Nemi Jessica Walding, Rebecca Williams, Pete Rowley , Natasha Joanne Dowey 

Pyroclastic Density Currents (PDCs) are hazardous, multiphase currents of heterogeneous volcanic material and gas. Their high mobility can be partially attributed to fluidisation mechanisms. Moisture (as liquid or gas) can enter a PDC through external (e.g., interaction with bodies of water) or internal (e.g., initial eruptive activity style) processes and presence of moisture can be recorded within distinct deposit layers. We use analogue experiments to explore the behaviour of volcanic material with increasing moisture percentages from 0.00 – 10.00%. Our results show that: 1) the cohesivity of ignimbrite material changes with the addition of small amounts of moisture; 2) Small increases in moisture content change the flow behaviour from a free-flowing material to a non-flowable material; 3) changes in moisture can affect the formation of gas escape structures, and fluidisation profiles, 4) gas flow through a deposit can lead to a moisture profile and resulting mechanical heterogeneity within the deposit and 5) where gas escape structure growth is hindered by cohesivity driven by moisture, pressure can increase and release in an explosive fashion. This work highlights how a suite of dynamic and varied gas escape morphologies can form within the deposit resulting from moisture content heterogeneity, explaining variation in gas escape structures as well as providing a potential mechanism for secondary eruptions.