A model forecast map of the March 10th, 2011 tsunami wave heights across the Pacific.Click to enlarge image
Animation showing the predicted spread time and wave height following the 2011 earthquake offshore Japan. See YouTube video
Photo of Santa Cruz Harbor Patrol attempting to secure one of many boats that was drifting in the Harbor. Click to enlarge image
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.
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.
Water pressure plot for March 11-12th (in GMT time) at the deepwater (891 m) cabled observatory MARS (Monterey Bay). Data from early morning on the 11th show normal tidal cycles. The affect of the tsunami on water depth is most extreme around 1540 GMT (7:40 AM PST) on the 11th, but continues through the 12th. Click to enlarge the image.
Water depth plot for March 10-11th at Morro Bay, CA. Data from the 10th 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.
Water depth (observed and predicted) plot for March 12-15th in Humboldt Bay, CA. The affect of the tsunami on water depth can be seen on the blue line on the graphs (red line is normal tidal cycle). Included is second plot of just the tsunami affect and a third showing turbidity in the Bay. Click to enlarge the image.
On March 10th, 2011, a 9.0 earthquake occurred just off the east coast of Japan (see USGS report). The quake produced a large tsunami that 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. Thousands of lives were lost, homes and infrastructure were destroyed and a nuclear plant was significantly damaged (see NY Times Article). The tsunami waves spread in all directions throughout the Pacific Ocean, coming ashore in northern California around 8 AM on March 11th (see image and animation on right column). Tsunami waves are generated when underwater landslides occur, usually the result of large earthquakes. Tsunamis are characterized by their long wave length (~ 120 miles), small wave height (a few feet) and high speed at which they move (~ 500 mph) in the open ocean. As the tsunami approaches land it slows down greatly and grows enormously in height, creating the large breaking waves seen in some places. NOAA uses NDBC Deep-ocean Assessment and Reporting of Tsunamis (DART) ocean buoys to measure wave heights and predict tsunami waves as they move across the ocean. DART buoys are few and far apart in the vast expanse of the Pacific, making accurate predicitions challenging, but the timing of the wave hiting the California coast was very close to the forecast by the NOAA Tsunami Warning Center.
Damage due to the tsunami hitting California will likely top $50 million, mostly affecting harbors and marinas where surges were not blocked by beaches or cliffs (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 the harbors as a result. Crescent City was especially badly hit (See Assoc. Press Article) but Santa Cruz Harbor also sustained significant damage (see Santa Cruz Sentinel article). Several people in Crescent City were swept out to sea due to tsunami waves, most were rescued but one man drowned (see news story) and one fishing boat narrowly escaped (see High Country News story).
The tsunami wave signature can be seen in plots of water depth from March 11th at California coastal stations. CeNCOOS operates several of these stations along the coast. Examples of the data from 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 the tidal cycles, a basically smooth progression from low to high tide, but during tsunami events the plot looks much more erratic with highs and lows much closer together. The tsunami was also detected at the pressure sensor on the MBARI operated Monterey Accelerated Research System (MARS), located on the seafloor at 891 m (2,923 ft) depth in the middle of Monterey Bay (see pressure plot image indicating depth change on right column).
The diagram below displays data from three CeNCOOS stations in SF Bay (see map of locations). The graph starts at 12 AM March 11, the day of the Japan earthquake. During the first eight hours the graphs show normal sea level changes due to tides. At approximately 08:23 March 11, the first signal of the tsunami registered on the Ft. Point, SF tidal gauge. Six minutes later, at 08:29, the tsunami arrival registered on the RTC Tiburon tidal gauge. There is a small decrease in the tsunami amplitude between Ft. Point and Tiburon. The tsunami signal was not seen at Vallejo until over an hour later at 09:36 and the amplitude was greatly reduced.
Data from CeNCOOS Stations, image created by SFSU Romberg-Tiburon Center. Click to enlarge.
The figures below (created by CeNCOOS) are based on water level data from 12 coastal stations from southern Oregon to San Diego (latitudes on the left side) for the 4-Day Period (left) and the day (right) of the March 11th, 2011 tsunami as it hit the California coast. Brightest reds indicate fastest increasing water levels, darker blues are fastest decreases.
Arrival of tsunami waves along the coast can also be tracked through time on the figures. The figures show waves first appeared at the stations furthest north (top of the figures) and later showed up further south. Click the images below to enlarge:
Water depth/pressure graphs from coastal stations, especially those withing bays, demonstrate that the tsunami generated surges continue long after the initial arrival. The dynamic water level (rising and falling faster than normal tides) continues days later. This is due to a combination of factors: 1) the tsunami waves traveling across the Pacific travel by multiple paths, arriving at different times, 2) aftershocks continue to generate new tsunamis 3) the tsunami can reflect from the ocean boundaries 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. The cause of seiches can be several, 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.
At coastal tide stations, such as those used by NOAA to predict tide heights, the predicted tidal change (without tsunami impact) can be compared to the observed tidal change (with tsunami surge) to assess how much of an affect the tsunami had on the coast. The difference in water height (observed minus predicted) shows the tsunami height at tide stations (see image on right column bottom for the Crescent City, CA tide station).
Could a tsunami the size of the one that hit Japan happen in California someday? Experts say that although big tsunami waves (larger than those that hit the coast during this event) could occur here, they would be very unlikely to be the size of the waves that hit Japan and would likely cause less damage. Earthquakes have and will continue to happen off the California coast, potentially generating tsunamis, but the magnitudes are not predicted to approach those off Japan, thus waves should be smaller. Damage was high in Japan due to the size of the waves, but also because the coastline is fairly flat in many places, allowing the tsunami to travel many miles inland. The California coast is much steeper in most places, preventing tsunami progress inland in all by a few places (mainly harbors). California harbors can sustain considerable damage from tsunamis as seen in this most recent event, but a large tsunami could devastate these areas.
A multitude of video footage from California and Japan clearly showed the arrival of the tsunami surge and its affects:
- 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)
- Japan: Aereal View of Incoming Tsunami Waves (YouTube video)
- Tsunami hits Japanese town
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 TsunamiWatcher email list.
Images from the Santa Cruz Harbor Showing Impacts of Tsunami surges (by Tom Wadsworth):
Videos from the Santa Cruz Harbor Showing Impacts of Tsunami surges (by Tom Wadsworth):- Tsunami surge flowing out of lower harbor
- Surge moves submerged boats etc. near harbor mouth
- Surge breakes up dock and sinks boat in upper harbor
- Sailboat floats free in upper harbor
- Tsunami surge enters upper harbor
- Small craft floats free in upper harbor
Images from the Crescent City Harbor Showing Impacts of Tsunami surges: