10 October 2018

Two developing large landslides – Mannen (again) and Diamante

Posted by Dave Petley

Two developing large landslides – Mannen (again) and Diamante

News today of two interesting landslides under development, at Diamante in Argentina and Mannen (once again) in Norway


Diamante is, according to Wikipeda, “a city in the west of the province of Entre Ríos, Argentina, on the eastern shore of the Paraná River. It has about 20,000 inhabitants as per the 2001 census“. Over recent weeks a large tension crack has developed, defining a block some 130 m long, causing the evacuation of 60 families.  Concern was raised about the incipient failure on Saturday, since when the incipient landslide has continued to develop:-


A part of the large tension crack at Diamante in Argentina. Image via infobae.com


Mannen is creeping again

Meanwhile, in Norway our old friend the Mannen rockslope failure is moving rapidly once again.  This large incipient rockslope failure has gone through a number of periods of accelerated creep, but yesterday the rate of movement increased to about 40 cm per day in the upper part of the slope.  This has been associated with increased rockfall activity, which is generally an indication of increased deformation of the creeping rockmass as strain develops.  Overnight the rate has increased a little more, reaching 2 cm per hour.  As a consequence, the long suffering residents were evacuated once again, the fifth time since August, and the tenth time since 2014.


Scematic diagram showing the Mannen landslide in Norway. Image via NVE and NRK


There is a live webcam showing the site in this newspaper report.  Should failure occur it is estimated that the landslide will have a volume in the range of 120,000 to 180,000 m³.  NVE has a webpage that is providing regular updates on the landslide, including screenshots of the monitoring data.

The challenges of forecasting failure

In both cases the problems with forecasting future behaviour are well-illustrated.  Evacuating the local people is essential at each of the two sites, but the geologists will be very aware of the impact that this will be having on the community.  The experts will be feeling immense pressure, but there are huge uncertainties when trying to extrapolate future behaviour of natural slopes.  It is frustrating for all involved.


Thanks to Donaldo for highlighting the Diamante landslide