Volcanoes at oceanic spreading centers are responsible for resurfacing two thirds of the Earth's surface and may have played an important role in the origin of life on our planet. The Juan de Fuca Ridge is one of the most intensively studied mid-ocean ridges in the world and is often cited as an archetype of an intermediate spreading rate ridge. Two sites in particular, the Endeavour Segment and Axial Volcano, have been the focus of intensive studies of mantle melting, crustal formation, and linkages between seafloor volcanoes and chemosynthetic-based biological communities. These same sites are now being instrumented for long-term cabled observatories. This theme provides an avenue for papers that cumulatively synthesize our current knowledge of the tectonic, volcanic, and hydrothermal processes on the entire Juan de Fuca Ridge including ongoing efforts to expand the scope and duration of time series investigations.
Associate Editors: William Wilcock, James Holden, James Gill, Edward Baker

Table of Contents

Free Access

Sulfide geochronology along the Endeavour Segment of the Juan de Fuca Ridge

Key Points

  • 226Ra/Ba dating can be used to reconstruct segment scale venting history
  • Hydrothermal venting within the Endeavour axial valley is over 3000 years old
  • 226Ra/Ba bridges an important dating age gap between 200 to 2000 years old

Free Access

Subseafloor nitrogen transformations in diffuse hydrothermal vent fluids of the Juan de Fuca Ridge evidenced by the isotopic composition of nitrate and ammonium

Key Points

  • Isotopic composition (N) of ammonium in high- and low-temperature vent fluids
  • Nitrate N and O isotopes and nitrogen consumption in diffuse vent fluids
  • Evidence for microbial nitrate regeneration in diffuse vent fluids

Free Access

New packer experiments and borehole logs in upper oceanic crust: Evidence for ridge-parallel consistency in crustal hydrogeological properties

Key Points

  • Similar hydrogeological structure is seen in two boreholes ~825 m apart
  • Lateral consistency suggests continuity of upper crustal hydrological structure
  • Highest basement permeabilities occur deeper than uppermost few tens of meters

Free Access

The 1998 eruption of Axial Seamount: New insights on submarine lava flow emplacement from high-resolution mapping

Key Points

  • The 1998 eruption at Axial Seamount created four lava flows totaling 31 x 106 m3
  • Nearly the entire area of the flows was mapped with 1-m resolution bathymetry
  • The detailed morphology and other mapping data help interpret their emplacement

Free Access

Observations of the volume flux of a seafloor hydrothermal plume using an acoustic imaging sonar

Key Points

  • COVIS is capable of long-term, quantitative monitoring of a hydrothermal plume
  • Plume flow velocity and volume flux show significant temporal variations
  • Tidal flows affect the plume flow velocity via the current-driven entrainment

Free Access

Termination of a 6 year ridge-spreading event observed using a seafloor seismic network on the Endeavour Segment, Juan de Fuca Ridge

Key Points

  • Over 38,000 earthquakes were located along the Endeavour from 2003-2006
  • Two swarms involved intrusions on both limbs of an overlapping spreading center
  • The 2005 swarms represent the termination of a six-year spreading event

Free Access

The influence of porosity and crack morphology on seismic velocity and permeability in the upper oceanic crust

Key Points

  • Area of asperity contact accounts for variations of velocity in Layer 2A
  • The porosity of Layer 2A does not decrease with age after 0.2 Ma
  • Crack morphology controls both velocity and permeability in Layer 2A

Free Access

Deep sea hydrothermal plumes and their interaction with oscillatory flows

Key Points

  • Long-term acoustic measurement of hydrothermal plume vertical velocity
  • Entrainment of ambient ocean water is enhanced by horizontal cross flows
  • Vertical rise height of the plume is dependent on the horizontal cross flow

Free Access

Origin of minor and trace element compositional diversity in anorthitic feldspar phenocrysts and melt inclusions from the Juan de Fuca Ridge

Key Points

  • Melt inclusions trap some of the geochemical signal of their parent magma
  • Different levels of diffusive re-equilibration are evident in plagioclase
  • Geochemical patterns observed in plagioclase phenocrysts vary between samples

Free Access

Upper crustal seismic structure of the Endeavour segment, Juan de Fuca Ridge from traveltime tomography: Implications for oceanic crustal accretion

Key Points

  • Seismic velocity structure of mid-ocean ridge segment is strongly heterogeneous
  • Slow velocities at segment ends reflect recent history of ridge propagation
  • Off-axis structure attributed to locally thick layer 2A and cooling of layer 2B

Open Access

Geologic history of the summit of Axial Seamount, Juan de Fuca Ridge

Key Points

  • All 35 lava flows inside the caldera erupted within the last 800 years
  • More primitive and depleted lavas erupted only from 700-800 years ago
  • The summit caldera formed ~31 kyr ago

Open Access

Petrological variability of recent magmatism at Axial Seamount summit, Juan de Fuca Ridge

Key Points

  • Multiple basalt types erupted at Axial summit in a time sequence
  • Parental magmas vary subtly, and lava share a uniform differentiation path
  • Recharge varies in space, time, & composition on centennial scales

Free Access

Numerical modeling of phase separation at Main Endeavour Field, Juan de Fuca Ridge

Key Points

  • Modeling MEF to explain temperature and salinity gradients
  • Bottom temperature alone does not explain observed gradients
  • Heterogeneous permeability likely results in observed gradients