Juan de Fuca Ridge Cruise
July 20 - August 1, 2000
Over 650 km (~400 miles) off the Washington-Oregon Coast
Cruise History & Purpose
The mid ocean ridge is the source of the driving force behind plate tectonics. At the ridge, which wraps itself around the world's oceans much like the seams on a baseball, volcanic activity slowly releases magma from the earth's mantle into the bottom of the ocean which forms new oceanic crust. Click here for a moving model showing the motion of the earth's plates.
Read more about plate tectonics in this article by Ken Macdonald and Paul Fox::
Mid Ocean Ridge Article
The Juan de Fuca Ridge lies at the intersection of two plates on the earth's surface, the Pacific Plate and the Nazca Plate. We will be visiting two sites along this section of the mid-ocean ridge, which lie a few hundred kms off shore from the Washington-Oregon border. The two sites are called "Axial Seamount" (or volcano) and the "Cleft Segment". This area of the mid-ocean ridge is extremely unique for two reasons: First, it is located VERY close to shore. Most areas of the ridge are much farther away from home and require much longer expeditions. Second, it is a volcanically active region. We will be visiting some of the active vent sites in Axial's caldera. Thomas and Josh will be studying the dissolved ions and gasses in the hydrothermal vent fluids, while Debra and her team will be looking at the geology of the region. Click on their names to read about what they and the other crew are studying in more detail.
Axial Seamount site (left) is located at 46°N, 130°W, at the intersection of the Juan de Fuca ridge and the Cobb seamount chain. It is 1100m (3,609 ft.) higher than the seafloor around it, and its shallowest portion is 1400m (4,593ft) below the ocean surface. Axial is a seamount, that is, a submarine volcano, which experienced a large eruption in January of 1998. Since the eruption, many researchers from MBARI and around the world have visited the seamount in order to study the changes in the seafloor as well as the biological communities around the site. Axial seamount contains several active hydrothermal vent communities within its caldera, seen as the indentation in the red-orange area on the image above.
The Cleft Segment of the southern Juan de Fuca Ridge is a spreading center which spreads at a rate of 6 cm/year, in other words, it creates 6 cm of new oceanic crust each year. During 1998, the Cleft Segment was examined in detail by scientists from MBARI, Oregon State University, and Brown University using high resolution mapping systems. One of these mapping systems was mounted on the ROV Jason. Based on the data from this experiment, scientists were able to propose a model for the crustal evolution of this section of the mid-ocean ridge. "The cleft segment during a more-robust magmatic phase was an axial ridge up to 8 km across that erupted voluminous flows onto the ridge. Waning of this magmatic phase resulted in ridge-parallel inward facing normal faults and formation of axial valley walls. The most recent major eruptive event filled the floor of the valley and partially buried the remnants of the walls. The Cleft was the source for this most recent volcanic event [D. Stakes]." Evolutions such as this are very important for scientists to learn about smaller-scale events that shape the mid-ocean ridge as a whole and can lead to predictions about future events.
Shown to the left is a sonar image of the "Cleft Segment", the other site that will be visited during the cruise. This image was taken from the hull mounted sonar swath mapping system used on the 1998 cruise. The EM300 is a 30kHz multi-beam sonar mapping system which was used to survey the entire Cleft Segment of the ridge.
Cruise Location: Juan de Fuca Ridge
Ship: Western Flyer
Chief Scientist: Debra Stakes
Scheduled Start Time: 6a.m. July 20, 2000
Scheduled End Time: 11:30p.m. August 1, 2000
Purpose: Rock coring/sampling at 2 sites on ridge
Required Equipment: ROV Tiburon, Rock coring sled
Planned Track/Site: Axial Seamount & North Cleft Segment
Participants: Debra Stakes, Karen Salamy, Greg Moretti, Tony Ramirez, Josh Plant, Thomas Chapin, Maurice Tivey, Michael Perfit
Click on the links above to find out more about this exciting cruise!