Dive 1461 was the seventh of nine dives during a sea-going field program to investigate hydrothermal activity along the crest of the southern Juan de Fuca Ridge. During this dive on the Plume site, ALVIN crossed the western floor of the axial valley and traversed about 300 ra of the rim and floor of the narrow inner cleft. Hydrotherraal vents were observed only along the east wall of the inner cleft, and venting was concentrated in a single area less than 50 ra long near the base of that wall. The principal vents extended up the wall from the floor of the cleft to a height of about 10 m. Deposits of hydrothermal minerals occur as incrustations and chimneys on the floor and wall of the cleft. Associated with the...
The morphometric characteristics of the axial regions of oceanic spreading centers are determined by (1) the type of volcanic flows, (2) the relation between primary volcanic relief (on a scale of a few meters to tens of meters) and degree of sediment cover, and (3) the extent of surficial expression and timing of tectonic disruption of the young oceanic crust. Even within a single, continuous, linear spreading-ridge segment with relatively uniform axial valley dimensions over a distance of 50 or more kilometers, such as along the southern Juan de Fuca Ridge, the changes in morphometric characteristics along axis within the youngest crust indicate distinct variation in tectonic and volcanic activity over short distances...
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