Flood and vortex scour were observed in the Prosna channel (Central Poland) in the years 1980-1985. Flood scour increases the thickness of the reworked channel deposits by 30 per cent to 66 per cent, in relation to the thickness determined by the elevation of the normal bed and the bankfull stage. Vortex scour can increase the thickness by as much as 90-95 per cent. Knowledge of these properties of contemporary alluvium allows correct palaeohydrological and stratigraphic interpretation of the alluvial fills of valley floors.

Tsu nami de pos its have not pre vi ously been re corded along the south ern coast of the Bal tic Sea. The re sults of pres ent research pro vide ev i dence of high-en ergy event lay ers that oc cur on the bot tom of two hemi spher i cal hol lows cut into glaciolimnic silt and glaciofluvial sand and gravel of Late Weichselian age. The event de pos its are rep re sented by poorly sorted ma rine sand with ad mix tures of peb bles and allochthonous biogenic de tri tus: ma rine, brack ish and oc ca sion ally fresh wa ter shells and shell de bris of bi valves and snails, plant macrofossils from the nearshore zone, shreds and lumps of peaty ma te rial, gyttja and organogenic silt, lumps of char coal, wood pieces and tree branches and trunks. All these fea tures are com monly con sid ered in dic a tive of tsu na mis. The age of the biogenic de tri tus found in the tsu nami layer ranges from 6,630 to 10,390 cal. yr BP, whereas the old est gyttja cov er ing the event lay ers is 6,600 cal. yr BP old. This means that the tsunami oc curred be tween 6,600 and 6,630 cal. yr BP. Var i ous causes of the tsu nami event are con sid ered, in clud ing the impact of me te or ites within the coastal plain and the lit to ral zone of the south ern Bal tic Sea.

No abstract

The determination of the bottom of a subfossil meandering palaeochannel is important for investigations of the palaeohydrology of valley bottoms, and crucial for the quantitative estimation of past river discharges. The authors present a procedure on the basis of which the bottom of a palaeochannel can be precisely determined. It is based on an analysis of the stratigraphic variability of such features of deposits as: mean diameter, standard deviation of the grain-size composition, the percentage of sand, and ignition loss.