Tsunami
A tsunami is a strong, fast-moving wave or series of waves. They are generated when geologic events, such as earthquakes, landslides, submarine landslides, or volcanic activity, cause large, rapid movements in the sea floor that displace the water column above. In Puget Sound, tsunamis can be caused by local landslides from surrounding bluffs. The displacement of water creates a series of high-energy waves that radiate outward like pond ripples. Offshore tsunamis can strike adjacent shorelines in minutes and cross the ocean at speeds as great as 600 miles per hour to strike distant shores. Kitsap County is at risk from tsunamis of both local and distant origin. These destructive waves are most commonly caused by submarine earthquakes. Our current technology gives us adequate warning for tsunamis produced by distant quakes; however, an earthquake on the Seattle fault would have near immediate impacts (only two to three minutes before the first set of waves hit).
Bainbridge Island is located in the tsunami inundation zone and current modeling indicates a tsunami resulting from a Seattle Fault and/or Cascadia Fault earthquake could impact certain low-lying waterfront areas around the island. We are also at risk for a landslide-induced tsunami. This type of tsunami has the potential to be slightly larger, but more localized.
The Department of Natural Resources (DNR) has produced models indicating the tsunami inundation resulting from a 9.0 Cascadia Fault rupture and a 7.5 Seattle Fault rupture. The models can be viewed by clicking the links below.
Tsunami Modeling:
DNR has recently published two sets of tsunami data; one based on a 9.0 Cascadia subduction zone earthquake and one based on a 7.5 Seattle fault earthquake.
Cascadia Model
Modeling suggests that a Cascadia caused tsunami would reach Bainbridge Island in a little over two hours.
Seattle Fault Model
A Seattle fault caused tsunami poses the biggest risk to Bainbridge Island. The first issue of concern is the short time span between an earthquake on the Seattle Fault and the first tsunami waves. For a 7.5-magnitude quake, the expectation is that the first large waves will hit Bainbridge shores within just 2 to 3 minutes. What this means is that, if you're on the shoreline and you feel a quake, don't pause to figure out if it was a Cascadia quake or a Seattle Fault quake. Get to higher ground immediately.
The second concern raised is the likelihood of significant inundation on Bainbridge coastline. The simulation shows the following potential depth of flooding in specific locations:
- Fay Bainbridge: 11 feet
- Manitou Beach/Murden Cove: 32 feet
- Yeomalt Point: 24 feet
- Eagle Harbor: 21 feet
- Pritchard Park: 26 feet
Again, what this means is, immediately following a quake, if you're on the shore or on property less than 30 feet above the coastline, get to higher ground: 30 to 40 feet higher. Accompanying the ensuing tsunamis will be an increase in water currents. Again, if you're on the shore or if you're in a boat or kayak, take immediate evasive action after an earthquake. Here are predicted current speeds:
- Port Madison: 19 knots
- Murden Cove: 25+ knots
- Bill Point: 25+ knots
- Blakely Harbor: 25+ knots
- Restoration Point: 25+ knots
- Point White: 25+ knots
- Fletcher Bay (entrance): 25+ knots
- Agate Passage: 25+ knots
Warning Signs of a Tsunami
A tsunami may be about to hit if you:
- Receive a tsunami alert
- Feel a strong earthquake (a strong earthquake is one that knocks people down, damages buildings, or lasts for longer than 20 seconds)
- Notice a very large approaching wave
- See the water in the Puget Sound recede
- Notice an unusual rapid rise in sea level
- Notice a landslides that falls or slides into the sound
Evacuate to higher ground immediately! if you notice any of these signs.
Know how to evacuate on foot, even if that means walking along the road of the evacuation route. Learn about your tsunami hazard and where you should go during an evacuation.
Review the Bainbridge Island tsunami inundation map for neighborhood specific information.