Mid-Atlantic Ridge: Earth's Longest Mountain Range, Underwater

Seafloor Spreading in Action

The Mid-Atlantic Ridge (MAR) is a divergent plate boundary running ~16,000 km down the Atlantic Ocean center. It is where the North American/Eurasian and South American/African plates pull apart.

Process: Seafloor Spreading

1. Plate Separation: Plates diverge at ~2–4 cm/yr (fingernail growth speed).
2. Upwelling: Reduced pressure → mantle rock melts → basaltic magma rises.
3. Crust Formation: Magma erupts at axial valley, cools, forms new oceanic crust (basalt).
4. Rift Valley: Central graben (10–30 km wide, 1–3 km deep) marks the active spreading axis.
5. Aging: Crust moves outward, cools, subsides, sediments accumulate. Magnetic stripes record geomagnetic reversals.

Key Features

• Transform Faults: Offset ridge segments (fracture zones) – e.g., Charlie-Gibbs, Romanche.
• Hydrothermal Vents: Black smokers (350°C+) support chemosynthetic ecosystems (tube worms, vent shrimp, extremophile bacteria).
• Volcanism: Frequent basaltic eruptions (fissure eruptions). Iceland is the MAR exposed on land.
• Earthquakes: Shallow, frequent, low-magnitude along ridge and transforms.

Global Significance

• Creates 2/3 of Earth's surface (oceanic crust).
• Drives plate tectonics (ridge push).
• Regulates ocean chemistry (hydrothermal flux).
• Records paleomagnetic history (seafloor spreading proof).

The MAR is the planet's most extensive volcanic feature—a 65,000 km global mid-ocean ridge system's Atlantic segment.