共查询到20条相似文献，搜索用时 15 毫秒
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A series of trenches about a metre deep, 20 to 30 m wide, and as much as 2 km in length occurs in central Wisconsin, along the east shore of proglacial Lake Wisconsin. They are interpreted to be collapse trenches formed when shore ice melted after being buried beneath an expanding outwash plain. 相似文献
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The enthalphy of the heat carrying fluids liquid water or mixture of water plus steam) which feeds the biggest Kamchatka geyser, Velican is obtained from the critical quantity of heat Qcritical, which is the net heat lost during the previous eruption and must be resupplied (stored) to trigger the next eruption. There are two unknowns in the heat balance equation for the geyser that cannot be determined from observations on the geyser in its natural state: critical and the enthalpy of the heat-carrying fluids Io. In order to obtain a system of two equations for unambiguous determination of these parameters, we made temporary physical changes that affected the natural interval between geyser eruptions and constructed the heat balance equations for the different regimes (i.e., natural and induced intervals).The changes in interval of Velican geyser were achieved by changing the area of its surface pool, using dams. For geysers with large surface pool areas, the heat loss from the surface (mainly through evaporation) is of the same order and sometimes larger than the losses from discharge of hot water. The change of surface pool area for Velican geyser from 12 m2 (in natural state) to 4.5 and 36.7 m2 in experiments leads to changes of its interval from an average of 5 hours and 35 minutes in natural state to 4 hours and 59 minutes and 8 hours and 8 minutes, respectively. From the three independent equations of heat balance we obtained three sets cf values for the enthalpy, Io and the critical energy, Qcritical, which differ from each other by less than 1%: Io= 176 kcal/kg*, Qcritical = 3.78 × 106 kcal.The interval between eruptions of Velican geyser tends to change linearly with vent area (within our experimental range). The range or interval values (the difference between maximal and minimal periods) also depends linearly on vent area. These two systematics are due to the facts that the increase of vent surface area causes increased heat loss by evaporation, and that changes of external conditions (wind velocity, atmospheric pressure, and air temperature) greatly influence the geyser interval.In order to simplify comparison of intervals of eruption of different geysers or of the 相似文献
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David P. Dethier 《地球表面变化过程与地形》1988,13(4):321-333
A simple mixing model demonstrates that chemical variations in Cascade surface waters reflect flow from three general zones: alpine areas, forested colluvial slopes, and seasonally saturated areas. The chemistry of weathering solutions in alpine portions of the Williamson Creek catchment (North Cascade Range) results from alteration of plagioclase, hornblende, and biotite to kaolinitic material and vermiculite. Surface and shallow groundwater in forested portions of the catchment reflect these reactions, dissolution of small quantities of carbonate, and biologic activity. Both at-a-point and downstream chemical variations are explained quantitatively by the volume of water that originates in each of the hydrogeochemical source areas. Water from the forested colluvial slopes is most significant on an annual basis. However, summer low-flow is a mixture of colluvial waters and dilute solutions from the alpine zone, whereas 10 to 30 per cent of peak flow in snowmelt and rainstorms is produced from seasonally saturated areas. Poor concentration/discharge (C/Q) correlations, typical of Cascade rivers, result from mixing of significant C/Q relations for water leaving each source area. Model predictions could be substantially improved by better data for the effects of temperature, water-contact time, and biologic cycling on the chemistry of soil water from forested zones. 相似文献
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A latite dome in northwest Arizona contains a rare occurrence of primary SO4-rich scapolite phenocrysts. The total phenocryst assemblage consists of plagioclase (An20?An33), hornblende, biotite, and scapolite (Me68). Microphenocrysts include allanite and oxidized low-Ti magnetite. Electron microprobe analyses show that the scapolite contains about 1.74 wt.% S, which indicates an atomic S/(S + C) of 0.58. Although scapolite occurs in xenoliths in volcanic rocks and diatremes, as well as a metamorphic mineral in granulites, its occurrence as a primary igneous mineral is extremely rare.Ca-rich scapolite has been crystallized experimentally by others from melts with a wide range of SiO2, CaO, and Na2O contents, at temperatures above 825°C and pressures ranging from 3 to 15 kbar. Comparison of scapolite from this latite with synthetic scapolite crystallized from nepheline syenite melt suggests that the Arizona phenocrysts crystallized under conditions of 850 to 900°C, 3–6 kbar total pressure, and unusually high ?CO2 and ?SO2. The rarity of scapolite as a phenocryst mineral suggests that high partial pressures of CO2 and SO2 are rare in the magmatic environment. 相似文献
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A summary of the available data on the peralkaline rocks of S. Pietro and S. Antioco islands, together with, new chemical analyses and some preliminary K-Ar ages are reported. Peralkaline rocks occur as ignimbrites, lava flows and domes usually deeply affected by hydrothermal alteration. Pantelleritic varieties are found within the dominantly comenditic association, which display K2O contents higher than Na2O ones. K-Ar data indicate that these peralkaline rocks have a middle Miocene age (? 15 m.y.). They occur in close field association with coheval andesitic and subalkaline acid volcanics belonging to the final products of the Tertiary calc-alkaline volcanic cicle of Sardinia. 相似文献
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Alan R. Dutton 《水文研究》1989,3(1):75-89
Permian evaporite deposits have been extensively dissolved beneath the perimeter of the Southern High Plains in the Texas Panhandle. Hydrologic and geochemical data were collected from six test wells to determine hydrogeochemical processes involved and the source and flow paths of ground water moving in salt-dissolution zones. Geochemical similarities and hydraulic-head relationships indicate that ground water dissolving halite and anhydrite moves downward from aquifers in post-Permian formations and follows flow paths influenced by topography. Holocene salt-dissolution rates probably are lower than Tertiary and Pleistocene rates owing to regional changes in physiography and climate that probably decreased the amount of recharge to salt-dissolution zones. Present as well as palaeohydrologic ground-water velocities and salt-dissolution rates are probably less beneath the Southern High Plains than in adjacent, peripheral salt-dissolution zones because of lower hydraulic conductivities and lower hydraulic-head gradients. Salinities in peripheral salt-dissolution zones are low (67 000 to 95 000 mg L?1) despite high solubility of halite, reflecting relatively open circulation of ground water. In interior salt-dissolution zones beneath the Southern High Plains, ground-water circulation is low and water composition tends to reach halite saturation. 相似文献
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North Menan Butte is a tuff cone near Idaho Falls, Idaho. It is a result of the eruption of basaltic magma through shallow water-saturated river alluvium of the Snake River. The cone is characterized by primary fractures that can be classified into four groups on the basis of their physical properties and their orientations relative to the symmetry elements of the cone. Type I fractures are short, closely spaced and usually confined to individual beds. They strike approximately at right angles to cone radii and always dip toward the rim of the tuff cone. Bed segments separated by these fractures have undergone rotation, resulting in normal displacements. Type II fractures have similar attitudes but are more continuous, less frequent, and show no shear displacement. Type III fractures also strike at right angles to cone radii, but they dip away from the cone rim. They cut across several beds and reveal inconsistent senses of shear displacement. Type IV fractures are radial, steeply dipping and tend to be the most continuous of all fracture types. Type I fractures were the earliest to develop; age relationships otherwise are uncertain. Examples of all four types of fractures are exposed on the inner and outer eroded slopes of the cone.Evidence from the cone indicates that the fractures developed in an unconsolidated aggregate of tuff with low cohesion; therefore, analysis of fracture genesis should be constrained by principles of soil mechanics. Type I fractures originated as tension fractures related to early downslope mass movement. Later movement on Type I fractures accompanied the development of Type III shear fractures and possible bedding plane displacements, all caused by overloading the crest of the cone by late-stage eruptive products. The origin of Type II fractures is unknown; shrinkage due to desiccation or large-scale creep are possible explanations. The radial Type IV fractures may be a consequence of desiccation shrinkage or possibly of subcone processes such as magma doming or radial hydraulic fracturing. 相似文献
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《Ground Water Monitoring & Remediation》1988,8(1):98-103
Ground water monitoring is considered to be a significant component of the geological service in the U.S.S.R. Currently, the total number of ground water monitoring wells exceeds 30,000. They are divided into two categories, which are the first class, or basic observation wells, and the second class, or auxiliary observation wells. The main objectives of both monitoring networks are briefly described. The general scheme of ground water monitoring organization is also presented. 相似文献
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Palaeomagnetic measurements on the pre-Miocene carbonatite volcanics of Tororo, S.E. Uganda, have yielded a pole at 75.8°N, 195.5°E with A95 = 9.4°. Along with the Tertiary poles from East African rift systems, the Eocene-Oligocene pole from Ethiopia and the mean Mesozoic pole from the rest of Africa, a polar wander path for Africa fromMesozoic to present is suggested. 相似文献