Loess accumulation and soil formation in central kansas,United States,during the past 400 000 years

Based on interpolation of thermoluminescence dates and the mean accumulation rate of 0.034 mm yr^?1, four cycles of pedogenic CaCO₃ accumulation are found within the Loveland Loess: 415–325 ka, 325–250 ka, 250–195 ka and 195–95 ka. The four CaCO₃ peaks correspond chronologically to marine oxygen isotope stages 11, 9, 7 and 5, respectively. The early Wisconsin (95–70 ka) was characterized by sand dune activity. The reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very slow rate of silt accumulation (0·016 mm yr^?1). The Gilman Canyon pedocomplex, enriched in organic matter and dated at 35–20 ka, was formed under a strong physical weathering regime and a relatively high rate of silt accumulation (0·15 mm yr^?1), indicating a windy, relatively moist, probably cool environment. It developed when the Laurentide ice sheet was advancing and dust content in Greenland ice core was low. The Peoria Loess was accumulated at a rate of 0·3 mm yr^?1 in central Kansas under cold dry conditions when the ice sheet fluctuated around its maximum position and the dust content in the Greenland ice core was the highest. Even the warm substage around 13 ka has some corresponding evidence in the central Great Plains. The well-developed Brady Soil, dated at 10·5–8·5 ka, indicates that the early Holocene was the optimal time for soil development since 20 ka. The poorly weathered Bignell Loess might have been deposited during the Altithermal Period from 8·5 to 6 ka.     

Ar/Ar geochronology of the West Greenland Tertiary volcanic province

Paleocene volcanic rocks in West Greenland and Baffin Island were among the first products of the Iceland mantle plume, forming part of a larger igneous province that is now submerged beneath the northern Labrador Sea. A ⁴⁰Ar/³⁹Ar dating study shows that volcanism commenced in West Greenland between 60.9 and 61.3 Ma and that 80% of the Paleocene lava pile was erupted in 1 million years or less (weighted mean age of 60.5±0.4 Ma). Minimum estimates of magma production rates (1.3×10⁻⁴ km³ year⁻¹ km⁻¹) are similar to the present Iceland rift, except for the uppermost part of the Paleocene volcanic succession where the rate decreases to <0.7×10⁻⁴ km³ year⁻¹ km⁻¹ (rift). The timing of onset of volcanism in West Greenland coincides with the opening of the northern Labrador Sea and is also strikingly similar to the age of the oldest Tertiary volcanic rocks from offshore SE Greenland and the British–Irish province. This is interpreted as manifesting the impact and rapid (>1 m/year) lateral spreading of the Iceland plume head at the base of the Greenland lithosphere at 62 Ma. We suggest that the arrival, or at least a major increase in the flux, of the Iceland mantle plume beneath Greenland was a contributing factor in the initiation of seafloor spreading in the northern Labrador Sea. Our study has also revealed a previously unrecognised Early Eocene volcanic episode in West Greenland. This magmatism may be related to movement on the transform Ungava Fault System which transferred drifting from the Labrador Sea to Baffin Bay. A regional change in plate kinematics at 55 Ma, associated with the opening of the North Atlantic, would have caused net extension along parts of this fault. This would have resulted in decompression and partial melting of the underlying asthenosphere. The source of the melts for the Eocene magmatism may have been remnants of still anomalously hot Iceland plume mantle which were left stranded beneath the West Greenland lithosphere in the Early Paleocene.     

East Greenland freshwater runoff to the Greenland‐Iceland‐Norwegian Seas 1999–2004 and 2071–2100

In this paper, we quantify the terrestrial flux of freshwater runoff from East Greenland to the Greenland‐Iceland‐Norwegian (GIN) Seas for the periods 1999–2004 and 2071–2100. Our analysis includes separate calculations of runoff from the Greenland Ice Sheet (GrIS) and the land strip area between the GrIS and the ocean. This study is based on validation and calibration of SnowModel with in situ data from the only two long‐term permanent automatic meteorological and hydrometric monitoring catchments in East Greenland: the Mittivakkat Glacier catchment (65°N) in SE Greenland, and the Zackenberg Glacier catchment (74°N) in NE Greenland. SnowModel was then used to estimate runoff from all of East Greenland to the ocean. Modelled glacier recession in both catchments for the period 1999–2004 was in accordance with observations, and dominates the annual catchment runoff by 30–90%. Average runoff from Mittivakkat, ～3·7 × 10^?2 km³ y^?1, and Zackenberg, ～21·9 × 10^?2 km³ y^?1, was dominated by the percentage of catchment glacier cover. Modelled East Greenland freshwater input to the North Atlantic Ocean was ～440 km³ y^?1 (1999–2004), dominated by contributions of ～40% from the land strip area and ～60% from the GrIS. East Greenland runoff contributes ～10% of the total annual freshwater export from the Arctic Ocean to the Greenland Sea. The future (2071–2100) climate impact assessment based on the Intergovernmental Panel on Climate Change (IPCC) A2 and B2 scenarios indicates an increase of mean annual East Greenland air temperature by 2·7 °C from today's values. For 2071–2100, the mean annual freshwater input to the North Atlantic Ocean is modelled to be ～650 km³ y^?1: ～30% from the land strip area and ～70% from the GrIS. This is an increase of approximately ～50% from today's values. The freshwater runoff from the GrIS is more than double from today's values, based largely on increasing air temperature rather than from changes in net precipitation. Copyright © 2008 John Wiley & Sons, Ltd.     

Greenland iceBe concentrations and average precipitation rates north of 40°N to 45°N

A model of¹⁰Be deposition within the subarctic and arctic is developed based on the behavior of⁹⁰Sr in the troposphere. Measured¹⁰Be fluxes, based on analyses of¹⁰Be in one year's snow fall (1979–1980) from the Dye-3 site in southwest Greenland and on published data, and predicted¹⁰Be fluxes, based on the¹⁰Be deposition model, agree. These results indicate that with regard to¹⁰Be, the troposphere north of 40°N to 45°N presently behaves as if it is well-mixed and that the average precipitation rate within that reservoir controls in large part the concentration of¹⁰Be in Greenland ice. Inversion of the Greenland ice core¹⁰Be concentration record with the aid of the model indicates: (1) that the average precipitation rate in the subarctic and arctic was lower than the present rate during the Maunder minimum of solar activity, and higher than the present rate during the Wolf and Sporer solar activity minimums; and (2) that during the Wisconsin-Holocene transition the average precipitation rate in the subarctic and arctic was about one third the present precipitation rate.     

The importance of oxygen isotope provenance in relation to solute content of bulk meltwaters at Imersuaq Glacier,West Greenland

Stable oxygen isotope analysis and measurement of several dissolved cations and anions of bulk meltwater samples have provided information about the hydrochemical environment of the glacial hydrological system at Imersuaq Glacier, an outlet tongue from the Greenland ice‐sheet, West Greenland. The samples were collected at frequent intervals during the period 20–28 July 2000 in a small (<20 L s^?1) englacial meltwater outlet at the glacier margin. The results document the following findings: (i) a marked diurnal variation of δ¹⁸O is related to the composition of oxygen isotope provenances, mainly near‐marginal local superimposed ice and basal up‐sheared ice further up‐glacier; (ii) a relationship is seen between all base cations (Na⁺, K⁺, Ca²⁺, Mg²⁺), SO₄^2? and δ¹⁸O, indicating that solute acquisition is provided by solid–solution contact with the up‐sheared ice—as the relationship with Cl^? is weak the influence of seasalt‐derived solutes is small in the area; (iii) when the melt rate is high, two diurnal maxima of δ¹⁸O values and solute concentrations are measured, and it is suggested that a snow meltwater component is responsible for the second maximum of δ¹⁸O—a short residence time leads to a delayed decrease in ion concentrations. Copyright © 2003 John Wiley & Sons, Ltd.     

Using in situ cosmogenic 10Be to identify the source of sediment leaving Greenland

We use the concentration of in situ ¹⁰Be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to Greenland's sediment budget. We sampled along the western, eastern, and southern margins of the Greenland Ice Sheet, and collected sediment sourced from glacerized (n = 19) and non‐glacerized terrain (n = 10), from channels where sediment from glacerized and non‐glacerized terrain is mixed (n = 28), from Holocene glacial‐fluvial terraces (n = 4), and from one sand dune. In situ ¹⁰Be concentrations in sediment range from 1600 to 34 000 atoms g^‐1. The concentration of in situ ¹⁰Be in sediment sourced from non‐glacerized terrain is significantly higher than in sediment sourced from glacerized areas, in mixed channel sediment, and in terrace sediment that was deposited during the Holocene. To constrain the timing of landscape exposure for the deglaciated portion of the Narsarsuaq field area in southern Greenland, we measured in situ ¹⁰Be concentration in bedrock (n = 5) and boulder (n = 6) samples. Paired bedrock and boulder ages are indistinguishable at 1σ uncertainty and indicate rapid exposure of the upland slopes at ~10.5 ka. The isotope concentration in sediment sourced from non‐glacerized terrain is higher than in sediment sourced from glacerized terrain because the non‐glacerized landscape has been exposed to cosmic radiation since early Holocene deglaciation. Sediment from glacerized areas contains a low, but measurable concentration of ¹⁰Be that probably accumulated at depth during a prolonged period of exposure, probably before the establishment of the Greenland Ice Sheet. The concentration of ¹⁰Be in mixed fluvial sediment and in terrace sediment is low, and similar to the concentration in sediment from glacerized areas, which indicates that the Greenland Ice Sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we sampled. Copyright © 2014 John Wiley & Sons, Ltd.     

液化侧扩流场地桥梁群桩效应分析

基于u-p有限元公式模拟饱和砂土中水和土颗粒完全耦合效应,建立液化侧向流场地群桩动力反应分析的三维数值模型。模型中,砂土采用多屈服面弹塑性本构模型模拟、黏土采用多屈服面运动塑性模型模拟,群桩在计算过程中保持线弹性状态;采用20节点的六面体单元和考虑孔压效应的20-8节点分别划分黏土层和饱和砂层;选用剪切梁边界处理计算域的人工边界,模拟地震过程中土层的剪切效应;应用瑞利阻尼考虑体系的阻尼效应。随后对比分析2×2群桩中各单桩的地震反应规律,结果表明,各单桩的弯矩、位移时程规律基本一致,峰值弯矩及峰值位移出现时刻滞后于输入加速度峰值时刻,上坡向桩的弯矩和位移峰值大于下坡向的桩的反应值。接着通过改变桩间距研究群桩效应,随着桩间距增加,群桩中各单桩的弯矩最大值均出现在土层分界处,且各单桩的弯矩、桩顶位移逐渐增大。最后给出液化侧向流场地群桩效应的基本原因,得出该类场地群桩抗震设计的基本认识。     

Author index volume 36

Using the single zircon technique, two areas which give some of the oldest ages on earth have been investigated, namely the Minnesota River Valley and West Greenland.The results on single zircons from the Minnesota River Valley and from the Amîtsoq gneisses (West Greenland) do not differ significantly from the results of Farhat (1975) and Baadsgaard (1973) at about 3.3 and 3.65 b.y., respectively.The U-Pb analyses of single zircons from acid boulders from the conglomerate unit at Isua (West Greenland) yield the oldest age so far reported for a terrestrial rock, namely 3.824_?0.009^+0.012 b.y.     

可液化场地大直径扩底桩的动力p-y曲线特征研究

可液化场地大直径扩底桩-土动力相互作用p-y曲线研究对扩底桩抗震设计具有重要意义。基于有限差分程序FLAC~(3D),分别建立扩底桩和等直径桩的三维有限差分模型,通过在模型底部输入正弦波,得到可液化场地中不同埋深下扩底桩与等直径桩的桩-土动力相互作用p-y曲线,对两者的动力p-y曲线特征进行对比分析。结果表明:正弦波输入下扩底桩动力p-y曲线多呈倒"S"形,随着埋深增加,动力p-y曲线滞回圈面积及面积增长速度逐渐减小,斜率逐渐增大;扩底桩与等直径桩动力p-y曲线所围成的图形相似,两者动力p-y曲线斜率均随埋深增加逐渐增大,扩底桩动力p-y曲线滞回圈面积及面积增长速度在各埋深处均大于等直径桩,利于能量耗散,抗震性能更好。     

SO2 from episode 48A eruption,Hawaii: Sulfur dioxide emissions from the episode 48A East Rift Zone eruption of Kilauea volcano,Hawaii

An SO₂ flux of 1170±400 (1) tonnes per day was measured with a correlation spectrometer (COSPEC) in October and November 1986 from the continuous, nonfountaining, basaltic East Rift Zone eruption (episode 48A) of Kilauea volcano. This flux is 5–27 times less than those of highfountaining episodes, 3–5 times greater than those of contemporaneous summit emissions or interphase Pu'u O'o emissions, and 1.3–2 times the emissions from Pu'u O'o alone during 48A. Calculations based on the SO₂ emission rate resulted in a magma supply rate of 0.44 million m³ per day and a 0.042 wt% sulfur loss from the magma upon eruption. Both of these calculated parameters agree with determinations made previously by other methods.     

A quantitative look at the demise of a basaltic vent: the death of Kupaianaha,Kilauea Volcano,Hawai'i

 The Kupaianaha vent, the source of the 48th episode of the 1983-to-present Pu'u 'O'o–Kupaianaha eruption, erupted nearly continuously from July 1986 until February 1992. This investigation documents the geophysical and geologic monitoring of the final 10 months of activity at the Kupaianaha vent. Detailed very low frequency (VLF) electromagnetic profiles across the single lava tube transporting lava from the vent were used to determine the cross-sectional area of the molten lava within the tube. Combined with measurements of lava velocity, these data provide an estimate of the lava output of Kupaianaha. In addition, lava temperatures (calculated from analysis of quenched glass) and bulk-rock chemistry were obtained for samples taken from the tube at the same site. The combined data set shows the lava flux from Kupaianaha vent declining linearly from 250 000 m³/day in April 1991 to 54 000 m³/day by November 1991. During that time surface breakouts of lava from weak points along the tube occurred progressively closer to the vent, consistent with declining efficiency in lava transport. There were no significant changes in lava temperature or in bulk MgO content during this period. Another eruptive episode (the 49th) began uprift of Kupaianaha on 8 November 1991 and erupted lava concurrently with Kupaianaha for 18 days. Lava flux from Kupaianaha decreased in response to this new episode, but the response was delayed by approximately 1 day. After 14 November 1991, lava velocities were no longer measurable in the tube because the lava stream beneath the skylight had crusted over; however, the VLF-derived electrical conductances documented the decreasing flux of molten lava through the tube. Kupaianaha remained active, but output continued to decrease until early February 1992 when the last active surface flows were seen. In November 1991 we used the linearly decreasing effusion rate to accurately predict the date for the death of the Kupaianaha vent. The linear nature of the decline in lava tube conductance and the delayed and slow response of the Waha'ula tube conductances to the 49th eruptive episode led us to speculate that (a) the Kupaianaha vent shut down because of a decrease in driving pressure and not because of a freeze-up of the vent, and (b) that Pu'u 'O'o, episode 49, and Kupaianaha were fed nearly vertically from a source deep within the rift zone. Received: 29 September 1995 / Accepted: 21 November 1995     

Snow-distribution and melt modelling for glaciers in Zackenberg river drainage basin,north-eastern Greenland

A physically based snow-evolution modelling system (SnowModel) that includes four sub-models: MicroMet, EnBal, SnowPack, and SnowTran-3D, was used to simulate eight full-year evolutions of snow accumulation, distribution, sublimation, and surface melt from glaciers in the Zackenberg river drainage basin, in north-east Greenland. Meteorological observations from two meteorological stations were used as model inputs, and spatial snow depth observations, snow melt depletion curves from photographic time lapse, and a satellite image were used for model testing of snow and melt simulations, which differ from previous SnowModel tests methods used on Greenland glaciers. Modelled test-period-average end-of-winter snow water equivalent (SWE) depth for the depletion area differs by a maximum of 14 mm w.eq., or ∼6%, more than the observed, and modelled test-period-average snow cover extent differs by a maximum of 5%, or 0·8 km², less than the observed. Furthermore, comparison with a satellite image indicated a 7% discrepancy between observed and modelled snow cover extent for the entire drainage basin. About 18% (31 mm w.eq.) of the solid precipitation was returned to the atmosphere by sublimation. Modelled mean annual snow melt and glacier ice melt for the glaciers in the Zackenberg river drainage basin from 1997 through 2005 (September–August) averaged 207 mm w.eq. year⁻¹ and 1198 mm w.eq. year⁻¹, respectively, yielding a total averaging 1405 mm w.eq. year⁻¹. Total modelled mean annual surface melt varied from 960 mm w.eq. year⁻¹ to 1989 mm w.eq. year⁻¹. The surface-melt period started between mid-May and the beginning of June and lasted until mid-September. Annual calculated runoff averaged 1487 mm w.eq. year⁻¹ (∼150 × 10⁶ m³) (1997–2005) with variations from 1031 mm w.eq. year⁻¹ to 2051 mm w.eq. year⁻¹. The model simulated a total glacier recession averaging − 1347 mm w.eq. year⁻¹ (∼136 × 10⁶ m³) (1997–2005), which was almost equal to previous basin average hydrological water balance storage studies − 244 mm w.eq. year⁻¹ (∼125 × 10⁶ m³) (1997–2003). Copyright © 2007 John Wiley & Sons, Ltd.     

地震荷载下边坡抗滑桩桩土机理的三维模拟分析

地震是诱发边坡破坏的重要因素之一,而抗滑桩是一种重要的边坡防治工程措施,因此开展地震作用下抗滑桩机理对于边坡防护具有重要的工程意义。本文以广东省梅州市茶阳车站为工程实例,运用ABAQUS软件建立三维模型,对地震作用下的桩土作用机理进行数值模拟分析。研究表明:(1)在地震作用下,边坡中上部水平位移较大,最大值为87.05mm,凹陷处水平位移远小于凸起处;(2)地震作用下抗滑桩会由于地震荷载产生远大于地震前的应力:静力作用下桩身最大值是147.24kPa,地震波输入14s时桩身最大值达到了326.36kPa;(3)地震作用下抗滑桩的应变亦远大于静力作用下的应变:静力作用下抗滑桩应变最大值是4.63×10~(-5),在地震波输入的第14s时桩身应变最大值是34.10×10~(-5)。因此在工程实践中对于地震作用下的抗滑桩边坡加固需要考虑桩的强度与刚度。研究结论对于边坡防治以及工程实践具有一定的指导意义。     

Using GIS for modelling the impact of current climate trend on the recharge area of the S. Susanna spring (central Apennines,Italy)

Though the S. Susanna spring system is one of the biggest water sources in the central Apennines, its hydrogeological dynamics have been scarcely investigated. This study tried to clarify some of the factors controlling the recharge/discharge processes of this spring by modelling the available climate series, water balance equations and new isotopic and quantitative data, using statistical and raster overlay functions embedded in a Geographic Information System (GIS). Oxygen and hydrogen isotopic data were recorded monthly over a 2‐year period at the spring itself and in eight rain gauges in Reatini Mountains. The effective infiltration rate was calculated using the Kennessey coefficients and the Turc equation. Finally, the recharge area was identified with the help of an expert evaluation procedure. Local δ¹⁸O and δD versus altitude regression curves were used to validate the digital recharge model by comparing their expected values with the values actually measured. Recharge process was framed within the perspective of the ongoing local climate trends. The current discharge rate of 4·1 m³·s^?1 is significantly lower than the average value of 5·5 m³·s^?1 measured up to the 1980s, confirming the fall in the recharge/discharge rate. The hydrogeological system shows a delayed response, due to an average groundwater residence time in the aquifer, which is estimated to be about 15/20 years on the basis of the offset between calculated and observed isotope data at the main spring. For this reason the system is presently not equilibrated and is gradually changing towards a final equilibrium discharge estimated in about 3·4 m³·s^?1. Copyright © 2009 John Wiley & Sons, Ltd.     

Solute movement through intact columns of cryoturbated Upper Chalk

Cryoturbated Upper Chalk is a dichotomous porous medium wherein the intra‐fragment porosity provides water storage and the inter‐fragment porosity provides potential pathways for relatively rapid flow near saturation. Chloride tracer movement through 43 cm long and 45 cm diameter undisturbed chalk columns was studied at water application rates of 0·3, 1·0, and 1·5 cm h^?1. Microscale heterogeneity in effluent was recorded using a grid collection system consisting of 98 funnel‐shaped cells each 3·5 cm in diameter. The total porosity of the columns was 0·47 ± 0·02 m³ m^?3, approximately 13% of pores were ≥ 15 µm diameter, and the saturated hydraulic conductivity was 12·66 ± 1·31 m day^?1. Although the column remained unsaturated during the leaching even at all application rates, proportionate flow through macropores increased as the application rate decreased. The number of dry cells (with 0 ml of effluent) increased as application rate decreased. Half of the leachate was collected from 15, 19 and 22 cells at 0·3, 1·0, 1·5 cm h^?1 application rates respectively. Similar breakthrough curves (BTCs) were obtained at all three application rates when plotted as a function of cumulative drainage, but they were distinctly different when plotted as a function of time. The BTCs indicate that the columns have similar drainage requirement irrespective of application rates, as the rise to the maxima (C/C_o) is almost similar. However, the time required to achieve that leaching requirement varies with application rates, and residence time was less in the case of a higher application rate. A two‐region convection–dispersion model was used to describe the BTCs and fitted well (r² = 0·97–0·99). There was a linear relationship between dispersion coefficient and pore water velocity (correlation coefficient r = 0·95). The results demonstrate the microscale heterogeneity of hydrodynamic properties in the Upper Chalk. Copyright © 2007 John Wiley & Sons, Ltd.     

Helium isotopes in early Iceland plume picrites: Constraints on the composition of high 3He/4He mantle

A detailed study of the geochemistry of a new suite of early Iceland plume picrites shows that extremely high ³He/⁴He ratios (up to 50 R_a) are found in picrites from Baffin Island and West Greenland. High ³He/⁴He picrites display a wide range in ⁸⁷Sr/⁸⁶Sr (0.70288–0.70403), ¹⁴³Nd/¹⁴⁴Nd (0.51288–0.51308) and incompatible trace element ratios (e.g. La/Sm_n = 0.5–1.6). These overlap the complete range of compositions of mid-ocean ridge basalts and most northern hemisphere ocean island basalts, including Iceland. Crustal contamination modelling in which high-grade Proterozoic crustal basement rocks for the region are mixed with a depleted parent cannot account for the trend displayed by the Baffin Island and West Greenland picrites. This rules out the possibility that the incompatible trace element, Sr and Nd isotope range of the high ³He/⁴He picrites is due to crustal contamination. The compositional range at high ³He/⁴He is also inconsistent with derivation from a primordial-He-rich reservoir that is a residue of ancient mantle depletion. This implies that the composition of the high ³He/⁴He mantle cannot be determined simply by extrapolating ocean island basalt He–Sr–Nd–Pb–Os isotope data.The apparent decoupling of He from trace element and lithophile radiogenic isotope tracers is difficult to attain by simple mixing of a high-[He], high ³He/⁴He reservoir with various depleted and enriched He-poor mantle reservoirs. The possibility that primordial He has diffused into a reservoir with a composition typical of convecting upper mantle cannot be ruled out. If so, the process must have occurred after the development of existing mantle heterogeneity, and requires the existence of a deep, primordial He-rich reservoir.     

液化场地桥梁群桩-土耦合体系强震反应分析

针对振动台试验,采用u-p形式控制方程表述饱和砂土的动力属性,选用土的多屈服面塑性本构模型刻画饱和砂土和黏土的力学特性,引入非线性梁-柱单元模拟桩,建立试验受控条件下液化场地群桩-土强震相互作用分析的三维有限元模型,并通过试验结果验证数值建模途径与模拟方法的正确性。以实际工程中常用的2×2群桩为例,建立桩-土-桥梁结构强震反应分析三维有限元模型。基于此,针对不同群桩基础配置对液化场地群桩-土强震相互作用影响展开具体分析。对比发现,桩的数量相同时,桩排列方向与地震波输入方向平行时比垂直时桩基受力减小5%~10%,而对场地液化情况无明显影响;相同排列形式下,三桩模型中土体出现液化的时间约比双桩模型延缓5s,桩上弯矩和剪力减小33%~38%。由此可见,桩基数量增加,桩-土体系整体刚度更大,场地抗液化性能显著,桩基对上部桥梁结构的承载性能明显增强,其安全性与可靠性更高。这对实际桥梁工程抗震设计具有一定的借鉴意义。     

Earthquakes Along the Passive Margin of Greenland: Evidence for Postglacial Rebound Control

—?An intriguing observation in Greenland is a clear spatial correlation between seismicity and deglaciated areas along passive continental margins, a piece of evidence for earthquake triggering due to postglacial rebound. Another piece of evidence for induced seismicity due to deglaciation derives from earthquake source mechanisms. Sparse, low magnitude seismicity has made it difficult to determine focal mechanisms from Greenland earthquakes. On the basis of two normal faulting events along deglaciated margins and from the spatial distribution of epicenters, earlier investigators suggested that the earthquakes of Greenland are due to postglacial rebound. This interpretation is tested here by using more recent data. Broadband waveforms of teleseismic P waves from the August 10, 1993 (m _b = 5.4) and October 14, 1998 (m _b = 5.1) earthquakes have been inverted for moment tensors and source parameters. Both mechanisms indicate normal faulting with small strike-slip components: the 1993 event, strike = 348.9°, dip = 41.0°, rake =?56.3°, focal depth = 11?km, seismic moment = 1.03?×?10²⁴ dyne-cm, and M _w = 5.3; the 1998 event, strike = 61.6°, dip = 58.0°, rake =?95.5°, focal depth = 5?km, seismic moment = 5.72?×?10²³ dyne-cm, and M _w = 5.1. These and the two prior events support the theory that the shallow part of the lithosphere beneath the deglaciated margins is under horizontal extension. The observed stress field can be explained as flexural stresses due to removal of ice loads and surface loads by glacial erosion. These local extensional stresses are further enhanced by the spreading stress of continental crust and reactivate preexisting faults. Earthquake characteristics observed from Greenland suggest that the dominant seismogenic stresses are from postglacial rebound and spreading of the continental lithosphere.     

The Grand Brûlé exploration drilling: New data on the deep framework of the Piton de la Fournaise volcano. Part 2: Secondary minerals

The Grand Brûlé borehole intersects a thick pile of basaltic lavas, down to 1010 m, and a basic-ultrabasic intrusive complex, from 1010 to 3003.50 m.The lavas are, in general, unaltered except in two fractured zones, where hydrothermal fluids circulated at temperatures not exceeding 350 ° C. The main secondary minerals there are pyroxene, feldspar, epidote, actinolite and chlorite.The entire thickness of the intrusive body intersected contains secondary minerals representing three stages of cooling:

1. 1. A late magmatic episode (600–900°C) characterized by biotite, kaersutite, edenite and pargasite.

2. 2. A hydrothermal episode (T<- 350°C) characterized by epidote, albite, biotite, actinolite and chlorite.

3. 3. A phase of serpentinization (T≤ 350°C).

It is very likely that the two later events occurred simultaneously, with physical and chemical interference.     

Sulphur emissions to the stratosphere from explosive volcanic eruptions

 Two methods were used to quantify the flux of volcanic sulphur (as the equivalent mass of SO₂) to the stratosphere over different timescales during the Holocene. A combination of satellite-based measurements of sulphur yields from recent explosive volcanic eruptions with an appropriate rate of explosive volcanism for the past 200 years constrains the medium-term (∼10²years) flux of volcanic sulphur to the stratosphere to be ∼1 Mt a^–1, with lower and upper bounds of 0.3 and 3 Mt a^–1. The short-term (∼10- to 20-year) flux due to small magnitude (10¹⁰–10¹²kg) eruptions is of the order of 0.4 Mt a^–1. At any time the instantaneous levels of sulphur in the stratosphere are dominated by the most recent (0–3 years) volcanic events. The flux calculations do not attempt to address this very short timescale variability. Although there are significant errors associated with the raw sulphur emission data on which this analysis is based, the approach presented is general and may be readily modified as the quantity and quality of the data improve. Data from a Greenland ice core support these conclusions. Integration of the sulphate signals from presumed volcanic sources recorded in the GISP2 core provides a minimum estimate of the 10³–year volcanic SO₂ flux to the stratosphere of 0.5–1 Mt a^–1 over the past 9000 years. The short-term flux calculations do not account for the impact of rare, large events. The ice-core record does not fully account for the contribution from small, frequent events. Received: 27 September 1995 / Accepted: 13 December 1995