Earthquake-triggered subaerial landslides 14 that caused large scale fjord sediment deformation: Combined subaerial and submarine studies of the 2007 aysén fjord event, Chile

Abstract

On 21 April 2007 (Mw 6.2) an earthquake triggered more than 500 landslides near the epicenter along the Aysén fjord, Chile. One of the major failures occurred at the Punta Cola Valley involving a volume of 20.9 million cubic meters of rock. The main rockslide was followed by a rock/debris avalanche involving talus and glacio-fluvial deposits in the slope toe and valley floor that added a volume of 7.3 million cubic meters as entrained material. About half of the material involved in the rockslide-debris avalanche reached the shoreline and entered the fjord pushing deltaic deposits offshore while inducing a shoreline retreat of 100 m. The impact of the debris avalanche deformed an area of 7.6 km2 of the otherwise featureless and smooth sedimented fjord floor. The central part of the deformed area is currently deeper with respect to the undeformed floor, which suggests that between 1 and 10 m of sediment were eroded from an area of 1.85 km2 due to the direct impact of the avalanche. The combination of debris avalanche impact of this and other landslides, subaqueous failures and fjord floor deformation generated a series of displacement waves within the fjord with several meters to tens of meters high run-up along the shoreline.