The boundary between the Pacific and Juan de Fuca Plates is marked by a broad submarine mountain chain about 500 km long, known as the Juan de Fuca Ridge. Young volcanoes, lava flows, and hot springs were discovered in a broad valley less than 8 km wide along the crest of the ridge in the 1970’s. The ocean floor is spreading apart and forming new ocean crust along this valley or “rift” as hot magma from the Earth’s interior is injected into the ridge and erupted at its top.
In the Pacific Northwest, the Juan de Fuca Plate plunges beneath the North American Plate. As the denser plate of oceanic crust is forced deep into the Earth’s interior beneath the continental plate, a process known as subduction, it encounters high temperatures and pressures that partially melt solid rock. Some of this newly formed magma rises toward the Earth’s surface to erupt, forming a chain of volcanoes above the subduction zone.
PACIFIC PLATE Juan de Fuca Ridge JUAN DE FUCA PLATE NORTH AMERICAN PLATE Mt. Baker Glacier Peak Mt. Rainier MAGMA Magma Conduit
Located in the middle of the Pacific Plate, the volcanoes of the Hawaiian Island chain are among the largest on Earth. The volcanoes stretch 2,500 km across the north Pacific Ocean and become progressively older to the northwest. Formed initially above a relatively stationary “hot spot” in the Earth’s interior, each volcano was rafted away from the hot spot as the Pacific Plate moves northwestward at about 9 cm per year. The island of Hawaii consists of the youngest volcanoes in the chain and is currently located over the hot spot.
HAWAII NIIHAU KAUAI OAHU MOLOKAI LANAI MAUI KAHOOLAWE PACIFIC PLATE Oceanic Crust Fixed “Hot Spot” Zone of magma formation extends to Kilauea & Mauna Loa Direction of place movement
Recent Eruptions From U.S. Volcanoes
Hawaiian volcanoes
Few places on Earth allow closer or more dramatic views of volcanic activity than Mauna Loa and Kilauea volcanoes on the island of Hawaii. Their frequent but usually non-explosive eruptions make them ideal for scientific study. Kilauea’s eruptions are so intensely monitored that scientists have assembled a detailed picture of the volcano’s magma reservoir “plumbing” system and how it behaves before and during eruptions. Studies of these volcanoes and the surrounding ocean floor continue to improve our understanding of the geologic history of the Hawaiian Island chain and the ability of scientists to determine volcanic hazards that threaten island residents.
