Sometimes it's hard to tell if the bowl-shaped feature at the top of a volcano is a crater or a caldera. you can usually determine if it's one or the other by

Acrater is one that is usually small and are more likely circular than calderas. they act like exhaust vents of lava and smoke from the volcano. on the other hand, calderas are more irregularly formed and are usually larger, and is resulted from the collapse of rock underneath a volcano.