Santa Lucía landslide disaster, Chaitén-Chile, The: origin and effects

Abstract

On December 16, 2017, a rockslide was triggered in the headwaters of the Burrito River (Chaitén district, 43.4° SL) which produced debris and mud flows that flooded Villa Santa Lucía, destroying half of the town’s urban area. These mass wasting events covered an area of 3 square-kilometers on Rute 7 and 1 square-kilometer on Rute 235, which resulted in twenty-one fatalities and one person still missing. The rockslide was produced by an intense rainfall which took place on the 15th and 16th of December, same year. The rainfall’s measured depth totaled 122.8 mm in only 24 hours, with a high isotherm of 0° (2.700 m asl). This event was preceded by a two-week-long period of high temperatures (22°C daily maximum) previously registered. The main playing factors were the presence of deeply altered volcanic rocks (clay-iron oxides) of the Cordón Yelcho Pleistocene Volcanic Range (SERNAGEOMIN- BRGM 1995) plus vertical fractures, open cracks and very steep slopes. The rockslide impacted a covered glacier and ice-cored moraine that resulted in a very high-speed blast, followed by large debris and mud flows that traveled a distance of 8 kilometers, deeply eroding the Burrito valley walls including its forest, soil and sediments (Duhart et al., 2018). A 7.2 x 106 m3 total of sediments, water, ice and vegetal coverage were estimated and about 2 x 106 m3 were deposited on a 9 x 105 m2 fan area, covering the northern area of Santa Lucía village. An average velocity of 72 km/h was estimated for the higher part of the flow (Fernandez et al., 2018), although the initial blast was higher due to the trees that were uprooted and torn alongside the valley walls. As of today, the rockslide scar is still unstable with steep slopes, open cracks, a prominent hanging block and vertical fractures. A Laser Scan monitoring test was developed and is currently under assessment design. The implementation of permanent monitoring beneficial to the understanding of the rock’s failure origins in the generation zone may enhance the development of an alert system for landslide hazard risk reduction.