Colby A. Smith

LiDAR-derived inventory of post-glacial fault scarps in Sweden

Abstract Pre-existing bedrock structures that reactivated following deglaciation through a combination of tectonic and isostatic stresses are well documented in northern Fennoscandia. Due to their possible implications for seismic hazards, there is a need to document the locations and geometries of these features. The recent availability of a high-resolution, LiDAR-derived, digital elevation model covering most of Sweden provides an ideal base upon which to map post-glacial fault scarps that appear to crosscut glacial sediments and landforms. The current mapping project has identified new post-glacial fault scarps in central Sweden, and both refined and rejected scarps previously mapped by aerial photographic interpretation in northern Sweden. No post-glacial fault scarps, however, were identified in southern Sweden. The current inventory of post-glacial fault scarps is available for download and will be updated as more data become available.

Integrated use of LiDAR and multibeam bathymetry reveals onset of ice streaming in the northern Bothnian Sea

Abstract Geomorphological mapping from the new LiDAR (Light Detection and Ranging)-derived digital elevation model for Sweden and a high-resolution multibeam bathymetry data-set for the Gulf of Bothnia reveals a continuous system of glacial landforms crossing the transition between the modern terrestrial and marine environments. A palaeo-ice stream in the northern Bothnian Sea is reconstructed, with an onset tributary over the present-day Ångermanland–Västerbotten coastline. Systematic contrasts in landform morphology and lineation length indicate that this ice stream comprised a relatively narrow (∼40 km) corridor of fast flow, flowing first SW then S, and likely fed by converging flow around the upper Bothnian Sea. The geometry and landform associations of this system imply that ice, at the time period represented here, did not flow across the Gulf of Bothnia: SSE-ward ice flow indicators on the northern Swedish coast do not correspond directly with landform assemblages of the large SE-oriented Finnish deglacial lobes. Instead, we suggest they may contribute to a late-stage fast-flow event to the S and SW. Multibeam bathymetry data offer entirely new access into the rich, landform-scale geomorphological record on the seafloor of the Gulf of Bothnia. The combination of offshore multibeam with the new terrestrial LiDAR data provides unprecedented insight into and renewed understanding of the glacial dynamics of the Bothnian Sea sector of the Fennoscandian Ice Sheet, hitherto interpreted over large areas of unmapped ice sheet bed.

Coeval fluctuations of the Greenland ice sheet and a local glacier, central East Greenland, during late glacial and early Holocene time

We present a 10Be chronology of late glacial to early Holocene fluctuations of a Greenland ice sheet outlet glacier and the adjacent Milne Land ice cap in central East Greenland. Ages of boulders on bedrock indicate that both ice masses receded during the Younger Dryas (YD), likely due to rising summer temperatures. Since Greenland ice core records register cold mean annual temperatures throughout the YD, these ice-marginal data support climate conditions characterized by strong seasonality. The ice sheet outlet glacier and ice cap deposited inner Milne Land Stade moraines at 11.4 ± 0.8 ka and 11.4 ± 0.6 ka, respectively (mean moraine ages and 1σ uncertainties). Based on the coeval moraine ages, we suggest that both ice masses responded to climate conditions acting on the ice margins, specifically ablation. Moreover, the ice sheet responded sensitively (i.e., on the same time scale as a small ice cap) to climate conditions.

Glacial geomorphology of the south Swedish uplands – focus on the spatial distribution of hummock tracts

ABSTRACT We present the first comprehensive glacial-landform map of the south Swedish uplands (SSU), deglaciated 15–13 ka ago, using one consistent method and dataset; a Light Detection and Ranging-derived digital elevation model. In particular, this map focuses on the spatial distribution of hummock tracts. The distribution of hummock tracts reinforces previous thinking of a broad lobate east–west zone of hummocks across the southern part of the SSU. But this map also reveals a pattern of hummock tracts confined in what we call hummock corridors that have a radial pattern sub-parallel to the overall ice-flow direction. Hummocks occur in a wide variety of morphologies, but we also show the distribution of two distinct forms: V-shaped hummocks and ‘ribbed moraine’. Cross-cutting relationships between hummocks and glacial lineations indicate a more complex chronology than previously suggested. In places, lineations are overlain by hummocks and in other places hummocks are overlain by lineations. Additionally, directional variation of glacial lineations together with a complex end-moraine pattern suggests a dynamic ice sheet with multiple small lobes. Finally, mapped end moraines help to better correlate the deglacial timescales of western and eastern Sweden.

Quaternary geomorphology of the Siljan area, central Sweden

We present a 1:100,000 scale Quaternary geomorphic map covering 2500 km2 in Central Sweden and including the Siljan Impact Structure. Because of the crater, the area is currently under consideration to become a geopark, and this project was undertaken to document Quaternary geology that may be of interest to park organizers and future visitors. A high-resolution digital elevation model with a vertical resolution of 0.25 m and a lateral resolution of 2.0 m was used as the base to map sub-, pro-, and post-glacial landforms. Consideration of the suite of landforms indicates ice flow from the northwest, multiple paleo-lake levels, and unstable landscapes into the Holocene. Additionally, the impact structure has played a role in routing both glacial and post-glacial drainage.

Geomorphic and stratigraphic criteria used to date the Råda Landslide, Västra Götaland, Sweden

A high-resolution digital elevation model has been used to locate a large and previously unknown landslide in glacial-marine sediments in southwest Sweden. Interpretation of the geomorphology and stratigraphy allow for bracketing of paleo-sea level to between 68 and 71 m above sea level when the landslide occurred. Existing sea-level curves suggest that this elevation would have emerged above sea level, and the landslide would have occurred, about 10 800 calendar years before the present. We suggest that the presence of a confined aquifer beneath the area that slid created a weakness in the slope upon which it eventually failed.

Integration of Geohazards into Urban and Land-Use Planning. Towards a Landslide Directive. The EuroGeoSurveys Questionnaire

Exposure to hazards is expected to increase in Europe, due to rapid population growth in urban areas and the escalation of urbanization throughout many countries. In the framework of the European Geological Surveys (EGS), the Earth Observation and Geohazards Expert Group (EOEG) has carried out a survey based enquiry regarding the integration of geohazards (earthquakes, volcanoes, landslides, ground subsidence, floods and others) into urban and land-use planning. Responses from 19 European countries and 5 regions reveal heterogeneous policies across national borders. 17% of the countries have not yet implemented any legal measures to integrate geohazards into urban and land-use plans and half of the participating countries have no official methodological guides to construct geohazard maps. Additionally, there is a scarce knowledge about real social impacts of geohazards and resulting disasters in many of the countries, although they have a significant impact on their national economies. This overview stresses the need for a common legislative framework and homogenization of the national legislations as well as mutual guidelines which adopt the principles applicable to the management of geohazards and explain the process to be followed in the production of hazard documentation. This is especially relevant in case of landslide and subsidence hazards; although those are of great importance in Europe, there are no common guidelines and practices similar to Directive 2007/60/EC on the assessment and management of flood risk. Based on their expertise, EuroGeoSurveys (EGS) have the potential to coordinate this activity in European geohazard guidelines and to promote the interaction among stakeholders.

Geomorphic evidence of multiple surface ruptures of the Merasjärvi “postglacial fault”, northern Sweden

ABSTRACT Postglacial faults in Sweden are generally believed to have ruptured to the surface once either during or shortly after the late Weichselian deglaciation. Stratigraphic data from multiple scarps support or are consistent with this hypothesis and, until now, no data refute it. This study presents geomorphic evidence that a segment of the Merasjärvi fault in northern Sweden ruptured to the surface at least twice. The timing of the fault ruptures is poorly constrained because the scarp lies within a preserved glacial landscape. Crosscutting relationships indicate that the scarp is younger than the early Weichselian but suggest that parts of the scarp existed beneath the late Weichselian ice sheet.

Development of a Methodology for Quick Clay Mapping

Quick clays involve considerable risks because small initial slips may evolve into large landslides involving the entire quick clay formation. Most large clay slides in Sweden, Norway and Canada have been in quick clay areas. It is therefore necessary to develop cost-effective methods for mapping the extent of quick clay formations and areas with probable quick clay. The most important areas are those with existing infrastructure and buildings as well as areas planned for exploitation. The methodology should be well-designed in proper steps with different levels of accuracy and include overview studies of topographical and geological methods, detailed geophysical and geotechnical ground investigations, as well as airborne geophysical methods with greater coverage but less accuracy. Three areas in southwest Sweden and one area in the northeast have been selected for this study. In these areas, locations with and without quick-clay have been identified by geotechnical sounding and sampling. Airborne electromagnetic (ATEM) measurements have been carried out in all four areas. The preliminary results from the first two areas, which are presented in this paper, show a reasonable correlation between the different methods used.

Analysis of Ground Geophysical, Airborne TEM, and Geotechnical Data for Mapping Quick Clays in Sweden

Airborne transient electromagnetic (ATEM) data for mapping clay areas are acquired in four areas in Sweden. The resistivity models from the inversions of ATEM data are compared to the existing geotechnical, geological and ground geophysical data in one of the areas at Slumpan located in the Gota River valley. The ATEM models reveal information about layering and thickness of the sediments, the river depth and bedrock undulations. The estimated resistivities at the known locations of quick clays are within the range of 8–40 Ωm. The variation is dependent on the type of the surrounding sediments and the leaching process. The resistivity models have a limited resolution and must always be integrated with geotechnical and geological information for a confident and precise interpretation that leads to a realistic model. The method can be utilized as an effective tool prior to planning of any detailed and costly ground geotechnical investigations.