Typical conical stratovolcano in Chile. © S.Brown
Volcanic fields comprise numerous small volcanic cones over huge areas. Each cone normally develops in a single eruption, and normally won't erupt again. New eruptions can occur anywhere in the field. Each eruption is usually quite small, producing some localised tephra fallout and lava flows.
Right: small cones at Gollu Dag, Turkey. © S.Brown
Cone volcanoes like stratovolcanoes form as volcanic products build up around a vent that is repeatedly active, normally over thousands of years. Stratovolcanoes can be very large, with steep sides, and form from different layers of viscous lava and tephra.
Right: the Hasan Dag stratovolcano in central Anatolia. © S.Brown.
Calderas are large depressions that form as the reservoir of molten rock, magma, beneath the volcano is emptied during large eruptions causing the volcano to collapse in on itself. Calderas are often associated with very large eruptions. Some calderas contain lakes, or new volcanic cones, and some become largely obscured by new volcanic products.
Right: The 10km diameter Aniakchak caldera in Alaska. Photo: M.Williams, National Park Service, 1977.
Shield volcanoes are often large volcanoes, with low-angle slopes. They form as lava flows from successive eruptions pile up on top of each other. The lava at shields tends to be more fluid than at cone volcanoes and calderas, often basaltic in composition. These fluid lavas can run for greater distances and sometimes erupt from rift zones on the flanks.
Right: Mauna Loa shield volcano, Hawaii. Shutterstock.