地貌面、地文期与地貌演化——从华北地貌演化研究看地貌学的一些基本理论

华北地貌的形成演化研究以传统地貌学理论戴维斯等的"地貌面"和"侵蚀旋回"理论为指导。研究表明,它基本适用于华北地貌的形成与演化;同时也发现了传统地貌学理论的不足。该文用华北地貌形成演化的实际资料弥补了这个不足,并进一步探讨了地貌形成演化理论的某些新观点。     

The Fall of Threatening Rock: A Geomorphology Exercise Adaptation

Abstract

The Threatening Rock mass wasting event at Chaco Canyon, New Mexico, in 1941 introduces students to a well-documented geomorphology case study. Based on data from Schumm and Chorley (1964), students examine the event using rock movement measurements and weather data, undertaking the same analysis tasks as the original investigators. Students observe patterns of movement related to precipitation and temperature, and use regression to estimate the time of initial movement. Specific exercise questions guide students to logical conclusions regarding geomorphic processes and environmental influences. The exercise exemplifies geomorphic investigation from both a process and historic perspective.     

中国热带气候地貌几个问题的讨论

中国热带气候长期热湿,气候地貌的基本特征表现为强烈风化和持续剥蚀夷平,缺乏地貌的世代演替,所谓"双重风化"和"双重夷平"的经典概念,未必切合中国热带的实际情况.中国热带第四纪气候波动不明显,但是这种波动在气候地貌上仍有反映.红土砾石台地代表中更新世冷湿(砾石堆积)转热干(红土化)的气候地貌.老红砂台地代表晚更新世至全新世热干(风积)转热湿(红土化、古土壤)的气候地貌.海岸贝壳堤反映中全新世风暴潮增强的气候波动.广东、海南的所谓"冰臼群"实乃河流地貌的瓯穴.中国热带末次冰期的冰川遗迹仅见于台湾岛中央山脉.     

基于遥感与SRTM的青藏高原冰缘地貌信息提取方法——以1 ∶ 100万标准分幅拉萨幅(H46)为例

根据模型和分布函数,本文首先依据多年平均气温、地温和SRTM等数据对研究区域冰缘地貌的分布范围进行分别提取,并利用遥感数据和人工解译方式对其进行了修正。在此基础上,采用一定指标,利用SRTM数据对冰缘地貌次级类型(如起伏度、海拔高度和坡度等)进行了提取,从而完成研究区域冰缘地貌信息的提取。研究结果表明:①研究区域冰缘地貌总面积约5.15×10⁴km²,主要分布在研究区域的西北部和西南部,另外在东北部也有少量分布;通过提取,研究区域中最重要的冰缘地貌类型是冰缘作用的中起伏缓极高山,面积约0.82×10⁴km²,分布范围较广。②冰缘地貌的分布与海拔高度、气温和地温等有密切的关系,基于此提取的结果可为冰缘地貌的解译提供一定的参考;由于青藏高原气象站点较少,数据精度较低,自动提取精度受到很大限制,因此进行人工解译修正是非常重要和必不可少的。     

知识经济时代我国河流地貌学面临的机遇与挑战

21世纪将是知识经济占主导地位的时代 ,知识经济的一系列新的特征及所引起的相应的社会变革 ,为我国河流地貌学的发展提供了新的机遇 ,同时也对传统地貌学提出了严峻的挑战。充分发挥河流地貌学的传统优势 ,利用现代高科技手段 ,加强理论创新研究 ,促进研究成果的转化 ,是我们为迎接知识经济时代 ,从当前就应该着手准备解决的问题。     

Modelling Transient Ground Surface Temperatures of Past Rockfall Events: Towards a Better Understanding of Failure Mechanisms in Changing Periglacial Environments

Despite the rising interest in mountain permafrost due to climatic changes and a noticed increase of registered rockfall events in the European Alps and other mountain ranges, little is known about transient thermal conditions in the detachment areas of rockfalls. Temperature conditions prior to the rockfall events of 144 past events in the European Alps were modelled with a physically based ground temperature model. To minimise the impact that uncertainty has on interpretations, only relative values were used, that is, percentiles obtained from cumulative distribution functions of the modelled ground surface temperatures from the beginning of the meteorological measurement series up to the event dates. Our results suggest that small and mid‐sized rockfalls (volumes up to 100 000 m³) from high elevation occurred mainly during short‐term periods of unusually high temperatures. This was neither found to be a result of the seasonal distribution (most analysed events in higher elevations occurred from July to September) nor of the longer‐term temporal distribution (most analysed events occurred after 2000) only. Plausible explanations are either a destabilisation related to advective thaw or failure due to stress redistribution caused by large temperature variations. Large deep‐seated rock slope failures (≥100 000 m³) in high elevation occurred all year round.     

Beach Ridge Geomorphology at Cape Grinnell,northern Greenland: A Less Icy Arctic in the Mid-Holocene

Geografisk Tidsskrift—Danish Journal of Geography 110(2):337–355, 2010

In northern Greenland, the Cape Grinnell beach ridge plain offers a 9,000year multi-proxy record for isostatic recovery, storm history, and the hydrological changes related to precipitation and slope evolution. The chronology of uplifted beach ridges is constrained by ten geological 14C ages on shell and sea mammal bones and eleven upper limiting ages from archaeological sites that span the last 3,000 years. Beach ridges formed under the influence of open water storms with renewed frequency and intensity ca. 3 ka and 1 ka ago. A lack of shell may reflect cooler sea surface temperatures. The presence and absence of ice can be inferred by push-features. Three intervals of heightened precipitation produced extensive fan deltas: (a) after 9 ka BP (b) prior to 4.5 ka BP and (c) during the Little Ice Age (AD 1350–1900). Active solifluction lobes and colluvia cover beach ridge deposits that are between 9 and 7 ka old.     

GLACIAL GEOMORPHOLOGY OF THE WHITE MOUNTAINS,CALIFORNIA AND NEVADA: ESTABLISHMENT OF A GLACIAL CHRONOLOGY

The White Mountains, astride the California-Nevada stateline, are the highest and westernmost of the Great Basin ranges. This range was extensively glaciated during the Quaternary Period. Glacial landforms and scattered erratics were identified in the field using primarily morpho-and lithostratigraphic criteria, and mapped on aerial photographs and topographic maps. Topographic characteristics of the glacial deposits were analyzed using standard statistical procedures. A sequence of glacial deposits was identified in terms of six glacial stages, these glaciations named according to type site, and relative ages inferred. With the exception of perched Stage I (early) deposits along the range crest, reconstructed equilibrium-line altitudes and elevation of the glacier termini increase to the present, with glacier length and inferred size decreasing through time. Preliminary data suggest that weathering and pedogenesis are also progressive, though environmental gradients mask some of these distinctions between deposits. It is hypothesized that the White Mountains have a similar glacial chronology to the adjacent Sierra Nevada, but that with the intensification of the Sierran rainshadow during the Quaternary, the extent of glaciation in the White Mountains apparently decreased through time owing to regional tectonic uplift. This had led to the preservation of a more complete sequence of glacial deposits than in the Sierra Nevada, making the delineation of multiple mid-Quaternary events possible in many valleys. Further radiometric and chronometric dating of these deposits is in progress. [Key words: Glaciation, Quaternary, glacial geomorphology, White Mountains, California, Nevada.     

Numerical models of a subsidence mechanism in intracratonic basins: application to North American basins

McKenzie's model of sedimentary basin evolution and its modification, widely used in geophysics, sometimes fails to explain discrepancies between predicted and observed values of extension, thinning and subsidence of the Earth's crust, as for the North Sea. We develop a numerical model of sedimentary basin evolution based on the mechanism suggested by Lobkovsky. In the course of rifting, accompanied by thinning of lower parts of the lithosphere, the roof of the underlying asthenosphere moves upward. the material of the mantle lifts and partially melts owing to the reduction of pressure. the density difference between the melt and the crystalline skeleton results in the filtration of the lighter melt and its accumulation in the form of a magmatic lens. Due to changed P-T conditions, the material of the lens undergoes the gabbro-eclogite phase transformation. the resultant anomalously heavy eclogite lens sinks in the surrounding material. This induces a viscous flow, changing the surface topography and forming a sedimentary basin. We construct a 2-D numerical model describing a viscous flow induced by subsidence of a heavy body and compute changes of surface topography. to compute the flow we employ the Galerkin-spline approach, with modifications allowing for density discontinuities and time dependence of the phase transformation. We apply the model to the cases of the Illinois, Michigan and Williston basins. the computed and tectonic subsidence curves agree well for these cases. the proposed model is compatible with the seismic structure of the crust and upper mantle below these basins. the model is also consistent with gravity data. the approach is applicable to other intracratonic basins.     

River Classification as a Geographic Tool in the Age of Big Data and Global Change

Spatial classification is a well‐defined analysis method in geography, which involves defining regions of the Earth based on shared characteristics. An analogy can be made between classification in geography and taxonomy in biology, because both are used to reduce complexity. Just as modern evolutionary theory and genetics technologies have transformed biological taxonomy from the sometimes arbitrary classification of living things based on superficial similarities and differences into a system that reflects the history of life and relationships among organisms, modern advances in conceptual understanding and development of technology have similarly revolutionized classification in geography as a powerful method for describing and quantifying processes. Here, I describe the history and current trends of geographic classifications relevant to river systems. Overall, there is significant emerging potential in classification as a tool for understanding river processes     

Shorelines of the Uppsala Esker East-Central Sweden: Their Use as Indicators of Regional Differences in Shore Displacement

About 750 different shoremarks, mainly shore terraces, have been levelled along the Uppsala esker. Using various methods it has been possible to arrange the shoremarks to shorelines or rather shoremark zones containing more shoremarks than intervening parts. The material was divided into two major parts, i.e. shoremarks below c . 15 m above sea level and shoremarks above c . 15 m. It was found that shorelines on the whole were sloping towards the north. This was expected because of the faster shore displacement in the northern part of the area. However, the shorelines below c . 15 m a.s.l. indicated a slower increase in shore displacement than those of higher altitudes. A conclusion drawn from this might be that the increase towards the north is retarded in the area around Lake Mälar. This result is in reasonable agreement with recent isobase systems constructed from the evidence of mareograph records and repeated precise levellings. On the other hand, the shoreline studies give evidence of more pronounced regional differences in shore displacement in earlier Litorina times than those found today.     

Dating of thaw depths in permafrost terrain by the palaeomagnetic method: experimental acquisition of a freezing remanent magnetization

The acquisition of a freezing remanent magnetization (FRM) has been studied in controlled magnetic and thermal environments by successive freezing and thawing (−18 to +20°C) of samples of natural sediments from a frost polygon near Ny Ålesund, Spitsbergen. Successive freeze-thaw cycles cause a significant decrease in the intensity of the initially induced shock remanent magnetization (SRM), associated with directional trends towards the ambient magnetic field direction during the freezing phase. A slow increase in intensity commences after seven to 10 freeze-thaw cycles. The acquisition of a FRM in samples carrying an isothermal remanent magnetization shows a significantly smaller reduction in intensity and only minor directional variations. This result indicates that only a fraction of the magnetic grains in a natural sediment contributes to the natural remanent magnetization. Insignificant changes in lengths and directions of the principal susceptibility ellipsoid axes also indicate that magnetic fabric and remanent magnetization are carried by partly different populations of magnetic grains.
The acquisition of a FRM in nature has yet to be explored. If such a process is confirmed, however, it has the potential for obtaining age estimates of ancient thaw depths and for providing insights into material transport processes in frost polygons.     

Geomorphology and tectonics of uplifted coasts: New chronostratigraphical constraints for the Quaternary evolution of Tyrrhenian North Calabria (southern Italy)

The Tyrrhenian coastal sector of North Calabria, stretching between Torre S. Nicola and the Lao river, belongs to the inner extensional sector of the Neogene Apennines thrust belt. It is characterised by a stair of Quaternary marine and fluvial terraces representing the geomorphic response to the interaction between the Quaternary sea level fluctuations and the regional trend of tectonic uplift experienced by the margins of the Tyrrhenian back-arc basin. Since the last century, several authors studied the North Calabria coasts, where the flight of terraces preserves significant marine and continental successions, and proposed several paleo-geomorphological and tectonic reconstructions. In this paper we present a new stratigraphic and morphostructural setting of the North Calabria coasts based on both chronostratigraphical constraints obtained from marine deposits and detailed geomorphological analysis. A ten order stair of marine terraces, stepping between 240 and 0 m a.s.l., was recognized and time-constrained by the age of the Fornaci S. Nicola marine succession which was ascribed by integrated paleoecological, biostratigraphical and paleomagentic analyses to the early Middle Pleistocene (MIS 19–15). In particular, the 240, 200 and 160 m a.s.l. high strandlines were ascribed to the Early Pleistocene and the ones between 100 and 15 m a.s.l. to the Middle Pleistocene. The total amount of the vertical motion experienced by the studied area was estimated, and evaluation of the average rates of uplift for the Middle and Late Pleistocene times were also given. Considering the elevation a.s.l. of the oldest terraces, a tectonic uplift of at least 240 m was calculated for the North Calabria coasts since the Early Pleistocene times, 100 m of which gained from the beginning of the Middle Pleistocene. On the other hand, the 8-m high Late Pleistocene strandlines display a negligible vertical displacement affecting the area during the last 130 ka. The entire staircase of terraces preserves a record of slowing down in the rate of uplift, which attained an average value of 0.15 mm/year during the Middle Pleistocene.     

Prelude to Brazil: Leo Waibel's American Career as a Displaced Scholar

Beyond Germany, Leo Waibel (1888–1951) built a distinguished reputation for his work in Africa and the Americas. Today he is remembered especially in Brazil, where he boosted the development of geography as a research discipline in the years 1946–1950. During his tenure of the chair in geography at Bonn (1929–1937), Waibel's main research preoccupation became the role of the tropics in the world economy. In early 1937, he sought research leave to make an extended field trip to Brazil. Stripped on political grounds in the same year of his chair, Waibel came to the United States, where he became the only geographer to receive help from the Emergency Committee in Aid of Displaced Foreign Scholars. He would eventually serve as one of the very limited core staff on President Franklin Roosevelt's “M” Project on migration and settlement. This paper reconstructs the context of his work in the United States, clarifying especially the nature of his collaborations with Isaiah Bowman, widely regarded at the time as the leading geographer within the United States. Waibel's correspondence from the United States, and later from Brazil, reveals an international career marked by contradictions.     

浅析北美湿地林道规划及设计

通过分析北美湿地林地规划及设计的理念,特别推出了美国联邦政府对湿地林地规划及设计具体的法规及列举美国主要湿地林道路基类型。通过美国国际重要湿地和地方湿地公园湿地林道的几个具体实例,阐明北美遵循最优管理实践原则及联邦政府湿地林道规划设计法规,促进湿地生态系统可持续发展。     

A description of the external and internal quiet daily variation currents at North American locations for a quiet-Sun year

Summary. An order 4, degree 12 spherical harmonic analysis of the smoothed quiet geomagnetic daily variations was used to separate the external and internal geomagnetic S _q field at North American locations for the quiet-Sun year, 1965. These fields were represented by a month-by-month display of equivalent current vortex systems with dominant, pre-noon foci. The focus reached 40° latitude near the June solstice and about 30° latitude near the December solstice. The daily range of S _q current amplitudes was largest in late July to early August and smallest in mid-December. Semi-annual variations of S _q currents dominated only the equatorial region. Daily maxima in mid-latitudes, occurred mostly near local noon in December to February and about 1 hr before noon in June to mid-October. The ratio of external to internal current amplitude vxied from about 1.5 to 1.9 in the middle latitudes with both annual and semiannual changes. An error treatment indicated that the analysis reproduced the form of the surface field with a correlation coefficient of about 0.9 and the amplitudes of the surface field to about 10 per cent of the S _q daily range.     

Medium and small embankment dams on permafrost: A discussion of current concepts

This article discusses the current concepts of dam design and construction in permafrost regions. It is demonstrated that embankment dams often change their state from frozen to thawed and back during the operation period. It is shown that these transitions are not always attributable to observed climate warming. Where geotechnical, hydrogeological, and permafrost conditions are complicated, proper performance of embankment dams can only be provided by adhering to a selected thermal design for, as an example, a frozen state.