I think its the temperature and precipitation
A reef than surrounds a volcanic island is an : Atoll
Atoll usually takes shapes in a form of ring that surround the areas of volcanic island that consist of corals. It usually only exist in warm waters, so volcanic islands will provide perfect environment for the corals
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Answer:
Mercury is the smallest and closet to the sun.
Cinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone.