Wind remobilization of volcanic particles: field observations and physical processes

DOMINGUEZ, LUCIA; BONADONNA, COSTANZA; FORTE, PABLO; LEONARDO MINGARI; BRAN, DONALDO; JUANESTEBAN PANEBIANCO

Congreso; Cities on Volcanoes 10; 2022

IAVCEI

Several studies during the last couple of decades have provided new insights into our understanding of primary tephra fallout dynamics. Physical characterization of the deposits as well as important advances in analytical and numerical modelling have contributed to better understand tephra dispersal and sedimentation processes and develop accurate probabilistic hazard assessment strategies. However, less attention has been dedicated to the characterization of wind-remobilization as a secondary but often syn-eruptive volcanic hazard. Better understanding of this phenomenon is crucial to the mitigation of the associated impacts. In fact, public health and critical infrastructure functionality are often disrupted for long periods of time as a result of ash wind-remobilization exacerbating the consequences of primary hazards and local pre-existing conditions (e.g. droughts). In addition, wind-remobilization of volcanic particles is a global concern since it is not only confined to the source area (i.e. primary tephra deposit) but it can affect large areas up to several hundreds of kilometres far from the source. We present here a detailed physical characterization of wind-remobilized ash particles associated with the deposits of the 2011 Cordón Caulle eruption (Chile). This eruption produced plumes of 3-14 km a.s.l that were dispersed towards the East-Southeast, sedimenting about 1 km3 of tephra, covering vast areas of the Argentinian Andes and Patagonia. The finest and upper layer of the associated deposit has been remobilized since shortly after its deposition and it continues to be remobilized even up to today. We combine field observations, grain size and shape analysis with atmospheric parameters (e.g. wind velocity, precipitations) and surface conditions (e.g. roughness) to investigate wind-remobilization processes as well as their correlation with wind friction velocities and mass flux of remobilized volcanic ash in arid and semiarid regions (Patagonian steppe).