Swiss Alpine Foreland Research Articles

Impact of topography on in situ soil wetness measurements for regional landslide early warning – a case study from the Swiss Alpine Foreland

Abstract. Recent studies have demonstrated the potential of in situ soil wetness measurements to predict regional shallow landslides. Increasing availability of monitoring data from sensor networks provides valuable information for developing future regional landslide early warning systems (LEWSs); however, most existing monitoring sites are located on flat terrain. The question arises of if the representativeness for regional landslide activity would improve if sensors were installed on a landslide-prone hillslope. To address this, two soil wetness monitoring stations were installed at close proximity on a steep slope and on a flat location in the Napf region (Northern Alpine Foreland of Switzerland), and measurements were conducted over a period of 3 years. As both sites inhibit similar lithological, vegetation, and precipitation characteristics, soil hydrological differences can be attributed to the impact of topography and hydrogeology. At the sloped site, conditions were generally wetter and less variable in time, and evidence was found for temporary lateral water transport along the slope. These differences were systematic and could be reduced by considering relative soil moisture changes. The application of a statistical landslide forecast model showed that both sites were equally able to distinguish critical from non-critical conditions for landslide triggering, which demonstrates the value of existing monitoring sites in flat areas for the application in LEWSs.

Exploring possible links between Quaternary aggradation in the Upper Rhine Graben and the glaciation history of northern Switzerland

The Quaternary filling of the Upper Rhine Graben is an excellent archive to reconstruct sediment dynamics in response to climate change, in particular related to past glaciations of the Swiss Alpine Foreland. Here, a sediment sequence recovered by drilling for exploration purposes near Kronau is investigated, using a combination of sedimentological logging, provenance studies (heavy minerals and clast petrography), and luminescence dating. Several phases of coarse sediment aggradation are identified that possibly correlate to Marine Isotope Stages (MIS) 12 (478–424 ka), 10 (374–337 ka), 8 (300–243 ka), 6 (191–130 ka) and/or 4 (71–57 ka), and 2 (29–14 ka). Several of these phases have previously also been reported from cores recovered in the major Quaternary depo-centre near Heidelberg. This suggests that the observed coarse aggradation in the Upper Rhine Graben can be assigned to various glaciations in northern Switzerland: Möhlin (MIS 12), Habsburg (MIS 10 or 8), Beringen (MIS 6), an unnamed glacial advance during MIS 4, and Birrfeld (MIS 2). However, due to the limited data available, this hypothesis and the suggested correlations require further confirmation by applying the approach presented here to further cores from the Upper Rhine Graben.

Glacial overdeepenings in the Swiss Alps and foreland: Spatial distribution and morphometrics

Overdeepenings (ODs) are erosional features that have been excavated below the regional sea/fluvial base level to produce closed topographic basins. Accessing bedrock topography and OD volume is often challenging. Hence, despite constituting major landscape features and being widespread in (paleo-)glaciated regions, ODs have been overlooked and the subglacial processes involved in their evolution have remained debated. In the Swiss Alpine foreland and valleys, ODs are commonly found filled with water or large volumes of sediment. Using a GIS-Matlab approach based on topographic datasets and bedrock contour-curves, we mapped the spatial distribution of ODs in Switzerland and adjacent areas in the ice-free Alpine areas. The majority of the mapped ODs occurs in very-low bedrock erosional resistance, where ODs are larger, wider and shallower than in medium to high bedrock erosional resistance domains, evidencing a strong lithological control on OD geometry. Longitudinal asymmetry and hypsometric integral suggest a dominance of quarrying during OD evolution and, for selected glacial catchments, headward erosion propagation or high sediment evacuation efficiency. OD surface data (surface and length) can be tentatively used for extracting OD subsurface metrics (depths, nested valleys and first-order volume estimates). Our data seem to indicate that ODs may initiate as multiple small nested valleys and progress to a single and connected depression. Transversal cross-sections also suggest a negative feedback between the erosion potential for deep carving and the presence of low-resistance bedrock, where subglacial meltwater infiltration could have played a key role in OD evolution. Although insightful relationships have been evidenced for ODs in the Swiss Alps and foreland, we have also observed a high spatial variability in key OD metrics such as surface area and depth. This results in general (first-order) interpretations at regional scale, but currently prevent to quantitatively constrain physical subglacial processes at their origin. Comparisons with existing OD datasets under present-day ice (Greenland, Antarctica and modern Swiss glaciers) place our results in a broader context and allow a step forward in our understanding of the complex patterns and mechanisms of (sub-)glacial erosion and resulting landforms.

New chronological constraints on the timing of Late Pleistocene glacier advances in northern Switzerland

Abstract. Deposits of the Reuss Glacier in the central northern Alpine foreland of Switzerland are dated using luminescence methodology. Methodological considerations on partial bleaching and fading correction of different signals imply the robustness of the results. An age of ca. 25 ka for sediment directly overlying basal lodgement till corresponds well with existing age constraints for the last maximal position of glaciers of the northern Swiss Alpine Foreland. Luminescence ages imply an earlier advance of Reuss Glacier into the lowlands during Marine Isotope Stage 4. The presented data are compared to findings from other parts of the Alps regarding glacier dynamics and palaeoclimatological implications, such as the source of precipitation during the Late Pleistocene.

Changes in landscape evolution patterns in the northern Swiss Alpine Foreland during the mid-Pleistocene revolution

AbstractThe northern Swiss Alpine Foreland exemplifies a highly transient landscape characterized by multiple knickzones along the trunk valleys and distinct bedrock straths at their junction with tributary valleys. This landscape has evolved as a result of fast base level changes in response to repeated glaciations during the Quaternary. As the archives related to the evolution of this transient landscape are scarce, available quantitative information is limited, especially for the early and middle Pleistocene. In order to track the pace of the landscape evolution in the northern Swiss Alpine Foreland during the Pleistocene, in this study, we focus on the Deckenschotter sequences, the oldest Quaternary terrestrial sedimentary archives on the northern margin of the Central European Alps. These deposits have been morphostratigraphically divided into two: Höhere (Higher; HDS) and Tiefere (Lower; TDS) Deckenschotter. We analyzed seven different sites extending from Basel in the west to Schaffhausen in the east of Switzerland for the provenance signal, and we dated these archives by depth-profile and isochron-burial dating techniques with 10Be, 26Al, and 36Cl. Investigations on the petrographic compositions of the deposits revealed distinct provenances for the HDS and TDS deposits. During HDS time, the Alpine Rhine drained through Lake Constance and into the Danube River. Rerouting of the river toward the west and into the Upper Rhine Valley occurred between the end of HDS and the beginning of TDS accumulation. The results of the depth-profile and isochron-burial dating suggest that the HDS deposits accumulated at around 2 Ma as a result of a first widespread Alpine glaciation, whereas the TDS was deposited at around 1 Ma. Based on the provenance and the chronological information, we propose a scenario where the Rhine River captured the Alpine sources of the Danube and thus increased its runoff and enhanced its baseline lowering. Consequently, the landscape evolution has been accelerated possibly in response not only to the larger runoff but also to the climate change associated with the mid-Pleistocene revolution.

Multi-scale imaging of a slow active fault zone: contribution for improved seismic hazard assessment in the Swiss Alpine foreland

Seismic hazard assessment of slow active fault zones is challenging as usually only a few decades of sparse instrumental seismic monitoring is available to characterize seismic activity. Tectonic features linked to the observed seismicity can be mapped by seismic imaging techniques and/or geomorphological and structural evidences. In this study, we investigate a seismic lineament located in the Swiss Alpine foreland, which was discussed in previous work as being related to crustal structures carrying in size the potential of a magnitude M 6 earthquake. New, low-magnitude (−2.0 ≤ ML ≤ 2.5) earthquake data are used to image the spatial and temporal distribution of seismogenic features in the target area. Quantitative and qualitative analyses are applied to the waveform dataset to better constrain earthquakes distribution and source processes. Potential tectonic features responsible for the observed seismicity are modelled based on new reinterpretations of oil industry seismic profiles and recent field data in the study area. The earthquake and tectonic datasets are then integrated in a 3D model. Spatially, the seismicity correlates over 10–15 km with a N–S oriented sub-vertical fault zone imaged in seismic profiles in the Mesozoic cover units above a major decollement on top of the mechanically more rigid basement and seen in outcrops of Tertiary series east of the city of Fribourg. Observed earthquakes cluster at shallow depth (<4 km) in the sedimentary cover. Given the spatial extend of the observed seismicity, we infer the potential of a moderate size earthquake to be generated on the lineament. However, since the existence of along strike structures in the basement cannot be excluded, a maximum M 6 earthquake cannot be ruled out. Thus, the Fribourg Lineament constitutes a non-negligible source of seismic hazard in the Swiss Alpine foreland.

Timing of early Quaternary gravel accumulation in the Swiss Alpine Foreland

Deckenschotter (‘Cover Gravels’) are proximal glaciofluvial gravels located in the northern Alpine Foreland mainly beyond the extent of the Last Glacial Maximum. They cover Tertiary Molasse or Mesozoic bedrock with an erosional unconformity. In Switzerland, Deckenschotter are referred to as Höhere (Higher) and Tiefere (Lower) Deckenschotter based on their topographical positions with a significant phase of incision that separates these two units. For this study, we performed sedimentological analyses to identify the provenance, transport mechanisms and depositional environment of these gravels. In addition, we established the chronology of the Höhere Deckenschotter gravels at Stadlerberg using cosmogenic 10Be depth-profile dating technique. The inherited 10Be concentration then allowed estimation of a catchment-wide palaeo-denudation rate. The results from clast fabric investigations indicate that braided rivers within a glaciofluvial environment transported these sediments to the study site mainly as bedload. In addition, the petrographic composition of the deposits shows that a large portion of the gravels was derived through erosional recycling of Miocene Molasse conglomerates. Some material was additionally sourced in the northern Central Alps. We then conclude that gravel accumulation in the Swiss Alpine Foreland was completed at 1.9±0.2Ma. This age, however, represents a minimum age and the oldest 10Be depth-profile age ever obtained for a geological unit. Furthermore, a palaeo-denudation rate of c. 0.3–0.4mm/a was estimated for the catchment of Stadlerberg gravels. Finally, elevation differences between the bedrock underlying the Höhere Deckenschotter and the modern base level imply a long-term regional incision rate of c. 0.12mm/a.

Stress field sensitivity analysis in a sedimentary sequence of the Alpine foreland, northern Switzerland

Abstract. The stress field at depth is a relevant parameter for the design of subsurface constructions and reservoir management. Yet the distortion of the regional stress field due to local-scale features such as sedimentary and tectonic structures or topography is often poorly constrained. We conduct a stress sensitivity analysis using 3-D numerical geomechanical modelling with an elasto-plastic material law to explore the impact of such site-specific features on the stress field in a sedimentary sequence of the Swiss Alpine foreland. The model's dimensions are 14 × 14 × 3 km3 and it contains 10 units with different mechanical properties, intersected by two regional fault zones. An initial stress state is established involving a semi-empirical relationship between the ratio of horizontal to vertical stress and the overconsolidation ratio of argillaceous sediments. The model results indicate that local topography can affect the stress field significantly to depths greater than the relief contrasts at the surface, especially in conjunction with horizontal tectonic loading. The complexity and frictional properties of faults are also relevant. The greatest variability of the stress field arises across the different sedimentary units. Stress magnitudes and stress anisotropy are much larger in stiffer formations such as massive limestones than in softer argillaceous formations. The stiffer formations essentially carry the load of the far-field forces and are therefore more sensitive to changes of the boundary conditions. This general characteristic of stress distribution in the stiff and soft formations is broadly maintained also with progressive loading towards the plastic limit. The stress field in argillaceous sediments within a stack of formations with strongly contrasting mechanical properties like in the Alpine foreland appears to be relatively insensitive to changes in the tectonic boundary conditions and is largely controlled by the maximum stiffness contrast with respect to the load-bearing formations.

The first major incision of the Swiss Deckenschotter landscape

The Swiss Deckenschotter (“cover gravels”) is the oldest Quaternary units in the northern Swiss Alpine Foreland. They are a succession of glaciofluvial gravel layers intercalated with glacial and/or overbank deposits. This lithostratigraphic sequence is called Deckenschotter because it “covers” Molasse or Mesozoic bedrock and forms mesa-type hill-tops. Deckenschotter occurs both within and beyond the extent of the Last Glacial Maximum glaciers. The Swiss Deckenschotter consist of two sub-units: Höhere (Higher) and Tiefere (Lower) Deckenschotter. Although the Höhere Deckenschotter sub-unit (HDS) is topographically higher than the Tiefere Deckenschotter, it is older. The only available age for the Swiss Deckenschotter is 2.5–1.8 Ma based on mammal remains found in HDS at the Irchel site. In this study, we present an exposure age for the topographically lowest HDS, calculated from a cosmogenic 10Be depth-profile. Our results show that the first phase of the Deckenschotter glaciations in the Swiss Alps terminated at least 1,020\(_{ - 120}^{ + 80}\) ka ago, which is indicated by a significant fluvial incision. This line of evidence seems to be close to synchronous with the beginning of the Mid-Pleistocene Revolution, when the frequency of the glacial-interglacial cyclicity changed from 41 to 100 ka and the amplitude from low to high, between marine isotope stages 23 and 22.

Denudation rates of small transient catchments controlled by former glaciation: The Hörnli nunatak in the northeastern Swiss Alpine Foreland

Extensive glaciers repeatedly occupied the northern Alpine Foreland during the Pleistocene and left a strongly glacially overprinted low slope landscape. Only few islands appeared as nunataks standing above the surface of the large piedmont glacier lobes. These nunatak areas kept their original shape, manifested in steep catchments with mean slopes up to 33°. Even though not glaciated, these catchments where significantly affected by base-level changes occurring as a consequence of phases of glacier advances and retreats. Both domains, the glacially eroded and non-eroded, are therefore prone to different mechanisms and time-scales of fluvial and colluvial re-adjustment.In this study we investigate these effects by exploring the spatial distribution and magnitude of denudation in the Hörnli region of the eastern Swiss Alpine Foreland in the present Interglacial. The area represents both domains in a relatively small area with largely uniform tectonic, lithologic and climatic conditions. The differences in Holocene landscape evolution are investigated using topographic analyses and catchment-averaged denudation rates derived from 10Be concentrations in fluvial quartz sand. We find that in formerly non-glaciated, fluvially dominated catchments close hillslope-channel coupling prevails and that these catchments yield high average denudation rates of 350 mm/ka. Glacially overprinted catchments yielded catchment-wide denudation rates an order of magnitude lower. These low denudation rates are hypothesized to be the consequence of both (i) a dominance of slow hillslope processes and (ii) admixture of high concentration, pre-LGM glacial sediment. This suggests that a) a careful field investigation must accompany the denudation rate studies and b) that the concept of area-weighted cosmogenic nuclide denudation rates must be considered in light of the predominant catchment processes.

High magnitude and rapid incision from river capture: Rhine River, Switzerland

AbstractLandscape evolution is controlled by the development and organization of drainage basins. As a landscape evolves, drainage reorganization events can occur via river capture or piracy, whereby one river basin grows at the expense of another. The river downstream of a capture location will generate a transient topographic response as the added water discharge increases sediment transport and erosion efficiency. This erosional response will propagate upstream through both the captured and original river basins. Here we focus on quantifying the impact of drainage reorganization along the Rhine/Aare River system (~45,000 km2) during the late Pliocene/early Pleistocene, where gravel remnants indicate total incision of ~650 m during the last ~4.2 Myr in the region of the recent Aare‐Rhine confluence. We develop a numerical model of drainage capture to quantify the range of possible magnitudes of erosion and the transient river response resulting from the reorganization of the Rhine River. The model accounts for both fluvial incision and sediment transport. Our model estimates 400–800 m of river elevation change (lowering profiles) during the last ~4 Myr due to river capture events, providing an important component to the recent exhumation budget of the Swiss Alpine Foreland. The model indicates a rapid response to capture events (re‐equilibration timescale of ~1 Myr). The predicted incision magnitudes are consistent with incision measured from the elevation of Pliocene and early Pleistocene river gravels, suggesting that across northern Switzerland, a significant amount of incision can be explained by drainage reorganization.

A tribute to Burkart Engesser

Burkart Engesser is one the most renowned specialists onCenozoic rodents and insectivores worldwide. His career aspalaeontologist started 50 years ago as he entered theNatural History Museum Basel (NMB) in 1962 to work asassistant of Johannes Hu¨rzeler. This period lasted until1968 when he decided to undertake a PhD thesis under thesupervision of Hu¨rzeler who was then head of theDepartment of Osteology at the NMB and honorary lec-turer at the University of Basel. He studied the famousMiddle Miocene locality of Anwil located in the vicinity ofBasel. Burkart then started to be interested in small animalsbecause the rich locality mainly yielded tiny teeth, whichhe started to fall in love with. There is indeed an impal-pable emotion in bringing tens of millimetre-sized speciesback to life that are extracted from tons of sedimentsthrough the hard and time-consuming collecting-sieving-picking process. He became Doctor in Zoology in 1971 andhis seminal work was published in a regional Swiss journala year later. His talents as scientific illustrator becamewidely known as he illustrated the hundreds of teeth him-self, with incredible accuracy and remarkable aesthetics.Right after this, he was invited to the United States, atthe Carnegie Museum in Pittsburgh as a visiting museumspecialist for 9 months. There he further developed hisfield experience in various regions and met several mam-mal specialists including the curator for vertebrates, Dr.Mary Dawson, who participates in this volume.After coming back to Basel, he had the chance to takeover the curator position at the NMB after Hu¨rzeler’sretirement until his own retirement in 2007. His Museumwork includes research, for which he dedicated a large partof his time publishing more than 50 papers in variousjournals including the most prestigious ones. His contri-butions cover the fields of systematics, phylogeny, bio-chronology or palaeoecology mostly of the Europeancontinent and the Swiss Alpine foreland basin, but severalarticles and monographs also deal with faunas of the NewWorld and Asia (see publication list below). But Museumwork is also about conservation, in which he involvedhimself in keeping a high collection standard and in greatlyenriching the collection inherited from his famous prede-cessors Ru¨timeyer, Stehlin, Schaub and Hu¨rzeler amongothers. This enlargement is barely visible since tens ofthousands of teeth of rodents and insectivores take only acouple of compactor columns in the vast collection, thetons of sediments he brought to Basel being now washedaway, probably by the Rhine River! Working in collectionsalso means that you meet colleagues from the whole world,and this is the part Burkart always preferred. Most of thecontributing authors of this volume met him in the ‘‘Bun-ker’’ of the NMB (for those who do not know the expres-sion, it is a typical Swiss bomb shelter to protect scientificgoods) and developed projects with him while discussingbiochronology or systematics. Besides research and

The economy and environment of the 4th and 3rd millennia BC in the northern Alpine foreland based on studies of animal bones

The economic and environmental data presented here are based on identifications of more than 275000 animal bones from 126 Neolithic lake shore settlements dated to between 4300 cal. BC and 2500 cal. BC. Due to the excellent state of preservation of all organic material and the consequent precise dating, mostly by dendrochronology, only results from lake shore sites in the Swiss alpine foreland and the area of the Bodensee (Lake Constance) have been considered. Marked fluctuations in the importance of game animals can be recognised throughout the Neolithic lake dwelling period. These fluctuations coincide with climatically induced economic crises which, because of starvation, forced people to intensify hunting and gathering. Looking at the relative importance of the different domestic animals we notice chronologically and geographically influenced differences more than the effects of climatic factors. These differences are mainly due to the environmental evolution resulting from human impact. However, cultural factors may also have had an impact. A comparison of archaeozoological data from the Neolithic lake dwelling sites dated to between 4300 and 2500 cal. BC in the northern Alpine foreland shows a very complicated mosaic of factors influencing the economy of these sites. These include climatic conditions, the state of the environment, human impact and the topography, and all must be taken into account if an economic interpretation of a site, region or period is to be arrived at.

Re‐interpretation of the Meikirch pollen record, Swiss Alpine Foreland, and implications for Middle Pleistocene chronostratigraphy

AbstractThe Meikirch drilling site in the Swiss Midlands north of Bern is re‐interpreted using a combination of sedimentological logging, pollen analyses and luminescence dating. The sedimentary sequence comprises about 70 m of lacustrine deposits, overlain by about 39 m of coarse glacial outwash interpreted to represent at least two independent ice advances. Pollen analyses of the apparently complete limnic sequence reveal a basal late glacial period followed by three warm phases that are interrupted by two stadial periods (Meikirch complex). The warm periods were previously correlated with the Holsteinian and Eemian Interglacials. According to luminescence dating, and with consideration of evidence for Middle Pleistocene climate patterns at other central European sites, a correlation of the Meikirch complex with marine isotope stage (MIS) 7 is now proposed. If this correlation is correct, it implies the presence of three intervals with interglacial character during MIS 7. However, the late Middle Pleistocene vegetational features of the Meikirch complex show significant differences when compared with the pollen record from the Velay region, central France. Possible explanations for this discrepancy are distinct Middle Pleistocene patterns of atmospheric circulation over central Europe and a different distribution of vegetation refugia compared to the Eemian Interglacial and the Holocene. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Luminescence Dating of Sediments from the Luthern Valley, Central Switzerland, and Implications for the Chronology of the Last Glacial Cycle

The advancing glaciers of the last glacial maximum either eroded or deeply buried older sediments in the Swiss Alpine Foreland. However, part of the Swiss Plateau was not covered by ice and is therefore an excellent area for investigating climate and environmental change during the Upper Pleistocene. Repeated fluvial sequences can be studied in several pits along the Luthern Valley. The chronological framework is based on lithostratigraphy, pollen analysis, U/Th dating, and, recently, heavy mineral analysis and luminescence dating. The oldest unit, the Untere Zeller Schotter braided river deposit, represents cold climate conditions and presumably a glaciation prior to the Eemian Interglaciation. The last interglacial period and the very beginning of the last glacial cycle is represented by the Mittlere Zeller Schotter, sediments of a meandering fluvial system. Younger braided river sediments, the Obere Zeller Schotter, seem to correlate with the cold climate of oxygen isotope stage (OIS) 4. Weathering of the top of the Obere Zeller Schotter is likely to represent the OIS 3. The advancing Reuss glacier caused erosion of the recent Luthern Valley, cutting into older sediments, with local loess accumulation during the last glacial maximum as indicated by cover sediments on top of the fluvial sequence.

A Late-Pleistocene pollen sequence from the Jammertal, south-western Germany with particular reference to location and altitude as factors determining Eemian forest composition

Pollen analytical data from a 23-m core taken in the Jammertal subglacial basin, near Biberach an der Riss, has given a continuous sequence from the Rissian late-glacial to the beginning of the Mid-Wurmian. The Eemian interglacial is completely preserved and with a high temporal resolution. Two interstadials, Stafflangen I and II, are recognised in the Lower Wurmian. These two woodlands were dominant byPinus andPicea and there was a small but significant (up to 12%) component of thermophilous deciduous tree pollen. Stafflangen I and II are correlated with St. Germain I and II as known from Grande Pile. The north-eastern areal boundary of thermophilous deciduous trees lies between Jammertal and Grande Pile. Furthermore, it was possible for the first time to define and describe altitudinal zonation in Eemian vegetation. During the Eemian, the altitudinal boundary of shade-tolerant deciduous trees (Carpinus, Abies andPicea) lay at ca. 625 m in Upper Swabia and the Swiss Alpine foreland, and at ca. 560 m in Upper Bavaria to the east. The sites, which were dominated byCarpinus occur below this limit whereasAbies orPicea show a preference for habitats at higher altitudes.

Present-day and future tectonic underplating in the western Swiss Alps: reconciliation of basement/wrench-faulting and décollement folding of the Jura and Molasse basin in the Alpine foreland

The western Alps form a geodynamically active mountain belt showing the typical features of an evolving orogenic wedge with its pro-wedge geometry to the NNW and its retro-wedge structures to the SSE. Renewed tectonic underplating of European continental crust occurred after the orogenic wedge underwent major dynamic disequilibrium following the break-off of the southward subducting slab of the European passive margin. The most important of these basement imbricates are the Mont-Blanc–Aiguilles Rouges and Gastern–Aar crystalline massifs, also forming the Alps' highest mountains. The upper plate–present-day orogenic wedge of the western Alps includes the Molasse basin and the Jura fold-and-thrust belt, both decoupled from the basement over a basal décollement surface. The overall geometry of this wedge appears to be strongly unstable according to simple wedge models. In its attempt to regain stability, out-of-sequence thrusts form in the existing basement nappes; but also new basement nappes should develop beneath the southern portion of the Molasse basin. New out-of-sequence thrusts in the cover, trigger higher than average uplift rates concentrated around the newly forming structures and are accompanied by a concentration of earthquakes. Tectonic underplating is further corroborated by neotectonics and the tectonic structures observed in the Préalpes, Molasse basin and Jura. Similarly, uplift rates, and earthquakes along the southern edge of the Jura mountains seem to witness the development of a new/incipient basement nappe at depth (partial inversion of former Permo–Carboniferous grabens in the basement). A possible spatial coincidence of areas with strong earthquake activity and zones with uplift rates above surrounding values, suggest a common mechanism for their origin in the western Swiss Alpine foreland. Combined with information from basement geometry and wedge dynamics it is proposed that the common mechanism is the development of basement imbricates by tectonic underplating. The proposed model for ongoing and possible future tectonic underplating beneath an active Alpine orogenic wedge also allows to reconcile the models of basement/wrench-faulting in the Molasse basin and Jura with the distant push theory, where the Molasse basin and Jura develop over a basal décollement horizon.

Nebelkarten der Schweiz

Abstract. The analysis of fog distribution over Switzerland consists of two different studies: The first deals with the spatial determination of fog frequencies and fog types for the early morning. It was realized by using the daily observations of 320 stations. This point by point information was spatially interpolated with the aid ofthe information (mean fog cover frequency) of 94 typical fog distributions detected from NOAA satellite data. The derived fog map of Switzerland includes four different fog zones: ground fog zone, fog-free intermediary and high fog (stratus) zone, fog-free slope zone, lower up-slope fog zone. The result of the second study consists of four maps showing the fog cover frequency of the important weather types with fog layers over the Swiss Alpine foreland. They were traced out by using the above mentioned satellite data. The four maps indicate clearly that the fog and cold air distribution during anticyclonic weather situations is strongly determined by the sub-synoptic pressure and wind field.

The most complete quaternary record of the Swiss Alpine Foreland

The open pit section at Thalgut, near Berne (Switzerland), had already been considered as a “quite complete reference section”, with interglacial lacustrine beds, complex glacial sequences and evidence for morphogenetic activity during an earlier interglacial. By a drilling operation this section has been extended, and completed. A long core of a still older interglacial has been recovered containing palynostratigraphic segments characterized by high percentages of Pterocarya and Fagus pollen assemblages. With this discovery the Thalgut section has become the most complete Quaternary sequence of the Northern Alpine Foreland—with two different interglacial lacustrine beds and with a relic paleosoil, separated each by complex glacial and glaciolacustrine sediments. This record also implies a much older age for maximum erosion in the Alpine Foreland.

The Quaternary glaciations of Switzerland, with special reference to the Northern Alpine Foreland

Summary (1) The Quaternary glaciations of the Swiss Alpine Foreland comprise at least five major glacial advances beyond the northern border of the Alps within the time span of the classical chronology of the Alps. However, only two full interglacials are known hitherto between the glacigenic accumulations. This paucity of inter-glacial records and the lack of radiometric dates causes problems in correlation of the Swiss glacial sequence with neighbouring areas or with the deep-sea oxygen isotope record. (2) The Thalgut section to the south of Berne is the most complete lithogenetic Quaternary succession available. The discovery of Pterocarya -beanng inter-glacial deposits there is of regional importance (Hoistein Interglacial sensu Welten). This discovery implies that the most intensive erosion of the perialpine valleys must have taken place before the Riss glaciation of the classical chronology. This observation and the absence of glacigenic deposits at Meikirch and Niederweningen question the traditionally held view that the penultimate glaciation (Riss) was the ‘most extensive glaciation of the Swiss Alps’. ‘The big event’ antedates the Holstein Interglacial sensu Welten. (3) During the early stages of the second before last glaciation (‘Mindel’) or even before that event a change in the morphogenetic behaviour of the Swiss Plain occurred: predominant erosion of the main valleys is followed after that time by predominant accumulation of glacigenic, glacilacustrine and fluvial and lacustrine sediments. This morphodynamic change is most probably related to crustal movements because a change in fluvial or glacial dynamics alone cannot explain this evolution. (4) Traces of glaciations in the Alpine Foreland which antedate the fundamental morphogenetic change and the time period of the classical ‘four glaciations’ are recorded in the cover gravels of NE Switzerland and in the ‘Wanderblockformation’ of the northern Tabular Jura mountains. But these events may be Pre-Quaternary in age. (5) A schematic chronology of the glaciations recorded in the Quaternary sediments of the Swiss Alpine Foreland is given in Fig. 6.