Landslide generated impulse waves. 2. Hydrodynamic impact craters

Abstract

Landslide generated impulse waves were investigated in a two-dimensional physical laboratory model based on the generalized Froude similarity. Digital particle image velocimetry (PIV) was applied to the landslide impact and wave generation. Areas of interest up to 0.8 m by 0.8 m were investigated. PIV provided instantaneous velocity vector fields in a large area of interest and gave insight into the kinematics of the wave generation process. Differential estimates such as vorticity, divergence, and elongational and shear strain were extracted from the velocity vector fields. At high impact velocities flow separation occurred on the slide shoulder resulting in a hydrodynamic impact crater, whereas at low impact velocities no flow detachment was observed. The hydrodynamic impact craters may be distinguished into outward and backward collapsing impact craters. The maximum crater volume, which corresponds to the water displacement volume, exceeded the landslide volume by up to an order of magnitude. The water displacement caused by the landslide generated the first wave crest and the collapse of the air cavity followed by a run-up along the slide ramp issued the second wave crest. The extracted water displacement curves may replace the complex wave generation process in numerical models. The water displacement and displacement rate were described by multiple regressions of the following three dimensionless quantities: the slide Froude number, the relative slide volume, and the relative slide thickness. The slide Froude number was identified as the dominant parameter.

3-D numerical approach to simulate the overtopping volume caused by an impulse wave comparable to avalanche impact in a reservoir

“…These analyses show a small outward collapsing impact crater in the first seconds, but afterwards it converts into a backward collapsing impact crater. This behaviour also has great similarities to the studies of Fritz et al (2003b).…”

“…Depending on the location and time, the Froude number is approximately in the range of 7-8 (-) for the chosen set-up. According to Fritz et al (2003b), who used a higher bulk slide density ρ s of 1620 kg m −3 in his experiments, Froude numbers bigger than 4 (-) lead to an outward collapsing impact crater. Figure 3 shows in its left column six time steps starting after the first interaction of the model avalanche with the reservoir (starting at second 5.6 of the simulation with a t of 1 s between each picture).…”

Subaerial Landslide-Generated Waves: Numerical and Laboratory Simulations

“…The wave characteristics (e.g. amplitudes, velocity, wavelength and period) are governed by the water body geometry, depth, volume, and dimensions as well as the slide characteristics, and the slope angle (Fritz et al 2003;Panizzo et al 2005a;Zweifel et al 2006;Najafi-Jilani and Ataie-Ashtiani 2008). A schematic of a typical SALGW development at different stages of impulsive wave generation, propagation, runup, overtopping, and inundation is shown in Fig.…”

Numerical simulation of tsunami generation by cold volcanic mass flows at Augustine Volcano, Alaska

“…Recent studies of impact-generated waves have described the region from the shoreline to the area where the mass flow stops on the sea floor as the splash zone (Walder et al, 2003;Walder et al, 2006). The splash zone is an area of complicated wave dynamics and chaotic water behavior (Fritz et al, 2003a;Fritz et al, 2003b;Fritz et al, 2004) and for Augustine Volcano, this zone extends from about 4 to 9 km beyond the shoreline. Beyond the splash zone is a near-field zone, and this zone is the area of the wave domain where a well defined wave evolves from the splash zone.…”