Abstract
Some volcanoes are known for repeatedly producing explosive but short-lived eruptions (< half="" a="" day)="" every="" decade="" or="" so.="" these="" eruptions="" are="" often="" preceded="" by="" limited="" unrest="" signals="" and="" short="" run-up="" times="" to="" eruption="" (a="" few="" hours="" to="" months),="" and="" thus="" they="" are="" difficult="" to="" anticipate.="" some="" well-documented="" examples="" are="" the="" 1990="" and="" 2014="" eruptions="" of="" kelud="" volcano="" in="" indonesia,="" or="" the="" 2015="" calbuco="" eruption="" in="" chile.="" here="" we="" interrogate="" the="" rock="" record="" and="" obtain="" insights="" into="" the="" processes="" and="" pre-eruptive="" conditions="" that="" led="" to="" the="" 1990="" kelud="" eruption,="" which="" we="" integrate="" with="" monitoring="" data="" (seismicity,="" lake="" temperature="" and="" hydro-acoustics,="" sulfur="" emissions)="" towards="" a="" conceptual="" model="" for="" this="" type="" of="" events.="" mineral-melt="" geothermobarometers="" indicate="" that="" the="" basaltic="" andesite="" magma="" carried="" a="" crystal="" cargo="" from="" as="" deep="" as="" 15-19="" km,="" and="" reached="" volatile="" saturation="" at="" 4-9="" km="" with="" 2-4="" wt.="" %="" water="" in="" the="" melt.="" the="" textures="" and="" compositional="" zoning="" of="" orthopyroxene="" and="" plagioclase="" do="" not="" support="" intrusion="" of="" more="" primitive="" magma="" as="" the="" driver="" for="" the="" eruption,="" and="" we="" instead="" propose="" that="" pre-eruptive="" fluid="" accumulation="" and="" high-temperature="" fluid="" fluxing="" from="" depth="" (likely="" dominated="" by="" co2)="" played="" a="" major="" role="" in="" priming="" the="" eruption="" to="" occur.="" such="" pre-eruptive="" gas="" accumulation="" is="" also="" supported="" by="" mass="" balance="" calculation="" of="" the="" emitted="" excess="" so2="" gas.="" mg-fe="" diffusion="" profiles="" in="" reversely="" zoned="" pyroxenes="" constrain="" timescales="" of="" weeks="" to="" months="" before="" eruption="" for="" fluid="" addition="" to="" the="" reservoir,="" and="" such="" events="" may="" be="" recorded="" in="" the="" monitoring="" signals,="" especially="" in="" the="" change="" of="" hydroacoustics="" and="" water="" lake="" temperature,="" and="" probably="" in="" the="" seismic="" swarms.="" we="" propose="" that="" fluid="" exsolution="" and="" accumulation="" in="" the="" shallow="" reservoir="" plays="" a="" crucial="" role="" in="" modulating="" and="" triggering="" short-lived="" explosive="" eruptions="" with="" brief="" unrest="" at="" kelud="" and="" probably="" other="" volcanoes="">