Introduction to Endeavour
As crustal plates move, they meet along their edges and interact in one of the three ways: they can spread apart from each other, subduct underneath the other, or slide alongside each other. The interactions between tectonic plates produces magmatic, hydrothermal, and seismic activity. In the Pacific Northwest and British Colombia, the participating plates are the Juan de Fuca, Gorda, Explorer, North American, and Pacific plates (Fig.1). The Juan de Fuca plate is being subducted underneath the westward bound North American plate. This subducting plate system formed the volcanic Cascade Range, which is a part of the Pacific Ring of Fire.
Sea floor spreading happens due to the addition of crustal material from the underneath plates. Volcanoes bring up lava from below and create new seafloor. There are three different spreading ridges based on their spreading rates: slow, fast, and intermediate. In slow spreading ridges (spreading rate: 2-4 cm/yr), like the Mid-Atlantic spreading ridge, there is insufficient melt production to create an axial magma chamber (Wilcock et al. 2002). Hydrothermal circulation cools the lower crust on axis and a significant proportion of extension occurs on large inward facing normal faults leading to the formation of a deep axial valley. In contrast, in the East Pacific rise, which is a fast spreading ridge (11cm/year), the high melt production supports a steady axial magma chamber. The Juan de Fuca ridge resembles an intermediate spreading center due to the presence of an axial magma chamber. The magmatic products that are brought up from beneath form new seafloor along the Juan de Fuca ridge, on the western edge of the Juan de Fuca plate. The principal lava types in this region are lobate and pillow flows.
The Juan de Fuca spreading system has a full spreading rate of 6 cm per year. The entire segment is 90 km long and is bound north and south by overlapping spreading centers (Karsten et al, 1986) and the transform faults that are located between the Juan de Fuca, the Gorda and the Explorer plates. The actively spreading centers of the segment are flanked east and west by ridges and basins.
The Juan de Fuca region is home to vigorous hydrothermal venting at ridge crests. Venting happens due to sea floor spreading. The Endeavour vent field has been the focus of a series of studies over the past three decades. Five hydrothermal vent fields have been identified in the axial valley of the Endeavour segment on the Juan de Fuca ridge: Sasquatch, Salty Dawg, High Rise, Main Endeavour, and Mothra. These venting regions are created when large amounts of seawater circulate through the porous and permeable rocks that form the sea floor. As water sinks deeper, it gets heated and it reacts with the minerals in the rocks. Due to buoyancy effects, the water parcel rises rapidly through the hydrothermal vents.
Aside from hydrothermal vent fields, structures known as black smokers also occupy this region. The black smokers are formed when the superheated water reaches the sea floor and reacts with the cold ocean water. This causes the minerals in the water to precipitate out as solid particles, which can then form the chimney of the black smoker or rise in a plume of hot water that looks like black smoke.