Earthquake and Tsunami Dangers
Safety Concerns of Interest to Boaters and Coastal Residents
Tsunami generated by severe earthquake or submarine landslides pose a risk to boats, boaters and other coastal residents. Often they can be predicted and mitigated.
Coastal communities have much the same risk from earthquakes as those towns located more inland. An additional concern for those living along the shoreline is the generation of tsunami by severe earthquakes. Boaters living in tsunami prone areas need to aware of these risks.
Mechanisms of Tsunami Production - Tsunami waves can be generated by two general causes. Just to keep everyone alert, they can also be rarely spawned by volcanic eruptions, meteor strikes or nuclear explosions. The two common mechanisms are:
- Tsunami from a distance - The shifting of the seafloor during an earthquake can create a tsunami wave in deep water that can travel rapidly over long distances. A boat near the source of one of these waves would not likely notice a change in water height and arrival of these waves can be predicted
- Locally generated tsunami - Earthquakes can cause marine soils to slough off into deeper water creating a submarine landslide. Materials weighing thousands of tons displace water and generate a locally severe wave. These tsunami occur without warning
Open Ocean Tsunami - A tsunami generated in mid-ocean can be detected early and there is often time for adequate warning to coastal communities. Having long periods (distance) between crests and not much height in deep water characterizes these waves. Tsunami are not a single wave, but actually a series or train of waves that can travel at 800 kilometers per hour (500 miles per hour). The open ocean wave will slow and grow in height as it reaches shallow coastal waters.
Locally Generated Tsunami - Locally generated tsunami require a different approach. In the event one of these waves reach a marina, the only safe course of action is evacuate to higher ground. Warning signs are extreme changes in tides, a loud roaring noise or a felt earthquake that lasts more than 20 seconds.
Impact of Tsunami on Marinas - Increased wave action impinges directly on docks and moored vessels. Marine structures like piling and bulkheads can create unpredictable currents. These effects put boats and people at risk, so marinas should be evacuated during a tsunami warning. Vessels at sea should remain there until the danger has passed. Maintain a listening watch on NOAA weather radio.
Tsunami Strategies for Boaters - Since mid-ocean tsunami can be detected and there are often warnings issued long ahead of landfall, there could be an opportunity for some larger boats to leave the marina and move to water more than 100 fathoms (1,100 meters) deep. The effects of the waves are minimal in these deep waters. Any decision to move a boat would be strictly based on the skipper's personal evaluation of the risk and must not cause any safety problems for others located in the marina. Smaller boats are safer left in the marina.
Vessel owners should keep in close contact with their marina operator and Coast Guard. Follow the safety recommendations provided by these safety professionals. Remember that tsunami are a series of waves, so after the first has past, there is still risk from another landing. Many coastal communities are TsunamiReady and planned for these events.
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