gen-define-subduction-zones-and-give-one-short-worked-example-3c1e

Define subduction zones and give one short worked example.

# Subduction Zones **Definition:** A subduction zone is a convergent plate boundary where one tectonic plate (typically oceanic) descends beneath another plate (oceanic or continental) into the Earth's mantle. This occurs because the subducting plate is denser than the overriding plate. ## Key Features: - Deep ocean trenches - Volcanic arcs - Intense earthquake activity - Mountain building --- ## Worked Example: The Cascadia Subduction Zone **Location:** Pacific Northwest (Northern California to British Columbia) **Setup:** - **Subducting plate:** Juan de Fuca Plate (oceanic, ~8 km thick crust, density ~3.0 g/cm³) - **Overriding plate:** North American Plate (continental, ~35 km thick crust, density ~2.7 g/cm³) **Process:** 1. The denser oceanic Juan de Fuca Plate converges with the continental North American Plate at ~4 cm/year 2. It descends at an angle of ~10-15° beneath North America 3. At depths of 100-150 km, water released from the subducting plate melts the mantle wedge above it 4. This magma rises to form the **Cascade Volcanic Arc** (Mt. Rainier, Mt. St. Helens, Mt. Hood) **Result:** The Cascadia Trench offshore + active volcanoes onshore + major earthquake risk (last major quake: 1700 CE, M~9.0)