Active continental margins are those that are tectonically active, such as along much of the Pacific coast. Active margins are marked by earthquakes, volcanoes, and mountain belts. Unlike passive margins, they lack a continental rise and abyssal plain. Instead, the continental slope ends in an oceanic trench, and beyond the trench, the topography is hilly and irregular, often dotted with rugged volcanic seamounts.
An oceanic trench is a narrow trough parallel to the coastline that can reach a depth of 10 kilometers (6 miles) or more and a slope of 15 degrees. Volcanoes and earthquake‐producing Benioff zones are associated with oceanic trenches (Figure ). These trenches, such as the Mariana Trench, are the deepest features of the oceans.