Discussion


Analysis of landslide generated tsunamis and scaling the Lituya Bay Scenario

          Landslide generated tsunamis, because they do not always cause as large of a water column displacement as earthquake generated tsunamis, are seen to have smaller wavelengths.  However, the amplitude and wave run-up generated from landslide tsunamis is similar.  The particular scaling involved with this analog model leaves many aspects of the necessary equation constant.  The important components when dealing with landslide generated waves according to Kofoed-Hansen, Giménez and Kronborg in their work, is the instantaneous water depth, time varying bathymetry, surface evolution, flux densities, depth averaged velocities, acceleration due to gravity, wind friction, water density, and time.  For the purpose of this experiment the surface evolution, flux density, averaged depth velocities, and wind friction are considered to be constant due to the system the waves were generated in.  This gives a basic formula looking like:  ∂h/∂t - ∂d/∂t; exhibiting the change in instantaneous water depth with a change in time and then subtract the change in bathymetry with a change in time.  The particular bathymetry for the analog model is a flat plexi-glass surface, so this can be considered zero as well.  The design of this analog was more to display wave amplitude change with mass influx increases and wave dynamics, not the prediction of wave amplitudes based on certain constraints.
        Kofoed-Hansen, Giménez and Kronborg developed an actual equation using the integration of the conservation of mass and momentum to determine a vertical amplitude based on the time varying bathymetry of the area, as seen below:

  
 
                                            Integration involving bathymetric parameters and wave factors to decipher probable wave dynamics based on mathematic data.
http://www.dhisoftware.com/uc2001/Abstracts_Proceedigs/Papers01/036/036.htm

       This model uses the basis of kinetic energy to describe the wave sizes and dynamics via the all possible variables in a wave interaction system.  Conservation laws state that as the energy of the landslide transfers to the water it is converted into wave amplitude and turbulence, which can be viewed from the analog video.  The forces involved in this transfer are the mass of the landslide and the drag force that is create beneath the surface as the water column is displaced.   Wave turbulence and dynamic energy exchange can be seen in the analog lab as well as figure 2 below.


Figure 2: animation and bathymetry of Lituya Bay wave (http://students.washington.edu/hschwaig/webpage/research/mass_wasting/ls.html)

      With this integration it is possible to determine many dynamic parts to landslide generated tsunamis if predictions can be made of where possible landslides will occur.  The model indicated in figure 2, done by Washington University, discusses the scaling difficulty with simulating tsunami events triggered by landslides in a computer model, however using viscosity, density and initial mass distribution, calculated models can be made.  Due to the fact that the models presented here are all done on the Lituya Bay landslide, constants are held for mass influx and bathymetry, while viscosity and density variances are described to produce a wave similar to that in Lituya Bay in 1958.  With the analog experiment it was more important for an overall view of landslide generated tsunamis and the wave amplitude changes with mass influx to be visualized.

      Steven Ward, of the University of California at Santa Cruz, used a numerical model to develop a simulated video of the Lituya Bay tsunami based on the size of the landslide and the tsunami wave dynamics, seen here or via Steven Ward's computer simulations http://www.es.ucsc.edu/~ward/.  This model is just a look into what numerical modeling can bring to the prediction of landslide tsunami hazard zones.  Using the numerical model above and work like Ward's, it is possible to look into the devastation before it happens, allowing for precautions to be taken beforehand for a general populous in an area or structural stability.
       Other work done by Eric W. Weisstein and Michael Trott using supercomputers with complicated programs, discuss the present problem of scaling tsunamis without the use of partial differential equations involving the many aspects that inhibit tsunami waves.  The physics behind the tsunami is complicated and not fully understood as of yet.  The problem being that every tsunami is different because it is based on the initiating seismic activity, mass influx variances, and ocean floor bathymetry for example.  With these variables alone it is near impossible to predict the behavior of a tsunami wave and its dynamics without having complex algorithms and real spatial data to coincide with it.
        Tsunami research is gaining ground and the realization for importance has become evident.  This work is made possible by the advancements in today's computer systems as well as research development allowing for tsunami prediction and calculation of magnitude based on the system in which the wave interacts.   Many pacific coast institutions have begun funding for major work to be done into the prediction and development of how these massive waves of destruction evolve and function as to one day prevent the devastation that has taken place in the past.



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