Complex morphological architecture of the lava flow field related to the Alumbrera scoria cone, Southern Puna, Argentina

BAEZ W.; SOMMER C.; ARNOSIO M.; BUSTOS, E.; GIORDANO, G.; BARDELLI L.; CHIODI A.; VIRAMONTE JOSE G.

Congreso; VII Simpósio de Vulcanismo e Ambientes Associados; 2022

Despite the progress achieved in recent decades regarding lava flows modeling, understanding the dynamic of complex compound lava flow fields still requires field studies both during and after their emplacement. Improving the capability to infer eruption and emplacement parameters from the morphology of solidified lava flows is a main goal for the volcanology since this approach is essential to understanding effusive volcanism in the solar system. In addition, reconstruction of the eruptive dynamic of compound lava flows from its morphological architecture provides valuable information which enhances the ability to assess the hazard related to lava flows emplacement. The final surface morphology of a lava flow depends largely on the cinematic of crust formation and how it deforms under stress over time. The term “lava morphotype” is usually used to describe the characteristics of the surface morphology of a lava flow after solidification and can be understood as a specific stage of the lava flow emplacement. The Holocene Alumbrera scoria cone is located in the Antofagasta valley (Catamarca province, Argentina) and represents one of the best preserved volcanic centers of the Quaternary mafic suite of the Southern Puna plateau. In this work, we present a new detailed geomorphological map (morphotype map) of the lava flow field related to the Alumbrera scoria cone. This compound lava field is formed by countless lava flow units erupted during the same eruption and occupying an area of 35 km2 and has a volume of 0.38 km3. The lava flow field is composed of alkaline basaltic trachyandesites and was issued from many vents along the base of the Alumbrera volcano spreading mainly towards the S and OSO, and to a lesser extent to the NO. The S path reached the greatest distance since it followed the general slope of the Antofagasta valley. The OSO path was confined by the western edge of the basin and by the presence of older thick lava flows. The shorter NO path was developed as a result of the new topography generated by the lava field and confined by the general southwards slope of the basin. Lava flow morphotypes and structures were identified and described during fieldwork. Each morphotype was defined according to the stage of crust development as well as to the morphology and degree of detachment of fragments. Then, the spatial distribution of the lava morphotypes and main lava flow structures were mapped in a Geographical Information Systems (GIS) using high-resolution images from Google Earth and aerial photographs. We identified 5 lava morphotypes (Spiny-pahoehoe, Slabby-pahoehoe, Rubbly-pahoehoe, Rubbly-a´a, Cauliflower-a´a) which were later grouped into three cartographic units (Rubbly-dominated zones, Spiny-dominated zones, Mixed zones). Rubbly-dominated and Spiny-dominated zones are constituted by primary large channels and flow lobes (tens to hundreds of meters). Mixed zones are characterized by a complex juxtaposition of secondary small tongues (few to tens of meters) with highly variable surface morphology. In addition, several structures were identified in the field and mapped, including levee-channels systems, tumuli, lava rises, lava rise ridges, lava-rise pits, lava-inflation clefts and squeeze ups. The three main paths in the compound lava field are characterized by specific internal architectures that in turn represent the variable influence of the long-lasting unsteady effusion rate and topographic control during its emplacement.