One difference between wide & narrow craters is the presence of this to mix with magma & cause big steam explosions
[DOC] [TLE] Jeopary Questions page 1126 - "IRA" - TriviaBistro.com [PAR] UNDER THE VOLCANO: One difference between wide & narrow craters is the 
presence of this to mix with magma & cause big steam explosions  A SLICE OF... [DOC] [TLE] Okataina Volcanic Centre Geology / Volcano Geology and Hazards ... [PAR] Jan 25, 2010 ... Much less well known is that Mt Tarawera is only one volcano within the ... area 
of many recently active vents lying between Rotorua and Kawerau.