The eruption produced pyroclastic flows that melted summit glaciers and snow, generating four thick lahars that raced down river valleys on the volcano's flanks, destroying a small lake that was observed in Arenas' crater several months before the eruption. Water in such volcanic lakes tends to be extremely salty, and may contain dissolved volcanic gases. The lake's hot, acidic water significantly accelerated the melting of the ice, an effect confirmed by the large amounts of sulfates and chlorides found in the lahar flow.