Scale Dependency of Hydraulic Conductivity in Heterogeneous Media   总被引：8，自引：0，他引：8  

Dirk Schulze-Makuch  Douglas A. Carlson  Douglas S. Cherkauer  Peter Malik 《Ground water》1999,37(6):904-919

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Landslides control the spatial and temporal variation of channel width in southern Taiwan: Implications for landscape evolution and cascading hazards in steep,tectonically active landscapes          下载免费PDF全文

Brian J. Yanites  Nate A. Mitchell  Joshua C. Bregy  Grace A. Carlson  Kirstyn Cataldo  Margaret Holahan  Graham H. Johnston  Amelia Nelson  Jeffery Valenza  Matthew Wanker 《地球表面变化过程与地形》2018,43(9):1782-1797

Intense precipitation or seismic events can generate clustered mass movement processes across a landscape. These rare events have significant impacts on the landscape, however, the rarity of such events leads to uncertainty in how they impact the entire geomorphic system over a range of timescales. Taiwan is steep, tectonically active, and prone to landslide and debris flows, especially when exposed to heavy rainfall events. Typhoon Morakot made landfall in Taiwan in August of 2009, causing widespread landslides in southern Taiwan. The south to north trend in valley relief in southern Taiwan leads to spatial variability in landslide susceptibility providing an opportunity to infer the long‐term impact of such landslide events on channel morphology. We use pre‐ and post‐typhoon imagery to quantify the propagating impact of this event on channel width as the debris is routed through the landscape. The results show the importance of cascading hazards from landslides on landscape evolution based on patterns of channel width (both pre‐ and post‐typhoon) and hillslope gradients in 20 basins along strike in southern Taiwan. Prior to Typhoon Morakot, the river channels in the central part of the study area were about 3–10 times wider than the channels in the south. Following the typhoon, aggradation and widening was also a maximum in these central to northern basins where hillslope gradients and channel steepness is high, accentuating the pre‐typhoon pattern. The results further show that the narrowest channels are located where channel steepness is the lowest, an observation inconsistent with a detachment‐limited model for river evolution. We infer this pattern is indicative of a strong role of sediment supply, and associated landslide events, on long‐term channel evolution. These findings have implications across a range of spatial and temporal scales including understanding the cascade of hazards in steep landscapes and geomorphic interpretation of channel morphology. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Possible lower crustal rocks recovered on Leg 31 by deep-sea drilling in the Philippine Sea     

David M. Fountain  Richard L. Carlson  Matthew H. Salisbury  Nikolas I. Christensen 《Marine Geology》1975,19(5):M75-M80

Compressional wave velocities measured in gabbroic rocks and metabasites recovered from Site 293 of Leg 31 in the Philippine Sea (on the Central Basin Fault) are correlative with seismic velocities determined for Layer 3. The lower crustal origin for these rocks suggested by this data is further supported by the similarity between these samples, dredge haul samples from fracture zones in the main ocean basins and rocks found in ophiolite complexes. These plutonic rocks were possibly introduced to the sea floor by movements along the Central Basin Fault, a major tectonic feature in the Philippine Sea, or formed as part of new ocean crust within a leaky transform fault.  相似文献   

HF Accelerated Electron Fluxes,Spectra, and Ionization   总被引：1，自引：0，他引：1  

Herbert C. Carlson  Joseph B. Jensen 《Earth, Moon, and Planets》2015,116(1):1-18

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Characteristics of a Shallow River Plume: Observations from the Saco River Coastal Observing System     

Charles E. Tilburg  Shaun M. Gill  Stephan I. Zeeman  Amy E. Carlson  Timothy W. Arienti  Jessica A. Eickhorst  Philip O. Yund 《Estuaries and Coasts》2011,34(4):785-799

Interest in the coastal dynamics of river plumes has mainly focused on large rivers, but plumes from the more numerous smaller rivers have important local consequences and may, in aggregate, be significant contributors to coastal circulation. We studied the dynamics of the plume from the Saco River in Saco Bay, Gulf of Maine, over a 3-year period. The transport and salinity in the region are governed by river discharge, tides, winds, and interaction with the Western Maine Coastal Current. The dynamics of the flow field vary with location within the plume and discharge. The far-field dynamics of the Saco River plume are dominated by inertial processes (hence qualifying it as a small-scale river plume), during times of low discharge, with low salinity water present both up and downstream of the river mouth, but are dominated by rotational processes during times of high discharge (thus qualifying it as a large-scale river plume), with buoyant water primarily advected downshelf. Near-field dynamics are governed by weak, subcritical flow during low discharge but strongly inertial, supercritical flow during high discharge. Offshore movement of the plume is not governed by Ekman dynamics but is instead a result of discharge, wind-induced vertical mixing, and the geography of the coastline and adjacent islands.  相似文献   

Polar science news in brief     

David Carlson 《Environmental Earth Sciences》2013,68(6):1813-1821

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Use of Nested Flow Models and Interpolation Techniques for Science‐Based Management of the Sheyenne National Grassland,North Dakota,USA     

M.A. Gusyev  H.M. Haitjema  C.P. Carlson  M.A. Gonzalez 《Ground water》2013,51(3):414-420

Noxious weeds threaten the Sheyenne National Grassland (SNG) ecosystem and therefore herbicides have been used for control. To protect groundwater quality, the herbicide application is restricted to areas where the water table is less than 10 feet (3.05 m) below the ground surface in highly permeable soils, or less than 6 feet (1.83 m) below the ground surface in low permeable soils. A local MODFLOW model was extracted from a regional GFLOW analytic element model and used to develop depth‐to‐groundwater maps in the SNG that are representative for the particular time frame of herbicide applications. These maps are based on a modeled groundwater table and a digital elevation model (DEM). The accuracy of these depth‐to‐groundwater maps is enhanced by an artificial neural networks (ANNs) interpolation scheme that reduces residuals at 48 monitoring wells. The combination of groundwater modeling and ANN improved depth‐to‐groundwater maps, which in turn provided more informed decisions about where herbicides can or cannot be safely applied.  相似文献   

Prograde, peak, and retrograde P–T paths from aluminium in orthopyroxene: High-temperature contact metamorphism in the aureole of the Makhavinekh Lake Pluton, Nain Plutonic Suite, Labrador     

C. R. M. McFarlane  W. D. Carlson  J. N. Connelly 《Journal of Metamorphic Geology》2003,21(5):405-423

Static heating during intrusion of the Makhavinekh Lake Pluton (MLP) caused replacement of garnet in the adjacent country rocks (Tasiuyak Gneiss) by coronal assemblages of orthopyroxene + cordierite. Thermometry based on Al solubility in orthopyroxene, applied to relict garnet and neighbouring orthopyroxene, preserves a temperature gradient from 700 to 900 °C at distances between 5750 and 20 m from the intrusion, reaffirming the robustness of this thermometry technique. Intracrystalline and intergranular variations of Al zoning in orthopyroxene are well‐preserved, suggesting that little diffusional modification of Al growth zoning occurred. Maximum Al₂O₃ in orthopyroxene ranges from c. 2.0 wt% at 5750 m from the intrusion to a maximum of 4.3 wt% at the contact. Individual orthopyroxene grains show decreasing Al from core to rim in samples < 500 m from the intrusion, while those at greater distances show an increase from core to rim. These features are interpreted with the aid of numerical models for conductive heat flow in the aureole. Coronas in samples close to the intrusion grew at high temperatures and along T‐t paths dominated by cooling, so maximum Al content in orthopyroxene in these samples occurs in the cores of grains that grew during the earliest stages of garnet consumption. In contrast, the corona‐forming reactions in rocks further from the contact proceeded along prograde heating paths, so maximum Al content in orthopyroxene occurs in the rims of grains that grew during the final stages of garnet consumption. These results document the ability of Al‐in‐orthopyroxene thermometry to preserve a detailed record of thermal histories in contact‐metamorphic granulites; they suggest that similar intracrystalline and intergranular variations of Al zoning in orthopyroxene in regional granulites may also preserve portions of both the prograde and peak‐T evolution.  相似文献   

Hydrothermal alteration, fluid flow and volume change in shear zones: the layered mafic–ultramafic Kettara intrusion (Jebilet Massif, Variscan belt, Morocco)     

A. Essaifi  R. Capdevila  S. Fourcade  J. L. Lagarde  M. Ballèvre  CH. Marignac 《Journal of Metamorphic Geology》2004,22(1):25-43

During emplacement and cooling, the layered mafic–ultramafic Kettara intrusion (Jebilet, Morocco) underwent coeval effects of deformation and pervasive fluid infiltration at the scale of the intrusion. In the zones not affected by deformation, primary minerals (olivine, plagioclase, clinopyroxene) were partially or totally altered into Ca‐amphibole, Mg‐chlorite and CaAl‐silicates. In the zones of active deformation (centimetre‐scale shear zones), focused fluid flow transformed the metacumulates (peridotites and leucogabbros) into ultramylonites where insoluble primary minerals (ilmenite, spinel and apatite) persist in a Ca‐amphibole‐rich matrix. Mass‐balance calculations indicate that shearing was accompanied by up to 200% volume gain; the ultramylonites being enriched in Si, Ca, Mg, and Fe, and depleted in Na and K. The gains in Ca and Mg and losses in Na and K are consistent with fluid flow in the direction of increasing temperature. When the intrusion had cooled to temperatures prevailing in the country rock (lower greenschist facies), deformation was still active along the shear zones. Intense intragranular fracturing in the shear zone walls and subsequent fluid infiltration allowed shear zones to thicken to metre‐scale shear zones with time. The inner parts of the shear zones were transformed into chlorite‐rich ultramylonites. In the shear zone walls, muscovite crystallized at the expense of Ca–Al silicates, while calcite and quartz were deposited in ‘en echelon’ veins. Mass‐balance calculations indicate that formation of the chlorite‐rich shear zones was accompanied by up to 60% volume loss near the centre of the shear zones; the ultramylonites being enriched in Fe and depleted in Si, Ca, Mg, Na and K while the shear zones walls are enriched in K and depleted in Ca and Si. The alteration observed in, and adjacent to the chlorite shear zones is consistent with an upward migrating regional fluid which flows laterally into the shear zone walls. Isotopic (Sr, O) signatures inferred for the fluid indicate it was deeply equilibrated with host lithologies.  相似文献   

Geochemical constraints on the Laurentide Ice Sheet contribution to Meltwater Pulse 1A     

Anders E. Carlson 《Quaternary Science Reviews》2009,28(17-18):1625-1630

Planktonic and benthic δ¹⁸O records adjacent to the runoff outlets of the Laurentide Ice Sheet (LIS) indicate that the LIS contributed to the abrupt ～20 m rise in sea level ～14.6 ka, Meltwater Pulse 1A (MWP-1A). However, the magnitude of the LIS contribution still remains unresolved. Here, I use a freshwater runoff–ocean mixing model to calculate the LIS meltwater required to explain the decreases in planktonic and benthic δ¹⁸O observed during MWP-1A at the southern, eastern and northern runoff outlets of the LIS. Maximum LIS contributions in equivalent sea level rise for a 500-year long MWP-1A are 2.7 m discharged into the Gulf of Mexico as a combined hyperpycnal and hypopycnal flow, 2.1 m discharged into the North Atlantic, and 0.5 m into the Arctic Ocean, for a total LIS contribution of ≤5.3 m. A LIS contribution of <30% to MWP-1A supports the hypothesis that a significant component of this MWP was sourced from the Antarctic Ice Sheet.  相似文献