Axial Volcano

West M., Menke W., Tolstoy M., Webb S., and Sohn R. (2001) Magma storage beneath axial volcano on the Juan de Fuca mid-ocean ridge. Nature 413, 833—836. 

Rona P. A. and Trivett D. A. (1992) Discrete and diffuse heat transfer at ASHES vent field, axial volcano, Juan de Euca Ridge. Earth Planet. Sci. Lett. 109, 57—71. 

Kennedy, C.B., Scott, S.D. Ferris, F.G. (2003) Characterization of bacteriogenic iron oxide deposits from Axial Volcano, Juan de Fuca Ridge, Northeast Pacific Ocean. Geomicrobiology Journal 2d, 199-214. 

Fig. 8.2 Erupting snowblower vent at Axial Volcano (JDFR).

Fig. 8.3 Scanning electron microscope photomicrograph of floe material from a snowblower - type vent at Axial Volcano, JDFR. The material is dominated by sulphur with little carbon, though it is presumably a microbial product. Scale Bar = 20 pm. Photomicrograph and compositional analysis by C. Levesque.

Because event plumes represent the sudden injection of exploitable reducing chemical substrates, as well as inhibitory constituents, they are likely to induce successional changes in the microbial community structure and activity within plume waters over time (Cowen etal., 1998). For example, in studies following the 1998 Axial Volcano eruption, abundant putative bacterial sulphur filaments were observed in August 1998 (Feely etal., 1999), though they were not initially found in plumes in February 1998 (Cowen etal., 1999). 

In comparison, Fe oxidation and deposition appear to be much less common in plumes. About half the Fe in the hydrothermal fluids combines with H2S and is rapidly transformed into Fe sulphides within a few seconds of release (e.g. Rudnicki Elderfield, 1993 James etal., 1995), and much of the Fe2+ that escapes sulphide precipitation is rapidly and spontaneously oxidized in well-oxygenated seawater making it difficult to evaluate the bacterial contribution to the redox transformations of hydrothermal Fe in plumes (Lilley etal., 1995 Winn etal., 1995). Nevertheless, high Fe/Mn particles and Fe-encrusted capsule forms have been observed in plumes at Axial Volcano (JDFR) the physicochemical characteristics of the capsules may be responsible for the passive or surface-enhanced deposition of iron (Cowen etal., 1999). Thiosulphate, the primary product of sulphide autooxidation, may also serve as a useful energy source, but this is yet to be documented in hydrothermal plumes (Winn etal., 1995 Cowen German, 2002). 

Cowen, J.P., Shackelford, R., McGee, D., Lam, P., Baker, E.T. and Olson, E. (1999) Microbial biomass in the hydrothermal plumes associated with die 1998 Axial Volcano Eruption. Geophysical Research Letters, 26, 3637—3640. 

Significant hydrothermal sites are known from a number of on- and off-axis seamounts. These include the Axial Volcano site on the JFR, a large sulfide deposit on a near-axis volcano at 13°N EPR, Loihi seamount in the Hawaiian-Emperor chain, the Lucky Strike hot-spot-related seamount site on the MAR, and a number of other localities. Axial Volcano and Lucky Strike have been studied most thoroughly, and have high-temperature hydrothermal systems. The Ashes vent field on the summit of Axial Volcano was the first to show effects of boiling at the reduced pressures encountered on the seamount relative to a normal ridge crest (Massoth et al. 1989). Many ridge-crest vent fields have been discovered in the last decade that show the effects of phase-separation into low-salinity vapor and more saline fluid (Butterfield 2000). 

Mariana Trough is a back-arc spreading center that occurs between a remnant arc and the currently active Mariana arc. On the flanks of axial volcanoes in the central Mariana Trough are several vent fields with measured temperatures up to 287°C and sulfide-sulfate chimneys comprised of sphalerite, galena, and barite, due to metal sources from the underlying andesitic crust. An unusual occurrence in the northeast portion of the Mariana Arc is a serpentinite mud volcano called Conical Seamount. Carbonate (calcite, aragonite) and silicate (Mg silicate) chimneys occur near the mud volcano summit. Associated fluids are cold, sulfate-sulfide-carbonate-silica-rich, and have pHs as high as... 

Lonsdale P, Becker K (1985) Hydrothermal plumes, hot springs, and conductive heat flow in the Southern Trough of Guaymas Basin. Earth Planet Sci Lett 73 211-225 Massoth GJ, Butterfield DA, Lupton JE, McDuff RE, Lilley MD, Jonasson IR (1989) Submarine venting of phase-separated hydrothermal fluids at Axial Volcano, Juan de Fuca Ridge. Nature 340 702-705 McKenzie DP, Davies D, Molnar P (1970) Plate tectonics of the Red Sea and east Africa. Nature 226 243-248... 

Submarine venting of phase-separated hydrothermal fluids at Axial Volcano, Juan de Fuca Ridge. Nature, 340 702-765. 

This allocation of experiments has the effect of making the normalized uncertainty and normalized information contours more axially symmetric (the design isn t quite rotatable there are still only four mirror-image planes of reflection symmetry). However, because no experiments are now being carried out at the center point, the amount of uncertainty is greater there (and the amount of information is smaller there). The overall effect is to provide a normalized information surface that looks like a slightly square-shaped volcano. 

In vivo identification of plaque eomposition with suffieient resolution should enable the detection of vulnerable plaque before rupture enabling some local treatment. Being able to image vulnerable plaques may lead to the detection of the eharacteristics of a vulnerable plaque that could allow the development of predietive models to assess the risk that a vulnerable plaque poses to the patient [33]. Current state-of-the-art IVUS systems, sueh as those that use VH from Volcano Corporation, do not measure the thin fibrous cap explicitly as the axial resolution is too poor to detect the thin caps. Rather, when a necrotic core is with in 125 microns of the lumen, it is assumed to be covered by a thin fibrous cap and is deemed vulnerable [29,51]. 

---