One difference between wide & narrow craters is the presence of this to mix with magma & cause big steam explosions
[DOC] [TLE] Steam Explosions, Quakes, and Volcanic EruptionsWhat's in ... [PAR] Mar 7, 2005 ... As this magma-which drives one of the world's largest volcanic systems-rises, ... 
created the 35-mile-wide, 50-mile-long (55 by 80 km) Yellowstone Caldera.