Landscape Evolution Studies Research Articles

Geomorphological of a portion of the Andes and Pre-Andes of San Juan, Argentina

A detailed geomorphological map is presented for a portion of a poorly investigated mountainous region of the Dry Frontal Andes and Western Pre-Andes of San Juan province around 30°S latitude. This map shows the presence and extension of landforms and geomorphic processes in an area of 2175.9 km2 and is the result of detailed aerial photograph and remotely sensed data interpretation, including digital elevation models, supported by field survey. The landforms have been distinguished according to morphogenetic criteria, into: (i) glacial landforms; (ii) periglacial landforms; (iii) mass movement landforms; (iv) fluvial landforms: (v) polygenic landforms and (vi) neotectonic landforms. The objective of this map is to provide information on the landforms present in the selected area, allowing it to be used as a baseline for the study of landscape evolution or support guidelines for territorial management and planning.

Characteristics of landslides in western Colorado, USA

Mass movement can be activated by earthquakes, rapid snowmelt, or intense rainstorms in conjunction with gravity. Whereas mass movement plays a major role in the evolution of a hillslope by modifying slope morphology and transporting material from the slope to the valley, it is also a potential natural hazard. Determining the relationships of frequency and magnitude of landslides are fundamental to understanding the role of landslides in the study of landscape evolution, hazard assessment, and determination of the rate of hillslope denudation. We mapped 735 shallow and active landslides in the Paonia to McClure Pass area of western Colorado from aerial photographs and field surveys. The study area covers ∼815 km2. The frequency–magnitude relationships of the landslides illustrate the flux of debris by mass movement in the area. The comparison of the probability density of the landslides with the double Pareto curve, defined by power scaling for negative slope (α), power scaling for positive slope (β), and location of rollover (t), shows that α = 1.1, β = 1.9, and t = 1,600 m2 for areas of landslides and α = 1.15, β = 1.8, and t = 1,900 m3 for volumes of landslides. The total area of landslides is 4.8 × 106 m2 and the total volume of the landslides is 1.4 × 107 m3. The areas (A) and the volumes (V) of landslides are related by V = 0.0254 × A 1.45. The frequency–magnitude analysis shows that landslides with areas ranging in size from 1,600 to 20,000 m2 are the most hazardous landslides in the study area. These landslides are the most frequent and also do a significant amount of geomorphic work. We also developed a conceptual model of hillslope development to upland plateau driven by river incision, shallow landsliding, and deep-seated large landsliding. The gentle slope to flat upland plateau that dominated the Quaternary landscape of the study area was modified to the present steep and rugged topography by the combined action of fluvial incision and glacial processes in response to rock uplift, very-frequent shallow landsliding, and less-frequent deep-seated landsliding.

Amplitude Change Detection with ENVISAT ASAR to Image the Cultural Landscape of the Nasca Region, Peru

ABSTRACTSynthetic aperture radar (SAR) amplitude information from ENVISAT C‐band advanced SAR (ASAR) data was used to analyse the cultural landscape of the Nasca region, southern Peru. A multispatial environmental analysis was performed over the whole drainage basin of the Rio Grande, by extracting the radar backscattering coefficient (σ0) of both natural and anthropogenic features between 2003 and 2005. Co‐registration of the ASAR scenes to a single master resulted in precisions of less than 0.1 pixels along both the range and azimuth directions. Four different products were generated based on the co‐registered ASAR stack: (i) temporally averaged radar signatures of the targets between 2003 and 2005; (ii) time series of spatially averaged radar signatures within selected areas of interest; (iii) amplitude change detection products based on (iii) image ratios and (iv) RGB colour composites between different scenes. Comparisons of annual and seasonal records through amplitude change detection maps highlighted σ0 changes over the floodplains of the Rio Ingenio and Rio Nazca, which correlate well with evidence from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data acquired in 2003, 2004 and 2007. Inferences about land use and soil conditions were retrieved from the σ0 change patterns, thereby proving the capability of this approach to support landscape evolution studies, even with SAR imagery of medium resolution (~30 m). Our results also demonstrated actual potential for monitoring mass movements and land surface processes, to assess the susceptibility of archaeological heritage and cultural landscape to natural hazards. Copyright © 2013 John Wiley & Sons, Ltd.

Landscape evolution and ice-sheet behaviour in a semi-arid polar environment: James Ross Island, NE Antarctic Peninsula

Abstract This study of landscape evolution presents both new modern and palaeo process-landform data, and analyses the behaviour of the Antarctic Peninsula Ice Sheet through the Last Glacial Maximum (LGM), the Holocene and to the present day. Six sediment-landform assemblages are described and interpreted for Ulu Peninsula, James Ross Island, NE Antarctic Peninsula: (1) the Glacier Ice and Snow Assemblage; (2) the Glacigenic Assemblage, which relates to LGM sediments and comprises both erratic-poor and erratic-rich drift, deposited by cold-based and wet-based ice and ice streams respectively; (3) the Boulder Train Assemblage, deposited during a Mid-Holocene glacier readvance; (4) the Ice-cored Moraine Assemblage, found in front of small cirque glaciers; (5) the Paraglacial Assemblage including scree, pebble-boulder lags, and littoral and fluvial processes; and (6) the Periglacial Assemblage including rock glaciers, protalus ramparts, blockfields, solifluction lobes and extensive patterned ground. The interplay between glacial, paraglacial and periglacial processes in this semi-arid polar environment is important in understanding polygenetic landforms. Crucially, cold-based ice was capable of sediment and landform genesis and modification. This landsystem model can aid the interpretation of past environments, but also provides new data to aid the reconstruction of the last ice sheet to overrun James Ross Island.

Far-flung moraines: Exploring the feedback of glacial erosion on the evolution of glacier length

Over many glacial cycles, the glacial erosion of alpine valleys can be sufficient to reduce the length of glaciers in the most recent cycles. We document field cases illustrative of this erosional feedback and model the long-term evolution of glacier lengths analytically and numerically. The general feature we target is a moraine deposited well beyond the last glacial maximum (LGM) limit, which we refer to as a “far-flung” moraine. Firstly, we assemble published observations to illustrate that far-flung moraines are documented around the world. The observations suggest that the downvalley distance to such far-flung moraines can exceed the distance to LGM moraines by up to twofold. Secondly, we address the problem analytically, making several simplifying assumptions, to demonstrate that glacier length scales linearly with erosion depth. Finally, we employ a numerical model to test the analytical solution. This 1D (depth-integrated) flowline model includes: (i) a depth-averaged longitudinal coupling stress approximation, (ii) prescribed winter and summer surface mass balance profiles, (iii) evolving ice temperature calculated via the conventional heat equation, and (iv) glacier sliding velocity parameterized as a function of basal ice temperature and spatially and temporally variable prescribed flotation fraction. The simulated alpine landscape is modified through the competing processes of glacier erosion, which is dependent on glacier sliding velocity and prescribed bedrock erodibility, and prescribed uplift rate. The climate controlling surface mass balance is prescribed by time series of air temperature and snowfall approximated by the sum of two sinusoidal cycles. The recurrence statistics of these prescribed climate drivers closely match those of the marine isotopic record; hence the prescribed climate drivers faithfully mimic observed long-term climate drivers.Consistent with earlier landscape evolution studies, we find that the primary effect of repeated glaciations is to flatten a valley floor and steepen its headwall, effectively cutting a longitudinal notch in a fluvial valley profile. Analytical and numerical model results also demonstrate that far-flung moraines are an inevitable consequence of repeated glaciations: glaciers in tectonically inactive regions can sufficiently erode their valleys so that the earliest glaciations leave moraines many kilometers down-valley from moraines left by the latest glaciations, despite similar climates. This suggests that a different landscape, rather than a different climate, is capable of explaining the early glacier extents. As a corollary, the long-term drift toward reduced glacier length favors the survival of early moraines in the face of later glacial advances. Finally, rock uplift can defeat this erosional feedback, while rock subsidence enhances the feedback.

Morphometric dating of the fluvial landscape response to a tectonic perturbation

Despite constant progress in numerical and field studies of landscape evolution, time evolution is still poorly constrained in many uplifted areas where low denudation rates prevent the use of low temperature thermochronology, especially outside high relief mountainous areas. Here, I show that regional statistics of the landscape metric R involving hypsometric integrals at three nested levels of a catchment are able to isolate the time effect on landscape geometry during the latter's transient response to a tectonic perturbation. Analysis of 210 catchments from 9 regions of known uplift age worldwide shows that the regionally characteristic, R‐derivedSRindex is in inverse power law relation with the time elapsed since a base level lowering. Suggesting a response time of ∼5 My, this finding has important implications for quantifying the rate of landform evolution and determining whether a landscape has reached steady‐state form.

Constraining long‐term denudation and faulting history in intraplate regions by multisystem thermochronology: An example of the Sudetic Marginal Fault (Bohemian Massif, central Europe)

The Rychlebské hory Mountain region in the Sudetes (NE Bohemian Massif) provides a natural laboratory for studies of postorogenic landscape evolution. This work reveals both the exhumation history of the region and the paleoactivity along the Sudetic Marginal Fault (SMF) using zircon (U‐Th)/He (ZHe), apatite fission track (AFT), and apatite (U‐Th)/He (AHe) dating of crystalline basement and postorogenic sedimentary samples. Most significantly, and in direct contradiction of traditional paleogeographic reconstructions, this work has found evidence of a large Cretaceous sea and regional burial (to >6.5 km) of the Carboniferous‐Permian basement in the Late Cretaceous (∼95–80 Ma). During the burial by sediments of the Bohemian Cretaceous Basin System, the SMF acted as a normal fault as documented by offset ZHe ages across the fault. At 85–70 Ma, the basin was inverted, Cretaceous strata eroded, and basement blocks were exhumed to the near surface at a rate of ∼300 m/Ma as evidenced by Late Cretaceous–Paleocene AFT ages and thermal modeling results. There is no appreciable difference in AFT and AHe ages across the fault, suggesting that the SMF acted as a reverse fault during exhumation. In the late Eocene–Oligocene, the basement was locally heated to <70°C by magmatic activity related to opening of the Eger rift system. Neogene or younger thermal activity was not recorded in the thermochronological data, confirming that late Cenozoic uplift and erosion of the basement blocks was limited to less than ∼1.5 km in the study area.

U and Pb variability in older speleothems and strategies for their chronology

Speleothem proxy records, coupled with U–Th chronologies, are widely used in studies of palaeoclimate, landscape and faunal evolution. The prospect of extending such studies beyond ∼500 ka has fuelled considerable interest in the U–Pb dating method. While theoretical mechanisms for the transport and incorporation of both U and Pb in speleothem calcite remains a matter of debate, it is clear that natural samples span a broad spectrum of compositional variation, and likely contain Pb components with multiple origins and/or transport pathways. Based upon these observations, optimal methods for sample selection are proposed and a variety of techniques for age estimation are explored. Laser ablation ICPMS and autoradiography are ideal rapid screening methods for reconnaissance studies. Common Pb isotopic variability is a key parameter in the choice of analytical strategy for age determination. In large U–Pb studies where invariant common Pb can be established, common Pb corrected ages can be produced for individual sample aliquots promoting rapid throughput and permitting the establishment of detailed age-depth models. Even with these technologies, however, age resolution becomes an issue beyond a few million years, at which time alternative strategies for developing internal speleothem chronologies, such as lamina counting, must be considered in unison with U–Pb dating.

Reconstruction of the Landeskrone Scoria Cone in the Lusatian Volcanic Field, Eastern Germany — Long-term degradation of volcanic edifices and implications for landscape evolution

Remnants of numerous monogenetic volcanoes are preserved in the Central European Volcanic Province (CEVP). The Landeskrone Hill, a monogenetic scoria cone in the Lusatian Volcanic Field, is reconstructed here. This was done using measurements of the dip of columnar jointing of lava lake basalts and the detailed mapping of the volcaniclastic rocks. The reconstruction implies a large scoria cone and a lava lake; filling the crater with a thickness of more than 110m. Volcanic activity was characterized by strombolian eruptions possibly after an opening phreatomagmatic phase. A scoria cone was developed in an initial maar-diatreme volcano. A late phreatomagmatic phase could explain the unusual modified crater of the scoria cone. The conduit was emptied and so the crater was widened in this late eruption stage. An increased magma flux probably induced a change in the eruptive style and, finally, the crater was filled in a single event by a lava lake. This effusive phase completed the multi-stage volcano development.The 34Ma-old volcano is an excellent example for the persistence of relicts of monogenetic volcanoes over a long period of time. There are some other remnants of monogenetic scoria cones that survived degradation processes in the area. With respect to the present surface, the reconstruction of the paleosurface implies low uplift and erosion rates of about 3mm/ka since the Oligocene. These denudation values support and expand on the previously published fission track data (prior to the Upper Cretaceous) and glacial-sedimentological data on neotectonic movements since the Middle Pleistocene. The erosion rate estimated by physical volcanological data implies stagnation of tectonic uplift from the Upper Paleogene to the Middle Neogene and a reactivation of tectonic movement for the Lusatian Massif in the Middle Pleistocene. Thus, the reconstructed edifice provides a powerful tool for the study of landscape evolution by clearly defining the characteristics of the paleosurfaces at certain times.

A physical model for seismic noise generation from sediment transport in rivers

Measuring sediment flux in rivers remains a significant problem in studies of landscape evolution. Recent studies suggest that observations of seismic noise near rivers can help provide such measurements, but the lack of models linking observed seismic quantities to sediment flux has prevented the method from being used. Here, we develop a forward model to describe the seismic noise induced by the transport of sediment in rivers. The model provides an expression for the power spectral density (PSD) of the Rayleigh waves generated by impulsive impacts from saltating particles which scales linearly with the number of particles of a given size and the square of the linear momentum. After incorporating expressions for the impact velocity and rate of impacts for fluvially transported sediment, we observe that the seismic noise PSD is strongly dependent on the sediment size, such that good constraints on grain size distribution are needed for reliable estimates of sediment flux based on seismic noise observations. The model predictions for the PSD are consistent with recent measurements and, based on these data, a first attempt at inverting seismic noise for the sediment flux is provided.

Lithological and seasonal control on rainfall thresholds for the possible initiation of landslides in central Italy

We compiled a catalogue of 442 rainfall events with landslides in the Abruzzo, Marche, and Umbria regions, central Italy, between February 2002 and August 2010. For each event, we determined the duration D (in hours) and the cumulated (total) event rainfall E (in mm), using rainfall measurements obtained from a dense network of 150 rain gauges. Landslides were mapped as single points using Google Earth®, and were attributed a level of mapping accuracy P, in four classes ( P 1 < 1 km 2, P 10 < 10 km 2, P 100 < 100 km 2, P 300 < 300 km 2). Using this information, we determined cumulated event rainfall–rainfall duration ( ED) thresholds, which are entirely equivalent to rainfall intensity–duration ( ID) thresholds, and avoid unnecessary conversions. To determine the ED thresholds, we modified a statistical method first proposed to determine ID thresholds. Adopting a bootstrapping statistical technique, we expanded the method to determine the uncertainty associated with the parameters that define the power law threshold model, and the sensitivity of the thresholds to the number of ( D, E) data points in the empirical data set. We determined ED thresholds for 1% and 5% exceedance probability levels: (i) for the entire study area, and for the three individual regions in the study area (Abruzzo, Marche, and Umbria); (ii) for three main lithological domains in the study area (post-orogenic sediments, flysch deposits, carbonate rocks); and (iii) for two seasonal periods (May–September, October–April). Comparison of the ED thresholds indicates that the cumulated amount of rainfall necessary to trigger landslides in flysch deposits is larger than in post-orogenic sediments and carbonate rocks. However, the ED thresholds for post-orogenic sediments and carbonate rocks were statistically indistinguishable in the study area. Also, the seasonal thresholds were statistically different for rainfall durations shorter than 12 h and longer than 100 h, but were indistinguishable in the range 12 < D < 100 h. The results obtained are directly applicable to landslide forecasting based on empirical rainfall thresholds, and have implications for landslide hazard and risk assessment, as well as for landslide erosion and landscape evolution studies, both in the study area and in the neighboring regions.

Multitemporal ALSM change detection, sediment delivery, and process mapping at an active earthflow

ABSTRACTRemote mapping and measurement of surface processes at high spatial resolution is among the frontiers in Earth surface process research. Remote measurements that allow meter‐scale mapping of landforms and quantification of landscape change can revolutionize the study of landscape evolution on human timescales. At Mill Gulch in northern California, USA, an active earthflow was surveyed in 2003 and 2007 by airborne laser swath mapping (ALSM), enabling meter‐scale quantification of landscape change. We calculate four‐year volumetric flux from the earthflow and compare it to long‐term catchment average erosion rates from cosmogenic radionuclide inventories from adjacent watersheds. We also present detailed maps of changing features on the earthflow, from which we can derive velocity estimates and infer dominant process. These measurements rely on proper digital elevation model (DEM) generation and a simple surface‐matching technique to align the multitemporal data in a manner that eliminates systematic error in either dataset. The mean surface elevation of the earthflow and an opposite slope that was directly influenced by the earthflow decreased 14 ± 1 mm/yr from 2003 to 2007. By making the conservative assumption that these features were the dominant contributor of sediment flux from the entire Mill Gulch drainage basin during this time interval, we calculate a minimum catchment‐averaged erosion rate of 0·30 ± 0·02 mm/yr. Analysis of beryllium‐10 (10Be) concentrations in fluvial sand from nearby Russian Gulch and the South Fork Gualala River provide catchment averaged erosion rates of 0·21 ± 0·04 and 0·23 ± 0·03 mm/yr respectively. From translated landscape features, we can infer surface velocities ranging from 0·5 m/yr in the wide upper ‘source’ portion of the flow to 5 m/yr in the narrow middle ‘transport’ portion of the flow. This study re‐affirms the importance of mass wasting processes in the sediment budgets of uplifting weak lithologies. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Integrating records of explosive and effusive activity from proximal and distal sequences: Mt. Taranaki, New Zealand

A complete record of eruption activity is required for a robust volcanic hazard assessment, characterising the types and magnitude of possible activity and the relative frequency of these different types of eruptions. This paper documents a record of Holocene volcanic eruptions from Mt. Taranaki, New Zealand, with the aim of integrating the records of explosive and effusive style eruptions from this volcano. Discriminant function analysis of titanomagnetites from Mt. Taranaki is used to correlate a set of well-dated tephras from lake cores with comparatively poorly dated eruption units that outcrop on the flanks of the cone. Using this process the stratigraphic sections reveal that much of the current edifice was constructed between 6000 and 5000 Cal. BP by prolific lava effusion events. The period of intensive effusive activity followed edifice modification by a major flank-collapse and debris avalanche. This demonstrates that trends in the frequency of effusive activity may vary independently of explosive eruption patterns. Examining the range of processes controlling the occurrence of a range of eruption types and the distribution of their products is essential for the production of robust probabilistic-based eruption forecasting models. In addition, the geochemical data on the widely dispersed Taranaki tephras presented here, tied to this new high-resolution eruption chronology, can be used to constrain future studies of landscape and climatic evolution across large areas of the North Island of New Zealand.

Paleovalley morphology and fluvial system evolution of Eocene-Oligocene sediments ("auriferous gravels"), northern Sierra Nevada, California: Implications for climate, tectonics, and topography

Research Article| September 01, 2011 Paleovalley morphology and fluvial system evolution of Eocene–Oligocene sediments (“auriferous gravels”), northern Sierra Nevada, California: Implications for climate, tectonics, and topography Elizabeth J. Cassel; Elizabeth J. Cassel † 1Department of Earth and Environment, Franklin and Marshall College, Lancaster, Pennsylvania 17604, USA †E-mail: ejcassel@gmail.com Search for other works by this author on: GSW Google Scholar Stephan A. Graham Stephan A. Graham 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Elizabeth J. Cassel † 1Department of Earth and Environment, Franklin and Marshall College, Lancaster, Pennsylvania 17604, USA Stephan A. Graham 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA †E-mail: ejcassel@gmail.com Publisher: Geological Society of America Received: 21 Jun 2010 Revision Received: 03 Oct 2010 Accepted: 09 Nov 2010 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2011 Geological Society of America GSA Bulletin (2011) 123 (9-10): 1699–1719. https://doi.org/10.1130/B30356.1 Article history Received: 21 Jun 2010 Revision Received: 03 Oct 2010 Accepted: 09 Nov 2010 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Elizabeth J. Cassel, Stephan A. Graham; Paleovalley morphology and fluvial system evolution of Eocene–Oligocene sediments (“auriferous gravels”), northern Sierra Nevada, California: Implications for climate, tectonics, and topography. GSA Bulletin 2011;; 123 (9-10): 1699–1719. doi: https://doi.org/10.1130/B30356.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract In the northern Sierra Nevada, California, Eocene–Oligocene fluvial sediments (the “auriferous gravels”) rest unconformably in well-defined basement-incised paleovalleys, providing a record of paleolandscape geomorphology and drainage system evolution. Paleovalley surface mapping shows that local topography and bedrock lithology controlled the location of broad, terraced paleovalley segments, which formed in the central and eastern metamorphic bedrock belts and subsequently became areas of significant fluvial deposition. High-gradient, high-energy deposits are present near the edges of these areas, suggesting that tributaries and outlets resided in steeper, narrow paleovalleys. Multiple strath terraces are common in broad paleovalleys, indicating that incision events occurred both before deposition and during paleovalley widening, followed by periods of aggradation. Broad paleovalley deposits contain predominantly braided stream facies deposited in an energetically variable system. Multiple upward-fining cycles, bounded by erosional surfaces, are composed of alternating coarse-grained channel-belt and fine-grained floodplain packages. An overall upward-fining succession suggests that the locus of fluvial deposition shifted and depositional energy waned over time as the system backfilled successive broad paleovalleys.Paleochannel slope estimates of 0.004–0.055 were obtained based on average grain sizes of coarse channel fills. Anomalously thick (up to 11 m), laterally continuous (1–3 km) floodplain units, containing kaolinite-rich clay and Oxisol intervals, record high fine-grained sediment supply, driven by high rates of chemical weathering in the warm Eocene climate. Based on sedimentary characteristics, combined with floral and detrital zircon data, braided stream deposition within the basin occurred from the late early Eocene through late Eocene, and aggradation primarily occurred in broad, lower-gradient reaches behind a major bedrock knickpoint, created in the late Mesozoic–early Cenozoic, possibly due to asymmetric batholith unroofing. The diachronous, localized nature of paleovalley incision and braided stream aggradation within the northern Sierra Nevada invalidates previous estimates of the timing and amount of range uplift based on paleochannel reconstructions and gradients. Both internal and external drivers influenced the evolution of the fluvial system through (1) the pattern of basin filling, as the locus of deposition migrated east to west, (2) the warm Eocene climate, which increased chemical weathering and contributed a high sediment supply, and (3) changes in base level due to eustasy and/or Laramide tectonism. This record of Laramide tectonics in the Sierra Nevada and Basin and Range is important for the timing of Sierra Nevada uplift, for tectonic reconstructions of western North America, and for studies of landscape evolution in tectonically active orogens. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geomorphology of the Montejunto massif (Portugal)

Please click here to download the map associated with this article. The present paper describes a geomorphological map of the Montejunto massif protected area located approximately 50 km to the north of Lisbon, Portugal. The map is based on large-scale field surveys at the scale of 1:10,000 and is published at the scale of 1:20,000. Symbols and legend organization follow the work of Tricart (1970) and Pellegrini et al. (1993). Landforms and processes are grouped according to their morphogenesis and are represented with different colours: Brown—Structural and tectonic-controlled landforms; Purple—Karst and fluvio-karst landforms and deposits; Red—Gravity-induced landforms and processes; Green—Landforms, processes and deposits formed by running water; Blue—Hydrography; Black and Grey—Anthropogenic landforms. The objective of this map is to provide information on the landforms and deposits present in the protected area, allowing it to be used as a baseline for the study of landscape evolution or support guidelines for territorial management and planning.

Interações entre evolução sedimentar e ocupação humana pré-histórica na costa centro-sul de Santa Catarina, Brasil

Desde o começo da ocupação humana no litoral centro-sul de Santa Catarina, Brasil, a articulação entre processos naturais e antrópicos modelou uma paisagem fortemente domesticada, marcada pela construção massiva de concheiros de dimensões monumentais e pela permanência milenar. Na planície costeira entre Passagem da Barra (município de Laguna) e lago Figueirinha (município de Jaguaruna), 76 sambaquis foram mapeados, dos quais 48 possuem datação. O levantamento sistemático de sítios e datações permitiu identificar padrões de distribuição espacial nos sambaquis da região, quanto a contexto sedimentar da época de construção, estratigrafia e idade. Desse modo, reconheceram-se nos sítios da região: cinco contextos geológico-geomorfológicos de localização; três padrões estratigráficos; e quatro fases de ocupação sambaquieira baseadas na quantidade de sítios e no tipo de padrão construtivo dominante. O modelo integrado de evolução sedimentar e distribuição tempo-espacial de sambaquis indica que estes sítios eram construídos em áreas já emersas e pouco alagáveis, e que sítios interiores, afastados dos corpos lagunares, podem não se ter preservado ou não estarem expostos devido ao processo de assoreamento contínuo que caracterizou a região após a máxima transgressão holocênica. O cruzamento de dados aqui proposto evidencia a importância de abordagens integradas entre arqueologia e geociências no estudo da evolução das paisagens.

The post-glacial downcutting history in the Waihuka tributary of Waipaoa River, Gisborne district: Implications for tectonics and landscape evolution in the Hikurangi subduction margin, New Zealand

Determining the spatial and temporal deliveries of sediment from the Waipaoa River catchment in the post-glacial period is a major goal of integrated source-to-sink landscape evolution studies in the region. In a 2.2 km long section of the Waihuka tributary (217 km 2) of the Waipaoa River (2150 km 2) in eastern North Island, New Zealand, a sequence of at least ten fluvial terraces and abandoned meanders up to 45 m above the present river records rates and times of post-glacial downcutting. Dateable organic and tephra horizons in the terrace and meander infill stratigraphy indicate that downcutting at this location on the Waihuka tributary was dominated by a short-lived event in the early Holocene from 10–8 ka BP, when as much as half of the downcutting was accomplished in only 10–15% of post-glacial time. The large downcutting event is interpreted to record the passing of a succession of major knickpoints or a knickzone through this tributary. The initiation of knickpoint retreat in the catchment was primarily a consequence of reduction in sediment supply at the end of MIS 2. Based on the timing of rapid downcutting in the Waipaoa River mainstem, we estimate that the rate of knickpoint retreat along the Waihuka tributary was about 2 km/kyr. In the period before and after rapid downcutting in the Waihuka tributary, modest incision rates, averaging 1–2 mm/yr, probably represent the regional tectonic uplift rate.

Bedrock detection using 2D electrical resistivity imaging along the Peikang River, central Taiwan

We use the two-dimensional (2D) electrical resistivity imaging (ERI) method to detect the contact between sediment and bedrock in a modern fluvial system. We performed eight 2D electrical resistivity surveys along the Peikang River in Kuohsing area, central Taiwan, with a pole–pole array of 1-m electrode spacing to produce a spatial resolution of about 1 m. The resistivity data were inverted into subsurface electrical structures using the least-squares inversion techniques. Then, the contact between the bedrock and sediment was found by using an image processing technique called Laplacian edge detection (LED), which represents an objective approach in interpreting various geophysical images. Numerical modeling demonstrates that isoresistivity lines are not in good agreement with the hypothetical interfaces between the bedrock and sediment, but the zero-lines of the Laplacian operation are strikingly accurate. Our results indicate a well-defined boundary in the resistivity structure that can be used to estimate the quantity of sediments covering bedrock, thus highlighting the utility of this technique in studies of landscape evolution, sediment transport, and sediment budgets.

THE ACQUISITION OF LOCAL TOPOGRAPHIC RELIEF AND ITS APPLICATION: AN SRTM-DEM ANALYSIS

Topographic analysis has been widely used in the study of landscape evolution and surface process,and the researches in this field have become more and more quantitative.Local topographic relief,which is defined as the difference between local maximum elevation and local base level,is one of the key methods in topographic analysis.Based on a spatial analysis of the SRTM-DEM,this paper puts forward two methods for the acquisition of local topographic relief,i.e.,Swath Profile and Threshold Value.The quantitative analysis of the erosion within a typical area of the Loess Plateau has been preliminarily realized by extending the Threshold Value method.

Chronology of Upper Pleistocene sequences at Sidi Messaoud (wadi Noun, southwestern Morocco) based on 14C, optical and U-series dating

The Sidi Messaoud site provides a 40 m thick sedimentary infilling of great importance for the study of environmental changes and landscape evolution during the Upper Pleistocene in the Western Sahara. In this study, chronological results obtained by the 14C, U-series and optical dating techniques are compared. Each individual age, depositional environment and post-deposition history of the various samples are evaluated, in order to explain the methodological reasons for discordances and concordances. Stratigraphic and palaeoenvironmental implications for the last 120 ka history in southwestern Morocco are also inferred: the wadi Noun gorges had been incised before MIS 5, and later, during MIS 3, the valley has been filled in with a mean sedimentation rate of ∼1 m/ka.