H. L. Jessberger (Ruhr University, Bochum) with a team of geotechnical engineers, continues to apply artificial ground freezing for tunnelling in Germany and abroad. This technology has been used for the subway line U5 in downtown Berlin, where the subsoil is dominated by Holocene sand with a high water table. Freeze pipesplaced in microtunnels, produce a frozen soil ring at least 2 m thick. For high capacity railroad tunnels and road tunnels of 3.5 to 6.5 km length in the Netherlands, artificial ground freezing was used for the construction of traverse galleries between the two parallel main tunnel tubes. The traverse galleries of up to 26 per tunnel are constructed in very difficult subsoil conditions (fine to medium sand or very soft organic clays with high water content and with about 400 kN water pressure). The relevant tunnels cross the Rotterdam Harbour (Botlek railroad tunnel), the Westerschelde (Westerschelde Tunnel at Vlissingen) and the Groene Hardt. In Boston (USA), Rome and Naples (Italy) several major ground freezing applications are in design state. Permafrost aggradation and degradation during the last 200 000 years was simulated numerically for two sections across Northern Germany (Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover) as part of a multinational EU-project. Calculations are based on a detailed climate curve for this time period provided by Jeff Boulton, University of Edinburgh and on detailed knowledge of the geological subsurface conditions. Calculations suggest up to eight periods of permafrost development with maximum permafrost thickness varying between 40 - 150m The roles of rivers and lakes in preventing permafrost development, talik-formation was included in this modelling effort. Special attention was paid to likely permafrost degradation scenarios in front of the Scandinavian ice shield at the time of its maximum advance into Northern Germany during the Weichselian stage.

The Potsdam Research Unit of the Alfred Wegener Institute for Polar and Marine Research (Hans Hubberten) coordinates the multidisciplinary terrestrial portion of the joint German-Russian project “Laptev Sea System 2000”. As part of this research project, an expedition to the Lena Delta region took place in July and August 1998. The expedition group was divided into three
Team 1 focused on modern processes in permafrostaffected soils and used a biological station of the Lena Delta Reserve on the Samoylov Island in the central part of the Lena Delta. Instruments were installed at 4 measuring sites during 1998 fieldwork. Ongoing multidisciplinary studies focus on the seasonal variability of modern processes in tundra soils. The main scientific objectives were: 1 Study of the energy and water balances of the active layer and the upper part of permafrost; 2 Quantification of the climatic, pedogenic and soil microbial parameters which control the production, oxidation and emission rates of trace gases in soils; 3 Measurement of the carbon flux balances (CO2, CH4) at differing tundra sites within the study area.
Team 2 focused on modern and ancient sedimentation in the Lena Delta and worked aboard the vessel Dunay. The main scientific goals were: 1 Sedimentation history reconstruction of the Lena Delta; 2 Understanding the influence of global, regional and local climatic variability on sedimentation in the Lena Delta; 3 Modern and ancient sediment budget of the Lena Delta.
Team 3 focused on climate signals in ice-rich permafrost deposits and worked at the key section of the Late Pleistocene Ice Complex, Mamontovy Khayata, on the Bykovsky Peninsula. Their multidisciplinary research programme includes: 1 Complex cryolithological studies; 2 Ground ice research, especially on ice wedges of differing ages using various isotope and hydrochemical analyses; 3 Systematic paleontological research (mammal bones, insect fossils, rodents, plant remains, seeds); 4 Extensive sampling for radiocarbon and OSL dating; 5 Study of modern geocryological processes. The second expedition, started in April 1999, consisted of 7 field groups. They studied the processes listed above for a full seasonal cycle, from spring to late autumn. Sediment coring from the ice cover on lakes and lagoons in the spring, and an extensive coastal process investigation in the Lena Delta and Laptev Sea in summer comprise an investigation of the environmental history of the Lena Delta. Paleoclimatic signals in ice-rich permafrost are investigated on the Bolshoy Lyakhovsky Island and extend
the sample base created in 1998. In addition, projects emphasising hydrologic and thermal dynamics of the active layer, silicate weathering and the carbon cycle in high Arctic soils are ongoing. Automated sites were installed in 1998 close to Ny-Ålesund, Spitsbergen and at Zackenberg, NE Greenland, with water, gas and soil sampling.
To identify sedimentary and permafrost structures within the Lena Delta, sampling of sedimentary sequences by shallow coring and through natural exposures, ground penetrating radar, and shallow seismic studies, have all been carried out. Mineralogy and geochemistry of the sediments show details about the processes controlling the late Quaternary conditions of accumulation and deposition. The geophysical methods of sub-bottom profiling were twofold: (1) A RAMAC impulse radar system proved to be a viable technique for mapping subsurface structures on land. The 100 MHz radar signal penetrated the permafrost down to 30 m maximum and indicated wedges and ice layers. Drilling was used to determine the geologic composition. (2) A sediment echo sounder was used as high-frequency pulse source for seismic surveying of sediments of Lake Nikolay in the western Lena Delta. It was possible to characterise the geometry of basin fills and changes in lake sedimentation as well as to identify the permafrost table below talik zones.
The research group of the Geographical Institute, University of Giessen, continued its studies in the EUproject PACE. In summer 1999 extensive field checks were carried out concerning periglacial and natural hazard features originating in permafrost areas in the Mattertal valley. At the new Grächen-Seetalhorn test site geomorphological mapping of periglacial features and microclimatological measurements in the coarse blocky debris flow are being carried out. Correlation between slope processes and permafrost distribution were analysed using GIS.
Slope processes were surveyed by geomorphologic mapping, permafrost distribution was investigated by modelling (PERMAKART (F. Keller) and PERMAMAP (M. Hoelzle)) and BTS-mapping. The results of the geomorphologic mapping show many different periglacial forms and processes in the Gornergrat area such as rock glaciers, solifluction, rockfall and debris flows. By combining the results of the permafrost models and those of the BTS-measurements the calculation of a realistic permafrost distribution was carried out. The results of the GIS-analysis indicate a dependency of solifluction forms upon permafrost. The activity of rock glaciers seems closely connected to the occurrence ofperennially frozen ground. Modelling of rockfall- and debris flow-trigger zones show that both processes can occur in permafrost as well as in non-permafrost areas. Alpine permafrost is also studied in the Zugspitz summit area (highest peak in Germany) as part of the EU-project PACE by M. Gude (Department of Geography, Jena). Permafrost thermal conditions are monitored by temperatures measurements in surface and bedrock sites. Based on model PERMAKART and PERMAMAP the distribution of permafrost in the area is evaluated. Monitoring and model results are aimed at improving risk assessment and management related to thawing permafrost and slope instability in the area.

The occurrence and ecological implications of sporadic permafrost in blocky scree slopes of non-alpine mountains in central Europe (altitudes less than 1000 m asl.) is subject of a joint research programmeme by Martin Gude/Roland Mäusbacher (Department of Geography,
Jena) in co-operation with Roland Molenda (Department of Zoology, Jena) and other biologists. The main aim is to understand the thermal regime and the
stability of these permafrost sites by means of field monitoring and modelling approaches. Ground temperatures have been monitored in several block scree slopes in Germany and France for more than four years. Investigations on snow hydrologic processes and related sediment transport in the permafrost area of Swedish Lappland (Kärkevagge, Abisko area) are being
continued by Martin Gude in co-operation with Dieter Scherer (Department of Geography, Basel, Switzerland) and Christer Jonasson (Abisko Scientific Research Station) in the framework of MOSAIC (Modelling of Snowmelt and its Consequences).

A field measurement campaign was undertaken in 1998 and the next field research is planned for 2000. In the Austdalur drainage basin (23 km²), located in the mountains of the Icelandic Eastern Fjords (Austfirðir), A. Beylich, Halle University, has started studies of recent gravitational and fluvial mass transfer in a subarcticoceanic periglacial environment free of permafrost, but with Pleistocene glaciations and a steep, alpine relief. Annually, fluvial sediment transport in the main channels clearly dominates over slope processes. Aquatic slope denudation (slope and rill wash) is the most important slope process, followed by geochemical denudation, avalanches, rock- and boulder falls, creep, debris slides/debris flows, and deflation. The intensity of recent processes is low.

Lorenz King & Martin Schlerf (lorenz.king@geo.uni-giessen.de)