77 research outputs found
Insolation dans les Andes argentines: Lothar Schrott, 1994, Die Solarstrahlung als steuernder Faktor im Geosystem der subtropischen semiariden Hochanden
No full textMainguet Monique. Insolation dans les Andes argentines: Lothar Schrott, 1994, Die Solarstrahlung als steuernder Faktor im Geosystem der subtropischen semiariden Hochanden. In: Annales de Géographie, t. 104, n°585-586, 1995. pp. 623-624
Map of permafrost distribution for Austria, Europe
No full textThis dataset contains a simulation of regional permafrost distribution for Austria based on the Permakart 3.0 modell developped by Schrott et al. (2012). The original model was created and calibrated using validation data from the Hohe Tauern range only. Here we used the same modelling parameter and extended the simulation to the entire Austrian Alps. Please note: The simulation was not validated for other parts of the country and may be erronous. Furthermore, the field evidence was collected between 2009 and 2011 and may not be valid anymore.
The raster dataset contains values from 0-100 representing a pseudo-probability of permafrost occurence.
For more information on the modell and field data please refer to the original publication (see "Related to" Reference)
Persistent post-flood hillslope activity posing a potential landslide dam hazard in the Ahr valley, Germany
No full textAbstract
Background
Extreme floods are known to severely reorganise inhabited landscapes by inundation, clogging, scouring and damaging infrastructure and lives. However, their post-event impacts are poorly understood, especially concerning coupled hillslope channel feedbacks such as the reactivation of slope instabilities connected to the river and that may be able to block it upon sudden failure. The July 2021 Ahr valley flood exemplified this ability of concurrent and sustained landscape reorganisation. Here, we study a retrogressive slope instability near the town of Müsch, in the upper Ahr valley using field mapping, repeat airborne laser scanning, electrical resistivity tomography and passive seismic monitoring to reveal the failure geometry, its mechanisms and transient activity.
Results
The old landslide developed in lower Devonian rocks. It is 100 m wide, 200 m long and approximately 15–20 m deep, which leads to a total volume of about 430,000 m3. This landslide was severely undercut by the 2021 flood with 7000 m3 of material eroded at the landslide toe. The landslide has started to react. Given the narrow section of the river at this location, there is a potential landslide dam hazard. We modelled the inundation volumes and back fill times for different failure scenarios, ranging between 20,000 m3 and 330,000 m3 accumulating within 5 min and 20 h.
Conclusions
Our results imply a need to systematically screen flood impacted landscapes for sustained post-event hillslope activity that governs hillslope-channel coupling, driving both persistent sediment injection into the stream and sudden river blocking and subsequent damming
Permafrost in den argentinischen Anden, ein bedeutender Wasserspeicher
No full textDie semi-ariden Zentralanden Argentiniens werden durch eine weitfl ächige erbreitung von Permafrost und eine große vertikale Erstreckung von periglazialen Formen und Prozessen charakterisiert. Große Blockgletscherkomplexe mit eisreichem Permafrost werden in den Trockengebieten der Anden als bedeutende Wasserspeicher für die Zukunft angesehen. Die argentinische Regierung hat 2010 ein Gesetz zum Schutz der Gletscher und der periglazialen Höhenstufe erlassen, um diese Naturressourcen zu schützen. Die vorliegende Studie hat das Ziel, die Verbreitung der Blockgletscher aufzuzeigen und die wenig bekannten Eisgehalte dieser Periglazialformen zu quantifi zieren.Fil: Christian Halla. Universitat Bonn; AlemaniaFil: Jan Henrik Blöthe. Universitat Bonn; AlemaniaFil: Trombotto, Dario Tomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Lothar Schrott. Universitat Bonn; Alemani
Grundfragen des alpinen Periglazials. Ergebnisse, Probleme und Perspektiven periglazialmorphologischer Untersuchungen im Langzeitprojekt "Glorer Hütte" in der südlichen Glockner-/Nördlichen Schobergruppe (Südliche Hohe Tauern, Osttirol)
No full textSpatial patterns and bridge collapse interactions of erosional processes due to the 2021 Ahr valley flood
No full textAbstract The extreme flood event of July 14/15, 2021 caused massive geomorphological changes along the Ahr river in western Germany. The processes include mass movement and bank erosion, channel displacement and widening as well as deposition of material at the floodplains, all of which contributed to extreme damage. However, a comprehensive understanding of the actual control factors and drivers of these processes is lacking. Here, we analyse spatial patterns of erosional processes in three dimensional space and on a regional scale. We quantify bulk volumetric loss in 100 m long and 120 m wide segments along the Ahr river, using a differential terrain model build from pre-event and post-event airborne laser scanning data. We use a multiple linear regression model of net volumetric loss per segment as a proxy of flood power to explore relationships with peak discharge, valley floor width and river curvature. Both volumetric loss itself and the residuals of the regression model are used to examine effects of bridge failure and subsequent outburst waves. The analysis shows that the greatest volumetric loss values are explained by high peak discharges and narrow valley floors. River segments containing destroyed arch bridges show higher volumetric loss than segments with destroyed slab bridges, intact bridges or no bridge at all. These findings suggest that traditional arch bridges may be less effective in preventing the local augmentation of flood power by outburst waves resulting from bridge clogging and failure
Typische und atypische Permafrostvorkommen - Klimatische Bedingungen, geomorphologische Indikatoren und Prospektionsmethoden
No full textLothar Schrot
Permafrost und Sedimenthaushalt in einem alpinen Geosystem
No full textm Rahmen dieser Arbeit wurde die Rolle des Reliefs als Produkt und Regler unterschiedlicher geomorphologischer Prozesse in einem alpinen Geosystem (Turtmanntal, Wallis, Schweiz) untersucht, welches durch die Existenz von Permafrost sowie von periglazialen Prozessen und Formen gekennzeichnet ist. Als Teilprojekt des interdisziplinär angelegten DFG-Forschungsprojektes „Graduiertenkolleg 437: Das Relief – eine strukturierte und veränderliche Grenzfläche“ befasste sich die Arbeit vor allem mit der Analyse der Wechselwirkungen zwischen geomorphologischen Formen und Prozessen im Hochgebirge. Der Einfluss des Reliefs auf die Permafrostverbreitung wurde auf regionaler und lokaler Raumskale untersucht. Dementsprechend wurden skalenabhängige Messverfahren und Methoden angewandt. Auf regionaler Skale erfolgte zunächst die Kartierung von Blockgletschern als Permafrostindikatoren. Basierend auf diesen Daten wurde ein neuer empirisch-statistischer Ansatz zur Modellierung der regionalen Permafrostverbreitung entwickelt. Zur Validierung unterschiedlicher regionaler Permafrostmodelle und zur Analyse lokalskaliger Einflüsse des Reliefs auf die Permafrostverbreitung wurde eine Permafrostkartierung in einem Seitental des Untersuchungsgebietes durchgeführt. Die Kartierung basiert auf einem Monitoring der Basistemperatur der hochwinterlichen Schneedecke (BTS) sowie auf Messungen geophysikalischer Parameter des Untergrundes. Es zeigte sich ein kleinräumig stark differenziertes Bild, wobei eine starke Abhängigkeit der Permafrostverbreitung von den Eigenschaften des Reliefs auf kleiner Raumskale besteht. Die an die Existenz von Permafrost gebundenen Blockgletscher stellen bedeutende Speicher im Sedimenthaushalt vieler alpiner Geosysteme dar. Eine wesentliche Aufgabe dieser Arbeit bestand in der Ermittlung der Sedimentvolumina der Blockgletscher des Turtmanntals. Es wurde ein semiquantitativer Ansatz verfolgt, bei dem die Mächtigkeiten und Sedimentvolumina der Blockgletscher auf Grundlage eines hochaufgelösten Digitalen Höhenmodells bestimmt wurden. Für die Mächtigkeiten, Sedimentvolumina und -massen der Blockgletscher wurden zwei Szenarien entwickelt. Aufgrund der auffallend geringen Mächtigkeiten und Sedimentvolumina der Blockgletscher wird eine hohe Sensitivität dieser Formen gegenüber klimatischen Veränderungen angenommen. Im Turtmanntal stellen Blockgletscher daher sehr gute Indikatoren für die Permafrostverbreitung auf regionaler Skale dar.Permafrost and sediment budget in an alpine Geosystem In this study, the role of landform for different geomorphic processes within an alpine geosystem has been examined. The study area (Turtmann Valley, Switzerland) is characterized by the existence of permafrost and numerous periglacial processes and features. Being part of the interdisciplinary DFG Research Training Group “Landform – a structured and variable boundary layer” the analysis of interactions of geomorphic landforms and processes in a high mountain geosystem represented the key task of this study. Thus, the influence of landform on the development of permafrost on different spatial scales has been analyzed. Initially, rock glaciers in the study area have been mapped and compiled in an inventory serving primarily as a database for the development of an empirical-statistical modelling approach to simulate regional permafrost distribution. Furthermore, validation of different regional permafrost distribution models has been carried out by mapping permafrost on the local scale in a side valley of the study area. The role of different landform characteristics for the mapped permafrost distribution has been analyzed as well. Mapping is based on a monitoring of the base temperature of the winter snow cover (BTS) and on measurements of geophysical parameters of the substratum. The temperature data and the geophysical parameters revealed a distribution pattern of permafrost being highly variable in space. Small-scale landform characteristics proved to be responsible for the determined distribution pattern. Finally, rock glaciers represent important sediment stores and are major components of the sediment budget of many alpine geosystems. A main objective of this study consisted in determining the sediment volume of the rock glaciers of the Turtmanntal. Using a semi-quantitative approach and a high resolution Digital Elevation Model, the thickness and sediment volume of each rock glacier has been determined. Two scenarios for rock glacier thickness, sediment volume and sediment mass are presented in the study. Due to very low sediment volumes the rock glaciers in the Turtmanntal are assumed to react very sensitive to changes of the climatic boundary conditions. Thus, the rock glaciers in the Turtmanntal represent a suitable indicator for permafrost distribution on a regional scale
Modelling the holocene sediment budget of the Rhine system
No full textRivers transport large amounts of water, sediments, nutrients and carbon from the continents to the oceans. Thus, they are important links within the global biogeochemical cycle. To understand biogeochemical fluxes in river channels, holistic system-based approaches are needed that consider river channels and their corresponding catchments. Sediment fluxes in fluvial systems change in consequence of changing external controls (land use and climate). However, the system's response to land use and climate change varies depending on internal controls (e.g. catchment size and structure). While forcing-response mechanisms of small catchments are reasonably well understood, the response of larger drainage basins is less clear. In particular, the impact of land use and climate change on the Rhine system is poorly known owing to the catchment size (185 000 km²) and the long history of human cultivation, which started approx. 7500 years ago. A sediment budget is calculated to specify the amount of alluvial sediment and total organic carbon that deposited during the Holocene and to estimate long term soil erosion rates. The focus was driven to floodplains because they act as important sinks in terms of sediment and carbon flux and therefore, provide a range of potential sites of palaeoecological data. To obtain information on the temporal development of the Rhine system, a database of 14C-ages taken from colluvial and alluvial deposits was compiled and analysed in terms of i) cumulative frequency distributions of the ages and ii) changing sedimentation rates on floodplains and in palaeochannels. The results of the sediment budget suggest that 59±14 10^9 t of Holocene alluvial sediment is stored in the non-alpine part of the Rhine catchment (South and Central Germany, Eastern France, The Netherlands). About 50% of Holocene alluvial sediment is deposited along the trunk valley and the delta (Upper Rhine, Lower Rhine, coastal plain), while the rest is stored along the tributary valleys. The floodplain sediment storage corresponds to a mean erosion rate of 0.55±0.16 t/ha/year (38.5±10.7 mm/kyr) across the Rhine catchment outside the Alps. This Holocene-averaged estimate amounts for sediments that were delivered to the channel network and is at the lower limit of erosion rates from other studies of different methodology. The statistical analysis of 1948 organic carbon measurements in different parts of the Rhine catchment suggest a strong influence of the sedimentary facies on the organic carbon content. The analysis allowed the development of a conceptual carbon budget model of fluvial systems, which was coupled with the alluvial sediment storage, to estimate the Holocene sequestration rates of carbon storage in floodplains. Averaged over the Rhine catchment the sedimentary carbon sequestration ranges between 3.4 to 25.4 g m²/year with more reasonable values between 5.3 to 17.7 g m²/year. Compared to the recent particulate carbon export, these values are in the same order of magnitude but somewhat smaller indicating that approximately the same amount of the exported carbon may be stored in floodplains. However, compared to sedimentary carbon sequestration rates obtained elsewhere, the presented values are at the lower limit, corresponding to the lower mean Holocene soil erosion and floodplain accumulation rates. Based on the cumulative frequency distributions of the 14C-ages eight periods of geomorphic activity are identified (peaking at 8.2 kyr, 7.54 kyr, 5.6 kyr, 4.2 kyr, 3.3 kyr, 2.8 kyr, 2.3 kyr and since 1075 years BP). These periods were compared with climatic, palaeohydrological and human impact proxy data. Until 4200 years BP, events of geomorphic activity are mainly coupled to wetter and/or cooler climatic phases. Between 3300 and 2770 years BP, the increased geomorphic activity cannot unequivocally be related to climate. The growing population and the intensification of agricultural activities must be considered as an additional control during the Bronze age. Since 1075 years BP the growing population density is considered as the major external forcing. Additionally, it could be shown that the newly developed approach has major advantages compared to the approach used to analyse the 14C-database of Great Britain, Spain and Poland. Concerning the changing sedimentation rates on floodplains and in palaeochannels, three phases were identified, during the last 14 000 years: i) the Late Glacial-Holocene with medium sedimentation rates, ii) the Holocene Climatic Optimum with slightly decreasing rates and iii) the last 4000 years, which are characterised by increasing sedimentation rates. The results are in good correspondence with a conceptual model of the Holocene floodplain development in Europe. Until now, the spatially distributed sediment and carbon budgets and the temporal analysis of the C-database are analysed based on linear relationships of causes and effects. However, to understand the nonlinear response of the Rhine system to changes of land use and climate impacts during the Holocene, it is necessary to couple the temporal and spatial approaches that were developed in this thesis
New aspects of deglaciation in southern Norway : Climate variability derived from surface exposure ages of Late Quaternary and Holocene landforms
No full textThe investigation of periglacial and related landforms in South Norway is of high interest for exploring timings of deglaciation and to assess their geomorphological connectivity to palaeoclimatic changes during the Late Quaternary and the Holocene. The ice margins of the Scandinavian Ice Sheet during the Last Glacial Maximum (LGM) are fairly well known, the palaeo-ice thickness, however, which can only be estimated by modelling, remains unclear over large parts of Norway owing to rare field based evi-dences. Due to the significant influence of the former horizontal and vertical ice-sheet extent on sea-level rise, atmospheric and oceanic circulation patterns, erosive properties of glaciers and ice sheets, englacial thermal boundaries and deglaciation dynamics, it is crucial to better understand the topograph-ic features of the LGM ice sheet. Despite recent advances, there is a lack of terrestrial evidences from numerical data in South Norway. In this thesis two high-mountain regions and their surroundings in west (Dalsnibba, 1476 m a.s.l.) and east (Blåhø, 1617 m a.s.l.) South Norway were used to reconstruct palaeoclimatic conditions and deglaciation patterns. Terrestrial cosmogenic nuclides (10Be) and Schmidt-hammer exposure-age dating (SHD) have been utilized to determine the surface exposure of glacially transported boulders as well as of boulder-dominated glacial, periglacial and paraglacial landforms and bedrock outcrops. By developing calibration curves at both study sites for the first time, through young and old control points of known age, it was possible to obtain landform age estimates from Schmidt hammer R-(rebound) values. Beside age estimates, the formation and stabilization of those landforms and the involved processes have provided indications about the Late Quaternary and Holocene climate variability and its connectivity to landform development. The first deglaciation chronology for the western study area could be constructed based on 10Be sur-face exposure ages. Final local deglaciation on the summit of Dalsnibba probably started between 13.3 ± 0.6 and 12.7 ± 0.5 ka and progressed down to the valley bottom of Opplendskedalen (~1050 m a.s.l.) with an SHD age estimate of 7.47 ± 0.73 ka. Deglaciation during the Bølling–Allerød Interstadial (~14.7 – 12.9 ka) indicates that the summit was not ice-covered during the Younger Dryas (12.9 – 11.7 cal. ka BP). A glacially transported boulder in the summit area and summit bedrock ages without cos-mogenic nuclide inheritance further imply a minimum vertical ice extent of 1476 m and the presence of erosive warm-based ice. The SHD Dalsnibba results show that most landforms stabilized during the Holocene Thermal Maximum (~8.0 – 5.0 ka) and that their R-value characteristics with negative skew-ness were indicative for the reworking of boulders or continuous debris supply. The SHD ages from Dalsnibba imply that periglacial landforms in the western maritime setting sensitively reacted to Holo-cene climate variability. Rock-slope failures investigated at both study sites demonstrate that they do not necessarily occur shortly after local deglaciation as often inferred. Furthermore, most of the recorded rock-slope failures appear to have occurred during warm climatic conditions. Most likely, prevailing warm conditions led to permafrost degradation, enhanced snow melt and increasing cleftwater pres-sure contributed to slope instabilities probably resulting in rock-slope failures. The Blåhø SHD ages also suggest landform response on climate variations, though, in a different tem-poral context. Landforms above 1450 m a.s.l. largely shared overlapping ages and therefore appear to have stabilized during the Karmøy/Bremanger readvance (∼18.5 – 16.5 ka). This, however, seems to have been the last major geomorphic activity of these landforms as they were not reactivated by several, partly severe cold climate events such as the Younger Dryas. The SHD ages from landforms above 1450 m a.s.l. are in contrast to the previous deglaciation chronology which suggested cold-based ice coverage and slow thinning down to ∼1450 m a.s.l. at 15.0 ± 1.0 10Be ka. Based on the results from this thesis, a severe periglacial climate without ice coverage since about 18 ka is proposed for the sum-mit area of Blåhø. The 10Be ages from Blåhø with 20.9 ± 0.8 ka for the erratic boulder and 46.4 ± 1.7 ka for the bedrock, which extend the previous deglaciation chronology, are discussed within the framework of the two most popular scenarios. Within the first scenario the boulder age represented the timing of deglaciation and the bedrock age showed inherited cosmogenic nuclides, suggesting the pres-ence of low erosive cold-based ice at Blåhø during the LGM. In the second scenario, the boulder age was affected by post-depositional disturbance, frost heave processes or shielding, potentially indicating ice-free conditions on Blåhø since at least 46.4 ± 1.7 ka. Analyzing the different onset of deglaciation in the study areas within a rather short west-east distance, together with the timing of deglaciation in neighboring regions, demonstrates complex deglaciation dynamics in southern Norway. Not only the timing of deglaciation was highly variable, the results also imply diverse basal ice temperatures within this relatively small area. In general, this thesis positively contributes new evidences pointing to a more complex and dynamic Scandinavian Ice Sheet throughout the last glacial cycle than previously assumed
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