Answer:
1. seawalls
2. volcanic
3. mass wasting
4. ocean basin
5. erosion
Step-by-step explanation:
6. Reefs form from volcanic activity on an island in the ocean. This initially forms a fringing reef, but sea level rise can cause the reef to lie farther out from the island, forming a barrier reef. If the island ever subsides below sea level, the reef is called an atoll.