The Vesuvius represents a cratered small cone within a larger crater. Mt. Vesuvius had a caldera type crater prior to the eruption of 79 A.D. and was called Monte Somma. The modern cone has been built by a number of explosions since 79 A.D. During 1930, a secondary cone of pyroclastics was built giving the cone-in-cone or ‘cratered-cone within cratered-cone’ form.

Fairbridge has distinguished volcanic craters into six categories in increasing order of the viscosity of the erupted material:

(i) Pit craters due to the fall of lava level in ‘lava lake’ or magma chamber,

(ii) Spatter cone craters (where small cones and scoriae mounds have been formed by the ejection of liquid parts of lava propelled out by the gas or fire-fountains).

ADVERTISEMENTS:

(iii) Craters on small cones of pyroclastics.

(iv) Ring- wall craters developed in lava-free weak eruptions, the walls being composed of pyroclastics.

(v) Maars or generally water-filled bowl-shaped craters caused by steam and gas explosion which is also associated with pyroclastics that build low rims above the general level of the country,

(vi) Erosion craters, developed by the erosion of the relatively weak part of the cinder cone as compared to the stronger volcanic neck of solidified lava round which the erosion crater, much larger than the original crater on the top of the cone, has come into existence.