The impact of a major Quaternary river capture on the alluvial sediments of a beheaded river system, the Rio Alias SE Spain   总被引：1，自引：0，他引：1  

Elizabeth Maher  Adrian M. Harvey  Derek France 《Geomorphology》2007,84(3-4):344

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Beaches and dunes of developed coasts: Nordstrom, Karl F. Cambridge University Press, Cambridge, 2000, 338 pages+xiii, 57 figures (b&w photographs and b&w diagrams), 8 tables, UK£45, US$74.95, Hardback, ISBN 0 521 47013 7     

Derek J. McGlashan 《Geomorphology》2001,36(3-4)

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The Llullaillaco volcano, northwest Argentina: construction by Pleistocene volcanism and destruction by sector collapse     

J. P. Richards  M. Villeneuve 《Journal of Volcanology and Geothermal Research》2001,105(1-2)

Llullaillaco is one of a chain of Quaternary stratovolcanoes that defines the present Andean Central Volcanic Zone (CVZ), and marks the border between Chile and Argentina/Bolivia. The current edifice is constructed from a series of thick dacitic lava flows, forming the second tallest active volcano in the world (6739 m). K–Ar and new biotite laser ⁴⁰Ar/³⁹Ar step-heating dates indicate that the volcano was constructed during the Pleistocene (≤1.5 Ma), with a youngest date of 0.048±0.012 Ma being recorded for a fresh dacite flow that descends the southern flank. Additional ⁴⁰Ar/³⁹Ar measurements for andesitic and dacitic lava flows from the surrounding volcanic terrain yield dates of between 11.94±0.13 Ma and 5.48±0.07 Ma, corresponding to an extended period of Miocene volcanism which defines much of the landscape in this region. Major- and trace-element compositions of lavas from Llullaillaco are typical of Miocene–Pleistocene volcanic rocks from the western margin of the CVZ, and are related to relatively shallow-dipping subduction of the Nazca plate beneath northern Chile and Argentina.Oversteepening of the edifice by stacking of thick, viscous, dacitic lava flows resulted in collapse of its southeastern flank to form a large volcanic debris avalanche. Biotite ⁴⁰Ar/³⁹Ar dating of lava blocks from the avalanche deposit indicate that collapse occurred at or after 0.15 Ma, and may have been triggered by extrusion of a dacitic flow similar to the one dated at 0.048±0.012 Ma. The avalanche deposits are exceptionally well preserved due to the arid climate, and prominent levées, longitudinal ridges, and megablocks up to 20-m diameter are observed.The avalanche descended 2.8 km vertically, and bifurcated around an older volcano, Cerro Rosado, before debouching onto the salt flats of Salina de Llullaillaco. The north and south limbs of the avalanche traveled 25 and 23 km, respectively, and together cover an area of approximately 165 km². Estimates of deposit volume are hampered by a lack of thickness information except at the edges, but it is likely to be between 1 and 2 km³. Equivalent coefficients of friction of 0.11 and 0.12, and excess travel distances of 20.5 and 18.5 km, are calculated for the north and south limbs, respectively. The avalanche ascended 400 m where it broke against the western flank of Cerro Rosado, and a minimum flow velocity of 90 m s⁻¹ can be calculated at this point; lower velocities of 45 m s⁻¹ are calculated where distal toes ascend 200 m slopes.It is suggested that the remaining precipitous edifice has a high probability for further avalanche collapse in the event of renewed volcanism.  相似文献   

Petroleum Hydrocarbon Bioventing Kinetics Determined in Soil Core, Microcosm, and Tubing Cluster Studies   总被引：2，自引：0，他引：2  

Ellen E. Moyer  David W. Ostendorf  Robin J. Richards  Steve Goodwin 《Ground Water Monitoring & Remediation》1996,16(1):141-153

Aerobic biodegradation of vapor-phase petroleum hydrocarbons was evaluated in an intact soil core from the site of an aviation gasoline release. An unsaturated zone soil core was subjected to a flow of nitrogen gas, oxygen, water vapor, and vapor-phase hydrocarbons in a configuration analogous to a biofilter or an in situ bioventing or sparging situation. The vertical profiles of vapor-phase hydrocarbon concentration in the soil core were determined by gas chromatography of vapor samples. Biodegradation reduced low influent hydrocarbon concentrations by 45 to 92 percent over a 0.6-m interval of an intact soil core. The estimated total hydrocarbon concentration was reduced by 75 percent from 26 to 7 parts per million. Steady-state concentrations were input to a simple analytical model balancing advection and first-order biodegradation of hydrocarbons. First-order rate constants for the major hydrocarbon compounds were used to calibrate the model to the concentration profiles. Rate constants for the seven individual hydrocarbon compounds varied by a factor of 4. Compounds with lower molecular weights, fewer methyl groups, and no quaternary carbons tended to have higher rate constants. The first-order rate constants were consistent with kinetic parameters determined from both microcosm and tubing cluster studies at the field site.  相似文献   

Competitive Exclusion of Sulfate Reduction by Fe(lll)-Reducing Bacteria: A Mechanism for Producing Discrete Zones of High-Iron Ground Water     

Francis H. Chapelle  Derek R. Lovley 《Ground water》1992,30(1):29-36

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Nant-y-moch grassland improvement study,A. M. Roberts,J. A. Hudson and G. Roberts,Institute of Hydrology,Report No. 104, 1990. No. of pages: 85. Price: £7.00. ISBN 0-948540-16-8     

Keith Richards 《地球表面变化过程与地形》1992,17(6):635-635

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The impact of the friction of distance on the early settlement and development of Eyre Peninsula,South Australia     

Derek. L. Smith 《The Australian geographer》1992,23(2):149-163

The cost of overcoming distance has played and continues to play an important role in the evolution of Australia's space‐economy. This paper examines the impact of the ‘friction of distance’, as well as the quality of the resource base, on the settlement and development of Eyre Peninsula in South Australia. A series of maps portraying the spread of pastoralism and then agriculture on Eyre Peninsula reveals clearly the importance of ‘accessibility’ in influencing the pattern and timing of settlement. It was not until well into this century that all the potentially agricultural land in the interior was occupied, for this required the construction of a railway and water pipeline up the centre of the peninsula.  相似文献   

LNAPL Retention in Sandy Soil     

David W. Ostendorf  Robin J. Richards  Frank P. Beck 《Ground water》1993,31(2):285-292

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A terrestrial shear pattern?     

T. Ll. Richards 《Pure and Applied Geophysics》1973,110(1):2012-2021

The concept of the strain ellipsoid is applied to indicate a possible regular shear pattern of earthquake distribution over the Earth's surface. A simple model of the Earth is assumed in the form of a rotating sphere with a plastic interior and a thin, fragile, crust. On this basis rotation of the Earth generates an internal radial pressure at the equator equivalent to 1/300g causing a proportionate distortion of the spherical shell. The system is in dynamic equilibrium with an increase in gravity at the equator. The ellipsoid representing the distortion, has orthogonal principal axes corresponding to the principal strains while radial directions at 54°44 from the poles are unchanged in length and are thus possible axes of shear generating the same distortion. The Alpide region of earthquakes extending from Lisbon to Tokyo and restriction of earthquakes mainly to the broad band between latitudes 55°N or S are in support of the proposed view.Four unique sets of orthogonal shear systems have been identified which form a regular pattern with a definite symmetry with respect to the plane of the ecliptic. This suggests that the hoop stress at the Equator associated with Earth rotation may be triggered off by tidal forces and that earthquake prediction may well be possible. Other implications of this new approach are also discussed.  相似文献   

Geochemistry of ice-covered, meromictic Lake A in the Canadian High Arctic     

John A. E. Gibson  Warwick F. Vincent  Patrick Van Hove  Claude Belzile  Xioawa Wang  Derek Muir 《Aquatic Geochemistry》2002,8(2):97-119

The geochemical processes occurring within meromictic Lake A (maxdepth 120 m) on northern Ellesmere Island, Canada, were investigated to determinethe history of the lake and to provide a baseline for future studies. The lake contained seawaterdiluted by freshwater input that had been mixed prior to the lake's isolation from tidalaction. Input of freshwater after isolation of the lake created vertical stratification resultingin the creation of distinct oxic, suboxic and anoxic zones. Dissolved oxygen was present to 13 m,and sulphide beneath 32 m. Manganese and iron cycling dominated the redox chemistrybetween these depths. Total manganese concentrations reached 176 M, higher thanin most other natural stratified lake or marine environments.  相似文献