Geographia Polonica (1988) vol. 53

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Main phases of erosion and accumulation in the Prosna valley in the last glacial-interglacial cycle

Karol Rotnicki

Geographia Polonica (1988) vol. 53, pp. 53-66

Abstract

The problem of associating the main phases of erosion and accumulation in rivervalleys with specific climatic phases of the glacial-interglacial cycle has been known for along time (Soergel 1921; Penck 1938; Trevisan 1949; Jahn 1956a, b; Schumm 1965;Rotnicki 1974a; Kozarski and Rotnicki 1977, 1978, 1983; Starkel 1983). In the initialperiod of the investigation of this problem the prevailing view was that expressed bySoergel (1921), among others, that conditions existing in cold periods of the Pleistocenefavoured intensive accumulation in river valleys resulting in high valley filling. By thesame view, interglacial periods were characterized by deep erosion.

As the time passed, newer and newer studies kept modifying this view. Jahn(1956a, b) expressed the opinion that the erosion phase appears twice in theglacial-interglacial cycle: first at the turn of an interglacial and a glacial, and then at thetransition from the glacial to a temperate period. Schumm (1965) presents a somewhatdifferent view on this problem. According to him, the erosion appears in a late glacialand keeps operating well into early phase of an interglacial, and the tendency towardsvertical stabilization of valley floors appears in the optimum of the interglacial. He is ofthe opinion that in interglacial periods accumulation and aggradation cannot be tracedin river valleys. They appear only at the beginning of a next cold period. There is noerosion phase between those of interglacial stabilization and cold aggradation assumedby Jahn (1956a, b).

Later, opinions on this matter underwent further evolution, especially concerningthose river valleys which were directly affected by the recession of the last inland ice. Insuch valleys the phase of deep erosion took place much earlier, viz. when deglaciationstarted, that is, about 18000 years BP. This was pointed out by Rotnicki (1966, 1974a),Galon (1968), Maruszczak (1968) and Różycki (1972). It should also be added thatopinions concerning Holocene tendencies of fluvial processes are not as undivided asthose referring to Pleistocene interglacial periods.

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Karol Rotnicki, Quaternary Research Institute, Adam Mickiewicz University, Poznań, Poland