Tsunamis that threaten the coast of Maine can originate in the open ocean or within the Gulf of Maine. Those originating outside the Gulf of Maine can produce damaging impacts along the entire Maine coast while those originating in the Gulf of Maine are likely to have more localized impacts.
TSUNAMI WAVES ENTERING THE GULF OF MAINE...
The shallow waters of Georges Bank and the continental shelf greatly lessen the threat of tsunamis in Maine. When tsunami waves that are generated outside the Gulf of Maine encounter the shallow waters of Georges Bank, the tsunami loses speed and begins to break and a portion of the wave energy is reflected back out to sea. Wave energy, however, can still permeate the Gulf of Maine through the deeper water of Northeast and Great South Channels. The deeper water allows the waves to continue to travel at faster speeds through the channels than in the shallower waters on either side. Much of the incoming tsunami wave energy would then be refracted to the right and left of the channels and that initial energy would be redirected toward Georges Bank and Nova Scotia. However, ensuing reflections and refractions of this wave energy would lead to rapid and chaotic fluctuations of water levels in the Gulf of Maine that could last for more than 6 hours. These fluctuations could cause strong, dangerous, and damaging currents along the coast and could cause inundation at the time of high tide.
The two most significant tsunami sources outside the Gulf of Maine would be a major earthquake along the subduction zone of the Puerto Rican Trench (just to the north of Puerto Rico) or a large sediment slide on the continental slope of the East Coast. If a tsunami were to originate in the Puerto Rican Trench, much of the tsunami wave energy would be directed north toward the Gulf of Maine. This tsunami would reach Maine between 5 and 6 hours after the earthquake, which allows time for a warning or advisory. Although this tsunami poses a threat to Maine, the impacts to northern New England of a tsunami generated along the Puerto Rican Trench would be relatively small compared to those on Puerto Rico and Bermuda.
A large sediment slide or slump along the continental slope can also generate a tsunami with the potential to enter the Gulf of Maine. The exact impacts of slide or slump depend on the orientation of the slide or slump with respect to the Northeast and Great South Channels and magnitude of the slide or slump.
TSUNAMI WAVES GENERATED IN THE GULF OF MAINE...
Sediment slides or slumps in the Gulf of Maine can also cause tsunami waves, though these are more likely to be localized. Slides or slumps are most likely to occur near the coast or along the northern edge of one of the banks or ledges in the Gulf of Maine. The exact impacts of the tsunami waves depend on the orientation and magnitude of the movement of the continental slope. There would be little warning time for the subsequent tsunami because of their proximity to the coastline of Maine.
Locally sourced tsunamis can also be generated by the atmospheric pressure waves. Also known as meteotsunamis, these waves are caused by a harmonic resonance between the atmosphere and the ocean. This resonance allows the ocean wave to grow with time as both waves move in unison. Since the forward speed of the wave is determined by the depth of the ocean, the atmospheric feature needs to move at the just the right speed as determined by the ocean depth. In the Gulf of Maine, very fast moving weather systems can meet this requirement. The movement of both the atmospheric and the ocean waves need to move toward the coast to threaten Maine. A meteotsunami caused the unusual tidal fluctuations that occurred along the mid-coast in October 2008.