Research on permafrost in the Abisko area of northern Sweden date from the 1950s. A mean annual air temperature of −3°C in the Abisko mountains (i.e. 1000 m a.s.l.) and −1°C beyond the mountain area at an altitude of around 400m suggests that both moun− tain and arctic permafrost occur there. Several geophysical surveys were performed by means of resistivity tomography (ERT) and electromagnetic mapping (EM). Wherever pos− sible the geophysical survey results were calibrated by digging tests pits. The results show that permafrost occurs extensively in the mountain areas, especially those above 900m a.s.l. and also sporadically at lower altitudes. At 400 m a.s.l. permafrost may be up to 30 m thick. Its thickness and extent are determined largely by the very variable local rock and soil con− ditions. Fossil permafrost is also likely to occur in this area.
On the ground of results obtained by the seismoacoustic profiling carried out in 1985 and primary examination of core samples the following main seismoacoustic units are distinguished and characterized: unit A — bedrock, unit B — till and/or compacted glaciomarine deposit, unit C — glaciomarine ice-front deposit, unit D — glaciomarine mud. These results enabled to present the distribution of seismoacoustic units along the fiord and its extension on the shelf, as well as to determine a relation of bottom structures to Late Vistulian(?) deglaciation and the action of Holocene tributary glaciers, probably during the Little Ice Age. The position of marginal structures corresponding to local retreat stages of the glacier front is also presented.
The paper presents results of investigations of bottom sediments in Hornsund, Wijdefjorden and Isfjorden as well as of the shelf around the Bjornoya. carried out in 1982—1985 by a continuous seismic profiling. Geophysic structures and bottom sediments on the bedrock to a depth of 170 ms have been recognized, particularly in the Hornsund region. The following seismoacoustic units have been distinguished: unit A — bedrock, unit В — till and/or compacted glaciogenic deposit, unit С — glaciomarine ice-front deposit, unit D — glaciomarine mud. These results allowed to present a model of glaciomarine sedimentation in a fiord, fed by warm tidewater glaciers.
The results of the detailed seismoacoustic profilling (CSP, boomar) are presented. The investigation has been carried out in February 1985 and 1988 during two Geodynamical Expeditions organized by the Institute of Geophysics of the Polish Academy of Sciences. The boomar penetration of the caldera floor went down to 150 msec. Four seismoacoustic units of volcanic formations have been determined. The unit A corresponds to pre-caldera series and occurred only in the border part of the flooded caldera. The unit contains mainly pyroclastic rocks (consolidated agglomerates and tuffs) and probably some intercalations of lavas. The units B, C and D fill up the caldera bottom and correspond to post-caldera series. The units are composed of pyroclastic rocks, containing also materials redeposited by lahars, glaciers, landwaters and by wind. The units C and D (the youngest one) were certainly deposited under water. All the units are cut by numerous faults, vents and other types of intrusions. The larger faults, en echelon type, are situated around the bottom and form a ring-fracture. Caldera was formed by succesive stages of collapsing. This process is not finished yet and volcanic activity is still alive (especially in the western part of the flooded caldera).
In the present report worked out in the form of a communication the general description of course and realization of the scientifical and technical programmes of the VIth Expedition to the Polish Polar Station in the Hornsund fiord on Spitsbergen is given. The details of the programme and results of investigations on particulat items constitute already or will constitute within the next time a subject of special publications.
The succesive fifth whole-year research expedition stayed at the polar station of the Institute of Geophysics, Polish Academy of Sciences, in the Hornsund fiord from July 1982 to August 1973. Continuous observations as well as sejsmologic, magnetic and meteorological records, constituting continuation of the investigations started in summer 1978. were carried out by the wintering group of 8 men. Also separate research programmes: physics of atmosphere and ionosphere, sedimcntologo-oceanological, geomorphological and medical investigations, including observations of white bears, were realized. Many technical works, repairs and adaptations were carried out as well.