The ocean floor and coastal areas have a unique geology that has developed over millions of years as a result of tectonic movement, wave action, erosion, and deposition. Far from being a flat, empty surface, the ocean floor has many interesting features, such as underwater mountain ranges, islands, deep trenches, and smoking hydrothermal vents.
The coastline is constantly changing. Both emergent and submergent coasts have unique features from continued erosion and deposition of sediments. Humans try to reduce the effects of erosion in order to protect personal property by building structures to keep the coastline stable, but they can only do so much when up against the powerful ocean day after day.