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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

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Pacific Ring of FireMargins of Pacific Ocean

Majority of world’s active volcanoes and earthquakes

Marked by convergent boundaries

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Ocean Trenches and Ring of Fire

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Mid-Ocean RidgeLongest mountain chain

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

Wholly volcanic

Basaltic lava

Divergent plate boundary

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Mid-Ocean Ridge

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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

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Mid-Ocean Ridge FeaturesSeamount Pillow lava

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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)

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Hydrothermal Vents

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Fracture Zones and Transform Faults

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Transform Faults and Fracture Zones

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Oceanic IslandsVolcanic activity

Hotspots

Island arcs