information for the CeNCOOS region

You can greatly minimize your vulnerability to a tsunami by following simple rules before and during the arrival of waves provided by these authorities:
- The Federal Emergency Management Agency (FEMA)
- Humboldt State University: "Surviving a Tsunami in Northern California"
- U.S. Geological Survey: "Surviving a Tsunami" report

Tsunami evacuation plans may be available for your area, including maps showing routes and signs posted along those routes. These can be created by state, county or city agencies as well as private sector work places. Examples of these tsunami plans are below:
- Crescent City: city plan (PDF) | Triplicate newspaper (website)

General Preparedness
California Emergency Preparedness Information

Due to the high speed of tsunamis, people living on the coast may have less than an hour to reach safety on higher ground. The evacuation time depends on the distance the earthquake occurs from each population center on the coast. Coastal areas closest to the earthquake center will receive the largest tsunamis waves, but these waves can still do damage thousands of miles from the point of origin. If you are in coastal areas it is important to know what to do in case of a tsunami. The first step is being aware of how to get information on tsunamis. A few areas in the U.S. have tsunami warning sirens at this time (see San Francisco sirens info), but many areas have systems to notify residents via phone and most make announcements via local radio and television stations. Tsunami warnings are also available via the NOAA Tsunami Warning Center Tsunami email list and website. Many areas vulnerable to tsunamis also have evacuation routes and signs in place (see image on right column). Many places also have or are developing preparedness plans specific to harbors and marinas. It is important to understand that the danger does not pass with the first tsunami wave to arrive. Tsunami generated waves and surges may appear for days afterwards. This is due to a combination of factors: 1) the tsunami waves crossing the ocean travel by multiple paths, arriving at different times, 2) earthquake aftershocks can generate new tsunamis 3) the tsunami can reflect from the ocean boundaries and islands and continue to travel in the ocean, and 4) the tsunami can reflect from the boundaries of partially enclosed bodies of water (like coastal bays) and continue to travel around the bay. The phenomenon described in #4, known as a seiche, is similar to water in a bathtub continuing to slosh up and down after a person inside stops moving to disturb the water. There are several causes for seiches in the ocean, but tsunamis are known to produce this effect. The waves of a seiche are referred to as 'standing waves' because they only move up and down, not forward like typical wind (or tsunami) produced waves in the open ocean.

Planning Ahead

Communities should not wait for a tsunami warnings to prepare. Information has been developed throughout the state to help communities and workplaces create tsunami evacuation plans. Below are some resources for coastal planners and managers:
- California State-wide Inundation Maps
- NOAA Model for Tsunami Inundation

Tsunami Science Basics

A tsunami is a wave generated when the seafloor is abruptly changed at a location, displacing the overlying ocean water upwards. This can be caused by a large underwater earthquake or landslide. The waves are formed as gravity forces the displaced water mass to regain its equilibrium. Tsunamis in the open ocean are characterized by their long wave length (~ 120 miles), small wave height (less than 10 feet) and high speed (~ 600 mph). The magnitude, depth beneath the seafloor and type of earthquake or the size of underwater landslides controls the initial size of a tsunami by altering the size and speed of the vertical seafloor shift. However, the depth of the ocean is also important. As the tsunami approaches shallower depths near a coastline it slows down greatly and grows enormously in height (see animation and image on right column). When it reaches shore a tsunami may appear as a rapidly rising or falling tide, a tidal bore (like a raging river), or a series of small or (rarely) huge breaking waves. Factors that influence the size of a tsunami along the coast include the shoreline orientation and depth of water near shore. A tsunami wave that is only a few feet larger than another tsunami wave in the deep ocean could be many times larger when the two waves reach shallow depths near shore.

Measuring, Tracking and Forecasting Tsunamis in the Pacific

The NOAA Tsunami Warning Center uses NDBC Deep-ocean Assessment and Reporting of Tsunamis (DART) ocean buoys to measure wave heights, track progress and predict the arrival of tsunami waves as they move across the ocean (see image on right column). DART buoys are few and far apart in the vast expanse of the Pacific Ocean, making tsunami arrival predictions challenging, but researchers have become very accurate in recent years. Alerting residents near the tsunami starting point soon enough to save lives remains a major concern. Without the ability to forecast earthquakes up to the minute, the only solution is to create a widespread warning network that records and announces a tsunami within minutes. One recent warning system has the ability to identify a potential tsunami and send an announcement within about 10 minutes of an earthquake (see Science Daily article). In many cases it will take 30 minutes for the first waves to reach a coastline so this warning system may be valuable if it is proven to work worldwide. However, in some cases, even this is not enough time to warn coastal residents. High-Frequency Radar (HFR) can also be used to warn of an impending tsunami by measuring the unusual surface currents associated with these events. However, the distance from shore that a tsunami can be detected decreases with seafloor depth, making the warning time short for the California coast (~15 mins) due to the relatively narrow continental shelf (see CNN article | Remote Sensing journal article). For the benefit of those living further away from the tsunami starting point, the NOAA Center for Tsunami Research creates maps and animations showing the forecast size and distribution of tsunami waves across the ocean (see map and animation examples on right column).

CeNCOOS Tsunami Tracking Figure. The figure below is based on water level data from 12 coastal stations from southern Oregon to San Diego (latitudes on the left side). It will appear blank unless water level on the coast changes very quickly, which would most likely indicate a tsuanami. Brightest reds indicate fastest increasing water levels, darker blues are fastest decreases. A tsunami would cause very large increases and decreases in water level, appearing close together in time on the figure. Arrival of tsunami waves along the coast can also be tracked through time on the figure. In most cases, the waves would first appear at the the top (furthest north) and later show up toward the bottom. The figure is updated at 6 AM and 6 PM daily.

 

Examples of how tsunami waves would look on the real-time figure above are shown below for the 4-Day Period (left) and the day (right) of the March 11th, 2011 tsunami as it hit the California coast. Click images to enlarge.
   
 

2011 Tsunami - An Extreme Example

A 9.0 earthquake off Japan in March 2011 generated one of the most disastrous tsunamis in recent history. The wave initially traveled at speeds over 700 mph. Although it slowed down near shore, the closest population center had only about 10 minutes to prepare for the wave arrival. This tsunami was recorded at 9-12 feet high in the deep water off Japan, but when it reached the Japanese coastline, waves of over 100 feet tall were reported, traveling up to 6 miles inland. The size of the waves that hit Japan in this tsunami should be considered extremely unusual, caused by one of the largest earthquakes ever recorded.

The tsunami also crossed the Pacific to cause ~$50 million in damages in California harbors (see LA Times article). Tsunami wave heights across northern California varied from approximately 8 feet (Crescent City) to 4 feet (Monterey Bay). Although these wave heights are not unusual for California, the speed and wave length created a series of surges resembling flash floods that flowed in and out of the harbors with high speed and force, reversing direction every 15-20 minutes. Many boats and docks were sunk or set loose in harbors, espcially at Crescent City and Santa Cruz.

A multitude of video footage from Japan and California clearly showed the arrival of the tsunami surge and its affects (also see images at page bottom):

- Japan: Aereal View of Incoming Tsunami Waves (YouTube video)
- Tsunami hits Japanese town
- Collection of YouTube videos from Santa Cruz Harbor
- Time Lapse Video of Cowell's Beach in Santa Cruz
- Real-time video of tsunami entering San Francisco Bay: video 1 | video 2
- Aerial Video of Crescent City Harbor Damage - concluding with fishing boat narrowly escaping (You Tube)

CeNCOOS Response: CeNCOOS created a webpage devoted to this 2011 tsunami event and the impacts in California. The tsunami wave signature can be seen in plots of water depth recorded at coastal stations. CeNCOOS operates several of these stations along the coast. Data from the 2011 tsunami at Fort Point (San Francisco) and Tiburon (inside San Francisco Bay) show similar timing and wave heights (see right column images). Depth records at these stations typically record tidal cycles, a smooth progression from low to high tide. During tsunami events the plot looks much more erratic with highs and lows much closer together in time. Figure showing coastal water level fluctuations over the timeline of the tsunami were also created (shown above).

Tsunami Outlook For California

Experts say that big tsunami waves, larger than those that hit the California coast following the earthquake offshore Japan in March 2011, have occurred in the past and could once again occur here. However, the waves would be very unlikely to be the size of the waves that hit Japan (over 100 ft high) and would likely cause less damage, although it may still be a major disaster. Earthquakes have and will continue to happen off the California coast, potentially generating tsunamis; but the California quake magnitudes are not predicted to be nearly that of the 2011 Japanese quake, so waves should be smaller. Damage in Japan in 2011 and similarly in Indian Ocean countries in 2004 was high due to the size of the tsunami waves, but also because the coastlines in these countries is fairly flat in many places, allowing the tsunami to travel many miles inland. The California coast, especially northern and central regions, is relatively steep in most places, preventing tsunami progress inland in all by a few places (mainly harbors). However, California harbors can sustain considerable damage from even small tsunamis as seen in March 2011, a large tsunami could devastate these areas.

 

Sources of further information:

Live in a coastal area? Just want to know about potential tsunamis headed for the U.S. West Coast? Join the NOAA Tsunami email list.

Researchers develop new system to warn of tsunamis within minutes

NOAA Pacific Ocean Tsunami Warning Center

NOAA Center for Tsunami Research

USC Tsunami Research Center

USGS Earthquake Maps - U.S. and World

NOAA Tides and Currents program