New Zealand study shows how mountain stream moves landslide

WELLINGTON, Sept. 5 (Xinhua) — It could take decades to centuries for landslide remnants to move out of the river, which may be longer than the period between similar earthquake-landslide events, according to a New Zealand study published on Thursday.
The study helps to paint a picture of the high variability of erosion rates in mountain valleys, said the study published in the journal of Science Advances.
About 6.6 million cubic meters of landslide debris, which was deposited straight into the upper reaches of the Hapuku River in the wake of the 2016 Kaikoura earthquake, has not budged much following the largest landslide triggered by the earthquake, showed three-dimensional imagery.
It took around two years before the river began making a dent in the sediment, according to data from 13 airborne surveys of the research conducted by the University of Auckland, Victoria University of Wellington, and GNS Science.
The Hapuku landslide offered an unprecedented opportunity to study the many after-effects of tens of thousands of seismically triggered mass movements immediately after the Kaikoura earthquake, including the cascading effects of a large landslide in a steep alpine catchment, said Associate Professor Jon Tunnicliffe of the University of Auckland.
So far, the roughly two-thirds of the sediment stored along the upper reaches of the river system seems to be eroded only incrementally during storm events, Tunnicliffe said, adding they now have a much better understanding of how these systems adjust and buffer sediment delivery to downstream areas.
The study helps understand how mountain valleys evolve, if they are unable to erode their bed because they are laden with landslide sediment, he said, adding the process observations from this work will help to inform and refine future modeling work that can help better anticipate impacts from major seismic events in New Zealand. ■