Thermal condition of Surtsey     

V. Stefansson  G. Axelsson  O. Sigurdsson  G. Gudmundsson  B. Steingrimsson 《Journal of Geodynamics》1985,4(1-4)

The island Surtsey was created by a submarine volcanic eruption which started on the 14th of November 1963, 21 km southwest of the Westman Islands. Volcanic activity continued in this area for nearly 4 years. During the summer of 1979 a 181 m deep continuously cored borehole was drilled on the Surtsey island. Several temperature profiles have been measured in the hole since 1979. The results of these temperature measurements are used as the basis for a discussion of the thermal condition of Surtsey. The hypothesis that intrusions rather than pillow lavas are responsible for the excess heat content of Surtsey is favored. It is found that the 13 m thick discontinuous dike complex, observed in the drill core, is sufficient to explain the excess heat content in the vicinity of the borehole and the shape of the temperature profiles recorded. It is demonstrated that the heat transfer in Surtsey has been dominated by hydrothermal convection and that the system is vapor dominated above sea level. It is estimated that the permeability of a 40 m thick section of altered tuff below sea level is 4.1 × 10⁻¹³ m², while the permeability of the unaltered tuff above sea level is estimated as 1.2 × 10⁻¹⁰ m².  相似文献   

An improved Kajak-type gravity core sampler for soft bottom sediments     

Sven Blomqvist  Berndt Abrahamsson 《Aquatic Sciences - Research Across Boundaries》1985,47(1):81-84

A new, modified model of the Kajak tube core sampler is presented. The new sampler is intended for use on soft sediments, and hence of light weight (12 kg). The improved sampler offers the following advantages. (1) increased robustness, (2) simplified attachment of the coring tube to the holder and valve assembly, permitting quick exchange of sampling tubes, (3) unimpeded flow of water through the tube during slow descent, (4) a reliable, automatic mechanism closing the top of the core tube after impact, and (5) an easily dismantled supporting frame, which also protects the sampler from damage against the side of the boat in rought weather. The operation of the sampler has been observedin situ and during ordinary shipboard collection of core samples, with satisfactory results.  相似文献   

The 1982 eruptions of El Chichon volcano,Mexico (3): Physical properties of pyroclastic surges     

H. Sigurdsson  S. N. Carey  R. V. Fisher 《Bulletin of Volcanology》1987,49(2):467-488

Two major pyroclastic surges generated during the 4 April 1982 eruption of El Chichon devastated an area of 153 km² with a quasi-radial distribution around the volcano. The hot surge clouds carbonized wood throughout their extent and were too hot to allow accretionary lapilli formation by vapor condensation. Field evidence indicates voidage fraction of 0.99 in the surge cloud with extensive entrainment of air. Thermal calculations indicate that heat content of pyroclasts can heat entrained air and maintain high temperatures in the surge cloud. The dominant bed form of the surge deposits are sand waves shaped in dune forms with vertical form index of 10–20, characterized by stoss-side erosion and lee-side deposition of 1–10 cm reversely graded laminae. A systematic decrease in maximum lithic diameter with distance from source is accompanied by decrease in wavelength and amplitude. Modal analysis indicates fractionation of glass and pumice from the surge cloud relative to crystals, resulting in loss of at least 10%–25% of the cloud mass due to winnowing out of fines during surge emplacement. Greatest fractionation from the –1.0–0.0– grain sizes reflects relatively lower pumice particle density in this range and segregation in the formative stages of the surge cloud. Extensive pumice rounding indicates abrasion during bed-load transport. Flow of pyroclastic debris in the turbulent surge cloud was by combination of bed-load and suspended-load transport. The surges are viewed as expanding pyroclastic gravity flows, which entrain and mix with air during transport. The balance between sedimentation at the base of the surge cloud and expansion due to entrainment of air contributed to low cloud density and internal turbulence, which persisted to the distal edge of the surge zone.  相似文献   

Geochemical aspects of some accumulation models for primary magmas     

Sven Maaløe  A. Dana Johnston 《Contributions to Mineralogy and Petrology》1986,93(4):449-458

The compositions of primary magmas depend to some degree on the dynamic processes occurring in the partially molten region of the mantle. The compositional dependence is estimated for three models which assume either accumulation from a migmatized source region or accumulation entirely by the interstitial flow of magma. Accumulation from a migmatised region results in magmas with higher concentrations of incompatible elements than does batch melting, whereas accumulation by interstitial flow results in magmas with lower concentrations of these elements. The concentrations of refractory elements are almost independent of both the accumulation process and the degree of partial melting and are therefore usefull for the identification of primary magmas.  相似文献   

Pine forest microclimate simulation using different diffusivities     

Sven Halldin  Anders Lindroth 《Boundary-Layer Meteorology》1986,35(1-2):103-123

Proper understanding of, e.g., evaporation from a forest requires an understanding of its microclimate. A well established, steady-state model was used to simulate microclimate and evaporation of a sparse pine forest in central Sweden. Model input included profiles of turbulent diffusivity, boundary-layer resistance, stomatal resistance, wind speed, net and global radiation and needle area density. Momentum balance, energy balance and exponentially decreasing diffusivities were used to study the sensitivity of the evaporation rates and of the temperature and humidity profiles. Model output proved to be unreliable when measured temperature and humidity at the bottom of the stand were used instead of a measured ground heat flux as the lower boundary condition. Energy balance diffusivity was usually larger than momentum balance diffusivity at the canopy top but decreased rapidly to a minimum at approximately the height where the momentum balance diffusivity had its maximum. Energy balance diffusivity commonly showed a secondary maximum below the height of the maximum needle area density. Profiles of Richardson number showed that thermal effects became important just below the canopy top. Bluff-body effects distinguished the energy balance from the momentum balance diffusivity and both were subject to shelter effects. Total evaporation was not very sensitive to the choice of diffusivity when soil heat flux was given as the lower boundary condition.  相似文献   

A Younger Dryas Ash Bed in western Norway,and its possible correlations with tephra in cores from the Norwegian Sea and the North Atlantic     

Jan Mangerud  Sven Erik Lie  Harald Furnes  Inger Lise Kristiansen  Leif Lømo 《Quaternary Research》1984,21(1):85-104

A bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western Norway. It is formally mamed the Vedde Ash Bed, and its age is approximately 10,600 yr B.P., i.e., mid-Younger Dryas. The bed consits of pure glass having a bimodal basaltic and rhyolitic somposition. The geochemistry of the glass shards suggests an Icelandic source. By means of stratigraphic position and geochemistry, the ash is correlated with ash zones found in cores from the continental shelf, the Norwegian Sea, and the North Atlatic.  相似文献   

Population density and zoning of olivine phenocrysts in tholeiites from Kauai,Hawaii     

Sven Maaløe  Ole Tumyr  Dodie James 《Contributions to Mineralogy and Petrology》1989,101(2):176-186

The population density of olivine phenocrysts of the tholeiites display an exponential variation, which is typical of igneous as well as contact metamorphic rocks. The exponential variation is explained by a new growth probability model, which is consistent with experimental work. The forsterite content of the olivine phenocrysts decreases with decreasing size. Various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber, after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place.  相似文献   

The entrance of pyroclastic flows into the sea, II. theoretical considerations on subaqueous emplacement and welding     

R.S.J. Sparks  H. Sigurdsson  S.N. Carey 《Journal of Volcanology and Geothermal Research》1980,7(1-2)

The submarine counterparts of late Quaternary subaerial pyroclastic flow deposits off the western flanks of Dominica, Lesser Antilles, have been investigated by 3.5 kHz seismic profiling and dredging (cruise EN20 of R/V “Endeavor”). Block-and-ash flow deposits formed by dome collapse and a welded ignimbrite from a prominent fan at Grande Savanne, Dominica. This fan can be traced underwater as a major constructional ridge (2–4 km wide and 200–400 m thick) to over 13 km offshore at a water depth of 1800 m. The submarine ridge has a volume of 14 km³ and has the characteristic morphology of a debris flow apron composed of several individual units. The evidence suggests that pyroclastic flows can move underwater without losing their essential character.  相似文献   

Implication for mantle flow from the Hawaiian-Emperor chain     

Sven Maale  Ole Tjugen 《Earth and Planetary Science Letters》1988,91(1-2)

Assuming that Rayleigh-Benard flow occurs within the upper mantle, ascending plumes must undergo horizontal displacement during ascent that can be traced at the surface. It is shown that the Hawaiian-Emperor bend cannot be formed if the convection rate is of the same order of magnitude as the ascent rate of the plumes. The plume patterns obtained by push-pull or lithospheric sliding are similar to that of the Hawaiian-Emperor chain. Hence the present results support the sliding model.  相似文献   

Automated Multi-class Classification of Remotely Sensed Hyperspectral Imagery Via Gaussian Processes with a Non-stationary Covariance Function     

Anna Chlingaryan  Arman Melkumyan  Richard J. Murphy  Sven Schneider 《Mathematical Geosciences》2016,48(5):537-558

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