A reappraisal of explosive–effusive silicic eruption dynamics: syn-eruptive assembly of lava from the products of cryptic fragmentation

Silicic volcanic eruptions range in style from gently effusive to highly explosive, and may switch unpredictably during a single eruption. Direct observations of subaerial rhyolitic (Chaiten 2008, Cordón Caulle 2011–2012, Chile) challenged long-standing paradigms explosive eruptive styles led the formulation new models hybrid activity. However, processes that govern such explosive–effusive activity remain poorly understood. Here, we bring together well-studied 2011–2012 eruption with textural petrologic data on erupted products, video still imagery We infer all – effusive, was fed by fragmentation at depth, behaviour arose sticking sintering, shallow vent region, clastic products deeper, cryptic fragmentation. use scaling approach determine there is sufficient time available, emplacement, for diffusive pyroclast degassing sintering produce degassed plug occludes conduit, feeding clastogenic, apparently lava-like deposits. Based evidence Caulle, other similar eruptions, further argue driven episodic gas-fracking occluding lava plug, underlying pressurized ash- pyroclast-laden region. The presence pocket ash-laden gas within conduit provides mechanism generation harmonic tremor, syn-eruptive laccolith intrusion, both which were features conclude more consistent available than prevailing model effusion silicic assume coherent non-fragmental rise magma depth surface without wholesale • Sintered textures are common Caulle. Explosive can explain low H2O lavas. ‘cryptic fragmentation’ dusty source tremor. under be pyroclastic rubble.