Analog Model Results
After setting up the analog wave tank to produce waves on a scale for analysis, experiments were conducted using varying mass influxes into the system to produce waves of varying amplitude. Results can be viewed below: click image or trial number to initiate video (must support quick time).
Trial 2: Influx volume of 2287.5 cubic centimeters
1787.5 cubic centimeters. (must support quick time) Trial 4: Influx volume of 3287.5 cubic centimeters
Each trial volume was conducted several times producing similar wave patterns. In trial 2, during the 9 second frame, if viewed slowly gives a good view of wave turbulence when a wave comes down on a shoreline or in the case of Lituya Bay the wave rolls up the opposite hillside. The same wave dynamics can be viewed in the trial 4 during the frame of the eleventh second. As the wave crashes down in front and begins rolling over, there is another turbulence near the rear of the wave, giving a good full view of landslide tsunami wave dynamics.
In comparison, tests were done using a wave tank with a motor attachment. This tank provides a view of a wave that is not in constant contact with the sea floor. The wave produced from this tank gives a reference as to what open ocean tsunami waves may look like on a small scale. Click image to view open ocean simulation wave:
This wave simulation provides a good idea of the amplitude and wavelength of an open ocean tsunami versus the amplitude viewed in the above results from a landslide generated tsunami. The open ocean wave has a long wavelength and small amplitude compared to that of the landslide tsunami running up the shore or hillside as energy is dissipated. The ocean here is deep enough that the wave base does not contact the ocean floor, leaving waves to move along with minimal energy loss.
Amplitudes of the generated waves were found to increase as mass influx increased throughout the tests. The mean maximum wave amplitude (centimeters) for each test is as follows: trial 1 - 3.33; trial 2 - 4.83; trial 3 - 5.33; trial 4 - 6.33, also seen in the graph showing wave amplitude versus volume influx below.
This data gives a direct correlation with the mass displacement of the landslide and the wave amplitude produced from the event. There are other factors involved in landslide tsunamis dictating their size and speed that will be viewed in the discussion.
Mechanical and Theoretical Problems
When doing this experiment is became quickly evident that the recreation of a tsunami on such a scale becomes an issue. Initially the experiment was to analog the two parts of tsunami dynamics, open ocean long wavelength, small amplitude transferring energy into small wavelength, large amplitude upon reaching shore. In order to model this it would have been necessary to have a much larger tank that could produce massive water column displacement in a deep area of the tank and analyze the wave as it came in contact with a shallow part of the tank. Since this wave tank was of constant depth, it would not produce such a good analog for transition of energy into amplitude. In an attempt to fix this problem, another tank was used that was much more shallow, but had a longer width and length. This tank, however, would not produce waves without refraction from the sides before reaching a modeled sand shoreline.
After careful consideration and analysis of how waves were being created, the best natural scenario for the analog wave that was being produced with the current method of generation was to model a tsunami created from landslides. Quickly it became evident that these waves that were being produced modeled those of a quick influx of mass into a static system. Through coordination of material one particular event was close to exactly the sort of experiment that was being conducted, that was the 1958 landslide generated tsunami of Lituya Bay, Alaska. With mechanical difficulties worked out, and a natural example for which to model the system after, Liutya Bay became the basis of research. Theoretical problems arose as to how it is possible to analyze and compare the Lituya Bay tsunami to that of a wave tank. This had been worked out to simulate that of Lituya Bay and use numerical models to illustrate the dynamics of landslide generated tsunamis.
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