Question

which term is defined as a coral reef that originally formed around the edges of a volcanic island?
an atoll
a mid - ocean ridge
a submarine canyon
a continental margin

Explanation:

An atoll is a ring - shaped coral reef, island, or series of islets. Atolls develop from coral reefs that grow upward from submerged volcanic islands. As the volcanic island erodes and sinks below sea level, the coral reef continues to grow, forming a lagoon inside the reef. A mid - ocean ridge is an underwater mountain range formed by plate tectonics. A submarine canyon is a steep - sided valley cut into the seabed. A continental margin is the edge of a continent that lies under the ocean.

Answer:

an atoll