The Alemania rockfall dam: A record of a mid-holocene earthquake and catastrophic flood in northwestern Argentina

Abstract

Follow this and additional works at: http://digitalcommons.unl.edu/geosciencefacpub This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska -Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska -Lincoln.Wayne, William J., "The Alemanía rockfall dam: A record of a mid-holocene earthquake and catastrophic flood in northwestern Argentina" (1999). Papers in the Earth and Atmospheric Sciences. 426. AbstractA prehistoric rockfall, probably caused by an earthquake with a magnitude of 5.0 or greater, blocked Río de las Conchas 2 km upstream from Alemanía (Salta Province, Argentina) in the southern part of the Cordillera Oriental. The rockfall created a dam that formed a lake at least 16 km long. Shells of Biomphalaria, preserved in the lake sediments and, dated by radiocarbon, established the time of this event to be about 5500-6000 years ago. When the natural dam failed, probably either by piping or overtopping, the lake drained catastrophically, eroding a trench through the chaotic mass of sandstone rubble.

Rock avalanching into a landslide-dammed lake causing multiple dam failure in Las Conchas valley (NW Argentina) ? evidence from surface exposure dating and stratigraphic analyses

“…An additional landslide dam formed~30 km down-valley at Alemanía around 5,655-5,600 yr cal BP and was preserved for 800-1,400 calendar years (Wayne 1999. The Holocene age derived here for the impoundment of Las Conchas valley at Cerro Zorrito allows to explain for the first time why the Alemanía rock-fall-dammed lake existed for such a long time, in contrast to the dam stability concept as suggested by Ermini and Casagli (2003).…”

“…1). Detailed 14 C-age determinations on organic plant material and carbonate shells indicate that this lake formed around 5,655-5,600 yr cal BP and was preserved for 800-1,400 calendar years (Wayne 1999. The rock-fall-dammed basin did not fill up, but sedimentation ended with a flood event and the dam most likely failed catastrophically as indicated by coarse gravel deposits downriver from the dam (Wayne 1999).…”

“…Both domains are separated by an uncertainty domain with 2.75<DBI <3.08. The landslide dam height at Alemanía is 75 m, the landslide volume 6010 6 m 3 (Wayne 1999), and the catchment area 19,820 km 2 . This yields a DBI of 4.39, which is clearly in the instability domain.…”

“…In contrast, some landslide dams are long-lived and their basins fill up with sediment to form lacustrine plains (FauquØ and Tchilinguirian 2002, Schuster in press). However, between these extremes there are natural dams which prevail up to 10 3 years, but may ultimately fail catastrophically (Groeber 1916, Wayne 1999. Lakes impounded by such dams are common and are frequently used for recreation (Nicoletti et al 1993, Jerz 1999, Weidinger et al 2002.…”

Indicative Structures of Paleoseismicity in the Acequion River Valley, San Juan Province, Central-Western Argentina

“…Moreover, it is very likely that RA-1 and RA-2 rock avalanches had a seismic origin as the occurrence of rock avalanches in the Argentine Andes has been mainly, if not exclusively, related to high magnitude earthquakes [42] [43][44] [45]. This matches with the regional tectonic framework, the presence of Quaternary faults east of the Eastern Precordillera, and the presence of the liquefaction features in paleo-lakes.…”