A: Esther from Seaside asked, "Would the huge canyon in the Monterey Bay lessen the impact of a tsunami here or worsen it?" She also asked, "would the water be able to come as far inland since we have the canyon and we have hills?"
Our Chief Meteorologist Norm Hoffmann has the answer.
The wave that hit us in March was only 2 to 4 feet. Should a much larger wave be generated it would take something like 6 to 8 feet just to get into Seaside and Marina. Of course it would impact the beaches, but not very far inland. It would only travel inland as far as the peak of the wave which would be possibly 8 to 10 feet above sea level because the wave crests as it approaches the shore. The one that hit Japan was 30 feet. If a wave that hight were to hit the Central Coast, that would cover much of downtown New Monterey, Portions of Downtown Monterey, Seaside and Marina, but only up to 30 or 40 feet above Sea Level. It might go into some of the valleys, but no where higher that 30 to 40 feet above sea level. Look at some of the Tsunami Inundation maps that are on the National Weather Service Web site. http://wcatwc.arh.noaa.gov/ They have already done the studies and the City and County Emergency Services Agencies already have those. They are located at: http://www.conservation.ca.gov/cgs/geologic_hazards/Tsunami/Inundation_Maps/Pages/Statewide_Maps.aspx when you get there, click on Monterey County and they will have a number of other boxes and click on the box you are interested in and it will enlarge the area and show the coastline. The red areas are inundation areas for a 8 to 10 foot wave. It is for Tsunami Emergency Planning to help Emergency Responders evacuate people in a Tsunami Warning. The state of California has maps for all the coastal areas at the site above. I hope that helps. There are a lot of resources out there just check the Website http://wcatwc.arh.noaa.gov/ and happy reading. That is where I get most of my information as well.
Tsunami waves are generated from the bottom of the ocean from movement of the land due to an earthquake (as off Japan) or a large land slide under water. That motion pushes the surface water up (or down) and then the water at the surface it undulates up and down a number of times generating waves, like dropping a stone in the water. Once is reaches the surface the wave travels across the ocean on the surface as speeds as high as 300 to 500 miles per hour. If you are below the sea surface, you will not even know the wave is going by you. In fact the wave crests are so far apart that if you are on a boat on the surface you cannot tell the wave is passing.
The bottom line is the wave travels on the surface of the water. The topography of the bottom of the ocean does affect the wave, but only as it approaches the shore and the water gets shallower. So as the wave approaches the shore it is the bottom of the ocean that affects how the wave crests and breaks. In a way the deep canyon in the Monterey Bay does have a small effect on the wave. The wave will not build and crest (basically show up) until it gets closer to the shore. If the Bay were very shallow that would then build the wave very high inside the Bay and it would be easy to see. However it is the shape of the Bay that affects the wave even more. The mouth of the Bay is narrower than the inside of the Bay therefore some of the Waves energy spreads out as it move into the Bay and therefore is spread over a larger area as the Bay widens and thus the energy is not as strong.
The bottom does have a small affect on the wave, but only near shore (where it is shallow) and the wave travels along the surface of the ocean.