Lichenometry in dating recent glacial landforms and deposits, southeast Iceland

Lichenometry curves were derived for the glacier forelands of Breidamerkurjokull and Skalafellsjökull using measurements of the collective species, Rhizocarpon geographicum , from independently dated surfaces deglaciated during the period since the late-19th century ice maximum episode in the area. The form of the curves appears to be linear. Several methods of predicting the ages of undated surfaces were compared for specific test examples, including single lichenometry curves, families of curves and multiple curves based on randomly selected largest lichens. The last method provided a useful means of assessing the reproducibility of predicted ages. Where substrate conditions were highly variable, a lichenometry curve based on single largest lichens provided a preferred result.     

Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments

Striberger, J., Björck, S., Ingólfsson, Ó., Kjær, K. H., Snowball, I. & Uvo, C. B. 2010: Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments. Boreas, 10.1111/j.1502‐3885.2010.00153.x. ISSN 0300‐9483. Properties of varved sediments from Lake Lögurinn in eastern Iceland and their link to climate and glacial processes of Eyjabakkajökull, an outlet glacier of the Vatnajökull icecap, were examined. A varve chronology, which covers the period AD 1262–2005, was constructed from visual observations, high‐resolution images, X‐ray density and geochemical properties determined from X‐radiography and X‐ray fluorescence scanning. Independent dating provided by ¹³⁷Cs analysis and eight historical tephras verify the varve chronology. The thickness of dark‐coloured seasonal laminae, formed mainly of coarser suspended matter from the non‐glacial river Grímsá, is positively correlated (r=0.70) with winter precipitation, and our 743‐year‐long varve series indicates that precipitation was higher and more varied during the later part of the Little Ice Age. Light‐coloured laminae thickness, controlled mainly by the amount of finer suspended matter from the glacial river Jökulsáí Fljótsdal, increased significantly during the AD 1972 surge of Eyjabakkajökull. As a consequence of the surge, the ice‐dammed Lake Háöldulón formed and recurrently drained and delivered significant amounts of rock flour to Lake Lögurinn. Based on these observations, and the recurring cyclic pattern of periods of thicker light‐coloured laminae in the sediment record, we suggest that Eyjabakkajökull has surged repeatedly during the past 743 years, but with an increased frequency during the later part of the Little Ice Age.     

Geomorphic evidence for Holocene glacial advances and sea level fluctuations on eastern Vestfirðir, northwest Iceland

New geomorphic and chronological data of Holocene advances of the Drangajökull Ice Cap, located on eastern Vestfirðir, northwest Iceland, are presented. At least two glacial advances and two transgressions during the Holocene are interpreted from moraines and raised beach deposits, respectively. Geomorphic evidence is concentrated in the three valleys adjacent to the modern outlet glaciers of the Drangajökull Ice Cap: Kaldalónsjökull, Leirufjarðarjökull, and Reykjarfjarðarjökull. The valley surrounding Kaldalónsjökull contains a vegetated Holocene moraine with a minimum radiocarbon age of ∼2600 cal. yr BP, which provides geomorphic evidence for Neoglacial activity on eastern Vestfirðir. The second extensive Holocene glacial advance on eastern Vestfirðir occurred during the Little Ice Age, and moraines associated with this advance are present in all three outlet glacier valleys. The Neoglacial advance is the most extensive ice advance on eastern Vestfirðir. Raised beaches parallel to the coastlines of Ísafjarðardjúp and Jökulfirðir, at an elevation of approximately 5 m a.s.l., suggest a minor transgression at ∼3000 cal. yr BP based on radiocarbon ages of shells. A minor transgression of 0.3–0.5 m a.s.l. is associated with the timing of the Little Ice Age advance. Correlation of geomorphic events with sediment proxy records facilitates distinguishing local perturbations from regional North Atlantic climate signals. This study supports regional interpretations of climatic instability during the Holocene.     

The Fennoscandian uplift and glacial isostasy

Various hypotheses have been put forth in relation to the land uplift of Fennoscandia, which is well documented both by geological and geodetic observations. Most modern authors attribute the present uplift to an isostatic rebound of the earth after the last deglaciation. Recent information on the gravity field, both from the satellite data and land survey measurements is examined to ascertain whether the Fennoscandian uplift is associated with a gravity minimum and a mass deficit. Free air anomalies correlate well with the central area of uplift and predict a remaining uplift of about 100 m. Results of secular gravity measurements are inconclusive. Seismicity of Fennoscandia does not show a close association with the area of maximum uplift. Different rheological models proposed for the mantle below the Fennoscandian shield are reviewed and it is shown that the available data on the rates of uplift for the last 9000 years are more compatible with a low-viscosity (10²⁰ P) asthenosphere of 100–200 km thickness.     

2013年西藏嘉黎县“7.5”冰湖溃决洪水成因及潜在危害

冰湖溃决洪水（泥石流）是西藏自治区主要自然灾害之一. 2013年7月5日,西藏自治区嘉黎县忠玉乡发生“7.5”冰湖溃决洪水灾害事件,导致人员失踪,房屋被毁,桥梁、道路等基础设施遭到严重破坏,直接经济损失高达2.7亿元. 基于不同时间段地形图和遥感影像资料,利用地理信息技术,发现导致“7.5”洪灾的溃决冰湖为然则日阿错. 该冰湖溃决的直接诱因可能是雪崩和冰崩的共同作用,溃决前的强降水过程及气温的快速上升是其间接原因,而冰湖长期稳定的扩张导致水量聚集是其溃决并造成巨大灾害的基础. 然则日阿错溃决后形成2个冰湖,面积分别为0.25 km²和0.01 km²,再次发生溃决的概率极小. 这次溃决洪水和泥石流灾害事件阻塞了尼都藏布的罗琼沟及衣布沟,并形成2处面积分别为0.33 km²和0.13 km²堰塞湖,且存在溃决风险,在今后一段时间内应加强监测工作与排险工程实施.     

冰湖溃决泥石流形成的临界条件

随着全球气候的变暖, 在世界上许多高山峡谷区的冰湖溃决及其溃决洪水引发的泥石流, 经常对下游居民及其他基础设施造成极为严重的危害. 使用水槽试验的方法, 从单宽流量和库容、沟道纵坡、堆积物粒径3个方面探讨了冰湖溃决泥石流形成的影响因素和临界条件. 结果显示: 冰湖溃决泥石流形成与否不仅与溃决洪水提供的能量有关, 还与参与泥石流活动的沟床物质特性紧密相关. 通过对试验数据的分析, 当泥石流形成的特征参数K>2.66时, 冰湖溃决洪水可以演化为泥石流. 该种方法可以对危险性冰湖的预测提供理论参考.     

The role of meltwater in glacial processes

Water plays a dominant role in many glacial processes and the erosional, depositional and climatic significance of meltwaters and associated fluvioglacial processes cannot be overemphasized. At its maximum extent c. 20,000 years ago, the volume of the Laurentide ice sheet was 33 × 10⁶ km³ (about the same as the volume of all ice present today on planet Earth). The bulk of this was released as water in little more than 10,000 years. Pulses of meltwater flowing to the Atlantic Ocean from large ice dammed lakes altered thermohaline circulation of the world's oceans and global climate. One such discharge event via Hudson Bay at 8200 years BP released 160,000 km³ of water in 12 months. Global sea levels recovered from glacial maximum low stands reached at about 20,000 years ago at an average rate of 15 m per thousand years but estimates of shorter term rates suggest as much as 20 m sea level rise in 1000 years and for short periods, rates as high as 4 m per hundred years. Meltwaters played a key role in lubricating ice sheet motion (and thus areal abrasion) across the inner portions of the ice sheet where it slid over rigid crystalline bedrock of the Canadian Shield. The recharge of meltwater into the ice sheets bed was instrumental in generating poorly sorted diamict sediments (till) by sliding-induced shearing and deformation of overpressured sediment and soft rock. The transformation of overpressured till into hyperconcentrated slurries in subglacial channels may have generated a highly effective erosional tool for selective overdeepening and sculpting of bedrock substrates. Some workers credit catastrophic subglacial ‘megafloods’ with the formation of drumlins and flutes on till surfaces. Subglacial melt river systems were instrumental in reworking large volumes of glaciclastic sediment to marine basins; it has been estimated that less than 6% of the total volume of glaciclastic sediment produced during the Pleistocene remains on land. Fluvioglacial and glaciolacustrine sediments and landforms dominate large tracts of the ‘glacial’ landscape in North America. The recharge of subglacial meltwater into underlying bedrock and sediment aquifers created transient reversals in the long-term equilibrium flow directions of basinal fluids. With regard to pre-Pleistocene glacial record, meltwaters moved enormous volumes of terrestrial ‘glaciclastic’ sediment to marine basins and thus played a key role in preserving a record of glaciation, a record otherwise almost entirely lost on land.     

论内蒙古第四纪冰川和冰臼群的成因

通过内蒙古林东地区第四纪冰川地质和冰臼群成因专项调查工作,发现了晚更新世冰碛泥砾层和龟背石、熨斗石、龟裂石等典型的冰碛砾石及冰斗、刃脊、角峰、冰川槽谷中的表皮构造等山谷冰川遗迹。在花岗岩体中发育的岩臼群,可划分为冰期冰雪融水形成的冰臼、现代季节性降水形成的瓯穴和风蚀作用为主形成的风龛3种类型。本区冰臼同山谷冰川相伴随,未发现远源巨型漂砾等大陆冰盖证据。     

The relation between glacial ages and terrestrial magnetism

An attempt is made to show that the change of angular momentum of the earth, caused by glaciations, may compensate the slowing down effect from tidal friction forces and even reverse the polarity in the terrestrial magnetic field.     

The record of density-induced underflows in a glacial lake

As part of an overall study of sedimentation processes in a proglacial lake an effort was made to compare field results with some of the general equations for density flows. The results suggest that in relatively small glacial lakes the occurrence of underflows with lower sediment loads involves a complex interplay between thermal and sediment effects which is extremely sensitive to varying hydrologic and climatic conditions. In terms of actual transport mechanics the results: (i) indicate that a higher α value of 0·6 or 0·7 gives a closer agreement between the measured velocity values and the established equations on moderately shallow slopes; (ii) provide field support for the experimentally derived relationship of Britter & Linden (1980) for the velocity of underflows and suggest the equation may be applicable in situations below 5° slopes; and (iii) support the relationship between velocity of the front and body of a continuous underflow for moderate slope situations suggested by Middleton (1966b). Finally the velocity values measured by electromagnetic current meters stationed in the lake, the grain-size data obtained from mapping core data, and the application of other criteria support the concept that in this environment the underflows are capable of erosion.     

The cryosphere and glacial permafrost as its integral component

Since Earth sciences have undertaken studies of other celestial bodies, its various fields have moved beyond the scope of study assigned to them by name. Interest in space makes it necessary to abandon research geocentrism and reverse relations when comparing the structure of the Earth with other celestial bodies. As an exceptional place in the universe, it should not be the Earth which constitutes a reference point, especially in cryospheric research, but rather the other celestial bodies of our planetary system. This approach, referred to as ??Spatial Uniformitarianism,?? is the basis for determining the place of ice in the environment and for assigning it to the lithosphere. Ice can be penetrated by frost just as other minerals and rocks, so the occurrence of permafrost may yet be attributed to glaciers and ice-caps. In the article, the occurrence of glacial permafrost has been worked out on the basis of a thermal classification of glaciers with a thorough understanding of the phenomenon. This allows us to specify permafrost??s presence beneath glaciers and ice-caps, a concept which had been needlessly vague. Further, by considering rock glaciers as a mixture of two types of rocks, and by understanding the importance of movement in their evolution, we are now closer to fruitfully determining their role in the environment, their geomorphological significance.     

太原虎峪沟"1996-08-04"泥石流形成过程与发展趋势

1996年7月30日-8月5日，山西省太原市西山地区连降大雨，导致区内虎峪沟暴发特大型泥石流，严重损毁厂矿企业及市政设施，造成36人死亡，直接经济损失高达2．4亿元。本文在综合研究野外调查资料和历史灾情的基础上，通过对泥石流的形成条件、活动过程以及区内地质环境现状质量的分析，判定虎峪沟为中等易发高危险度泥石流沟，仍具有潜在的危害。采煤活动是泥石流的主要影响因素之一，既影响植被生长，又破坏岩土体原生结构，大大加剧崩、滑、流的发生；堆积的大量煤矸石，为泥石流的形成提供丰富的固体物源。为此，要因地制宜地采用生物、工程措施，对全区进行综合整治。     

The Little Ice Age glacier maximum in Iceland and the North Atlantic Oscillation: evidence from Lambatungnajökull, southeast Iceland

This article examines the link between late Holocene fluctuations of Lambatungnajökull, an outlet glacier of the Vatnajökull ice cap in Iceland, and variations in climate. Geomorphological evidence is used to reconstruct the pattern of glacier fluctuations, while lichenometry and tephrostratigraphy are used to date glacial landforms deposited over the past ˜400 years. Moraines dated using two different lichenometric techniques indicate that the most extensive period of glacier expansion occurred shortly before c . AD 1795, probably during the 1780s. Recession over the last 200 years was punctuated by re-advances in the 1810s, 1850s, 1870s, 1890s and c . 1920, 1930 and 1965. Lambatungnajökull receded more rapidly in the 1930s and 1940s than at any other time during the last 200 years. The rate and style of glacier retreat since 1930 compare well with other similar-sized, non-surging, glaciers in southeast Iceland, suggesting that the terminus fluctuations are climatically driven. Furthermore, the pattern of glacier fluctuations over the 20th century broadly reflects the temperature oscillations recorded at nearby meteorological stations. Much of the climatic variation experienced in southern Iceland, and the glacier fluctuations that result, can be explained by secular changes in the North Atlantic Oscillation (NAO) Advances of Lambatungnajökull generally occur during prolonged periods of negative NAO index. The main implication of this work relates to the exact timing of the Little Ice Age in the Northeast Atlantic. Mounting evidence now suggests that the period between AD 1750 and 1800, rather than the late 19th century, represented the culmination of the Little Ice Age in Iceland.     

The geochemistry of trace elements in geothermal fluids,Iceland

Trace element geochemistry was studied in geothermal fluids in Iceland. The major and trace element compositions of hot springs, sub-boiling, and two-phase (liquid and vapor) wells from 10 geothermal areas were used to reconstruct the fluid composition in the aquifers at depth. Aquifer fluid temperatures ranged from 4 to 300 °C, pH values between 4.5 and 9.3, and fluids typically contained total dissolved solids <1000 ppm, except in geothermal areas that have seawater and seawater-meteoric water mixtures. Trace alkali elements Li, Rb and Cs are among the most mobile elements in aquifer fluids, with concentrations in the range of <1 ppb to 3.49 ppm Li, <0.01 to 57 ppb Cs, and <1 ppb to 3.77 ppm Rb. Their chemistry is thought to be dominated by rock leaching and partitioning into Na- and K-containing major alteration minerals. Arsenic, Sb, Mo and W are typically present in concentrations in the range of 1–100 ppb. They are relatively mobile, yet Mo may be limited by molybdenite solubility. The alkaline earth elements Ba and Sr are quite immobile with concentrations in the range of <0.1–10 ppb Ba and <1–100 ppb Sr in the dilute fluids, but up to 5.9 ppm Ba and 8.2 ppm Sr in saline fluids. These elements show a systematic relationship with Ca, possibly due to substitution for Ca in Ca-containing major alteration minerals like calcite, epidote and anhydrite. Incorporation into major Ca-minerals may also be important for Mn. Many metals including Fe, Cr, Ni, Zn, Cu, Co, Pb and Ag have low mobility and concentrations, typically <1 ppb for Ag, Cd, Co, Cr, Cu, Ni, and Pb, <10 ppb for Zn and < 100 ppb for Fe, although for some metals higher concentrations are associated with saline fluids. Based on the metals assessed, saturation is approached with respect to many sulfide minerals and in some cases oxide minerals but Cu, Ni and Pb minerals are slightly but systematically undersaturated, and Ag phases significantly undersaturated. Evaluation of mineral-fluid equilibria for these metals is problematic due to their low concentrations, problems associated with assessing the aqueous species distribution by thermodynamic calculations, and uncertainties concerning the exact minerals possibly involved in such reactions. Reaction path calculations, poor comparison of concentrations measured in the samples collected at the wellhead and published downhole data as well as boiling, cooling and mass precipitation calculations suggest removal of many metals due to changes upon depressurization boiling and conductive cooling of the aquifer fluids as they ascend in wells. These results imply that processes such as mass precipitation upon fluid ascent may be highly important and emphasize the importance of considering mass movement in geothermal systems.     

Nomenclature and resolution in Holocene glacial chronologies

Most Quaternary research in Canada during the first half of the twentieth century focused on Pleistocene glaciation. Given the dramatic shifts in climate during the Pleistocene, it is not surprising that the Holocene was viewed as a time of benign climate. Holocene climate variability was first recognized around the middle of the century when paleoecologists found evidence that the early part of the epoch was warmer and drier than the later part. In 1970s and 1980s, another generation of geologists, geographers, and botanists began to recognize more complexity in Holocene climate and vegetation in western Canada. Several millennial-scale glacier “advances” postdating the early Holocene warm interval were defined, including the Garibaldi Phase (6.9–5.6 ka), the Tiedemann–Peyto Advance (3.5–1.9 ka), and the Little Ice Age (AD 1200–1900). Subsequently, application of dendrochronological techniques and stratigraphic studies in glacier forefields showed that the Little Ice Age was itself more complex than previously thought. During that 700-year period, glaciers repeatedly advanced and retreated in response to climatic variability on time scales ranging from centuries to decades. Recent work shows that the glacier record of the Garibaldi Phase and the Tiedemann and Peyto advances are similar in complexity to the Little Ice Age, with multiple advances of glaciers separated by intervals of more restricted ice cover. Researchers have also identified other times in the Holocene when glaciers expanded from restricted positions – 8.20, 4.90–3.80, and 1.70–1.40 ka. Continued research undoubtedly will reveal additional complexities, but with what is currently known the appropriateness of terms such as “Tiedemann Advance,” “Peyto Advance,” and “Little Ice Age” can be questioned. Only short periods of time separate these episodes as currently defined, and it seems likely that intervals of restricted glacier cover within each of these millennial-length intervals are just as long as the intervals separating them.     

The northern limits of glacial lake Algonquin in upper Michigan

A number of ancient shorelines formed by late-Pleistocene proglacial lakes have been found in eastern upper Michigan. These shorelines delimit several water planes, the uppermost of which is correlated with the Main Lake Algonquin stage. This correlation is based on the continuity of the highest water plane with Main Algonquin shorelines in Wisconsin and Ontario, the strength of the shoreline features, its altitudinal relationship with lower water planes, and a reinterpretation of radiocarbon dates from the Sault Ste. Maria area. The isobases of this water plane have a bearing of S75°E. At the time of the maximum extent of Lake Algonquin, ca. 10,600 yr B.P., its northern, ice-limited border lay along the Munising moraine, the northernmost of the two main morainic systems of eastern upper Michigan. This interpretation lends support to the idea of a period of slow deglaciation from ca. 11,000 to 10,000 yr B.P. An ice lobe occupied the central Lake Superior basin until early Holocene time. Radiocarbon dates on wood found beneath till or outwash at several sites indicate a minor ice readvance from the central Lake Superior basin ca. 10,000 yr B.P. If true, this would have prevented the development of the post-Duluth series of glacial lakes in the western Lake Superior basin until ca. 9900 yr B.P., well after the end of the main Lake Algonquin stage.