Institut für Erd- und Umweltwissenschaften
Refine
Has Fulltext
- yes (17) (remove)
Year of publication
- 2015 (17) (remove)
Document Type
- Doctoral Thesis (12)
- Postprint (4)
- Habilitation Thesis (1)
Is part of the Bibliography
- yes (17)
Keywords
- Abschätzung der Unsicherheiten (1)
- Altlasten (1)
- Argentina (1)
- Argentinien (1)
- Boden (1)
- Carbo-Iron (1)
- Carbo-Iron® (1)
- Cerrado (1)
- DANSER (1)
- Denudation (1)
Institute
This study presents the development of 1D and 2D Surface Evolution Codes (SECs) and their coupling to any lithospheric-scale (thermo-)mechanical code with a quadrilateral structured surface mesh.
Both SECs involve diffusion as approach for hillslope processes and the stream power law to reflect riverbed incision. The 1D SEC settles sediment that was produced by fluvial incision in the appropriate minimum, while the supply-limited 2D SEC DANSER uses a fast filling algorithm to model sedimantation. It is based on a cellular automaton. A slope-dependent factor in the sediment flux extends the diffusion equation to nonlinear diffusion. The discharge accumulation is achieved with the D8-algorithm and an improved drainage accumulation routine. Lateral incision enhances the incision's modelling. Following empirical laws, it incises channels of several cells width.
The coupling method enables different temporal and spatial resolutions of the SEC and the thermo-mechanical code. It transfers vertical as well as horizontal displacements to the surface model. A weighted smoothing of the 3D surface displacements is implemented. The smoothed displacement vectors transmit the deformation by bilinear interpolation to the surface model. These interpolation methods ensure mass conservation in both directions and prevent the two surfaces from drifting apart.
The presented applications refer to the evolution of the Pamir orogen. A calibration of DANSER's parameters with geomorphological data and a DEM as initial topography highlights the advantage of lateral incision. Preserving the channel width and reflecting incision peaks in narrow channels, this closes the huge gap between current orogen-scale incision models and observed topographies.
River capturing models in a system of fault-bounded block rotations reaffirm the importance of the lateral incision routine for capturing events with channel initiation. The models show a low probability of river capturings with large deflection angles. While the probability of river capturing is directly depending on the uplift rate, the erodibility inside of a dip-slip fault speeds up headward erosion along the fault: The model's capturing speed increases within a fault.
Coupling DANSER with the thermo-mechanical code SLIM 3D emphasizes the versatility of the SEC. While DANSER has minor influence on the lithospheric evolution of an indenter model, the brittle surface deformation is strongly affected by its sedimentation, widening a basin in between two forming orogens and also the southern part of the southern orogen to south, east and west.
The Brazilian Cerrado is recognised as one of the most threatened biomes in the world, as the region has experienced a striking change from natural vegetation to intense cash crop production. The impacts of rapid agricultural expansion on soil and water resources are still poorly understood in the region. Therefore, the overall aim of the thesis is to improve our understanding of the ecohydrological processes causing water and soil degradation in the Brazilian Cerrado.
I first present a metaanalysis to provide quantitative evidence and identifying the main impacts of soil and water alterations resulting from land use change. Second, field studies were conducted to (i) examine the effects of land use change on soils of natural cerrado transformed to common croplands and pasture and (ii) indicate how agricultural production affects water quality across a meso-scale catchment. Third, the ecohydrological process-based model SWAT was tested with simple scenario analyses to gain insight into the impacts of land use and climate change on the water cycling in the upper São Lourenço catchment which experienced decreasing discharges in the last 40 years.
Soil and water quality parameters from different land uses were extracted from 89 soil and 18 water studies in different regions across the Cerrado. Significant effects on pH, bulk density and available P and K for croplands and less-pronounced effects on pastures were evident. Soil total N did not differ between land uses because most of the cropland sites were N-fixing soybean cultivations, which are not artificially fertilized with N. By contrast, water quality studies showed N enrichment in agricultural catchments, indicating fertilizer impacts and potential susceptibility to eutrophication. Regardless of the land use, P is widely absent because of the high-fixing capacities of deeply weathered soils and the filtering capacity of riparian vegetation. Pesticides, however, were consistently detected throughout the entire aquatic system. In several case studies, extremely high-peak concentrations exceeded Brazilian and EU water quality limits, which pose serious health risks.
My field study revealed that land conversion caused a significant reduction in infiltration rates near the soil surface of pasture (–96 %) and croplands (–90 % to –93 %). Soil aggregate stability was significantly reduced in croplands than in cerrado and pasture. Soybean crops had extremely high extractable P (80 mg kg–1), whereas pasture N levels declined. A snapshot water sampling showed strong seasonality in water quality parameters. Higher temperature, oxi-reduction potential (ORP), NO2–, and very low oxygen concentrations (<5 mg•l–1) and saturation (<60 %) were recorded during the rainy season. By contrast, remarkably high PO43– concentrations (up to 0.8 mg•l–1) were measured during the dry season. Water quality parameters were affected by agricultural activities at all sampled sub-catchments across the catchment, regardless of stream characteristic. Direct NO3– leaching appeared to play a minor role; however, water quality is affected by topsoil fertiliser inputs with impact on small low order streams and larger rivers. Land conversion leaving cropland soils more susceptible to surface erosion by increased overland flow events.
In a third study, the field data were used to parameterise SWAT. The model was tested with different input data and calibrated in SWAT-CUP using the SUFI-2 algorithm. The model was judged reliable to simulate the water balance in the Cerrado. A complete cerrado, pasture and cropland cover was used to analyse the impact of land use on water cycling as well as climate change projections (2039–2058) according to the projections of the RCP 8.5 scenario. The actual evapotranspiration (ET) for the cropland scenario was higher compared to the cerrado cover (+100 mm a–1). Land use change scenarios confirmed that deforestation caused higher annual ET rates explaining partly the trend of decreased streamflow. Taking all climate change scenarios into account, the most likely effect is a prolongation of the dry season (by about one month), with higher peak flows in the rainy season. Consequently, potential threats for crop production with lower soil moisture and increased erosion and sediment transport during the rainy season are likely and should be considered in adaption plans.
From the three studies of the thesis I conclude that land use intensification is likely to seriously limit the Cerrado’s future regarding both agricultural productivity and ecosystem stability. Because only limited data are available for the vast biome, we recommend further field studies to understand the interaction between terrestrial and aquatic systems. This thesis may serve as a valuable database for integrated modelling to investigate the impact of land use and climate change on soil and water resources and to test and develop mitigation measures for the Cerrado in the future.
The ICDP "PaleoVan" drilling campaign at Lake Van, Turkey, provided a long (> 100 m) record of lacustrine subsurface sedimentary microbial cell abundance. After the ICDP campaign at Potrok Aike, Argentina, this is only the second time deep lacustrine cell counts have been documented. Two sites were cored and revealed a strikingly similar cell distribution despite differences in organic matter content and microbial activity. Although shifted towards higher values, cell counts from Lake Potrok Aike, Argentina, reveal very similar distribution patterns with depth. The lacustrine cell count data are significantly different from published marine records; the most probable cause is differences in sedimentary organic matter composition with marine sediments containing a higher fraction of labile organic matter. Previous studies showed that microbial activity and abundance increase centimetres to metres around geologic interfaces. The finely laminated Lake Van sediment allowed studying this phenomenon on the microscale. We sampled at the scale of individual laminae, and in some depth intervals, we found large differences in microbial abundance between the different laminae. This small-scale heterogeneity is normally overlooked due to much larger sampling intervals that integrate over several centimetres. However, not all laminated intervals exhibit such large differences in microbial abundance, and some non-laminated horizons show large variability on the millimetre scale as well. The reasons for such contrasting observations remain elusive, but indicate that heterogeneity of microbial abundance in subsurface sediments has not been taken into account sufficiently. These findings have implications not just for microbiological studies but for geochemistry as well, as the large differences in microbial abundance clearly show that there are distinct microhabitats that deviate considerably from the surrounding layers.
The Central Pontides is an accretionary-type orogenic area within the Alpine-Himalayan orogenic belt characterized by pre-collisional tectonic continental growth. The region comprises Mesozoic subduction-accretionary complexes and an accreted intra-oceanic arc that are sandwiched between the Laurasian active continental margin and Gondwana-derived the Kırşehir Block. The subduction-accretion complexes mainly consist of an Albian-Turonian accretionary wedge representing the Laurasian active continental margin. To the north, the wedge consists of slate/phyllite and metasandstone intercalation with recrystallized limestone, Na-amphibole-bearing metabasite (PT= 7–12 kbar and 400 ± 70 ºC) and tectonic slices of serpentinite representing accreted distal part of a large Lower Cretaceous submarine turbidite fan deposited on the Laurasian active continental margin that was subsequently accreted and metamorphosed. Raman spectra of carbonaceous material (RSCM) of the metapelitic rocks revealed that the metaflysch sequence consists of metamorphic packets with distinct peak metamorphic temperatures. The majority of the metapelites are low-temperature (ca. 330 °C) slates characterized by lack of differentiation of the graphite (G) and D2 defect bands. They possibly represent offscraped distal turbidites along the toe of the Albian accretionary wedge. The rest are phyllites that are characterized by slightly pronounced G band with D2 defect band occurring on its shoulder. Peak metamorphic temperatures of these phyllites are constrained to 370-385 °C. The phyllites are associated with a strip of incipient blueschist facies metabasites which are found as slivers within the offscraped distal turbidites. They possibly represent underplated continental metasediments together with oceanic crustal basalt along the basal décollement. Tectonic emplacement of the underplated rocks into the offscraped distal turbidites was possibly achieved by out-of-sequence thrusting causing tectonic thickening and uplift of the wedge. 40Ar/39Ar phengite ages from the phyllites are ca. 100 Ma, indicating Albian subduction and regional HP metamorphism.
The accreted continental metasediments are underlain by HP/LT metamorphic rocks of oceanic origin along an extensional shear zone. The oceanic metamorphic sequence mainly comprises tectonically thickened deep-seated eclogite to blueschist facies metabasites and micaschists. In the studied area, metabasites are epidote-blueschists locally with garnet (PT= 17 ± 1 kbar and 500 ± 40 °C). Lawsonite-blueschists are exposed as blocks along the extensional shear zone (PT= 14 ± 2 kbar and 370–440 °C). They are possibly associated with low shear stress regime of the initial stage of convergence. Close to the shear zone, the footwall micaschists consist of quartz, phengite, paragonite, chlorite, rutile with syn-kinematic albite porphyroblast formed by pervasive shearing during exhumation. These types of micaschists are tourmaline-bearing and their retrograde nature suggests high-fluid flux along shear zones. Peak metamorphic mineral assemblages are partly preserved in the chloritoid-micaschist farther away from the shear zone representing the zero strain domains during exhumation. Three peak metamorphic assemblages are identified and their PT conditions are constrained by pseudosections produced by Theriak-Domino and by Raman spectra of carbonaceous material: 1) garnet-chloritoid-glaucophane with lawsonite pseudomorphs (P= 17.5 ± 1 kbar, T: 390-450 °C) 2) chloritoid with glaucophane pseudomorphs (P= 16-18 kbar, T: 475 ± 40 °C) and 3) relatively high-Mg chloritoid (17%) with jadeite pseudomorphs (P= 22-25 kbar; T: 440 ± 30 °C) in addition to phengite, paragonite, quartz, chlorite, rutile and apatite. The last mineral assemblage is interpreted as transformation of the chloritoid + glaucophane assemblage to chloritoid + jadeite paragenesis with increasing pressure. Absence of tourmaline suggests that the chloritoid-micaschist did not interact with B-rich fluids during zero strain exhumation. 40Ar/39Ar phengite age of a pervasively sheared footwall micaschist is constrained to 100.6 ± 1.3 Ma and that of a chloritoid-micaschist is constrained to 91.8 ± 1.8 Ma suggesting exhumation during on-going subduction with a southward younging of the basal accretion and the regional metamorphism. To the south, accretionary wedge consists of blueschist and greenschist facies metabasite, marble and volcanogenic metasediment intercalation. 40Ar/39Ar phengite dating reveals that this part of the wedge is of Middle Jurassic age partly overprinted during the Albian. Emplacement of the Middle Jurassic subduction-accretion complexes is possibly associated with obliquity of the Albian convergence.
Peak metamorphic assemblages and PT estimates of the deep-seated oceanic metamorphic sequence suggest tectonic stacking within wedge with different depths of burial. Coupling and exhumation of the distinct metamorphic slices are controlled by decompression of the wedge possibly along a retreating slab. Structurally, decompression of the wedge is evident by an extensional shear zone and the footwall micaschists with syn-kinematic albite porphyroblasts. Post-kinematic garnets with increasing grossular content and pseudomorphing minerals within the chloritoid-micaschists also support decompression model without an extra heating.
Thickening of subduction-accretionary complexes is attributed to i) significant amount of clastic sediment supply from the overriding continental domain and ii) deep level basal underplating by propagation of the décollement along a retreating slab. Underplating by basal décollement propagation and subsequent exhumation of the deep-seated subduction-accretion complexes are connected and controlled by slab rollback creating a necessary space for progressive basal accretion along the plate interface and extension of the wedge above for exhumation of the tectonically thickened metamorphic sequences. This might be the most common mechanism of the tectonic thickening and subsequent exhumation of deep-seated HP/LT subduction-accretion complexes.
To the south, the Albian-Turonian accretionary wedge structurally overlies a low-grade volcanic arc sequence consisting of low-grade metavolcanic rocks and overlying metasedimentary succession is exposed north of the İzmir-Ankara-Erzincan suture (İAES), separating Laurasia from Gondwana-derived terranes. The metavolcanic rocks mainly consist of basaltic andesite/andesite and mafic cognate xenolith-bearing rhyolite with their pyroclastic equivalents, which are interbedded with recrystallized pelagic limestone and chert. The metavolcanic rocks are stratigraphically overlain by recrystallized micritic limestone with rare volcanogenic metaclastic rocks. Two groups can be identified based on trace and rare earth element characteristics. The first group consists of basaltic andesite/andesite (BA1) and rhyolite with abundant cognate gabbroic xenoliths. It is characterized by relative enrichment of LREE with respect to HREE. The rocks are enriched in fluid mobile LILE, and strongly depleted in Ti and P reflecting fractionation of Fe-Ti oxides and apatite, which are found in the mafic cognate xenoliths. Abundant cognate gabbroic xenoliths and identical trace and rare earth elements compositions suggest that rhyolites and basaltic andesites/andesites (BA1) are cogenetic and felsic rocks were derived from a common mafic parental magma by fractional crystallization and accumulation processes. The second group consists only of basaltic andesites (BA2) with flat REE pattern resembling island arc tholeiites. Although enriched in LILE, this group is not depleted in Ti or P.
Geochemistry of the metavolcanic rocks indicates supra-subduction volcanism evidenced by depletion of HFSE and enrichment of LILE. The arc sequence is sandwiched between an Albian-Turonian subduction-accretionary complex representing the Laurasian active margin and an ophiolitic mélange. Absence of continent derived detritus in the arc sequence and its tectonic setting in a wide Cretaceous accretionary complex suggest that the Kösdağ Arc was intra-oceanic. This is in accordance with basaltic andesites (BA2) with island arc tholeiite REE pattern.
Zircons from two metarhyolite samples give Late Cretaceous (93.8 ± 1.9 and 94.4 ± 1.9 Ma) U/Pb ages. Low-grade regional metamorphism of the intra-oceanic arc sequence is constrained 69.9 ± 0.4 Ma by 40Ar/39Ar dating on metamorphic muscovite from a metarhyolite indicating that the arc sequence became part of a wide Tethyan Cretaceous accretionary complex by the latest Cretaceous. The youngest 40Ar/39Ar phengite age from the overlying subduction-accretion complexes is 92 Ma confirming southward younging of an accretionary-type orogenic belt. Hence, the arc sequence represents an intra-oceanic paleo-arc that formed above the sinking Tethyan slab and finally accreted to Laurasian active continental margin. Abrupt non-collisional termination of arc volcanism was possibly associated with southward migration of the arc volcanism similar to the Izu-Bonin-Mariana arc system.
The intra-oceanic Kösdağ Arc is coeval with the obducted supra-subduction ophiolites in NW Turkey suggesting that it represents part of the presumed but missing incipient intra-oceanic arc associated with the generation of the regional supra-subduction ophiolites. Remnants of a Late Cretaceous intra-oceanic paleo-arc and supra-subduction ophiolites can be traced eastward within the Alp-Himalayan orogenic belt. This reveals that Late Cretaceous intra-oceanic subduction occurred as connected event above the sinking Tethyan slab. It resulted as arc accretion to Laurasian active margin and supra-subduction ophiolite obduction on Gondwana-derived terranes.
Effect of mass wasting on soil organic carbon storage and coastal erosion in permafrost environments
(2015)
Accelerated permafrost thaw under the warming Arctic climate can have a significant impact on Arctic landscapes. Areas underlain by permafrost store high amounts of soil organic carbon (SOC). Permafrost disturbances may contribute to increased release of carbon dioxide and methane to the atmosphere. Coastal erosion, amplified through a decrease in Arctic sea-ice extent, may also mobilise SOC from permafrost. Large expanses of permafrost affected land are characterised by intense mass-wasting processes such as solifluction, active-layer detachments and retrogressive thaw slumping. Our aim is to assess the influence of mass wasting on SOC storage and coastal erosion.
We studied SOC storage on Herschel Island by analysing active-layer and permafrost samples, and compared non-disturbed sites to those characterised by mass wasting. Mass-wasting sites showed decreased SOC storage and material compaction, whereas sites characterised by material accumulation showed increased storage. The SOC storage on Herschel Island is also significantly correlated to catenary position and other slope characteristics. We estimated SOC storage on Herschel Island to be 34.8 kg C m-2. This is comparable to similar environments in northwest Canada and Alaska.
Coastal erosion was analysed using high resolution digital elevation models (DEMs). Two LIDAR scanning of the Yukon Coast were done in 2012 and 2013. Two DEMs with 1 m horizontal resolution were generated and used to analyse elevation changes along the coast. The results indicate considerable spatial variability in short-term coastline erosion and progradation. The high variability was related to the presence of mass-wasting processes. Erosion and deposition extremes were recorded where the retrogressive thaw slump (RTS) activity was most pronounced. Released sediment can be transported by longshore drift and affects not only the coastal processes in situ but also along adjacent coasts.
We also calculated volumetric coastal erosion for Herschel Island by comparing a stereo-photogrammetrically derived DEM from 2004 with LIDAR DEMs. We compared this volumetric erosion to planimetric erosion, which was based on coastlines digitised from satellite imagery. We found a complex relationship between planimetric and volumetric coastal erosion, which we attribute to frequent occurrence of mass-wasting processes along the coasts. Our results suggest that volumetric erosion corresponds better with environmental forcing and is more suitable for the estimation of organic carbon fluxes than planimetric erosion.
Mass wasting can decrease SOC storage by several mechanisms. Increased aeration following disturbance may increase microbial activity, which accelerates organic matter decomposition. New hydrological conditions that follow the mass wasting event can cause leaching of freshly exposed material. Organic rich material can also be directly removed into the sea or into a lake. On the other hand the accumulation of mobilised material can result in increased SOC storage. Mass-wasting related accumulations of mobilised material can significantly impact coastal erosion in situ or along the adjacent coast by longshore drift. Therefore, the coastline movement observations cannot completely resolve the actual sediment loss due to these temporary accumulations. The predicted increase of mass-wasting activity in the course of Arctic warming may increase SOC mobilisation and coastal erosion induced carbon fluxes.
Analysis and modeling of transient earthquake patterns and their dependence on local stress regimes
(2015)
Investigations in the field of earthquake triggering and associated interactions, which includes aftershock triggering as well as induced seismicity, is important for seismic hazard assessment due to earthquakes destructive power. One of the approaches to study earthquake triggering and their interactions is the use of statistical earthquake models, which are based on knowledge of the basic seismicity properties, in particular, the magnitude distribution and spatiotemporal properties of the triggered events.
In my PhD thesis I focus on some specific aspects of aftershock properties, namely, the relative seismic moment release of the aftershocks with respect to the mainshocks; the spatial correlation between aftershock occurrence and fault deformation; and on the influence of aseismic transients on the aftershock parameter estimation. For the analysis of aftershock sequences I choose a statistical approach, in particular, the well known Epidemic Type Aftershock Sequence (ETAS) model, which accounts for the input of background and triggered seismicity. For my specific purposes, I develop two ETAS model modifications in collaboration with Sebastian Hainzl. By means of this approach, I estimate the statistical aftershock parameters and performed simulations of aftershock sequences as well.
In the case of seismic moment release of aftershocks, I focus on the ratio of cumulative seismic moment release with respect to the mainshocks. Specifically, I investigate the ratio with respect to the focal mechanism of the mainshock and estimate an effective magnitude, which represents the cumulative aftershock energy (similar to Bath's law, which defines the average difference between mainshock and the largest aftershock magnitudes). Furthermore, I compare the observed seismic moment ratios with the results of the ETAS simulations. In particular, I test a restricted ETAS (RETAS) model which is based on results of a clock advanced model and static stress triggering.
To analyze spatial variations of triggering parameters I focus in my second approach on the aftershock occurrence triggered by large mainshocks and the study of the aftershock parameter distribution and their spatial correlation with the coseismic/postseismic slip and interseismic locking. To invert the aftershock parameters I improve the modified ETAS (m-ETAS) model, which is able to take the extension of the mainshock rupture into account. I compare the results obtained by the classical approach with the output of the m-ETAS model.
My third approach is concerned with the temporal clustering of seismicity, which might not only be related to earthquake-earthquake interactions, but also to a time-dependent background rate, potentially biasing the parameter estimations. Thus, my coauthors and I also applied a modification of the ETAS model, which is able to take into account time-dependent background activity. It can be applicable for two different cases: when an aftershock catalog has a temporal incompleteness or when the background seismicity rate changes with time, due to presence of aseismic forces.
An essential part of any research is the testing of the developed models using observational data sets, which are appropriate for the particular study case. Therefore, in the case of seismic moment release I use the global seismicity catalog. For the spatial distribution of triggering parameters I exploit two aftershock sequences of the Mw8.8 2010 Maule (Chile) and Mw 9.0 2011 Tohoku (Japan) mainshocks. In addition, I use published geodetic slip models of different authors. To test our ability to detect aseismic transients my coauthors and I use the data sets from Western Bohemia (Central Europe) and California.
Our results indicate that:
(1) the seismic moment of aftershocks with respect to mainshocks depends on the static stress changes and is maximal for the normal, intermediate for thrust and minimal for strike-slip stress regimes, where the RETAS model shows a good correspondence with the results;
(2) The spatial distribution of aftershock parameters, obtained by the m-ETAS model, shows anomalous values in areas of reactivated crustal fault systems. In addition, the aftershock density is found to be correlated with coseismic slip gradient, afterslip, interseismic coupling and b-values. Aftershock seismic moment is positively correlated with the areas of maximum coseismic slip and interseismically locked areas. These correlations might be related to the stress level or to material properties variations in space;
(3) Ignoring aseismic transient forcing or temporal catalog incompleteness can lead to the significant under- or overestimation of the underlying trigger parameters. In the case when a catalog is complete, this method helps to identify aseismic sources.
A main limitation in the field of flood hydrology is the short time period covered by instrumental flood time series, rarely exceeding more than 50 to 100 years. However, climate variability acts on short to millennial time scales and identifying causal linkages to extreme hydrological events requires longer datasets. To extend instrumental flood time series back in time, natural geoarchives are increasingly explored as flood recorders. Therefore, annually laminated (varved) lake sediments seem to be the most suitable archives since (i) lake basins act as natural sediment traps in the landscape continuously recording land surface processes including floods and (ii) individual flood events are preserved as detrital layers intercalated in the varved sediment sequence and can be dated with seasonal precision by varve counting.
The main goal of this thesis is to improve the understanding about hydrological and sedimentological processes leading to the formation of detrital flood layers and therewith to contribute to an improved interpretation of lake sediments as natural flood archives. This goal was achieved in two ways: first, by comparing detrital layers in sediments of two dissimilar peri-Alpine lakes, Lago Maggiore in Northern Italy and Mondsee in Upper Austria, with local instrumental flood data and, second, by tracking detrital layer formation during floods by a combined hydro-sedimentary monitoring network at Lake Mondsee spanning from the rain fall to the deposition of detrital sediment at the lake floor.
Successions of sub-millimetre to 17 mm thick detrital layers were detected in sub-recent lake sediments of the Pallanza Basin in the western part of Lago Maggiore (23 detrital layers) and Lake Mondsee (23 detrital layers) by combining microfacies and high-resolution micro X-ray fluorescence scanning techniques (µ-XRF). The detrital layer records were dated by detailed intra-basin correlation to a previously dated core sequence in Lago Maggiore and varve counting in Mondsee. The intra-basin correlation of detrital layers between five sediment cores in Lago Maggiore and 13 sediment cores in Mondsee allowed distinguishing river runoff events from local erosion. Moreover, characteristic spatial distribution patterns of detrital flood layers revealed different depositional processes in the two dissimilar lakes, underflows in Lago Maggiore as well as under- and interflows in Mondsee. Comparisons with runoff data of the main tributary streams, the Toce River at Lago Maggiore and the Griesler Ache at Mondsee, revealed empirical runoff thresholds above which the deposition of a detrital layer becomes likely. Whereas this threshold is the same for the whole Pallanza Basin in Lago Maggiore (600 m3s-1 daily runoff), it varies within Lake Mondsee. At proximal locations close to the river inflow detrital layer deposition requires floods exceeding a daily runoff of 40 m3s-1, whereas at a location 2 km more distal an hourly runoff of 80 m3s-1 and at least 2 days with runoff above 40 m3s-1 are necessary. A relation between the thickness of individual deposits and runoff amplitude of the triggering events is apparent for both lakes but is obviously further influenced by variable influx and lake internal distribution of detrital sediment.
To investigate processes of flood layer formation in lake sediments, hydro-sedimentary dynamics in Lake Mondsee and its main tributary stream, Griesler Ache, were monitored from January 2011 to December 2013. Precipitation, discharge and turbidity were recorded continuously at the rivers outlet to the lake and compared to sediment fluxes trapped close to the lake bottom on a basis of three to twelve days and on a monthly basis in three different water depths at two locations in the lake basin, in a distance of 0.9 (proximal) and 2.8 km (distal) to the Griesler Ache inflow. Within the three-year observation period, 26 river floods of different amplitude (10-110 m3s-1) were recorded resulting in variable sediment fluxes to the lake (4-760 g m-2d-1). Vertical and lateral variations in flood-related sedimentation during the largest floods indicate that interflows are the main processes of lake internal sediment transport in Lake Mondsee. The comparison of hydrological and sedimentological data revealed (i) a rapid sedimentation within three days after the peak runoff in the proximal and within six to ten days in the distal lake basin, (ii) empirical runoff thresholds for triggering sediment flux at the lake floor increasing from the proximal (20 m3s-1) to the distal lake basin (30 m3s-1) and (iii) factors controlling the amount of detrital sediment deposition at a certain location in the lake basin. The total influx of detrital sediment is mainly driven by runoff amplitude, catchment sediment availability and episodic sediment input by local sediment sources. A further role plays the lake internal sediment distribution which is not the same for each event but is favoured by flood duration and the existence of a thermocline and, therewith, the season in which a flood occurred.
In summary, the studies reveal a high sensitivity of lake sediments to flood events of different intensity. Certain runoff amplitudes are required to supply enough detrital material to form a visible detrital layer at the lake floor. Reasonable are positive feedback mechanisms between rainfall, runoff, erosion, fluvial sediment transport capacity and lake internal sediment distribution. Therefore, runoff thresholds for detrital layer formation are site-specific due to different lake-catchment characteristics. However, the studies also reveal that flood amplitude is not the only control for the amount of deposited sediment at a certain location in the lake basin even for the strongest flood events. The sediment deposition is rather influenced by a complex interaction of catchment and in-lake processes. This means that the coring location within a lake basin strongly determines the significance of a flood layer record. Moreover, the results show that while lake sediments provide ideal archives for reconstructing flood frequencies, the reconstruction of flood amplitudes is a more complex issue and requires detailed knowledge about relevant catchment and in-lake sediment transport and depositional processes.
In a recent BAMS article, it is argued that community-based Open Source Software (OSS) could foster scientific progress in weather radar research, and make weather radar software more affordable, flexible, transparent, sustainable, and interoperable.
Nevertheless, it can be challenging for potential developers and users to realize these benefits: tools are often cumbersome to install; different operating systems may have particular issues, or may not be supported at all; and many tools have steep learning curves.
To overcome some of these barriers, we present an open, community-based virtual machine (VM). This VM can be run on any operating system, and guarantees reproducibility of results across platforms. It contains a suite of independent OSS weather radar tools (BALTRAD, Py-ART, wradlib, RSL, and Radx), and a scientific Python stack. Furthermore, it features a suite of recipes that work out of the box and provide guidance on how to use the different OSS tools alone and together. The code to build the VM from source is hosted on GitHub, which allows the VM to grow with its community.
We argue that the VM presents another step toward Open (Weather Radar) Science. It can be used as a quick way to get started, for teaching, or for benchmarking and combining different tools. It can foster the idea of reproducible research in scientific publishing. Being scalable and extendable, it might even allow for real-time data processing.
We expect the VM to catalyze progress toward interoperability, and to lower the barrier for new users and developers, thus extending the weather radar community and user base.
The Tien-Shan and the neighboring Pamir region are two of the largest mountain belts in the world. Their deformation is dominated by intermontane basins bounded by active thrust and reverse faulting. The Tien-Shan mountain belt is characterized by a very high rate of seismicity along its margins as well as within the Tien-Shan interior. The study area of the here presented thesis, the western part of the Tien-Shan region, is currently seismically active with small and moderate sized earthquakes. However, at the end of the 19th beginning of the 20th century, this region was struck by a remarkable series of large magnitude (M>7) earthquakes, two of them reached magnitude 8.
Those large earthquakes occurred prior to the installation of the global digital seismic network and therefore were recorded only by analog seismic instruments. The processing of the analog data brings several difficulties, for example, not always the true parameters of the recording system are known. Another complicated task is the digitization of those records - a very time-consuming and delicate part. Therefore a special set of techniques is developed and modern methods are adapted for the digitized instrumental data analysis.
The main goal of the presented thesis is to evaluate the impact of large magnitude M≥7.0 earthquakes, which occurred at the turn of 19th to 20th century in the Tien-Shan region, on the overall regional tectonics. A further objective is to investigate the accuracy of previously estimated source parameters for those earthquakes, which were mainly based on macroseismic observations, and re-estimate them based on the instrumental data. An additional aim of this study is to develop the tools and methods for faster and more productive usage of analog seismic data in modern seismology.
In this thesis, the ten strongest and most interesting historical earthquakes in Tien-Shan region are analyzed. The methods and tool for digitizing and processing the analog seismic data are presented. The source parameters of the two major M≥8.0 earthquakes in the Northern Tien-Shan are re-estimated in individual case studies. Those studies are published as peer-reviewed scientific articles in reputed journals. Additionally, the Sarez-Pamir earthquake and its connection with one of the largest landslides in the world, Usoy landslide, is investigated by seismic modeling. These results are also published as a research paper.
With the developed techniques, the source parameters of seven more major earthquakes in the region are determined and their impact on the regional tectonics was investigated. The large magnitudes of those earthquakes are confirmed by instrumental data. The focal mechanism of these earthquakes were determined providing evidence for responsible faults or fault systems.
Continental rifts are excellent regions where the interplay between extension, the build-up of topography, erosion and sedimentation can be evaluated in the context of landscape evolution. Rift basins also constitute important archives that potentially record the evolution and migration of species and the change of sedimentary conditions as a result of climatic change. Finally, rifts have increasingly become targets of resource exploration, such as hydrocarbons or geothermal systems. The study of extensional processes and the factors that further modify the mainly climate-driven surface process regime helps to identify changes in past and present tectonic and geomorphic processes that are ultimately recorded in rift landscapes.
The Cenozoic East African Rift System (EARS) is an exemplary continental rift system and ideal natural laboratory to observe such interactions. The eastern and western branches of the EARS constitute first-order tectonic and topographic features in East Africa, which exert a profound influence on the evolution of topography, the distribution and amount of rainfall, and thus the efficiency of surface processes. The Kenya Rift is an integral part of the eastern branch of the EARS and is characterized by high-relief rift escarpments bounded by normal faults, gently tilted rift shoulders, and volcanic centers along the rift axis.
Considering the Cenozoic tectonic processes in the Kenya Rift, the tectonically controlled cooling history of rift shoulders, the subsidence history of rift basins, and the sedimentation along and across the rift, may help to elucidate the morphotectonic evolution of this extensional province. While tectonic forcing of surface processes may play a minor role in the low-strain rift on centennial to millennial timescales, it may be hypothesized that erosion and sedimentation processes impacted by climate shifts associated with pronounced changes in the availability in moisture may have left important imprints in the landscape.
In this thesis I combined thermochronological, geomorphic field observations, and morphometry of digital elevation models to reconstruct exhumation processes and erosion rates, as well as the effects of climate on the erosion processes in different sectors of the rift. I present three sets of results: (1) new thermochronological data from the northern and central parts of the rift to quantitatively constrain the Tertiary exhumation and thermal evolution of the Kenya Rift. (2) 10Be-derived catchment-wide mean denudation rates from the northern, central and southern rift that characterize erosional processes on millennial to present-day timescales; and (3) paleo-denudation rates in the northern rift to constrain climatically controlled shifts in paleoenvironmental conditions during the early Holocene (African Humid Period).
Taken together, my studies show that time-temperature histories derived from apatite fission track (AFT) analysis, zircon (U-Th)/He dating, and thermal modeling bracket the onset of rifting in the Kenya Rift between 65-50 Ma and about 15 Ma to the present. These two episodes are marked by rapid exhumation and, uplift of the rift shoulders. Between 45 and 15 Ma the margins of the rift experienced very slow erosion/exhumation, with the accommodation of sediments in the rift basin.
In addition, I determined that present-day denudation rates in sparsely vegetated parts of the Kenya Rift amount to 0.13 mm/yr, whereas denudation rates in humid and more densely vegetated sectors of the rift flanks reach a maximum of 0.08 mm/yr, despite steeper hillslopes. I inferred that hillslope gradient and vegetation cover control most of the variation in denudation rates across the Kenya Rift today. Importantly, my results support the notion that vegetation cover plays a fundamental role in determining the voracity of erosion of hillslopes through its stabilizing effects on the land surface.
Finally, in a pilot study I highlighted how paleo-denudation rates in climatic threshold areas changed significantly during times of transient hydrologic conditions and involved a sixfold increase in erosion rates during increased humidity. This assessment is based on cosmogenic nuclide (10Be) dating of quartzitic deltaic sands that were deposited in the northern Kenya Rift during a highstand of Lake Suguta, which was associated with the Holocene African Humid Period. Taken together, my new results document the role of climate variability in erosion processes that impact climatic threshold environments, which may provide a template for potential future impacts of climate-driven changes in surface processes in the course of Global Change.