Long‐term landscape evolution: linking tectonics and surface processes

Research in landscape evolution over millions to tens of millions of years slowed considerably in the mid‐20th century, when Davisian and other approaches to geomorphology were replaced by functional, morphometric and ultimately process‐based approaches. Hack's scheme of dynamic equilibrium in landscape evolution was perhaps the major theoretical contribution to long‐term landscape evolution between the 1950s and about 1990, but it essentially ‘looked back’ to Davis for its springboard to a viewpoint contrary to that of Davis, as did less widely known schemes, such as Crickmay's hypothesis of unequal activity. Since about 1990, the field of long‐term landscape evolution has blossomed again, stimulated by the plate tectonics revolution and its re‐forging of the link between tectonics and topography, and by the development of numerical models that explore the links between tectonic processes and surface processes. This numerical modelling of landscape evolution has been built around formulation of bedrock river processes and slope processes, and has mostly focused on high‐elevation passive continental margins and convergent zones; these models now routinely include flexural and denudational isostasy. Major breakthroughs in analytical and geochronological techniques have been of profound relevance to all of the above. Low‐temperature thermochronology, and in particular apatite fission track analysis and (U–Th)/He analysis in apatite, have enabled rates of rock uplift and denudational exhumation from relatively shallow crustal depths (up to about 4 km) to be determined directly from, in effect, rock hand specimens. In a few situations, (U–Th)/He analysis has been used to determine the antiquity of major, long‐wavelength topography. Cosmogenic isotope analysis has enabled the determination of the ‘ages’ of bedrock and sedimentary surfaces, and/or the rates of denudation of these surfaces. These latter advances represent in some ways a ‘holy grail’ in geomorphology in that they enable determination of ‘dates and rates’ of geomorphological processes directly from rock surfaces. The increasing availability of analytical techniques such as cosmogenic isotope analysis should mean that much larger data sets become possible and lead to more sophisticated analyses, such as probability density functions (PDFs) of cosmogenic ages and even of cosmogenic isotope concentrations (CICs). PDFs of isotope concentrations must be a function of catchment area geomorphology (including tectonics) and it is at least theoretically possible to infer aspects of source area geomorphology and geomorphological processes from PDFs of CICs in sediments (‘detrital CICs’). Thus it may be possible to use PDFs of detrital CICs in basin sediments as a tool to infer aspects of the sediments' source area geomorphology and tectonics, complementing the standard sedimentological textural and compositional approaches to such issues. One of the most stimulating of recent conceptual advances has followed the considerations of the relationships between tectonics, climate and surface processes and especially the recognition of the importance of denudational isostasy in driving rock uplift (i.e. in driving tectonics and crustal processes). Attention has been focused very directly on surface processes and on the ways in which they may ‘drive’ rock uplift and thus even influence sub‐surface crustal conditions, such as pressure and temperature. Consequently, the broader geoscience communities are looking to geomorphologists to provide more detailed information on rates and processes of bedrock channel incision, as well as on catchment responses to such bedrock channel processes. More sophisticated numerical models of processes in bedrock channels and on their flanking hillslopes are required. In current numerical models of long‐term evolution of hillslopes and interfluves, for example, the simple dependency on slope of both the fluvial and hillslope components of these models means that a Davisian‐type of landscape evolution characterized by slope lowering is inevitably ‘confirmed’ by the models. In numerical modelling, the next advances will require better parameterized algorithms for hillslope processes, and more sophisticated formulations of bedrock channel incision processes, incorporating, for example, the effects of sediment shielding of the bed. Such increasing sophistication must be matched by careful assessment and testing of model outputs using pre‐established criteria and tests. Confirmation by these more sophisticated Davisian‐type numerical models of slope lowering under conditions of tectonic stability (no active rock uplift), and of constant slope angle and steady‐state landscape under conditions of ongoing rock uplift, will indicate that the Davis and Hack models are not mutually exclusive. A Hack‐type model (or a variant of it, incorporating slope adjustment to rock strength rather than to regolith strength) will apply to active settings where there is sufficient stream power and/or sediment flux for channels to incise at the rate of rock uplift. Post‐orogenic settings of decreased (or zero) active rock uplift would be characterized by a Davisian scheme of declining slope angles and non‐steady‐state (or transient) landscapes. Such post‐orogenic landscapes deserve much more attention than they have received of late, not least because the intriguing questions they pose about the preservation of ancient landscapes were hinted at in passing in the 1960s and have recently re‐surfaced. As we begin to ask again some of the grand questions that lay at the heart of geomorphology in its earliest days, large‐scale geomorphology is on the threshold of another ‘golden’ era to match that of the first half of the 20th century, when cyclical approaches underpinned virtually all geomorphological work. Copyright © 2007 John Wiley & Sons, Ltd.     

社会信息化、经济全球化与世界地理研究的全息景观化—以韩国地理的全息景观研究为例

知识经济与传统的农业经济和工业经济显著不同，由它推动着的社会信息化及经济全球化所带来的地理发展效应，无论是在发展因素的加入上，还是在地域的建造上都愈来愈向着全息化的方向发展。与之相应，世界地理的研究范式，也应该向着更为开放、更为兼容化的方向改进。为此笔者提出全息景观论，并以韩国为例，以展示这种理论的科学解释价值。     

Image resolution and evaluation of genetic hypotheses for planetary landscapes

The spatial resolution of image data tends to constrain the horizontal length scale of genetic hypotheses that are addressable by those data. No ‘simple’ formula exists when image resolution is sufficient to test a given geomorphic process, which is dependent on what characteristics are diagnostic of the particular process. Genetic hypotheses should be formulated along the lines of the “multiple working hypotheses” concept as described in a classic paper by Chamberlin [J. Geol. 5 (1897) 837]. An essential element of a viable working hypothesis is a clear indication of the characteristics predicted by, or a consequence of, the hypothesis. An untestable hypothesis is not an effective working hypothesis. The history of the study of lunar sinuous rilles is outlined as an illustration of the influence of image resolution and the formulation of genetic hypotheses on the subsequent advancement of understanding of the problem. Sinuous rilles on Venus and Mars, and controversial sinuous ridges on Mars are also reviewed. In the lunar case, the three-order-of-magnitude improvement in spatial resolution provided by Lunar Orbiter photographs over Earth-based telescopic photographs did not result in definitive examination and elimination of published hypotheses for the formation of sinuous rilles. Topographic data obtained from cartographically controlled Apollo orbital photographs, along with important observations and samples obtained by the astronauts on the lunar surface, did test and exclude several hypotheses. The formulation of a genetic hypothesis, including testable consequences of that hypothesis, is a greater determinant of its ultimate utility to the scientific community than is the image resolution available at any given time.     

天山北坡前山带景观分布特征的遥感研究

在前人研究前山带的基础上，借助地理信息系统技术与遥感图像处理技术，结合野外实地考察和遥感影像数据，论述了天山北坡前山带的形成，同时从遥感影像上定量分析了前山带构造带的分布规模和分布特征，阐述了前山带各类各类景观单元对区域气候气候河川径流，绿洲发展，土地利用和土地覆被以及生态环境等综合影响。     

广州市社会空间景观形态演化初探

相对于形体空间而言 ,社会空间是一个更深层面的城市空间领域 ,在城市形体空间日新月异的嬗变中 ,社会空间内涵的演化显得更为缓慢和深刻。以广州市为例 ,探讨这种景观形态演化的特性及其对现代城市形象建设和个性塑造的意义。     

Sandy desertification trend in western Northeast China Plain in the past 10 years

The west sandy land of the Northeast China Plain is located in the eastern huge sandy belt of mid-latitude in Eurasia and the eastern fringe of desertified land with best bio-climatic conditions in China. Over-extensive regional development has made the desertified landscape very obvious, especially in Horqin Sandy Land where desertification is more serious than that in Hushandake Sandy Land with worse bio-climatic conditions. There were some researches on the desertification in western No…     

On Invisible Trade Relations between Mesopotamian Cities during the Third Millennium B.C.

The idea that the emergence of writing was necessity due to the increase in both the number of economic transactions and political complexity has been recently emphasized by Matthews, who also underlines that writing acted as a feedback in enabling and encouraging the growth of ever more complex modes of exchange. The intertwinement of trade and writing suggests that clay tablets left by the civilizations from the third millennium B.C. in Mesopotamia, where writing was invented, may be considered as traces of trade links and transactions between cities. We estimate a gravity model based on clay tablets, as if they represented trade flows. The parameters lead us to conclude that Mesopotamia formed a strongly integrated market.     

生态旅游胜地—九顶山

对九顶山的生物景观，水体景观，地质遗迹景观，天然气景观和人文景观等方面进行了详尽的描述，并划分出平水河景区，云湖景区，楠木沟景区，紫岩山景区，白云山景区，仙女洞景区和天池景区等七个景区，从科学性，美学性，文化性以及区位条件和功能方面对景观进行了评述。进而提出了开发的初步构想。     

火山地区二维自然电位异常反演

将线性反演理论与正则化法相结合，提出一个火山地区二维自然电位（ＳＰ）异常反演方法．地下岩浆活动（对流体）是引起自电异常的极化源，反演的目的是计算地下视极化强度分布和极化源中心位置．可以通过用已知的各种资料改变地下极化源区域（简称源区）的方式来进行多次反演，以便获得一个比较合理的地下视极化强度分布模型．最后，分别给出意大利和墨西哥的两个火山地区的自然电位异常分析结果．     

Pyroclastic flows and surges over water: an example from the 1883 Krakatau eruption

Pyroclastic deposits from the 1883 eruption of Krakatau are described from areas northeast of the volcano on the islands of Sebesi, Sebuku, and Lagoendi, and the southeast coast of Sumatra. Massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km. Granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the Krakatau islands. The distal deposits exhibit a decrease in sorting coefficient, median grain size, and thickness with increasing distance from Krakatau. Crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards. The deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 August at approximately 10 a.m. Energetic flows spread out away from the volcano at speeds in excess of 100 km/h and traveled up to 80 km from source. The flows retained temperatures high enough to burn victims on the SW coast of Sumatra. Historical accounts from ships in the Sunda Straits constrain the area affected by the flows to a minimum of 4x10³ km². At the distal edge of this area the flows were relatively dilute and turbulent, yet carried enough material to deposit several tens of centimeters of tephra. The great mobility of the Krakatau flows from the 10 a.m. activity may be the result of enhanced runout over the sea. It is proposed that the generation of steam at the flow/seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective. The buoyant distal edge of these ash-and steam-laden clouds lifted off into the atmosphere, leading to cooling, condensation, and mud rain.