Effects of coastal submarine canyons on tsunami propagation and impact

Abstract

HighlightsCanyon incision, width and orientation modify tsunami wave arrival and run-up.Shoreward of a canyon head, tsunami height diminishes with increased incision.At both sides of the canyon, tsunami wave height increases.The presence of a canyon incised very close to the coast can produce edge waves. We analyse the variations produced on tsunami propagation and impact over a straight coastline 20 because of the presence of a submarine canyon incised in the continental margin. For ease of 21 calculation we assume that the shoreline and the shelf edge are parallel and that the incident wave 22 approaches them normally. A total of 512 synthetic scenarios have been computed by combining the 23 bathymetry of a continental margin incised by a parameterised single canyon and the incident 24 tsunami waves. The margin bathymetry, the canyon and the tsunami waves have been generated 25 using mathematical functions (e.g. Gaussian). Canyon parameters analysed are: (i) incision length into 26 the continental shelf, which for a constant shelf width relates directly to distance from the canyon 27 head to the coast, (ii) canyon width, and (iii) canyon orientation with respect to the shoreline. 28Tsunami wave parameters considered are period and sign. The COMCOT tsunami model from Cornell 29University was applied to propagate the waves across the synthetic bathymetric surfaces. Five 30 simulations of tsunami propagation over a non-canyoned margin were also performed for reference. 31 32The analysis of the results reveals a strong variation of tsunami arrival times and amplitudes reaching 33 the coastline when a tsunami wave travels over a submarine canyon, with changing maximum height 34 location and alongshore extension. In general, the presence of a submarine canyon lowers the arrival 35 time to the shoreline but prevents wave build-up just over the canyon axis. This leads to a decrease in 36 tsunami amplitude at the coastal stretch located just shoreward of the canyon head, which results in 37 a lower run-up in comparison with a non-canyoned margin. Contrarily, an increased wave build-up 38 occurs on both sides of the canyon head, generating two coastal stretches with an enhanced run-up. 39These aggravated or reduced tsunami effects are modified with (i) proximity of the canyon tip to the 40 coast, amplifying the wave height, (ii) canyon width, enlarging the areas with lower and higher 41 maximum height wave along the coastline, and (iii) canyon obliquity with respect to the shoreline and 42 shelf edge, increasing wave height shoreward of the leeward flank of the canyon. Moreover, the 43 presence of a submarine canyon near the coast produces a variation of wave energy along the shore, Tsunami; multi-scenario; numerical simulation; submarine canyon 54 55

Effect of Submarine Canyons on Tsunami Heights, Currents and Run-Up Off the Southeast Coast of India

“…The current speed was greater at 10 m water depth compared to the speed closer to the coast. The flow velocities in the canyon were greater than the flow velocities along the ridge, which is consistent with the observations made in other studies [18][19][20] . Focusing of velocity vectors on the shelf region of the ridge and divergence of velocity vectors at the canyon head can be clearly observed in this study.…”

“…The tsunami front along the canyon propagates faster to the canyon head, but also diverges and propagates along the canyon slopes thereby diffusing its energy in transverse directions. The tsunami front propagation observed in this modelling study is similar to those carried out in the literature 16,18,19 , wherein the processes of refraction, diffraction, shoaling, reflection and dissipation of tsunami waves are observed. The tsunami wave along the ridge is observed to steeper than the tsunami profile along the canyon transect.…”

“…Iglesias et al 19 analysed the results of tsunami propagation over synthetic submarine canyons and concluded that there is a strong variation of tsunami arrival times and tsunami amplitudes on the coastline for tsunami propagation over submarine canyon, with changing maximum height location and alongshore extension. Their study indicated that the presence of a submarine canyon not only reduces the arrival time at the shore but also prevents tsunami amplification just over the canyon axis, leading to a decreased tsunami height along the stretch of the coast shoreward of the canyon head.…”

“…Numerical modelling by Roger and Hébert 17 indicated the modification of nearshore wave heights by submarine canyons, but no observation data were available for verification. Other notable studies are those by Aránguiz and Shibayama 18 , and Iglesias et al 19 . Using idealized bathymetry, and no ridges formed by adjacent canyons, these studies showed a reduced run-up behind the canyon and an increase in run-up and tsunami amplification at the adjacent coasts, which were consistent with field observations.…”

“…Thus, while general principles identified by Aránguiz and Shibayama 18 , and Iglesias et al 19 indicate the overall effect of canyons, care is needed when applying those findings to more complex natural bathymetry, and highquality field data are also needed for Model verification. The effect of the canyons and ridges present on the southeast coast of India on the local tsunami run-up heights has not been modelled in previous studies, nor have there been model comparisons with local field data along this coast.…”