Geohazards in the Fjords of Northern Patagonia, Chile

Abstract

A geomorphological analysis of the Comau Fjord was carried out to identify geohazards that are a product of current landform dynamics and processes. The geological setting of the area includes fractured metamorphic and volcanic rocks forming steep hillslopes in an active tectonic context due to the Liquiñe-Ofqui Fault Zone (LOFZ). Geomorphological and hazard mapping was performed using aerial photographs, GIS geoprocessing and fieldwork in January and May 2016 and February 2017. The susceptibility of landsliding was statistically assessed and validated with the inventory of landslides completed during fieldwork. The triggering of geohazards such as landslides and fluvial floods in the study area is associated with high annual precipitation (>5000 mm annually) with a concentration of rainfall that has increased in the last 50 years. Geohazard mapping demonstrated the potential for rock and earth falls, debris flows and river floods, as well as the potential impact of these geohazards on the area's intensive aquaculture industry and a main national highway projected for the eastern flank of the fjord. In a geographical scenario of environmental and territorial change, the present and future human occupation of Comau Fjord's coast constitutes potential hazard and risk conditions for aquaculture infrastructure and highway users.

Geodynamic ‘Hotspots’ in a Periglacial Landscape: Natural Hazards and Impacts on Productive Activities in Chilean Fjordlands, Northern Patagonia

“…A landslide inventory was compiled based on a detailed photointerpretation of aerial photographs (1982, 1997, 1:20,000, 1:70,000), Google Earth images, and field surveys as well as reconnaissance flights by helicopter that allowed a detailed landslide classification (Figure 2). The landslides inventory [29,30] was compiled in the field utilizing morphological evidence, according to [30][31][32][33][34] for the Andean fjordland environments. Recent landslides were identified in the field through specific vegetation patterns and compositions established after landslide events.…”

“…The topographic indices used in the model are the slope gradient, aspect, and elevation calculated according to [36] from SRTM X-SAR DEM. Moreover, the distance to the faults and/or linear tectonic structures, as well as the lithological units as evidence of geomorphological, hydrologic, and geological characteristics of the fjord, are used as independent variables in the modeling procedure [30]. The input data are shown in Table 1.…”

“…Studies of this 2007 event [23,47] documented that the earthquake may trigger gravitational slope processes in any of the several local branches that constitute the LOFZ. In addition, the regional presence of the active Liquiñe-Ofqui Fault Zone (LOFZ) [30,47] makes the area prone to recurrent seismic activity, which in turn triggers exogenous processes such as mass movements. Earthquake-induced landslides on resistant rock slopes, which occurred in the Aysen Fjord during a shallow crustal earthquake related to the LOFZ in 2007 [34], showed the general capacity of earthquakes along the LOFZ to trigger large mass movements in the fjordland region.…”

“…The areas affected by river floods were identified from the river geomorphology of the distal areas of the Andean basins of the Vodudahue and Huinay Rivers, through the identification of the river terraces, beds, and banks, showing evidence of past and current river action. This information was complemented with a flood susceptibility model [30].…”

“…[27] described the Aysén Fjord tsunami as associated with a 6.2 Mw shallow crustal earthquake, indicating that fjord environments are favorable to the occurrence of earthquake-landslide-tsunami sequences. Based on seismic-tectonic susceptibility [30] and recent seismic events linked to the LOFZ activity, the flooding areas of oceanic tsunamis due to interplate earthquakes and landslide tsunamis were considered. According to the data available from the Aysen Fjord tsunami in 2007, a height of 30 m.a.s.l.…”