13 February 2020
The fast-moving Alpine Gardens landslide in New Zealand
My friends at GNS Science in New Zealand published an article on the Geonet website yesterday about the Alpine Gardens landslide in the Fox Glacier Valley in New Zealand. Featuring the work of a team led by Saskia de Vilder, who like me used to work at the University of Durham, the article highlights the impacts of a remarkably active landslide that has required the rerouting of the track to the Fox Glacier viewpoint, an important tourist destination on the west coast of South Island.
This is a large landslide – GNS estimate that it has a volume of 50 million cubic metres. Through Geonet, Saskia and her team have set up a GPS monitoring station on the slide. In the last year, that monitoring station has displaced by about 50 metres, with the rate of movement being dependent upon the groundwater level. This means that on average it is moving at over 11 cm per day, but on some days the displacement exceeds half a metre. This is an unusually large amount.
The landslide itself is remote, but as the image above shows, debris released by the landslide forms large debris flows that travel down the side valley and into the main channel. Large volumes of material are being mobilised – Saskia estimates that over the year to June 2019, about 6 million m³ of material was incorporated into debris flows. About half of that amount was deposited onto the debris fan, whilst the other half was transported away by the Fox Glacier.
The upshot is a remarkable level of geomorphological change. The Google Earth image below shows the same site in am image collected in May 2006:-
At that time there was little evidence of active movement on what has become the Alpine Gardens Landslide, and of course there are no debris flow deposits in the valley. It is intriguing to consider the possible causes of this high current level of activity.