Oceanic trenches are among the most striking features of the seafloor and provide important evidence of how Earth's tectonic plates interact. This lesson introduces their basic form, global distribution, relationship to plate boundaries, and the history of their study.
An oceanic trench is a long, narrow depression in the ocean floor. Trenches are typically 50–100 km wide and 3–4 km below the surrounding seafloor, while some extend for thousands of kilometers. Their characteristic cross-section is generally V-shaped.
All flashcards
What is an oceanic trench?
A long, narrow depression of the ocean floor, usually associated with a convergent boundary where oceanic lithosphere begins to descend beneath another plate.
Where are most oceanic trenches located?
Most are around the Pacific Ocean, although trenches also occur in the eastern Indian Ocean and in shorter segments elsewhere.
How does a trench differ from a trough?
A trench typically has a V-shaped profile and marks subduction. A trough is generally an elongated depression with steep sides and a flat bottom; some trough-like shapes are not trenches at all.
What is a Wadati–Benioff zone?
A zone of earthquakes that extends beneath a volcanic arc and records the descent of a subducting plate.
What did the Challenger expedition contribute to trench research?
The 1872–1876 expedition made 492 deep-ocean soundings and discovered Challenger Deep, helping establish that extremely deep ocean features existed.
Quiz questions
How do the slopes of a typical oceanic trench compare?Answer: The inner slope is steeper, while the outer slope is gentler.
What happens at an erosive margin?Answer: The descending slab removes material from the lower edge of the overriding plate.
How does an accretionary wedge form?Answer: Sediment carried by the descending plate is scraped off and added to the overriding plate.
What is slab rollback?Answer: Backward retreat of the trench hinge as the subducting slab sinks.
How do chemotrophic microorganisms obtain energy?Answer: From chemical reactions rather than sunlight.
Based on the Wikipedia article Oceanic trench, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.