One difference between wide & narrow craters is the presence of this to mix with magma & cause big steam explosions
[DOC] [TLE] Geothermal Fields, Taupo Volcanic Zone, north ... - Anaspides.net [PAR] The TVZ occupies a narrow band 250 km long and 50 km wide which extends ... 
Calderas are remnants of volcanoes that have suffered magma chamber 
collapse.