What is a Tsunami ?
Although many people call tsunamis “tidal waves” they are not related to tides but rather a series of waves, or “wave trains,” usually caused by earthquakes. Tsunamis have also been caused by the eruption of some coastal and island volcanoes, submarine landslides, and oceanic impacts of large meteorites. Tsunami waves can become more than 30 feet high as they come into shore and rush miles inland across low-lying areas.
Tsunamis are often caused by earthquakes that lie along fault lines known as “subduction zones.” A subduction zone is an area where two tectonic plates meet each other and one is pushed beneath the other. As the plates pass each other they become stuck. Eventually the pressure becomes too much and the leading edge of the overriding plate springs free, raising the sea floor and the entire column of water above it. This displacement of the water results in the formation of a tsunami. The 2004 tsunami in Indonesia, and the recent tsunami in Japan, were both caused by subduction zone earthquakes.
Like Indonesia and Japan, we also have a subduction zone off of our coastline known as the Cascadia Subduction Zone. In this zone, the Juan de Fuca plate is moving inland, under the North America plate, which is moving seaward. The Cascadia Subduction Zone extends from northern California all the way to Washington and lies approximately 50 to 75 miles off of our coast.
The following animations explain how tsunamis are formed. The second one is geared for kids but contains valuable information for adults as well.
Courtesy of Incorporated Research Institutions for Seismology
Courtesy NOAA and the San Diego County Office of Emergency Services
How to Survive a Tsunami
1) During the Earthquake – DROP, COVER, and HOLD.
DROP to the ground. You want to avoid falling objects or injuries caused by being knocked off of your feet.
COVER. If you’re inside a building, find something sturdy to get under, such as a desk or table. If nothing is available, get close to a wall and cover your head. If you are outside you want to be in an open area, as clear as possible from falling objects such as buildings or trees.
HOLD on and keep down. Stay where you are until the shaking stops.
2) After the Earthquake
If you are in a building, carefully make you way to the exit. Avoid areas of a building that have suffered heavy damage. Before exiting make sure that your exit is safe and as you exit look for parts of the building that could fall on you.
Once you are outside be sure that you are watching out for other hazards, such as electrical wires that have fallen, and avoid areas that have and odor of natural gas, as pipe may have ruptured.
3) Immediate Evacuation
Once the earthquake is over, IMMEDIATELY begin moving inland and uphill as quickly as possible. Remember that during a Cascadia Subduction Zone event, you will have between 5 and 15 minutes to get out of any low-lying areas before the tsunami arrives.
Do not wait for Emergency Services personnel to tell you to evacuate or for the Community Warning System (COWS) to sound the tsunami alarm. Emergency Services personnel will not be able to notify everyone in the short amount of time between the earthquake event and the arrival of a tsunami. Also, it is possible that the COWS system could be damaged by the earthquake making it inoperable.
DO NOT DRIVE YOUR VEHICLE! The gridlock of vehicles will trap many people in deadly flood zones.
4) Wait for the Official “All Clear” Before Returning to Low Lying Areas
Please, until you receive an official “all clear,” stay outside of the tsunami inundation zones. As stated above, a tsunami event is not just one wave but a series of many waves. A tsunami event can last for hours. Just because the initial wave has reached the shore doesn’t mean that the danger is over. In fact, history has shown that many of the victims of tsunamis are not victims of the initial wave but rather were victims from subsequent waves because they had returned to the low-lying areas before an official “all clear.”
For information on tsunami inundation areas and evacuation assembly areas for the Cannon Beach and Arch cape areas click here —> TSUNAMI MAP & EVAC
For interactive maps, information on other coastal communities, or further information on tsunamis and tsunami preparedness click HERE
