Contrasting geomorphic response to structural control: The Loughros estuaries, northwest Ireland

Sediment-rich estuaries typically exhibit considerable dynamicity, with channel shifts and shoreline erosion/deposition occurring over timescales of years to decades. Contemporary behaviour is usually attributed to the immediate effect of short-term events (such as storms), longer-term forcing (such as sea-level change) or anthropogenic modifications to system controls (such as wave–tidal–fluvial regime and sediment supply). In this context, geological control is understood to provide an inherited framework within which an estuary will evolve. This paper examines the morphodynamics of two sand-filled, but sediment-limited, mixed-energy estuaries of Loughros Bay in northwest Ireland. Analysis of ebb channel morphometry shows that estuaries can be divided into upper and lower estuary components, which appear to represent a down-valley increasing energy gradient. Examination of historical ebb channel migration reveals three morphodynamic zones delimited by a significant spatial variability in channel mobility that reflects the distribution of specific structural controls along the estuary and their influence on the changing energy gradient. Based upon analysis of low tide channel migration over the last 172 years, three phases of geomorphic response are identified. In Loughros More, the behaviour is characterised by a 19th century phase of steady-state equilibrium; a subsequent period of dynamic response to extrinsic (storm) forcing; and, most recently, adjustment to intrinsically forced changes in structural control. In Loughros Beg, the phases are comparable, but contrast specifically in inlet and ebb-tidal behaviour. This analysis illustrates discontinuities in decadal- to century-scale forcing and morphological response, identified here as complex response. It suggests that the sedimentary evolution of coastal systems that have no appreciable external sediment supply is potentially more strongly determined by local variability in system character than climate or sea-level driven mechanisms.     

Development and decay of a lithalsa in Northern Québec: A geomorphological history

The complete life cycle of a permafrost mound is reconstructed from its growth until its degradation. The study site is a lithalsa, which is the subject of a long-term monitoring that includes geocryological observations, measurements of permafrost properties on cores, ground temperature measurements, and observations of landform changes. The landform likely grew as a palsa under cold climatic conditions in the past. The peat cover was subsequently eroded. Early stages of degradation are witnessed since 2003 as a new thermokarst pond is starting to form though mound collapse. Settlement of the structure has been observed, and a rim ridge has begun to form. Ultimately, the lithalsa shall disappear and be replaced by a circular thermokarst pond surrounded by a rampart, similar to many other ones in the study area. The monitoring of the thermal regime of the lithalsa illustrates the pattern of internal warming and points to the causes of its degradation.     

Landform classification from a digital elevation model and satellite imagery

The Iranian Soil and Water Research Institute has been involved in mapping the soils of Iran and classifying landforms for the last 60 years. However, the accuracy of traditional landform maps is very low (about 55%). To date, aerial photographs and topographic maps have been used for landform classification studies. The principal objective of this research is to propose a quantitative approach for landform classification based on a 10-m resolution digital elevation model (DEM) and some use of an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image. In order to extract and identify the various landforms, slope, elevation range, and stream network pattern were used as basic identifying parameters. These are extractable from a DEM. Further, ASTER images were required to identify the general outline shape of a landform type and the presence or absence of gravel. This study encompassed a relatively large watershed of 451 183 ha with a total elevation difference of 2445 m and a variety of landforms from flat River Alluvial Plains to steep mountains. Classification accuracy ranged from 91.8 to 99.6% with an average of 96.7% based upon extensive ground-truthing. Since similar digital and ASTER image information is available for Iran, an accurate landform map can now be produced for the whole country. The main advantages of this approach are accuracy, lower demands on time and funds for field work and ready availability of required data for many regions of the world.     

龙虎山世界地质公园丹霞地貌特征及与国内其他丹霞地貌的对比

江西龙虎山世界地质公园丹霞地貌景观发育于信江盆地中生代红层中,以发育老年早期孤峰、峰林、残丘类地貌景观为特征,是我国丹霞地貌发育最好的地区之一。断裂切割、岩性差异、流水侵蚀和重力崩塌作用,是造成丹霞地貌景观差异的主要原因,同时由于所处盆地内位置、出露的红层性质以及构造发育特征的不同,也影响地貌发育的特色。目前国内所发现的丹霞地貌主要分布于东南、西南和西北地区。由于它们所处的大地构造位置、地壳活动特征、自然地理条件的不同,丹霞地貌的成因机制也不相同。阐述了龙虎山世界地质公园丹霞地貌景观类型及其特色,并着重研究丹霞地貌景观的成因机制,以及与其他地质公园、遗产地进行比较研究。     

鄂尔多斯盆地北部深埋区“地貌—沉积”控水关键要素研究

鄂尔多斯盆地北部深埋煤田区地表主要有沙漠、基岩台地和黄土沟壑等地貌类型,沙漠区工作面涌水量比其他地貌区大1~2个数量级。为了查清煤层顶板直接充水含水层补给水源、导水通道和充水强度的控制要素,从地形地貌和地质沉积方面开展了研究,结果表明:沙漠地貌地势平缓,降水入渗系数大,第四系厚度大、富水性强,为下伏含水层提供了丰富的补给水源;基岩台地和黄土沟壑地貌,地形起伏大,降水入渗系数极小,浅部地层富水性极弱,是下伏含水层补给能力较弱的水源。陆相沉积形成的砂泥岩互层结构,不存在区域性稳定隔水层,各层段均属于弱-中等富水性含水层,3个矿井的白垩系含水层水位下降了20~130 m,证明浅部与深部含水层存在较密切的水力联系。煤层顶板主要发育七里镇砂岩和真武洞砂岩含水层,为厚度较大的中粗砂岩段,直接充水含水层地质沉积条件相似,但是沙漠区工作面顶板钻孔水量、累计预疏放水量和采空区涌水量均远大于其他地貌区,直接充水含水层富水性主要受地貌控制,深部含水层的水源为大气降水和第四系含水层。沙漠地貌区的不同矿井,工作面顶板钻孔水量、累计预疏放水量、采空区涌水量也存在较大差异,该差异与直接充水含水层厚度和岩性等有关,反映了地质沉积条件也是控制含水层富水性的重要因素。地形地貌和地质沉积是控制直接充水含水层富水性和工作面涌水量的关键要素。     

以综合思维引领丹霞地貌与旅游地理研究创新——彭华先生的地理学思想与学术贡献

彭华先生长期从事丹霞地貌和旅游地理研究,为中国丹霞事业和旅游发展做出了突出贡献,是“把论文写在祖国大地上”的科学家的典范。作为中国丹霞地貌研究国际化阶段的代表人物,彭华先生在丹霞地貌分类系统、丹霞地貌发育过程、国内外红层分布及其地貌发育的对比等方面开展了系列研究,同时,针对中国南方湿润环境下红层区严重的地貌灾害和荒漠化问题,用跨学科的思维和方法,开展了红层区地质构造—岩石特性—地貌发育—自然灾害—水土流失—生态退化—综合景观—社会经济发展之间相互关系的综合地理学研究实践,将原来的红层地表研究拓展为“地下+地表+地上”（红层的地质问题+地貌与土地问题+生态问题）的一体化研究,为丹霞地貌的未来研究指明了方向。彭华先生在旅游开发实践中不断总结新思想、新方法和新理论,在旅游地开发、旅游文化、城市旅游、区域旅游发展和旅游规划理论研究方面取得了大量成果,所提出的“大旅游”理念在学界有重要影响。在“大旅游”理念基础上提出的旅游系统及动力机制、旅游地发展阶段论、旅游开发与城市建设一体化、市场分类研究法、产品—需求对应分析法等理论,创新意义显著。彭华先生的学术研究典型体现了地理学的综合性思维和系统性思维。     

基于地表形态信息系统的岩溶生态环境的分析

本文基于地表形态信息系统对贵州省的岩溶生态环境的复杂性和多样性以及其脆弱性和生态被破坏的严重性进行了较系统的分析。最后就其生态环境的保护 ,提出了若干对策措施.     

山东临朐、昌乐地区晚第三纪火山地貌

山东临朐、昌乐地区是渤海盆地南缘,郯庐断裂带中段西侧晚第三纪火山地貌集中分布的地区之一。本文对区内火山地貌类型和地貌发育过程作了重点探讨。     

白龙江流域第三纪古喀斯特地貌的发现及其意义

笔者在白龙江流域的地貌考察中,首次发现了位于海拔2,000m以上的地区发育有古喀斯特地貌,并可分为三层,分别位于海拔2,200m、2,600m和3,000m的高度,可与区内广泛存在的三级夷平面对比。本文为近年来有关青藏高原古喀斯特发育问题争论提供了一个新的证据。     

Cosmogenic Be and Al exposure ages of tors and erratics, Cairngorm Mountains, Scotland: Timescales for the development of a classic landscape of selective linear glacial erosion

The occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre-Quaternary landscapes beneath protective covers of non-erosive dry-based ice. Here, we test for the preservation of pre-Quaternary landscapes with cosmogenic surface exposure dating of tors. Numerous granite tors are present on summit plateaus in the Cairngorm Mountains of Scotland where they were covered by local ice caps many times during the Pleistocene. Cosmogenic ¹⁰Be and ²⁶Al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected. Many Cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion, leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides. As the surfaces have been subject to episodic burial by ice, an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data. Exposure ages and weathering characteristics of tors are closely correlated. Glacially modified tors and boulder erratics with slightly weathered surfaces have ¹⁰Be exposure ages of about 15 to 43 ka. Nuclide inheritance is present in many of these surfaces. Correction for inheritance indicates that the eastern Cairngorms were deglaciated at 15.6 ± 0.9 ka. Glacially modified tors with moderate to advanced weathering features have ¹⁰Be exposure ages of 19 to 92 ka. These surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine Oxygen Isotope Stage 5 or earlier. Tors lacking evidence of glacial modification and exhibiting advanced weathering have ¹⁰Be exposure ages between 52 and 297 ka. Nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events. Maximum erosion rates estimated from ¹⁰Be range from 2.8 to 12.0 mm/ka, with an error weighted mean of 4.1 ± 0.2 mm/ka. Three of these surfaces yield model exposure-plus-burial ages of 295_− 71^+ 84, 520_− 141^+ 178, and 626_− 85^+ 102 ka. A vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long-term emergence rate of 31 ± 2 mm/ka. These findings show that dry-based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes. Bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous (too old) exposure ages. While many Cairngorm tors have survived multiple glacial cycles, rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre-Quaternary rock surfaces.