Dating of the Dome Fuji shallow ice core based on a record of volcanic eruptions from AD 1260 to AD 2001

We measured the concentration of non-sea-salt sulfate () in the Dome Fuji shallow ice core (Antarctica) from the surface to 40 m depth with the aim of dating the core with reference to the record of volcanic eruptions. Three huge spikes related to large-scale volcanic eruptions were detected at depths of 12.5, 29.9, and 38.8 m, correlated to the eruptions of Tambora (AD 1815), Kuwae (AD 1452) and an unknown event (AD 1259), respectively. We identified another nine spikes related to accurately dated eruption events. The shallow ice core was dated from AD 1260 to AD 2001 based on these 12 eruption events and the assumption of constant annual snow accumulation in the periods between eruption events. The results yield a maximum correction of ∼20 years compared with the dating proposed in a previous study. The annual accumulation varied within ±∼15% of the average water equivalent value over the study period (25.5 mm).     

Multiscale modeling of ice deformation behavior

Understanding the flow of ice in glaciers and polar ice sheets is of increasing relevance in a time of potentially significant climate change. The flow of ice has hitherto received relatively little attention from the structural geological community. This paper aims to provide an overview of methods and results of ice deformation modeling from the single crystal to the polycrystal scale, and beyond to the scale of polar ice sheets. All through these scales, various models have been developed to understand, describe and predict the processes that operate during deformation of ice, with the aim to correctly represent ice rheology and self-induced anisotropy. Most of the modeling tools presented in this paper originate from the material science community, and are currently used and further developed for other materials and environments. We will show that this community has deeply integrated ice as a very useful “model” material to develop and validate approaches in conditions of a highly anisotropic behavior. This review, by no means exhaustive, aims at providing an overview of methods at different scales and levels of complexity.     

Microstructure and fabric development in ice: Lessons learned from in situ experiments and implications for understanding rock evolution

In this contribution we present a review of the evolution of microstructures and fabric in ice. Based on the review we show the potential use of ice as an analogue for rocks by considering selected examples that can be related to quartz-rich rocks. Advances in our understanding of the plasticity of ice have come from experimental investigations that clearly show that plastic deformation of polycrystalline ice is initially produced by basal slip. Interaction of dislocations play an essential role for dynamic recrystallization processes involving grain nucleation and grain-boundary migration during the steady-state flow of ice. To support this review we describe deformation in polycrystalline ‘standard’ water-ice and natural-ice samples, summarize other experiments involving bulk samples and use in situ plane-strain deformation experiments to illustrate the link between microstructure and fabric evolution, rheological response and dominant processes. Most terrestrial ice masses deform at low shear stresses by grain-size-insensitive creep with a stress exponent (n ≤ 3). However, from experimental observations it is shown that the distribution of plastic activity producing the microstructure and fabric is initially dominated by grain-boundary migration during hardening (primary creep), followed by dynamic recrystallization during transient creep (secondary creep) involving new grain nucleation, with further cycles of grain growth and nucleation resulting in near steady-state creep (tertiary creep). The microstructural transitions and inferred mechanism changes are a function of local and bulk variations in strain energy (i.e. dislocation densities) with surface grain-boundary energy being secondary, except in the case of static annealing. As there is a clear correspondence between the rheology of ice and the high-temperature deformation dislocation creep regime of polycrystalline quartz, we suggest that lessons learnt from ice deformation can be used to interpret polycrystalline quartz deformation. Different to quartz, ice allows experimental investigations at close to natural strain rate, and through in-situ experiments offers the opportunity to study the dynamic link between microstructural development, rheology and the identification of the dominant processes.     

Timing of the Northern Prince Gustav Ice Stream retreat and the deglaciation of northern James Ross Island,Antarctic Peninsula during the last glacial–interglacial transition

The Northern Prince Gustav Ice Stream located in Prince Gustav Channel, drained the northeastern portion of the Antarctic Peninsula Ice Sheet during the last glacial maximum. Here we present a chronology of its retreat based on in situ produced cosmogenic ¹⁰Be from erratic boulders at Cape Lachman, northern James Ross Island. Schmidt hammer testing was adopted to assess the weathering state of erratic boulders in order to better interpret excess cosmogenic ¹⁰Be from cumulative periods of pre-exposure or earlier release from the glacier. The weighted mean exposure age of five boulders based on Schmidt hammer data is 12.9 ± 1.2 ka representing the beginning of the deglaciation of lower-lying areas (< 60 m a.s.l.) of the northern James Ross Island, when Northern Prince Gustav Ice Stream split from the remaining James Ross Island ice cover. This age represents the minimum age of the transition from grounded ice stream to floating ice shelf in the middle continental shelf areas of the northern Prince Gustav Channel. The remaining ice cover located at higher elevations of northern James Ross Island retreated during the early Holocene due to gradual decay of terrestrial ice and increase of equilibrium line altitude. Schmidt hammer R-values are inversely correlated with ¹⁰Be exposure ages and could be used as a proxy for exposure history of individual granite boulders in this region and favour the hypothesis of earlier release of boulders with excessive ¹⁰Be concentrations from glacier directly at this site. These data provide evidences for an earlier deglaciation of northern James Ross Island when compared with other recently presented cosmogenic nuclide based deglaciation chronologies, but this timing coincides with rapid increase of atmospheric temperature in this marginal part of Antarctica.     

Last Deglaciation Climatic Fluctuation Record by the Palaeo-Daocheng Ice Cap,Southeastern Qinghai-Tibetan Plateau

The last deglaciation, a key period for understanding present and future climate changes, has long been the hot topic for palaeoclimatological study. The Qinghai-Tibetan Plateau(QTP) is often a target study area for understanding hemispheric, or even global environment changes. The glacial landforms on the QTP provide a unique perspective for its climate change. In order to investigate the onset of the last deglaciation at the QTP and its regional correlation, the terrestrial cosmogenic nuclides(TCN) 10 Be and 26 Al surface exposure dating was chosen to date the roche moutonnée, the polished surface and the moraine debris located at the palaeo-Daocheng Ice Cap(pDIC), southeastern QTP. Our results show that the onset of the last deglaciation is at about 19 ka, followed by another warming event occurring around 15 ka in the p-DIC area. These timings agree well with other records, e.g. equivalent with a rapid sea level rise at 19 ka and the onset of B?lling warming event at about 15 ka. Thus, our new data can provide good reveal constraint on the climate evolution at the QTP.     

四川龙门山构造带活动的钟乳石记录

在四川龙门山地区开展构造地质调查过程中,沿龙门山构造带发现了大量灰岩及钙质胶结的砾岩溶洞,这些溶洞形成与构造带的分布密切相关,有些则直接发育在断裂带中。与其它地区溶洞所不同,发现这些溶洞顶部发育的钟乳石普遍发生了偏转现象,即钟乳石目前的最下部生长方向与铅直方向一致,而中部和上部石笋轴线明显与铅直方向存在一定角度的偏折,野外调查表明,沿龙门山构造发育的溶洞石钟乳及石笋的生长受断裂活动控制发生的明显的偏折和摆动现象,为研究龙门山构造活动特征提供了难得的实际材料。钟乳石生长轴线的偏转及AMS14C测年结果表明,龙门山构造带存在明显的周期性活动特征,已有的测年结果反映龙门山构造带于21.81 ka(或22.85 ka)、19.3 ka(或20.71 ka)处于构造活动期,显示了构造的幕次活动特征,测年结果记录到的幕次间隔期或周期为2.14~2.5 ka。结合地震分析,钟乳石生长揭示出石钟乳生长轴线的偏折是龙门山构造带幕次活动期短期内发生持续构造活动的结果,并导致在幕次构造活动期的短时段内伴生大量的地震等构造活动。     

The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia

The role of post-Little Ice Age (LIA) Neoglacial retreat on landslide activity is investigated in 19 alpine basins along the upper Lillooet River Valley, British Columbia. We examine how Neoglacial scouring and glacial recession have modified hillslope form and slope stability, and construct a decision-making flowchart to identify landslide hazards associated with glacial retreat. This work is based on field mapping, GIS analysis, statistical associations between landslides and terrain attributes, and a comparison between Neoglaciated and non-Neoglaciated terrain within each basin.The bedrock landslide response to glacial retreat varies appreciably according to lithology and the extent of glacial scour below the LIA trimline. Valleys carved in weak Quaternary volcanics show significant erosional oversteepening and contain deep-seated slope movement features, active rock fall, rock slides, and rock avalanches near glacial trimlines. Basins in stronger granitic rock rarely show increased bedrock instability resulting from post-LIA retreat, except for shallow-seated rock slides along some trimlines and failures on previously unstable slopes. In surficial materials, landslides associated with post-LIA retreat originate in till or colluvium, as debris slides or debris avalanches, and are concentrated along lateral moraines or glacial trimlines.Significant spatial association was also observed between recent catastrophic failures, gravitational slope deformation, and slopes that were oversteepened then debuttressed by glacial erosion. Eight out of nine catastrophic rock slope failures occurred just above glacial trimlines and all occurred in areas with a previous history of deep-seated gravitational slope movement, implying that this type of deformation is a precursor to catastrophic detachment.     

钻孔岩心倾角与岩层真倾角的关系及应用分析

长期以来,钻孔岩心倾角仅用于计算岩煤层真厚度。为了能由此导出岩层真倾角更广泛的使用,作者查阅了相关书籍,未发现对岩心倾角概念以及其和真倾角间关系详细论述。经过深入研究和实践验证,发现岩心倾角与岩层真倾角是不同的概念且一般不相等,两角之间是一种复杂的函数关系。经过理论分析和实践验证,得出了钻孔岩心倾角和岩层倾角之间的函数关系式,并进行了相关的讨论和说明,为隐伏地区的地质勘查提供了直接的倾角参数,从而提高了钻孔资料的分析利用程度,对于正确分析煤岩层赋存状态与地质构造、提高地质成果的质量等方面有重要作用。     

Huge Ice‐age lakes in Russia

During an early phase of the Last Ice Age (Weichselian, Valdaian), about 90 000 yr ago, an ice sheet formed over the shallow Barents and Kara seas. The ice front advanced on to mainland Russia and blocked the north‐flowing rivers (Yenissei, Ob, Pechora, Dvina and others) that supply most of the freshwater to the Arctic Ocean. The result was that large ice‐dammed lakes were formed between the ice sheet in the north and the continental water divides to the south. Here we present reconstructions and calculations of the areas and volumes of these lakes. The lake on the West Siberian Plain was nearly twice as large as the largest lake on Earth today. The well‐mapped Lake Komi in northeast Europe and a postulated lake in the White Sea Basin would also rank before the present‐day third largest lake. The lakes overflowed towards the south and thus the drainage of much of the Eurasian continent was reversed. The result was a major change in the water balance on the continent, decreased freshwater supply to the Arctic Ocean, and increased freshwater flow to the Aral, Caspian, Black and Baltic seas. A sudden outburst of the lakes' water to the Arctic Ocean when the ice sheet thinned is postulated. Copyright © 2001 John Wiley & Sons, Ltd.     

Tidal dissipation within large icy satellites: Applications to Europa and Titan

This paper describes a new approach based on variational principles to calculate the radial distribution of tidal energy dissipation in any satellite. The advantage of the model with respect to classical solutions, is that it relates in a straightforward way the radial distribution of the time-averaged dissipation rate to its sensitivity to the corresponding distribution of viscoelastic parameters. This method is applied to Io-, Europa-, and Titan-like interiors, and it is tested against the results obtained by two classical methods by determining global dissipation as well as radial and lateral distributions within satellite interiors. By exploring systematically the different parameters defining the interior models, we demonstrate that the presence of a deep ocean below an outer ice layer strongly influences the tidal dissipation distribution in both the outer ice layer and in the innermost part of the satellite. On the one hand, the ocean by imposing a large radial displacement at the base of the outer ice I layer, controls the distribution of tidal strain rate within the outer layer, making the tidal strain rate field very weakly sensitive to the viscosity variations. Conversely, in the high-pressure ice layer below the ocean, both tidal strain rate and dissipation are very sensitive to any variation of the ice viscosity. On the other hand, for identical structures of the mantle and of the core, the presence of a subsurface ocean reduces the strength of dissipation in the silicate mantle. The existence of a liquid layer within Europa makes models of the silicate mantle less dissipative than the predictions for Io.