5. Landslide Dams in the Central Andes of Argentina (Northern Patagonia and the Argentine Northwest)

Landslide dams are frequent phenomena in the Argentine Andes. We studied 20 landslide dams in NW Argentina and 41 landslide dams in northern Patagonia. These examples show that most of the landslide dams in both regions have longevity of several hundred to several tens of thousands of years. In those cases where the mode of dam erosion/breach was reconstructable it was either related to climatic variability influencing the inflow of water into the landslide-dammed lake or by landsliding into the landslide dammed lake causing a tsunami wave which overtopped the dam crown and caused its erosion. However such tsunami waves not always lead to dam failure. There is one case where flood deposits downriver a dam exist and the landslide dammed lake contains a voluminous landslide deposit, however the dam did not breach. Hence the flood deposits are related to the tsunami wave but not to a breach. In addition, our examples indicate the necessity of expanding the well established dam classification system used globally in the past 18 years. Here we define 4 further dam types which are related to (a) the diversion of the river away from the valley over bedrock (b) the diversion of the river into the neighbouring catchments (c) the deposition of the landslide in a drainage divide, and (d) the formation of multiple dams by the breach of a landslide dam itself. Furthermore, ponds on top of landslide deposits are frequent and depending on their size a catastrophic release may cause damage.