28 January 2010

Earthquake-driven coastal erosion (or a coastal lateral spread) in Haiti

Posted by Dave Petley

The Discovery Channel has news of a very interesting example of rapid coastal erosion driven by the earthquake in Haiti. The site is at Petit Paradis to the west of Port-au-Prince. Eye-witness reports suggest that the town was struck by a highly localised tsunami in the earthquake, apparently killing 20. This is interesting in part because it is quite likely such a localised event would have been caused by a (submarine?) landslide – not at all unusual in earthquakes. However, the before and after satellite images show the magnitude of the changes on the coastline in this area.


And after:

At first glance the change does not look so dramatic, but take a look at the location of the coastline in the before image in relation to the white building that I have highlighted below:

Actually, it is a little more interesting than you might initial suppose. First, note that the section of coast that has “disappeared” lies only between the two yellow dots that I have marked on the image above. To the east and the west the beach is intact. Second, take a look at this CNN video:


The key aspect is the picture of that lone tree standing upright in the ocean. A USGS report has suggested this is the site of a lateral spread (the same type of landslide that is evident in the port area of Port-au-Prince), which has caused the coastline to slip into the sea. As lateral spreads are essentially translational, a tree can remain upright. Unfortunately, as the coastline is now no longer protected by a beach, further erosion is likely. An interesting hypothesis is of course that this not-insubstantial slip caused the localised tsunami – or could it be that there was no wave at all, just the appearance of one to those people standing on the land as it slipped below the waves?