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1.
The dune system in Otindag sand field of northern China is sensitive to climate change, where effective moisture and related vegetation cover play a controlling role for dune activity and stability. Therefore, aeolian deposits may be an archive of past environmental changes, possibly at the millennial scale, but previous studies on this topic have rarely been reported. In this study, thirty-five optically stimulated luminescence (OSL) ages of ten representative sand-paleosol profiles in Otindag sand field are ob-tained, and these ages provide a relatively complete and well-dated chronology for wet and dry varia-tions in Holocene. The results indicate that widespread dune mobilization occurred from 9.9 to 8.2 ka, suggesting a dry early Holocene climate. The dunes were mainly stabilized between 8.0 and 2.7 ka, implying a relatively wet climate, although there were short-term penetrations of dune activity during this wet period. After ~2.3 ka, the region became dry again, as inferred from widespread dune activity. The "8.2 ka" cold event and the Little Ice Age climatic deterioration are detected on the basis of the dune records and OSL ages. During the Medieval Warm Period and the Sui-Tang Warm Period (570-770 AD), climate in Otindag sand field was relatively humid and the vegetation was denser, and the sand dunes were stabilized again. These aeolian records may indicate climate changes at millennial time scale during Holocene, and these climatic changes may be the teleconnection to the climate changes elsewhere in the world.  相似文献   

2.
Variation in the rubidium to strontium (Rb/Sr) ratio of the loess–palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of China. To characterize the Rb/Sr ratio of the dissolved loads of a single catchment, we analysed a 12·08 m sediment core from Daihai Lake in Inner Mongolia, north China. Dating control was provided by 210Pb, 137Cs and AMS‐14C. Sequential extraction experiments were conducted to investigate the concentrations of Rb and Sr on various chemical fractions in the lake sediments. Down‐core variation in the Rb/Sr ratios provides a record of Holocene weathering history. From 9 to 3·5 ka bp , accelerated chemical weathering was experienced throughout the Daihai catchment under mainly warm and humid conditions, and this reached a maximum at c. 5 ka bp . However, weathering was reduced between c. 8·25 and 7·90 ka bp , which may reflect the global 8·2 ka cooling event. After c. 2·5 ka bp , increased Rb/Sr ratios with higher frequency of fluctuations indicate reduced weathering within the Daihai catchment. The highest Rb/Sr ratios in the Little Ice Age lake sediments indicate the weakest phase of Holocene chemical weathering, resulting from a marked reduction in Sr flux into the basin. The Rb/Sr record also shows an enhancement of chemical weathering under today's climate, but its intensity is less than that of the Medieval Warm Period. Increased Rb/Sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to Rb/Sr decrease in the glacial loess layers in the loess–palaeosol sequence. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

3.
Estimating the extent and age of the last glacial maxima as well as the chronology of glacial recessions in various environmental contexts is key to source-to-sink studies and paleoclimate reconstructions. The Argentera-Mercantour massif is located at the transition between the Alps and the Mediterranean Sea, therefore, its deglaciation chronology can be compared to the sediment budget of the Var River basin. Based on 13 new cosmic-ray exposure (CRE) beryllium-10 (10Be) datings performed on moraines and polished crystalline bedrocks and 22 reassessed 10Be CRE ages from similar altitude nearby steep basement surfaces, and from a lake sediment core, we can constrain the deglaciation chronology of the Argentera-Mercantour massif. These data allow for the first time to fully reconstruct the deglaciation history at the scale of the entire massif in agreement with a major glacier recession at c. 15 ka, at the onset of Bølling transition between the Oldest and Older Dryas. Main deglaciation of the upper slopes [2700–2800 m above sea level (a.s.l.)] occurred after the Last Glacial Maximum (LGM) at 20.8–18.6 ka, followed by the main deglaciation of the lower slopes (2300 m a.s.l.) at 15.3–14.2 ka. Finally, the flat polished surfaces above 2600 m a.s.l. and the zones confined within narrow lateral valleys were likely affected by progressive ice melting of remaining debris covered glaciers and moraine erosion following the Younger Dryas re-advance stage between 12 and 8–9 ka. At lower elevations, the Vens Lake located at 2300 m a.s.l., allows evidence of the onset of lake sedimentation at c. 14 ka and a transition towards a vegetated environment that mainly occurred before 8 ka. Moraine final stabilization at 5 ka might reflect denudation acceleration during the Holocene humid phase. This contribution reveals a glacier–climate relationship more sensitive to warming phases in the southern Alps highlighted by a major decrease of glaciers after c. 15 ka. This major deglaciation is correlated with a 2.5-fold decrease of sediment discharge of rivers into the Mediterranean Sea. © 2019 John Wiley & Sons, Ltd.  相似文献   

4.
The 3 310-m-high Chia-min Lake records the climatic history since 4 ka B. P. in Taiwan. The warm/wet period before 2.2 ka B.P. seemed to correspond to the later part of the Holocene Megathermal, and the cold/dry period during 0–2.2 ka B. P. corresponded to the Katathermal. Before the termination of the Megathermal, an especially warm and humid segment (2.2–2.4 ka B. P.) emerged. The paleoclimatic records from Yuen-yang and Chi-tsai Lakes support the notion that the Megathermal in Taiwan terminated during 2—2.3 ka B. P. A warm segment (820–1 320 AD) in the Katathermal could be considered the Medieval Warm Period. The climate turned cold and dry after 1 320 AD and this indicated the onset of the Little Ice Age. These paleoclimatic variations are also in good agreement with those recorded in Great Ghost Lake.  相似文献   

5.
High-resolution peat humification records were obtained from Dajiuhu of the Shennongjia Mountains and Qianmutian of the Tianmu Mountains to study climate changes in East China. The analyses of pollen, organic matters, TOC, and Rb/Sr indicate a high degree of peat humification and thus strong decomposition of organic matter when climate was dry. Conversely, when climate was humid, the degree of humification is low because peat was preserved in a waterlogged condition. Peat humification from Dajiuhu occurred not only during the Younger Dryas (about 11.4–12.6 cal ka BP), the Bølling-Allerød Warm Period (12.6–15.2 cal ka BP), and the Oldest Dryas (about 15.2–16.0 cal ka BP), but also during the early Holocene (about 11.4–9.4 cal ka BP), the 8.2 cal ka BP cold event, and the Holocene Optimum (about 7.0–4.2 cal ka BP). Both peat humification records since nearly 5 ka BP are consistent, showing that mountain peatland has synchronous responses to the East Asia monsoon-induced precipitation. The LOI data confirm the above observation. The monsoon precipitation since nearly 5 ka BP recorded in these two peat profiles can be divided into three phases. During 4.9–3.5 ka BP, precipitation amount was high but fluctuated greatly. During 3.5–0.9 ka BP, precipitation amount was low. During 0.9–0 ka BP, degree of humification reduced gradually, indicating the increase of monsoon precipitation. Contrast to other high-resolution records from East China monsoon region shows that the monsoon precipitation records of the two peat profiles since nearly 16 ka BP are controlled by a common forcing mechanism of summer solar radicalization in the Northern Hemisphere.  相似文献   

6.
Holocene glaciers have contributed to an abundance of unstable sediments in mountainous environments. In permafrost environments, these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution under condition of a warming climate. To understand the influence of ground ice distribution on this activity since the Little Ice Age (LIA), we have investigated the Pierre Ronde and Rognes proglacial areas, two cirque glacier systems located in the periglacial belt of the Mont Blanc massif. For the first time, electrical resistivity tomography, temperature data loggers and differential global positioning systems (dGPS) are combined with historical documents and glaciological data analysis to produce a complete study of evolution in time and space of these small landsystems since the LIA. This approach allows to explain spatial heterogeneity of current internal structure and dynamics. The studied sites are a complex assemblage of debris‐covered glacier, ice‐rich frozen debris and unfrozen debris. Ground ice distribution is related to former glacier thermal regime, isolating effect of debris cover, water supply to specific zones, and topography. In relation with this internal structure, present dynamics are dominated by rapid ice melt in the debris‐covered upper slopes, slow creep processes in marginal glacigenic rock glaciers, and weak, superficial reworking in deglaciated moraines. Since the LIA, geomorphic activity is mainly spatially restricted within the proglacial areas. Sediment exportation has occurred in a limited part of the former Rognes Glacier and through water pocket outburst flood and debris flows in Pierre Ronde. Both sites contributed little sediment supply to the downslope geomorphic system, rather by episodic events than by constant supply. In that way, during Holocene and even in a paraglacial context as the recent deglaciation, proglacial areas of cirque glaciers act mostly as sediment sinks, when active geomorphic processes are unable to evacuate sediment downslope, especially because of the slope angle weakness. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

7.
Climate variability during the Mid‐Late Holocene has influenced the activity of geomorphic processes in the current periglacial belt of the Sierra Nevada. We studied two types of sedimentary records that reveal a synchronous timing for slope instability in this high semi‐arid massif: solifluction landforms and mountain lake sediments. Lithological and sedimentological properties of both records have recorded numerous cycles of different magnitude of slope processes in the massif. Solifluction deposits record seven phases of solifluction activity and soil development during the last 7 ka bp and lake sediments show evidence of eight periods with increased geomorphic activity in the catchments over the last 6 ka bp . Although present‐day climate conditions do not promote active solifluction processes in the Sierra Nevada, colder and wetter periods during the Holocene triggered solifluction and transported coarse‐grained sediments into the lakes. By contrast, warm phases favoured soil formation and spread an incipient vegetation cover over the headwaters of the highest valleys, diminishing the grain size of the particles reaching the lakes. Lake sediments record an aridification trend in the massif intensifying since 4·2 ka bp that has conditioned solifluction activity to shift gradually to higher elevations. During major cooler phases such as the Little Ice Age active solifluction was recorded back down to 2500 m altitude. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Lakes in arid zone are sensitive to climatic changes. The lacustrine sediment sequence in Sogo Nur has well and truly recorded climatic events such as the Sui-Tang Dynasty Warm Period, the Song-Liao Dynasty Cold Period, the Medieval Warm Period, the Little Ice Age and the 20th Century Warm Period. Commonly, the climate in warm Periods was relatively humid, accordingly the lake area extended and water level rose, and vice versa. Apart from climatic change, human activity is also an important factor of influencing lake vicissitude, and they played the dominant role alternatively during different periods; the factor of climatic change predominated in historical period, while since the beginning of the 20th century the utilization of water resources by human has became decisive.  相似文献   

9.
K–Ar ages of young basalts (<500 ka) are often higher than the actual eruption age, due to low potassium contents and the frequent presence of excess Ar in olivine and pyroxene phenocrysts. Geological studies in the San Francisco and Uinkaret volcanic fields in Arizona have documented the presence of excess 40Ar and have concluded that K–Ar ages of young basalts in these fields tend to be inaccurate. This new study in the San Francisco volcanic field presents 3Hec and 21Nec ages yielded by olivine and pyroxene collected from three Pleistocene basalt flows – the South Sheba (∼190 ka), SP (∼70 ka), and Doney Mountain (∼67 ka) lava flows, – and from one Holocene basalt, the Bonito Lava Flow (∼1.4 ka) at Sunset Crater. These data indicate that, in two of three cases, 40Ar/39Ar and K–Ar ages of the young basalts agree well with cosmic-ray surface exposure ages of the same lava flow, thus suggesting that excess 40Ar is not always a problem in young basalt flows in the San Francisco volcanic field. The exposure age of the Bonito lava flow agrees within uncertainty with dendrochronological and archeological age determinations. K–Ar and cosmogenic 3He and 21Ne ages from the SP flow are in agreement and much older than the OSL age (5.5–6 ka) reported for this lava flow. Furthermore, if the non-cosmogenic ages are assumed to be accurate, the subsequent calculated production rates at South Sheba and SP flow sample sites agree well with values in the literature.  相似文献   

10.
Lakes in arid zone are sensitive to climatic changes. The lacustrine sediment sequence in Sogo Nur has well and truly recorded climatic events such as the Sui-Tang Dynasty Warm Period, the Song-Liao Dynasty Cold Period, the Medieval Warm Period, the Little Ice Age and the 20th Century Warm Period. Commonly, the climate in warm Periods was relatively humid,accordingly the lake area extended and water level rose, and vice versa. Apart from climatic change, human activity is also an important factor of influencing lake vicissitude, and they played the dominant role alternatively during different periods; the factor of climatic change predominated in historical period, while since the beginning of the 20th century the utilization of water resources by human has became decisive.  相似文献   

11.
Surface temperature increases since the 1990s have often been associated with an increase in the speed of rock glaciers. Evidence of similar links on the centennial to millennial scale are, however, still lacking due to less focus to date on the medium‐ and long‐term kinematics of these landforms. In order to assess (palaeo)climatic variations in rock glacier kinematics, we analysed the movements of the Stabbio di Largario rock glacier in the southern Swiss Alps using three different timescales. The Schmidt hammer exposure‐age dating (SHD) was applied to study long‐term kinematics in order to extrapolate the minimal age of the formation of the rock glacier, which may have started its development after the Mid‐Holocene climate optimum, and to detect possible accelerations of the horizontal surface velocity during the Medieval Warm Period. Georeferentiation and orthorectification of six historical photographs of the rock glacier taken between ad 1910 and today were analysed using monoplotting to detect the rock glacier displacement on the decennial scale from the end of the Little Ice Age. Finally, differential global positioning system (dGPS) monitoring data available since ad 2009 were used to assess annual and seasonal creep rates of the rock glacier at present. Our results show a link between the periods of increase in mean air temperature on different timescales and variations in rock glacier kinematics and provide important new insights into rock glacier development and evolution on the long‐term scale. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

12.
The El Niño–Southern Oscillation (ENSO) is a climatic phenomenon that affects socio-economical welfare in vast areas in the world. A continuous record of Holocene ENSO related climate variability of the Indo-Pacific Warm pool (IPWP) is constructed on the basis of stable oxygen isotopes in shells of planktic foraminifera from a sediment core in the western Pacific Ocean. At the centennial scale, variations in the stable oxygen isotope signal (δ18O) are thought be a representation of ENSO variability, although an imprint of local conditions cannot be entirely excluded. The record for the early Holocene (10.3–6 ka BP) shows, in comparison with the mid- to late Holocene, small amplitude variations in the δ18O record of up to 0.3‰ indicating relatively stable and warm sea surface conditions. The mid- to late Holocene (6–2 ka BP) exemplified higher variability in δ18O and thus in oceanic IPWP conditions. Climatically, we interpret this change (5.5–4.2 ka BP) as a phenomenon induced by variability in frequency and/or intensity changes of El Niño. In the period 4.2–2 ka BP we identified several periods, centred on 1.9, 2.1, 2.7, 3.3, 3.7 and 4.2 ka BP, with in general heavy δ18O values. During these periods, the IPWP was relocated to a more eastward position, enhancing the susceptibility for El Niño-like conditions at the core site. Over the last 2000 yr precipitation increased in the area as a response to an increase in Asian monsoon strength, resulting in a freshening of the surface waters. This study corroborates previous findings that the present-day ENSO activity started around 5.5 ka BP.  相似文献   

13.
Optically stimulated luminescence (OSL) dating was performed on Late Quaternary deltaic sequences from a 55-m-long core sampled from the Nakdong River estuary, Korea. OSL ages obtained from chemically separated fine (4–11 μm) and coarse (90–212 μm) quartz grains ranged from 29.4 ± 2.6 to 0.4 ± 0.04 ka, revealing clear consistency between the grain-size fractions. The De values from the standardized growth curve (SGC) are consistent with those from the single-aliquot regenerative-dose (SAR) procedure, which suggests that the SGC is valid for the Nakdong deltaic sediments. The 14C ages of shells and wood fragments ranged from 11 to 2.9 ka, demonstrating reasonable agreement with the OSL ages, within the error range. However, the limited number and random sampling interval of the 14C age data (10 ages) result in a simple linear and exponential trend in the depth–age curve. In contrast, OSL ages obtained by high-resolution sampling show down-section variations in the depth–age curve, indicating the occurrence of rapid changes in sedimentation rate. It is suggested that the high-sampling-resolution OSL ages provide a more realistic and detailed depth–age curve and sedimentation rate. The Nakdong deltaic sediments were divided into five units based on sedimentation rate. The lowest (unit 5) shows a break in sedimentation between the last glacial maximum (LGM) and the Holocene. The sedimentation rate increased in units 4 and 3, presumably corresponding to the early to middle Holocene sea level rise and high stand. Unit 2 shows a gradually decreasing sedimentation rate following the regression of the shoreline, until about 2 ka. The progradation of the Nakdong River delta resulted in the rapid accumulation of unit 1 during the last 2000 years.  相似文献   

14.
Uranium is enriched in the border zones of magmatic bodies and the enrichment is believed to be caused by the migration of hydrous solutions which carry that element along intergranular paths towards the contact zone with the wall rock. We propose that the contact zone is a geochemical barrier at which the uranium, present in the solution, would be deposited if it were not for diffusion away from the increased concentration at the margins.The two particle flows, the one caused by migration and the other caused by diffusion, can be described by a differential equation, whose solution is the concentration of uranium as a function of time, diffusion coefficient and velocity of migration.The distribution of uranium in two intrusive bodies, the Mont Blanc granite (Swiss Alps) and a pluton in the Dshetui-Oguz massif (U.S.S.R.), gives the following parameters: duration of process 0.3–1 m.y., diffusion coefficient 4 × 10?4 to 5 × 10?4 cm2/s, and velocity of migration 0.1–0.3 cm/year.The combined process of migration and diffusion is assumed to be an important mechanism for controlling the distribution of uranium throughout the earth's crust and for its change in geological time.  相似文献   

15.
Rockfall release is a rather unpredictable process. As a result, the occurrence of rockfall often threatens humans and (infra)structures. The assessment of potential drivers of rockfall activity therefore remains a major challenge, even if the relative influence of rainfall, snowmelt, or freeze–thaw cycles has long been identified in short-term monitoring projects. In the absence of longer-term assessments of rockfall triggers and possible changes thereof, our knowledge of rockfall dynamics remains still lacunary as a result of the persisting scarcity of exhaustive and precise rockfall databases. Over the last decades, several studies have employed growth disturbances (GDs) in tree-ring series to reconstruct rockfall activity. Paradoxically, these series were only rarely compared to meteorological records. In this study, we capitalize on the homogeneity of a centennial-old reforestation plot to develop two reconstructions – R1 including only growth suppressions, and R2 based on injuries – with limited biases related to decreasing sample size and changes in exposed diameters back in time. By doing so, our study also and quite clearly highlights the large potential that protection forests have in terms of yielding reliable, multidecadal rockfall reconstructions. From a methodological perspective, we find no synchronicity between R1 and R2, as well as an absence of meteorological controls on rockfall processes in R1. This observation pleads for a careful selection of GDs in future reconstructions. In terms of process dynamics, we demonstrate that summer intense rainfall events (>10 mm day−1) are the main drivers for rockfall activity at our study site. Despite the stringency of our detection procedure, correlations between rockfall activity and meteorological variables remain comparable to those reported in previous studies, as a result of the complexity and multiplicity of triggering factors. We therefore call for a more systematic coupling of tree-ring analysis with rockfall and microclimatic monitoring in future studies. © 2020 John Wiley & Sons, Ltd.  相似文献   

16.
Oxygen and carbon data from eight stalagmites from northwest South Island are combined to produce composite records of δ18O and δ13C from 23.4 ka to the present. The chronology is anchored by 43 thermal ionization mass spectrometry (TIMS) uranium series ages. Delta 18O values are interpreted as having a first order positive relationship to temperature, but also to be influenced by precipitation in a complex manner. Delta 13C is interpreted as responding negatively to increases in atmospheric CO2 concentration, biological activity and precipitation amount.

Six climatic phases are recognized. After adjustment of 1.2‰ for the ice volume effect, the δ18O record between 23 and 18 ka varies around −3.72‰ compared to the Holocene average of −3.17‰. Late-glacial warming commenced between 18.2 and 17.8 ka and accelerated after 16.7 ka, culminating in a positive excursion between 14.70 and 13.53 ka. This was followed by a significant negative excursion between 13.53 and 11.14 ka of up to 0.55‰ depth that overlapped the Antarctic Cold Reversal (ACR) and spanned the Younger Dryas (YD). Positive δ18O excursions at 11.14 ka and 6.91–6.47 ka represent the warmest parts of the Holocene. The mid-Holocene from 6 to 2 ka was marked by negative excursions that coincide with increased glacial activity in the South Island. A short positive excursion from 0.71 to 0.57 ka was slightly later than the Medieval Warm Period of Europe.

Delta 13C values were high until 17.79 ka after which there was an abrupt decrease to 17.19 ka followed by a steady decline to a minimum at 10.97 ka. Then followed a general increase, suggesting a drying trend, to 3.23 ka followed by a further general decline. The abrupt decrease in δ-values after 17.79 ka probably corresponds to an increase in atmospheric CO2 concentration, biological activity and wetness at the end of the Last Glaciation, but the reversal identified in the δ18O record from 13.53 to 11.14 ka was not reflected in δ13C changes. The lowest δ13C values coincided with the early Holocene climatic suboptimum when conditions were relatively wet as well as mild.

Major trends in the δ18Oc record are similar to the Northern Hemisphere, but second order detail is often distinctly different. Consequently, at the millennial scale, a more convincing case can be made for asymmetric climatic response between the two hemispheres rather than synchronicity.  相似文献   


17.
The Mississippi and Missouri river valleys in the midcontinental United States contain extensive loess-paleosol sequences that are used to constrain the timing of expansion and retreat of the Laurentide Ice Sheet. Previous studies have been unsuccessful in producing finite ages for sediments older than ∼150 ka due to saturation of luminescence emissions. The thermally transferred optically stimulated luminescence (TT-OSL) dating technique is tested on the fine-grained (4–11 μm) quartz fraction of these loess deposits because the TT-OSL signal has been shown to grow with high (kGy) radiation doses. The TT-OSL signal continued to increase with radiation dose above 900 Gy. The optical and thermal stabilities of this TT-OSL signal are evaluated. Equivalent dose values are highly sensitive to preheat temperatures. Recycling ratios, zero-dose response values, and dose recovery tests all yield acceptable values for samples with burial doses >∼200 Gy. The apparent TT-OSL ages for the Roxana Silt (∼52–63 ka), Teneriffe Silt (∼66 ka), and Loveland Silt (∼133–192 ka) agree at 1σ level with previously published TL and IRSL ages derived from the same samples. For the oldest unit, the Crowley's Ridge Silt, TT-OSL ages (∼167–200 ka) are younger than IRSL or TL ages by ∼20%. This is interpreted as underestimation related to TT-OSL signal contamination, which can be avoided by isolating the fast component of the TT-OSL. Preliminary fast component TT-OSL ages for the Crowley's Ridge Silt (∼197–241 ka) favor deposition during marine oxygen-isotope stage (MIS) 7 or 8, contrary to a previous inference of a MIS 12 deposition.  相似文献   

18.
The Schmidt Hammer (SH) method is used to quantify the rock weathering degree and has been proposed as a relative dating tool. Terrestrial Cosmogenic Nuclide (TCN) methods provide absolute exposure ages for erosive surfaces. Few works combine both methods for surfaces older than the Holocene. We compare data obtained by both methods for c. 150 ka bp glacial and fluvial erosive granite surfaces from northwest Spain. Rebound values (R) have been firstly compared with the rock density to assess the correlation with the rock strength, independently from influence of factors such as wetness and roughness in the R‐values. For erosive glacial surfaces older than 100 ka R‐values are confined in a narrow range, with no differences within errors. Stepped fluvial surfaces of 700 m to 70 m above present sea level show an inverse correspondence between TCN ages and R‐values, although no age predictions can be done on the basis of the R‐values. Thus, age inferences exclusively based on R‐values may not be realistic, but SH studies could be a useful tool for selecting surfaces for TCN dating. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

19.
Sidewall erosion because of rockfalls is one of the most efficient erosional processes in the highest parts of mountain ranges; it is therefore important to quantify sidewall erosion to understand the long-term evolution of mountainous topography. In this study, we analyse how the 10Be concentration of supraglacial debris can be used to quantify sidewall erosion in a glaciated catchment. We first analyse, in a glaciated catchment, the cascade of processes that move a rock from a rockwall to a supraglacial location and propose a quantitative estimate of the number of rockfalls statistically mixed in a supraglacial sand sample. This model incorporates the size of the rockwall, a power law distribution of the size of the rockfalls and the mean glacial transport velocity. In the case of the Bossons glacier catchment (Mont Blanc massif), the 10Be concentrations obtained for supraglacial samples vary from 1.97 ± 0.24 to 23.82 ± 1.68 × 104 atoms g−1. Our analysis suggests that part of the 10Be concentration dispersion is related to an insufficient number of amalgamated rockfalls that does not erase the stochastic nature of the sidewall erosion. In the latter case, the concentration of several collected samples is averaged to increase the number of statistically amalgamated rockfalls. Variable and robust 10Be-derived rockwall retreat rates are obtained for three distinct rockfall zones in the Bossons catchment and are 0.19 ± 0.08 mm year−1, 0.54 ± 0.1 mm year−1 and 1.08 ± 0.17 mm year−1. The mean 10Be retreat rate for the whole catchment (ca. 0.65 mm year−1) is close to the present-day erosion rate derived from other methods. © 2019 John Wiley & Sons, Ltd.  相似文献   

20.
The multipart Riffeltal rock glacier, located in a tributary valley of the Kaunertal, Tyrol, Austria is investigated to enlarge the knowledge about spatial and temporal development of rock glaciers in and at the margins of pro‐glacial areas and to get a better understanding of glacier–rock glacier interactions. The subject of interest consists of a complex system of two adjacent rock glacier tongues and various superposed lobes with differing ages, origin and root zones, and therefore diverse development. To determine the reasons for their diverging development, the internal structure and permafrost occurrence on and in the surrounding area of the rock glacier were studied by application of geomorphological mapping, geophysical methods and measurement of the basal temperature of the winter snow cover (BTS). Permafrost modelling was performed on the basis of BTS data and land surface parameters derived from a high resolution airborne laser scanning (ALS) digital elevation model (DEM). Additionally, the ALS data were used to measure vertical and horizontal changes of the rock glacier surface between 2006 and 2012. Glacier–rock glacier interactions during and since the Little Ice Age (LIA) are evident for the development of the studied rock glacier. A geomorphic map gives important information about the connection between glacial advance or retreat and permafrost or ground ice occurrence. The combination of all information helps in the analysis of diverse kinematic action of neighbouring rock glacier tongues. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

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