30 August 2008
The award for the strangest landslide story of the week goes to this one, from southern Africa. Late last week reports started to emerge of strange tidal patterns around the southern Cape of Africa (Fig. 1).
In particular, on 21st August at about 8:45 am (local time) a series of tidal oscillations were recorded in St Helena Bay (Fig. 2). These tidal oscillations were reportedly large enough to damage some factories, pull a car into the sea and to cause problems for boats navigating into the harbours. A couple of days later, a report emerged from the National Sea Rescue Institute (NRSI) suggesting that the “mini-tsunami” was caused by a seismically-induced submarine landslide. Fig. 2 shows that some anomalous tidal activity certainly did occur.
In the last couple of days a more considered analysis from NSRI has been reported, recognising that the cause is more likely to be meteorological than the effects of a landslide. The South African Weather Service have proposed that atmospheric gravity waves might have been the cause, although they are sitting on the fence a little.
Whilst these tidal oscillations are clearly strange, a landslide cause does not really seem to be very likely.