Simulation of groundwater flow and environmental effects resulting from pumping

In coastal lowland plains, increased water demand on a limited water resource has resulted in declining groundwater levels, land subsidence and saltwater encroachment. In southwestern Kyushu, Japan, a sinking of the land surface due to over pumping of groundwater has long been recognized as a problem in the Shiroishi lowland plain. In this paper, an integrated model was established for the Shiroishi site using the modular finite difference groundwater flow model, MODFLOW, by McDonald and Harbaugh (1988) and the modular three-dimensional finite difference groundwater solute transport model, MT3D, by Zheng (1990) to simulate groundwater flow hydraulics, land subsidence, and solute transport in the alluvial lowland plain. Firstly, problems associated with these groundwater resources were discussed and then the established model was applied. The simulated results show that subsidence rapidly occurs throughout the area with the central prone in the center part of the plain. Moreover, seawater intrusion would be expected along the coast if the current rates of groundwater exploitation continue. Sensitivity analysis indicates that certain hydrogeologic parameters such as an inelastic storage coefficient of soil layers significantly contribute effects to both the rate and magnitude of consolidation. Monitoring the present salinization process is useful in determining possible threats to fresh groundwater supplies in the near future. In addition, the integrated numerical model is capable of simulating the regional trend of potentiometric levels, land subsidence and salt concentration. The study also suggests that during years of reduced surface-water availability, reduction of demand, increase in irrigation efficiency and the utilization of water exported from nearby basins are thought to be necessary for future development of the region to alleviate the effects due to pumping.     

Fault textures in volcanic conduits: evidence for seismic trigger mechanisms during silicic eruptions

It is proposed that fault textures in two dissected rhyolitic conduits in Iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows. Detailed field and petrographic analysis of such textures may shed light on the origin of long-period and hybrid volcanic earthquakes at active volcanoes. There is evidence at each conduit investigated for multiple seismogenic cycles, each of which involved four distinct evolutionary phases. In phase 1, shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow, forming the angular fracture networks that initiated faulting cycles. Transient pressure gradients were generated as the fractures opened, which led to fluidisation and clastic deposition of fine-grained particles that were derived from the fracture walls by abrasion. Fracture networks then progressively coalesced and rotated during subsequent slip (phase 2), developing into cataclasite zones with evidence for multiple localised slip events, fluidisation and grain size reduction. Phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction-controlled stick-slip behaviour. Increasing cohesion of cataclasites then led to aseismic, distributed ductile deformation (phase 3) and generated deformed cataclasite zones, which are enriched in metallic oxide microlites and resemble glassy pseudotachylite. Continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite-rich flow bands in obsidian (phase 4). Overall, the mixed brittle–ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle–ductile transition, with the rheological response mediated by strain-rate variations and frictional heating. Fault processes in highly viscous magma are compared with those elsewhere in the crust, and this comparison is used to appraise existing models of volcano seismic activity. Based on the textures observed, it is suggested that patterns of long-period and hybrid earthquakes at silicic lava domes reflect friction-controlled stick-slip movement and eventual healing of fault zones in magma, which are an accelerated and smaller-scale analogue of tectonic faults.Editorial responsibility: J. Stix     

Tomorrow’s Forests: Adapting to A Changing Climate

Today’s forests are largely viewed as a natural asset, growing in a climate envelope, which favors natural regeneration of species that have adapted and survived the variability’s of past climates. However, human-induced climate change, variability and extremes are no longer a theoretical concept. It is a real issue affecting all biological systems. Atmospheric scientists, using global climate models, have developed scenarios of the future climate that far exceed the traditional climate envelope and their associated forest management practices. Not all forests are alike, nor do they share the same adaptive life cycles, feedbacks and threats. Much of tomorrow’s forests will become farmed forests, managed in a pro-active, designed and adaptive envelope, to sustain multiple products, values and services. Given the life cycle of most forest species, forest management systems will need to radically adjust their limits of knowledge and adaptive strategies to initiate, enhance and plan forests in relative harmony with the future climate. Protected Areas (IUCN), Global Biosphere Reserves (UNESCO) and Smithsonian Institution sites provide an effective community-based platform to monitor changes in forest species, ecosystems and biodiversity under changing climatic conditions.     

Vertical seismic profile at Pike's Peak, Saskatchewan, Canada: turning rays and velocity anisotropy

First-arrival traveltimes from a multi-offset vertical seismic profile (VSP) were used to estimate velocity anisotropy in the presence of a vertical velocity gradient. A numerical model consisting of two layers with vertical velocity gradients of 3.1 and 1.2 s⁻¹, respectively, and global anisotropy parameters of =0.12±0.02 and δ=0.30±0.06 yielded first-arrival traveltimes that matched the observed traveltimes well. Shallow receivers were found to be crucial for constraining the vertical velocity field and for determining the parameters of anisotropy at depth.     

Sudbury Breccia (Canada): a product of the 1850 Ma Sudbury Event and host to footwall Cu–Ni–PGE deposits

The Sudbury Structure, formed by meteorite impact at 1850 Ma, consists of three major components: (1) the Sudbury Basin; (2) the Sudbury Igneous Complex, which surrounds the basin as an elliptical collar; and (3) breccia bodies in the footwall known as Sudbury Breccia. In general, the breccia consists of subrounded fragments set in a dark, fine-grained to aphanitic matrix. A comparison of the chemical composition of host rocks, clasts and matrices indicates that brecciation was essentially an in-situ process. Sudbury Breccia forms irregular-shaped bodies or dikes that range in size from mm to km scale. Contacts with the host rocks are commonly sharp. The aspect ratio of most clasts is approximately 2 with the long axes parallel to dike walls. The fractal dimension (Dr)=1.55. Although there appears to be some concentration of brecciation within concentric zones, small Sudbury Breccia bodies within and outside these zones have more or less random strikes and steep dips. Sudbury Breccia bodies near an embayment structure tend to be subparallel to the base of the Sudbury Igneous Complex. Sudbury Breccia occurs as much as 80 km from the outer margin of the Sudbury Igneous Complex. In an inner zone, 5 to 15 km wide, breccia comprises 5% of exposed bedrock with an increase in brecciation intensity in embayment structures. Sudbury Breccia may be classified into three types based on the nature of the matrix: clastic, pseudotachylite and microcrystalline. Clastic Sudbury Breccia, the dominant type in the Southern Province, is characterized by flow-surface structures. Possibly, a sudden rise in pore pressure caused explosive dilation and fragmentation, followed by fluidization and flowage into extension fractures. Pseudotachylite Sudbury Breccia, mainly confined to Archean rocks, apparently formed by comminution and frictional melting. Microcrystalline Sudbury Breccia formed as a result of the thermal metamorphism, of the North Range footwall, by the Sudbury Igneous Complex. This produced a zone, approximately 1.2 km wide, wherein the matrix of the breccia either recrystallized or, locally, melted. An overprint of regional metamorphism obliterated contact effects in the South Range footwall. The Ni–Cu–PGE magmatic sulphide deposits may be classified into four types based on structural setting: Sudbury Igneous Complex–footwall contact, footwall, offset, and sheared deposits. Sudbury Breccia is the main host for footwall deposits (e.g., McCreedy East, Victor, Lindsley). Sudbury Breccia locally hosts mineralization in radial (e.g., Parkin and Copper Cliff) and concentric (e.g., Frood–Stobie) offset dikes.     

The combined effect of F and H2O on interdiffusion between peralkaline dacitic and rhyolitic melts

The effective binary diffusion coefficient (EBDC) of silicon has been measured during the interdiffusion of peralkaline, fluorine-bearing (1.3 wt% F), hydrous (3.3 and 6 wt% H₂O), dacitic and rhyolitic melts at 1.0 GPa and temperatures between 1100°C and 1400°C. From Boltzmann-Matano analysis of diffusion profiles the diffusivity of silicon at 68 wt% SiO₂ can be described by the following Arrhenius equations (with standard errors): $$\begin{gathered} {\text{with 1}}{\text{.3 wt\% F and 3}}{\text{.3\% H}}_{\text{2}} {\text{O:}} \hfill \\ {\text{D}}_{{\text{Si}}} = \begin{array}{*{20}c} { + {\text{3}}{\text{.59}}} \\ {{\text{3}}{\text{.66}} \times {\text{10}}^{ - {\text{9}}} } \\ { - {\text{1}}{\text{.86}}} \\ \end{array} {\text{exp}}\left( {{{ - {\text{86}}{\text{.1}} \pm {\text{8}}{\text{.9}}} \mathord{\left/ {\vphantom {{ - {\text{86}}{\text{.1}} \pm {\text{8}}{\text{.9}}} {{\text{RT}}}}} \right. \kern-\nulldelimiterspace} {{\text{RT}}}}} \right) \hfill \\ {\text{with 1}}{\text{.3 wt\% F and 6}}{\text{.0\% H}}_{\text{2}} {\text{O:}} \hfill \\ {\text{D}}_{{\text{Si}}} = \begin{array}{*{20}c} { + {\text{3}}{\text{.59}}} \\ {{\text{3}}{\text{.51}} \times {\text{10}}^{ - {\text{8}}} } \\ { - {\text{1}}{\text{.77}}} \\ \end{array} {\text{exp}}\left( {{{ - {\text{109}}{\text{.5}} \pm {\text{8}}{\text{.9}}} \mathord{\left/ {\vphantom {{ - {\text{109}}{\text{.5}} \pm {\text{8}}{\text{.9}}} {{\text{RT}}}}} \right. \kern-\nulldelimiterspace} {{\text{RT}}}}} \right) \hfill \\ \end{gathered} $$ where D is in m²s^?1 and activation energies are in kJ/mol. Diffusivities measured at 64 and 72 wt% SiO₂ are only slightly different from those at 68 wt% SiO₂ and frequently all measurements are within error of each other. Silicon, aluminum, iron, magnesium, and calcium EBDCs were also calculated from diffusion profiles by error function inversion techniques assuming constant diffusivity. With one exception, silicon EBDCs calculated by error function techniques are within error of Boltzmann-Matano EBDCs. Average diffusivities of Fe, Mg, and Ca were within a factor of 2.5 of silicon diffusivities whereas Al diffusivities were approximately half those of silicon. Alkalies diffused much more rapidly than silicon and non-alkalies, however their diffusivities were not quantitatively determined. Low activation energies for silicon EBDCs result in rapid diffusion at magmatic temperatures. Assuming that water and fluorine exert similar effects on melt viscosity at high temperatures, the viscosity can be calculated and used in the Eyring equation used to determine diffusivities, typically to within a factor of three of those measured in this study. This correlation between viscosity and diffusivity can be inverted to calculate viscosities of fluorine- and water-bearing granitic melts at magmatic temperatures; these viscosities are orders of magnitude below those of hydrous granitic melts and result in more rapid and effective separation of granitic magmas from partially molten source rocks. Comparison of Arrhenius parameters for diffusion measured in this study with Arrhenius parameters determined for diffusion in similar compositions at the same pressure demonstrates simple relationships between Arrhenius parameters, activation energy-E_a, kJ/mol, pre-exponential factor-D_o, m²s^?1, and the volatile, X=F or OH^?, to oxygen, O, ratio of the melt {(X/X+O)}: $$\begin{gathered} {\text{E}}a = - {\text{1533\{ }}{{\text{X}} \mathord{\left/ {\vphantom {{\text{X}} {\left( {{\text{X}} + {\text{O}}} \right)}}} \right. \kern-\nulldelimiterspace} {\left( {{\text{X}} + {\text{O}}} \right)}}{\text{\} }} + {\text{213}}{\text{.3}} \hfill \\ {\text{D}}_{\text{O}} = {\text{2}}{\text{.13}} \times {\text{10}}^{ - {\text{6}}} {\text{exp}}\left[ { - {\text{6}}{\text{.5\{ }}{{\text{X}} \mathord{\left/ {\vphantom {{\text{X}} {\left( {{\text{X}} + {\text{O}}} \right)}}} \right. \kern-\nulldelimiterspace} {\left( {{\text{X}} + {\text{O}}} \right)}}{\text{\} }}} \right] \hfill \\ \end{gathered} $$ These relationships can be used to estimate diffusion in various melts of dacitic to rhyolitic composition containing both fluorine and water. Calculations for the contamination of rhyolitic melts by dacitic enclaves at 800°C and 700°C provide evidence for the virtual inevitability of diffusive contamination in hydrous and fluorine-bearing magmas if they undergo magma mixing of any form.     

Net deficits and the case for aquacultural geography

Summary The crisis in capture fisheries has placed an increased onus on aquaculture to supply the world fish demand. The advancing role of culture relative to capture fisheries has precipitated environmental and socio-economic transformations. Geographers have paid scant attention to these developments. This paper provides a literature review and proffers a research agenda for aquacultural geography.     

Interdiffusion of hydrous dacitic and rhyolitic melts and the efficacy of rhyolite contamination of dacitic enclaves

Effective binary diffusion coefficients of Si during the interdiffusion of hydrous, 3 and 6% H₂O, dacitic and rhyolitic melts have been determined at 1.0 GPa, 1100°–1400°C. Water is shown to enhance diffusivities by one to two orders of magnitude above dry Si diffusivities in the same compositional system for SiO₂ compositions 65–75wt%. The effect of silica content on diffusion is small and typically within experimental error. With 3% H₂O in the melts the Arrhenius equation for Si diffusion at 70% SiO₂ is: $${\text{D = }}2.583\operatorname{x} 10^{ - {\text{ }}8} {\text{ }}\exp ( - 126.5/R{\text{T}})$$ where D is the diffusivity in m²/s, the activation energy (126.5) is in kJ/mol, R is in J/mol and T in Kelvin. Although less-well constrained, the Si diffusivity at 70% SiO₂ with 6% H₂O in the melts can be described by: $${\text{D = }}2.692\operatorname{x} 10^{ - {\text{ }}7} {\text{ }}\exp ( - 131.4/R{\text{T}})$$ The activation energies for diffusion are substantially below the activation energy of 236.4kJ/mol measured during anhydrous interdiffusion in the same system (Baker 1990). The decrease in activation energy with the initial addition of 3% water and the relative insensitivity of the activation energy to the additional water is related to the abundance of OH species in the melt, and the reduction of (Si,Al)-O bond strengths due to the interaction of hydroxyls with the (Si,Al)-O network. Changes in the pre-exponential factor of Arrhenius equations are attributed to the abundance of H₂O species in the melts. No decoupling of non-alkalies from SiO₂ during interdiffusion of the two melts was observed, although alkalies diffuse much more rapidly than non-alkalies (but were not measured quantitatively in this study) and can become decoupled. Interdiffusion of Si and all non-alkalies is demonstrated to be predictable, at least to within a factor of ten, by the Eyring equation. Using the diffusion data of this study for nonalkalies and of other studies for alkalies and Sr isotopes the contamination of a host rhyolitic magma by dacitic enclaves, 5 and 50 cm radius, has been modeled for temperatures of 1000°, 900°, and 800° C with water contents of 3 and 6%. Even when the effects of phenocrysts on diffusion in the dacitic enclaves are estimated the results of the modeling demonstrate that significant contamination is possible in the case of small enclaves, and even large enclaves have the potential to affect the composition of their host magma in geologically short times.     

文县天池环境调查

根据文县天池首次实地科学考察资料，本文从自然地理，物理化学、生物及旅游诸方面论述了天池的基本特。