Ocean Floor Features: Ocean Trenches and Volcanic Arcs

© 2011 Pearson Education, Inc.

Ocean Trenches and Volcanic Arcs

Convergent margins generate ocean trenches.Deepest part of oceansMost in Pacific OceanDeepest trench – Mariana Trench at

11,022 meters (36,161 feet)

Volcanic arc on nonsubducted ocean plateMay produce island arc, e.g., Japan

Continental arc on land

© 2011 Pearson Education, Inc.

Pacific Ring of FireMargins of Pacific Ocean

Majority of world’s active volcanoes and earthquakes

Marked by convergent boundaries

© 2011 Pearson Education, Inc.

Ocean Trenches and Ring of Fire

© 2011 Pearson Education, Inc.

Mid-Ocean RidgeLongest mountain chain

On average, 2.5 km (1.5 miles) above surrounding sea floor

Wholly volcanic

Basaltic lava

Divergent plate boundary

© 2011 Pearson Education, Inc.

Mid-Ocean Ridge

© 2011 Pearson Education, Inc.

Mid-Ocean Ridge FeaturesCentral rift valley downdropped by seafloor

spreadingFissures and faults in rift valley

Seamounts – tall volcanoes

Pillow lava or pillow basalt – shapes formed when hot basaltic lava quickly cools

© 2011 Pearson Education, Inc.

Mid-Ocean Ridge FeaturesSeamount Pillow lava

© 2011 Pearson Education, Inc.

Mid-ocean Ridge FeaturesHydrothermal VentsSea floor hot springs

Foster unusual deep-ocean ecosystems able to survive without sunlight

Warm water vents – temperatures below 30°C (86°F)

White smokers – temperatures from 30–350°C (86–662°F)

Black smokers – temperatures above 350°C (662°F)

© 2011 Pearson Education, Inc.

Hydrothermal Vents

© 2011 Pearson Education, Inc.

Fracture Zones and Transform Faults

© 2011 Pearson Education, Inc.

Transform Faults and Fracture Zones

© 2011 Pearson Education, Inc.

Oceanic IslandsVolcanic activity

Hotspots

Island arcs