A 15-foot wall of water could roll across Grand Isle if a landslide occurred in the Mississippi Canyon, a trench in the Gulf of Mexico floor about 30 miles off the mouth of the Mississippi River.
And unlike a hurricane, residents would have just an hour’s notice – not days.
Such landslides have happened about once every 1,000 years in that area, and that time frame is almost up.
Although being a low probability event — one in a thousand — it still is a credible event, and would be of a high impact.
The National Weather Service has found evidence of previous slides in the canyon, which could cause significant tsunamis. The material falling into the canyon would displace the water that is already there, and that would cause the wave. It wouldn’t be very noticeable in the open Gulf, but as the wave reached the shallower water near the shore, it would rise up.
The hypothetical landslide used in National Weather Service computer model was 13 miles wide, 40 miles long and dumped enough rocks and sediment into the canyon to fill 38 Superdomes.
The resulting tsunami waves would reached about 14 to 15 feet at Grand Isle, 10.5 feet in St. Mary Parish, and about 4 feet in Cameron Parish.
The following video shows a physics-based computer simulation (by UCSC) of a tsunami generated by a submarine landslide in the Gulf of Mexico about 7000 years ago. The 500 cubic km landslide occurred in Mississippi Canyon and generated tsunamis from 2 to 20 meters which reached all shores of the Gulf.
So what would cause such a tsunami?
The likely trigger of a future slide would be seismic activity, which has been rare in this area; the eruption of large gas bubbles through the sediment layers at the base of the area; or the sheer weight of the sediment resting on the edge of the canyon.
If you thought sinking land and rising seas were the only things they had to worry about in south Louisiana, think again.
Tsunamis have now joined the list.