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Tsunami in the Gulf? It could happen...

Texas A&M Galveston shows us how

KRABI, THAILAND:  (FILES) File photo dated 26 December 2004 shows tourists caught by the first of six tsunami rolling towards Hat Rai Lay Beach, near Krabi in southern Thailand, following a 9.2-Richter submarine earthquake, which left 228,429 people dead and missing in the region. Sri Lankan authorities issued a tsunami warning calling for coastal evacuation, following an 8.2-Richter quake off the Indonesian island of Sumatra 28 March 2005.       (Photo credit should read AFP/AFP via Getty Images)
KRABI, THAILAND: (FILES) File photo dated 26 December 2004 shows tourists caught by the first of six tsunami rolling towards Hat Rai Lay Beach, near Krabi in southern Thailand, following a 9.2-Richter submarine earthquake, which left 228,429 people dead and missing in the region. Sri Lankan authorities issued a tsunami warning calling for coastal evacuation, following an 8.2-Richter quake off the Indonesian island of Sumatra 28 March 2005. (Photo credit should read AFP/AFP via Getty Images)

Houston, TX – Yesterday’s Caribbean earthquake prompted this question from KPRC2 viewer, Tom Stafford:

Just curious, with the recent earthquake activity around Cuba, Puerto Rico and Jamaica. Could there be a threat of a tidal wave impact to the US coast line?

First, thanks for the question. And to be clear, a tidal wave and tsunami are the same thing (“tsunami” is Japanese for “Harbor Wave”). A tsunami looks like any other wave you see in the ocean, only more wall-like, but those waves you usually see are caused by wind pushing the water rather than water being displaced, a concept you are also familiar with although you may not realize it!

If you’ve ever done a ‘cannonball’ dive in a pool, then you know how that displaces water--it splashes all the poor souls around and causes water to run to the pool edge and spill over. The water is displaced from above with the human body taking the place of the water, so the water has to go somewhere! A tsunami happens when the water is displaced from down below in the ocean.

How does that happen? Two obvious ways: an earthquake or a landslide below the surface. In an earthquake, the land shifts vertically or horizontally displacing the water with earth and causing deep waves to move outward, like a pebble in a lake. The waves get higher as they get closer to land where the coast is shallow. The water has to go somewhere and that somewhere is on land. These tsunamis are only a problem if they get to land and we’ve had them on the east coast and, more often, the west coast of the United States. But not the Gulf--we don’t have an earthquake zone and are protected by other landmasses. HOWEVER.....

A less familiar tsunami is caused by a sediment landslide. Imagine this as a mountain avalanche under the water. In the mountains, snow piles up until it’s so heavy it creates a landslide down the mountain. In the Gulf, thousands of years of sediment piles up (like the snow) until the weight causes a sudden landslide (avalanche) of the sediment into deeper waters. That can be pretty serious.

The Mississippi River continues to slowly but surely dump sediment into the Gulf. Look at the bathymetry and how deep the GOM, Gulf of Mexico, becomes in the middle:

The gulf is shallow at the coast but very deep in the middle!
The gulf is shallow at the coast but very deep in the middle!

So it’s easy to understand how a sediment landslide, or avalanche, into the deeper part could suddenly displace water and push it to the coast: a tsunami. Look at this map showing where these landslides have happened before and where TAMU studies indicate it could happen again.

Red is Historical Landslide areas while blue is Probabilistic areas
Red is Historical Landslide areas while blue is Probabilistic areas

Texas A&M Galveston started studying this possibility in 2005 and and modeling the results if such occurred:

The study is fascinating and includes lots of water inundation maps, including Galveston and San Luis Pass:

Galveston water inundation from a Tsunami up to 12'
Galveston water inundation from a Tsunami up to 12'
San Luis Pass Tsunami inundation up to 11'
San Luis Pass Tsunami inundation up to 11'

Take a look at the full study, the link to their Power Point presentation and the links to inundation maps. Notice that their leading paragraph does indicate “a very low threat." But any threat is a threat and worth exploring and understanding!

Prayers to the folks suffering from both the recent Puerto Rico and Caribbean earthquakes.

Frank

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