29 June 2011

The mini-tsunami on the south coast of England – a submarine landslide?

Posted by Dave Petley

A fascinating story has appeared in various news outlets in the Uk over the last few hours.  On Monday morning this week the southwest coast of the UK was affected by a highly anomalous marine event.  This is covered quite well in a BBC news article, which describes “rivers changing direction, fish leaping out of water and hair standing on end due to static” and brief tidal anomalies of 0.2 m in Newlyn, Cornwall, 0.3 m in Plymouth and 0.4 m in Portsmouth.  The event was also caught on video in the Yealm estuary near to Plymouth:

The various news reports ascribe this event to a submarine landslide.  Now, this is quite an interesting event actually.  The Google Earth map below shows the seafloor topography in this area and the locations that news reports suggest experienced the “tsunami”:

A few things to note here.  First, the locations that this was reported are widely spaced  Second the largest event was reportedly at Portsmouth (which is both a substantial distance to the east and sheltered by the Isle of Wight.  Third, the seas offshore the south coast of England are really quite shallow.  Fourth, the continental slope, which is the most likely location for a submarine landslide, are well to the west.

To me this is a somewhat strange event that requires some deeper investigation.  I wonder if the tsunami was observed on the coast of northwest France – if this was a continental slope event then it should have been, but I have seen no reports to suggest this.

Certainly something happened to cause this event on Monday, but I think the jury is still out as to what it might have been, and where.