Earthquakes, Subaerial and Submarine Landslides, Tsunamis and Volcanoes in Aysén Fjord, Chile

Wednesday, 17 December 2014
Galderic Lastras1, David Amblas2, Antonio M Calafat-Frau1, Miquel Canals1, Jaime Frigola1, Reginald L Hermanns3, Sara Lafuerza4, Oddvar Longva3, Aaron Micallef5, Sergio A Sepulveda6, Gabriel Vargas Easton6, María Azpiroz1, Ignacio Bascuñán7, Paul Duhart7, Olaia Iglesias1, Philipp Kempf8 and Xavier Rayo1, (1)Universitat de Barcelona, GRC Geociencies Marines, Barcelona, Spain, (2)Universitat de Barcelona, Barcelona, Spain, (3)Norges geologiske undersøkelse, Trondheim, Norway, (4)Fugro GeoConsulting S.A.S., Paris, France, (5)University of Malta, Msida, Malta, (6)University of Chile, Santiago, Chile, (7)Servicio Nacional de Geología y Minería, Puerto Varas, Chile, (8)Ghent University, Renard Centre of Marine Geology, Ghent, Belgium
The Aysén fjord, 65 km long and east-west oriented, is located at 45.4ºS and 73.2ºW in Chilean Patagonia. It has a maximum water depth of 345 m. It collects the inputs of Aysén, Pescado, Condor and Cuervo rivers, which drain the surrounding Patagonian Andes. The fjord is crossed by the Liquiñe-Ofqui Fault Zone, a seismically active trench parallel intra-arc fault system. On 21 April 2007, an Mw 6.2 earthquake triggered numerous subaerial and submarine landslides along the fjord flanks. Some of the subaerial landslides reached the water mass, generating tsunami-like displacement waves that flooded the adjacent coastlines, withlocal >50 m high run-ups, causing ten fatalities and damage to salmon farms.

The research cruise DETSUFA on board BIO Hespérides in March 2013, aiming to characterise the landslides and their effects, mapped with great detail the submerged morphology of the fjord. Multibeam data display deformation structures created by the impact of the landslides in the inner fjord floor. Landslide material descended and accelerated down the highly sloping fjord flanks, and reached the fjord floor at 200 m water depth generating large, 10-m-deep impact depressions. Fjord floor sediment was pushed and piled up in arcuate deformation areas formed by 15-m-high compressional ridges, block fields and a narrow frontal depression. Up to six >1.5 kmof these structures have been identified.

In addition, the cruise mapped the outer fjord floor beyond the Cuervo ridge. This ridge, previously interpreted as a volcanic transverse structure, most probably acted as a limit for grounding ice in the past, as suggested by the presence of a melt-water channel. The fjord smoothens and deepens to more than 330 m forming an enclosed basin, before turning SW across a field of streamlined hills of glacial origin. Three volcanic cones, one of them forming Isla Colorada and the other two totally submerged and previously unknown, have been mapped in the outer fjord. The largest one is 160 m high, 1.3 km in diameter and tops at 67 m water depth. This high-resolution data set illustrates a wide set of geohazards in the recent lively geological history of Aysén fjord.