Georelief, its origin and development in the coastal area between Pori and Uusikaupunki, south-western Finland

The georelief and its origin and development were studied in an area in which the principal bedrock consists of Subjotnian and Jotnian formations surrounded by an orogenic basement complex. The youngest rock of the Jotnian group present in the area, the diabase, was found to be very much more extensive in its occurrence there than was previously thought. The area slopes away in approximately a 100°‑280° direction, with a mean dif­ference in height between the summit and valley height trend surfaces of almost 30 m. The diabase areas normally stand out in height from the other bedrock types, while the sandstone areas lie at an obviously lower level. The mean height difference between these two surfaces is 25‑30 m, and that between the bedrock surfaces themselves 45‑50 m. These differences are attributed to differential resistance to erosion. Seven relief types are distinguished in the area on the basis of their morphogenesis and relative relief, and the distribution of these and indi­vidual special landforms is represented on a medium‑scale geomorpho­logical map in colour. The special landforms are classified into eight ge­netically distinct groups. The most extensive of the relief types is that dominated by bedrock erosion forms, which acquired virtually their present outlines in preglacial times, although the sandstone bedrock region features exclusively relief types arising from the deposition or erosion of surficial material with associated accumulation and erosion landforms. The deglaciation phase, which lasted just under 300 years in the area, involved local re‑activation of the ice margin and changes in the direction of ice movement occurring largely for topographical reasons. The dominant direction of ice movement was normally NW–SE, westerly orientations being local in extent and limited to the deglaciation phase, during which large numbers of N–S‑oriented end moraines were formed. The whole area occupied a subaquatic position upon the retreat of the ice, and postglacial sediments over 30 m in thickness are to be found in places. The majority of the area emerged from the sea during the Ancylus Lake and Litorina Sea phases, during which large numbers of beach ridges were created, especially in association with glaciofluvial landforms. The majority of the aeolian land­forms of the area are found close to the present coastline, and their material is on average finer and better sorted than that of the beach ridges. The present development of the georelief of the area is being profoundly in­fluenced by human activity