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River Incision (river + incision)
Selected AbstractsSlope development reconstruction at two sites in the Bohemian Forest MountainsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2010Filip Hartvich Abstract Although the Bohemian Forest is generally considered to be geomorphologically a rather stable region, there are localities which bear proof of a surprisingly high intensity of recent and even present day processes. A multidisciplinary methodology based on the analysis of slope systems was used for researching the present and past dynamics of two hillslopes. Using the results of direct dilatometric monitoring (the slow creep of rock blocks reached a maximum of 1,mm year,1), GPS field mapping, sedimentology, geodetic measurements and DEM analyses, several common rules have been observed for the behaviour of two model localities and a likely polycyclic development established, with recurrence of mass-wasting cycles related to material supply thresholds. Radiometric dating of debris flow activity showed that the cycles span approximately 4000 years. In this area of rather stable bedrock conditions, at least two factors that decrease slope stability need to act together to activate slope processes: i.e. a favourable structural predisposition (dip of major joint or bedding planes) and an increase in relief through either glaciation or river incision. Copyright © 2010 John Wiley & Sons, Ltd. [source] Amount and controls of the quaternary denudation in the Ardennes massif (western Europe)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2009A. Demoulin Abstract It is still debated whether the primary control on the middle Pleistocene denudation of the uplifted Ardennes massif (western Europe) is tectonic or climatic. Here, based on geomorphological observations, we calculate the amount of river incision and interfluve denudation in the Meuse basin upstream of Maastricht since 0·7 Ma and we show that the main response to tectonic forcing was incision. This allows us to provide first-order estimates of the tectonic and climatic contributions to the denudation of the Ardennes. From a dataset of 71 remnants of a terrace level dated ,0·7 Ma, we first derive a basin-scale functional relationship linking incision with distances to the regional base level (Lc) and to the source (Ls) in the Ourthe basin (pertaining to the Ardennian part of the Meuse basin). Expressed as I = I0*(1 , a*Lcb/Lsc), I0 being the incision measured at the basin outlet, this relationship calculates that river incision has removed 84 km3 of rock in the Meuse basin upstream of Maastricht since 0·7 Ma. In the same time, 292 km3 were eroded from the interfluves. A comparison of these volumes shows that the tectonically forced river incision accounts for ,22% of the total post-0·7 Ma denudation. Furthermore, the mean denudation rate corresponding to our geomorphological estimate of the overall denudation in the Meuse basin since 0·7 Ma amounts to 27 mm/ky, a figure significantly lower than the ,40 mm/ky mean rate derived from 10Be studies of terrace deposits of the Meuse (Schaller et al., 2004). This suggests that, taken as a basin average, the 10Be-derived rate is overestimated, probably due to an overrepresentation of the erosion products of the rapidly incising valleys in the alluvial deposits. Copyright © 2009 John Wiley & Sons, Ltd. [source] Tectonics and quaternary evolution of the Northern Apennines watershed area (upper course of Arno and Tiber rivers, Italy)GEOLOGICAL JOURNAL, Issue 1 2009Marco Bonini Abstract This work examines the connection between Quaternary tectonics and erosion/incision processes in the primary Tuscan-Romagna watershed of the Northern Apennines, which essentially coincides with the topographic culmination of the Nero Unit structural ridge. Tectonic and geomorphic information were collected in the area where this ridge is crossed by the upper Tiber River course forming a deep gorge. Structural analysis and field mapping have revealed that the region experienced polyphase tectonics with superposed thrust folding events identifiable both at the map and mesoscopic scales. Hinterland-SSW-verging thrusts and thrust-related folds deformed the whole thrust pile during the latest deformation phase. Backthrusts/backfolds controlled the development of intermountain basins nearby the main watershed during the Early Pleistocene and seemingly deformed, in the Tiber gorge, a low-relief landscape developed in the Early Pleistocene (ca. 1.1,Ma). Successively, the upper Tiber River course area and Apennines axial zone underwent a generalized uplift, which is manifested by the deep incision of palaeo-morphologies. This proposed sequence of events correlates well with the major geodynamic change of the Apennines revealed by an acceleration of uplift rates in the Middle,Late Pleistocene. This latter event may also correlate with increased rates of river incision recorded in Europe as a consequence of uplift and/or climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source] Miocene to Recent exhumation of the central Himalaya determined from combined detrital zircon fission-track and U/Pb analysis of Siwalik sediments, western NepalBASIN RESEARCH, Issue 4 2006Matthias Bernet ABSTRACT Fission-track (FT) analysis of detrital zircon from synorogenic sediment is a well-established tool to examine the cooling and exhumation history of convergent mountain belts, but has so far not been used to determine the long-term evolution of the central Himalaya. This study presents FT analysis of detrital zircon from 22 sandstone and modern sediment samples that were collected along three stratigraphic sections within the Miocene to Pliocene Siwalik Group, and from modern rivers, in western and central Nepal. The results provide evidence for widespread cooling in the Nepalese Himalaya at about 16.0±1.4 Ma, and continuous exhumation at a rate of about 1.4±0.2 km Myr,1 thereafter. The ,16 Ma cooling is likely related to a combination of tectonic and erosional activity, including movement on the Main Central thrust and Southern Tibetan Detachment system, as well as emplacement of the Ramgarh thrust on Lesser Himalayan sedimentary and meta-sedimentary units. The continuous exhumation signal following the ,16 Ma cooling event is seen in connection with ongoing tectonic uplift, river incision and erosion of lower Lesser Himalayan rocks exposed below the MCT and Higher Himalayan rocks in the hanging wall of the MCT, controlled by orographic precipitation and crustal extrusion. Provenance analysis, to distinguish between Higher Himalayan and Lesser Himalayan zircon sources, is based on double dating of individual zircons with the FT and U/Pb methods. Zircons with pre-Himalayan FT cooling ages may be derived from either nonmetamorphic parts of the Tethyan sedimentary succession or Higher Himalayan protolith that formerly covered the Dadeldhura and Ramgarh thrust sheets, but that have been removed by erosion. Both the Higher and Lesser Himalaya appear to be sources for the zircons that record either ,16 Ma cooling or the continuous exhumation afterwards. [source] Investigating the surface process response to fault interaction and linkage using a numerical modelling approachBASIN RESEARCH, Issue 3 2006P.A. Cowie ABSTRACT In order to better understand the evolution of rift-related topography and sedimentation, we present the results of a numerical modelling study in which elevation changes generated by extensional fault propagation, interaction and linkage are used to drive a landscape evolution model. Drainage network development, landsliding and sediment accumulation in response to faulting are calculated using CASCADE, a numerical model developed by Braun and Sambridge, and the results are compared with field examples. We first show theoretically how the ,fluvial length scale', Lf, in the fluvial incision algorithm can be related to the erodibility of the substrate and can be varied to mimic a range of river behaviour between detachment-limited (DL) and transport-limited (TL) end-member models for river incision. We also present new hydraulic geometry data from an extensional setting which show that channel width does not scale with drainage area where a channel incises through an area of active footwall uplift. We include this information in the coupled model, initially for a single value of Lf, and use it to demonstrate how fault interaction controls the location of the main drainage divide and thus the size of the footwall catchments that develop along an evolving basin-bounding normal fault. We show how erosion by landsliding and fluvial incision varies as the footwall area grows and quantify the volume, source area, and timing of sediment input to the hanging-wall basin through time. We also demonstrate how fault growth imposes a geometrical control on the scaling of river discharge with downstream distance within the footwall catchments, thus influencing the incision rate of rivers that drain into the hanging-wall basin. Whether these rivers continue to flow into the basin after the basin-bounding fault becomes fully linked strongly depends on the value of Lf. We show that such rivers are more likely to maintain their course if they are close to the TL end member (small Lf); as a river becomes progressively more under supplied, i.e. the DL end member (large Lf), it is more likely to be deflected or dammed by the growing fault. These model results are compared quantitatively with real drainage networks from mainland Greece, the Italian Apennines and eastern California. Finally, we infer the calibre of sediments entering the hanging-wall basin by integrating measurements of erosion rate across the growing footwall with the variation in surface processes in space and time. Combining this information with the observed structural control of sediment entry points into individual hanging-wall depocentres we develop a greater understanding of facies changes associated with the rift-initiation to rift-climax transition previously recognised in syn-rift stratigraphy. [source] Drainage patterns and tectonic forcing: a model study for the Swiss AlpsBASIN RESEARCH, Issue 2 2001A. Kühni ABSTRACT A linear surface process model is used to examine the effect of different patterns of rock uplift on the evolution of the drainage network of the Swiss Alps. An asymmetric pattern of tectonic forcing simulates a phase of rapid retrothrusting in the south of the Swiss Alps (,Lepontine'-type uplift). A domal pattern of tectonic forcing in the north of the model orogen simulates the phase of the formation of the ,Aar massif', an external basement uplift in the frontal part of the orogenic wedge (,Aar'-type uplift). Model runs using the ,Lepontine'-type uplift pattern result in a model mountain chain with a water divide in the zone of maximum uplift and orogen-normal rivers. Model runs examining the effect of ,Lepontine'-type uplift followed by ,Aar'-type uplift show that the initially formed orogen-normal river system and the water divide are both very stable and hardly affected by the additional uplift. This indifference to changes in tectonic forcing is mainly due to the requirement of a high model erosion capacity for the river systems in order to reproduce the exhumation data (high-grade rocks in the south of the Swiss Alps point to removal of a wedge-shaped nappe stack with a maximum thickness of about 25 km). The model behaviour is in agreement with the ancestral drainage pattern of the Alps in Oligocene and Miocene times and with the modern pattern observed in the Coast Range of British Columbia; in both cases river incision occurred across a zone of rapid uplift in the lower course of the rivers. The model behaviour does not, however, explain the modern drainage pattern in the Alps with its orogen-parallel rivers. When the model system is forced to develop two locally independent main water divides (simultaneous ,Lepontine'- and ,Aar'-type uplift), a zone of reduced erosional potential forms between the two divides. As a consequence, the divides approach each other and eventually merge. The new water divide remains fixed in space independent of the two persisting uplift maxima. The model results suggest that spatial and temporal changes in tectonic forcing alone cannot produce the change from the orogen-normal drainage pattern of the Swiss Alps in Oligocene,Miocene times to the orogen-parallel drainage observed in the Swiss Alps today. [source] Distribution and Forming Model of Fluvial Terrace in the Huangshui Catchment and its Tectonic IndicationACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2010Xianyan WANG Abstract: The Huang Shui River, a main tributary of the Yellow River, crosses a series of tectonically subsided and uplifted areas that show different patterns of terrace formation. The distribution of fluvial terrace of the Huang Shui River is studied through topographic and sedimentologic terrace mapping. Three terraces in the Haiyan Basin, four terraces in the Huangyuan Basin, 19 terraces in the Xi'ning Basin (the four high terraces may belong to another river), nine terraces in the Ping'an Basin, five terraces in the Ledu Basin and 12 terraces in the Minhe Basin are recognized. Sedimentology research shows that the geomorphologic and sedimentological pattern of the Huang Shui River, which is located at the margin of Tibet, are different from that of the rivers at other regions. The formation process of the terrace is more complicated at the Huang Shui catchment: both accumulation terrace and erosion terrace were formed in each basin and accumulation terraces were developed in some basins when erosion terraces were formed in other basins, indicating fluvial aggradation may occur in some basins simultaneously with river incision in other basins. A conceptual model of the formation process of these two kinds of fluvial terraces at Huang Shui catchment is brought forward in this paper. First, the equilibrium state of the river is broken because of climatic change and/or tectonic movement, and the river incises in all basins in the whole catchment until reaching a new equilibrium state. Then, the downstream basin subsides quickly and the equilibrium state is broken again, and the river incises at upstream basins while the river accumulates at the subsidence basin quickly until approaching a new equilibrium state again. Finally, the river incises in the whole catchment because of climatic change and/or tectonic movement and the accumulation terrace is formed at the subsidence basin while the erosion terrace is formed at other basins. The existence of the accumulation terrace implied the tectonic subsidence in the sub-basins in Huang Shui catchment. These tectonic subsidence movements gradually developed from the downstream Minhe Basin to the upstream Huangyuan Basin. Dating the terrace sequence has potential to uncover the relationship between the subsidence in the catchment and the regional tectonic at the northeastern Tibetan Plateau. [source] | ||||||||||