GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Automatic weather stations for basic and applied glaciological research
No full textSince the early 1980s, the Geological Survey of Denmark and Greenland (GEUS) glaciology group has developed automatic weather stations (AWSs) and operated them on the Greenland ice sheet and on local glaciers to support glaciological research and monitoring projects (e.g. Olesen & Braithwaite 1989; Ahlstrøm et al. 2008). GEUS has also operated AWSs in connection with consultancy services in relation to mining and hydropower pre-feasibility studies (Colgan et al. 2015). Over the years, the design of the AWS has evolved, partly due to technological advances and partly due to lessons learned in the field. At the same time, we have kept the initial goal in focus: long-term, year-round accurate recording of ice ablation, snow depth and the physical parameters that determine the energy budget of glacierised surfaces. GEUS has an extensive record operating AWSs in the harsh Arctic environment of the diverse ablation areas of the Greenland ice sheet, glaciers and ice caps (Fig. 1). The current GEUS-type AWS (Fig. 2) records meteorological, surface and sub-surface variables, including accumulation and ablation, as well as for example ice velocity. A large part of the data is transmitted by satellite near real-time to support ongoing applications, field activities and the planning of maintenance visits. The data have been essential for assessing the impact of climate change on land ice. The data are also crucial for calibration and validation of satellite-based observations and climate models (van As et al. 2014)
Katabatic winds and piteraq storms: observations from the Greenland ice sheet
No full textIn 2007 the Programme for Monitoring the Greenland Ice Sheet (PROMICE) was initiated to observe and gain insight into the mass budget of Greenland ice masses. By means of in situ observations and remote sensing, PROMICE assesses how much mass is gained as snow accumulation on the surface versus how much is lost by iceberg calving and surface ablation (Ahlstrøm et al. 2008). A key element of PROMICE is a network of automatic weather stations (AWSs) designed to quantify components of the surface mass balance, including the energy exchanges contributing to surface ablation (Van As et al. 2013)
The Lower Palaeozoic now fully cored and logged on Bornholm, Denmark
No full textA 558 m long, complete section of the Lower Palaeozoic succession preserved onshore southern Bornholm has been compiled from five fully cored scientific wells, carried out between 2005 and 2012. The scientific programme included coring and geophysical logging of the five scientific wells that yielded a total of c. 750 m of partially overlapping cores as well as re-logging of water wells and acquisition of shallow seismic data. The last well drilled, the Sommerodde-1, cored the youngest preserved Silurian strata on Bornholm including strata not exposed in outcrops. The well penetrated 168.1 m of Silurian shales, 42.7 m of Upper Ordovician shales and 27.9 m of Alum Shale before it terminated at a depth of 250.3 m in the Lower Cambrian Norretorp Member of the Læså Formation. Th e Sommerodde-1 well documents that the Lower Silurian Cyrtograptus shale is at least 91.7 m thick and that the Rastrites shale is 76.4 m thick. The complete Lower Cambrian succession has previously been covered by the 316.0 m deep Borggård-1 well that terminated in basement rocks (Nielsen et al. 2006)
Thrust-fault architecture of glaciotectonic complexes in Denmark
No full textCross sections of glaciotectonic complexes are exposed in coastal cliffs in Denmark, which allow structural studies of the architecture of thin-skinned thrust-fault deformation (Pedersen 2014). However, the basal part of the thrust-fault complex is never exposed, because it is located 50 to 100 m below sea level. It is in the basal part the most important structure – the décollement zone – of the complex is found. The décollement zone constitutes the more or less horizontal surface that separates undeformed bedrock from the displaced thrust-sheet units along the décollement level. One of the most famous exposures of glaciotectonic deformations in Denmark is the Møns Klint Glaciotectonic Complex. The structures above sea level are well documented, whereas the structures below sea level down to the décollement level are poorly known. Modelling of deep structures was carried out by Pedersen (2000) but still needs documentation. A glaciotectonic complex affecting comparable rock units, such as the chalk at Møns Klint, was recently recognised in seismic sections from Jammerbugten in the North Sea (Fig. 1). These sections provide an excellent opportunity for comparable studies of the upper and lower structural levels in thin-skinned thrust-fault deformation, which is discussed in this paper with examples from three major glaciotectonic complexes
Consistency of postglacial geodynamics for the Kattegat region, southern Scandinavia, based on seismological, geological and geodetic data
No full textThe earthquake map of Denmark is constantly being improved. Together with data from western Sweden and southern Norway it shows more and more convincingly a gradual, scattered earthquake activity across the Kattegat region from low activity in the Precambrian basement of Scandinavia to lack of earthquakes in south-western Denmark and northern Germany. The activity is only partly connected with mapped geological features
The Continental Shelf Project of the Kingdom of Denmark – status and issues
No full textThis paper summarises the status of the Continental Shelf Project of the Kingdom of Denmark after the recent submission for an extended continental shelf in the area to the north of Greenland. We discuss some of the similarities between the submission areas north of the Faroe Islands and north of Greenland including the morphological continuation of ridges extending seaward of the geomorphical continental shelf. Documentation of the sediment thickness in the adjoining basins and sediment continuity with the continental slope plays a vital role in the delineation of the outer limits of the extended continental shelf. Here, we compare how these issues were addressed around the well-studied Faroe Islands and in the sparsely surveyed Arctic Ocean
A multidisciplinary study of a geothermal reservoir below Thisted, Denmark
No full textThe first geothermal plant in Denmark was established in 1984 near the town of Thisted (Fig. 1). For nearly 30 years the plant has successfully produced c. 43°C hot water (surface temperature) from a highly permeable sandstone reservoir in the Late Triassic to Early Jurassic Gassum Formation and used the heat from the geothermal water for district heating. The 45°C hot water (formation temperature) is pumped up from a vertical production well, Thisted-2, from a depth of c. 1250 m and the cooled water (c. 12°C) is re-injected into the formation through a vertical injection well, Thisted-3, located 1.5 km east of the production well
Down-hole permeability prediction – a chemometric wire-line log feasibility study from a North Sea chalk well
No full textPermeability in chalk depends primarily on porosity but also on other factors such as clay and quartz content, and can theoretically be described by the Kozeny equation using empirically determined constants (Mortensen et al. 1998; Røgen & Fabricius 2002). Recent attempts to predict permeability from wire-line logs have shown that compressional velocity within operative chalk units, defined by specific surface and hydraulic properties established from stratigraphy and core plugs, can provide excellent well permeability predictions (Alam et al. 2011). High-quality predictions depend on a solid knowledge of a multitude of parameters of the relevant ‘operative rock types’. The more detailed this a priori knowledge is, the better predictions can be achieved. But this approach may, or may not, be fast enough for wellsite operations or when core data are lacking. In this study, we illustrate a situation for direct permeability prediction if only well-site, wire-line logs are available
Unique applied glaciology challenges of proglacial mining
No full textThe glaciology group at the Geological Survey of Denmark and Greenland (GEUS) has a tradition of applied glaciology consulting for hydropower projects in Greenland (Weidick & Thomsen 1982; Braithwaite & Olesen 1988; Ahlstrøm et al. 2008). This includes assessments for the hydropower plants now operating at Ilulissat and Nuuk (Braithwaite & Thomsen 1989; Thomsen et al. 1989; 1993), as well as the outburst potential of ice-dammed lakes such as Qorlortorsuup Tasia (Mayer & Schuler 2005). Several factors, including long-term increases in global resource demand, increasing air temperatures and glacier retreat due to climate change, and improved mining and prospecting techniques may now improve the economic feasibility of mining in Greenland (Colgan & Arenson 2013). Given that over 80% of Greenland is ice-covered, mining projects in Greenland often occur in ‘proglacial’ settings, meaning adjacent to, or close to, an ice margin. The Isukasia, Kvanefjeld, Maarmorilik and Malmbjerg prospects exemplify resource development in proglacial settings in Greenland