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Decadal and annual changes in biogenic opal and carbonate fluxes to the deep Sargasso Sea Decadal and annual changes in biogenic opal and carbonate fluxes to the deep Sargasso Sea

Analyses of samples from a 14-year series of sediment-trap deployments in the deep Sargasso Sea reveal a significant trend in the ratio of the sinking fluxes of biogenic calcium carbonate and silica. Although there are pronounced seasonal cycles for both flux components, the overall opal/CaCO3 ratio changed by 50% from 1978 to 1991 (largely due to a decrease of opal flux), while total...
Authors
W.G. Deuser, T.D. Jickells, Judith A. Commeau

Thermodynamics of gas and steam-blast eruptions Thermodynamics of gas and steam-blast eruptions

Eruptions of gas or steam and non-juvenile debris are common in volcanic and hydrothermal areas. From reports of non-juvenile eruptions or eruptive sequences world-wide, at least three types (or end-members) can be identified: (1) those involving rock and liquid water initially at boiling-point temperatures (‘boiling-point eruptions’); (2) those powered by gas (primarily water vapor) at...
Authors
L.G. Mastin

Volcano seismology, hazards assessment Volcano seismology, hazards assessment

The last few years have seen several impressive examples of seismic monitoring at volcanoes to provide warnings that have saved lives and property. Changes in the rates and character of volcanic earthquakes provided precursory signs to explosive eruptions of moderate size at Redoubt volcano (Alaska), Mount Unzen (Japan), Mount Spurr (Alaska), and Rabaul caldera (Papua New Guinea), as...
Authors
J. Mori

Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest

Mammoth Mountain, in the western United States, is a large dacitic volcano with a long history of volcanism that began 200 kyr ago and produced phreatic eruptions as recently as 500 ± 200 yr BP. Seismicity, ground deformation and changes in fumarole gas composition suggested an episode of shallow dyke intrusion in 1989–90. Areas of dying forest and incidents of near asphyxia in confined...
Authors
C. D. Farrar, M.L. Sorey, William C. Evans, J. F. Howle, B.D. Kerr, B. M. Kennedy, C.-Y. King, J. R. Southon

Velocities of southern Basin and Range xenoliths: Insights on the nature of lower crustal reflectivity and composition Velocities of southern Basin and Range xenoliths: Insights on the nature of lower crustal reflectivity and composition

To reconcile differences between the assessments of crustal composition in the southern Basin and Range province on the basis of seismic refraction and reflection data and lower-crustal xenoliths, we measured velocities of xenoliths from the Cima volcanic field in southern California. Lower-crustal samples studied included gabbro, microgabbro, and pyroxenite. We find that the mafic...
Authors
Thomas E. Parsons, Nikolas I. Christensen, Howard G. Wilshire
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