Abstract

Debris avalanches associated with partial sector collapse of volcanic edifices are common phenomena in the evolution of a volcano. These flows are formed by edifice instability, which could be due to several factors such as the presence of hydrothermally altered areas, climatic changes, earthquakes, shallow magma intrusions (cryptodomes and/or dykes) and/or fault activity beneath or close to the volcano. The final product of this avalanche flow, known as debris avalanche deposit (DAD) shows typical hummocky and closed drainage morphologies. More than 14 volcanic centers of the Central Andes have volcanic DAD's, being Tata Sabaya (Bolivia) one of them. The collapse that has originated the deposit could have been generated by a combination of magmatic and seismic activity in the volcano. The deposit associated to the partial collapse of Tata Sabaya volcano is distributed on its lower southern flank and partially fills the north-western part of the Salar de Coipasa basin. The deposit covers a minimum area of 230 km2 and has an estimated minimum volume of 6±1 km3. The deposit is formed by 6 different types of hummocks, according to their compositions: lavic, pyroclastic, sedimentary, mixed, pyroclastic breccia and basaltic-andesitic hummocks. Based on the predominant hummock type and the spatial distribution, the deposit has been divided into 6 different facies (Toreva Block Facies, Volcanic Hummocks Facies, Central Facies, Sedimentary Hummocks Facies, Mixed Facies and Pyroclastic Breccia Hummocks Facies). Taking into account the facies distribution and their characteristics, we infer the pre-collapse structure of the volcano.