Just 400 km (250 mi) off the coast of Oregon and Washington, the Juan de Fuca Ridge is spreading at a rate of 6 cm (2.4 in) per year more than twice as fast as the Mid-Atlantic Ridge. At the ridge crest, two plates slowly move apart. The eastward-moving plate descends beneath the North American Plate in the Pacific Northwest, triggering volcanic eruptions in the Cascade Range and occasional large earthquakes.

• Submarine Volcanoes in Action
• Black Smokers - Undersea Oases
• How the Sea Floor Got Its Stripes
• Drilling Beneath the Ocean Floor