a b s t r a c tIn the Great Hungarian Plain (GHP), one of the most complex fluvial systems of Europe developed through tectonic and climatic factors and vegetation change. The aim of the present study is to summarise these controlling factors and to describe the evolution of the GHP. Special attention is paid to the latest results on late Weichselian and Holocene development in the Tisza River and their effects on the river's largest tributary: the Maros River.Several tectonically active subsiding basins existing in the GHP have determined the direction of river courses and erosionaleaccumulational fluvial processes. As a result of uneven subsidence, the river's flow routes have shifted frequently. For example, the Danube and the Tisza shifted 80e100 km, abandoning their alluvial fans where extensive aeolian processes started. Upstream from the subsiding areas, incision propagated headward, which resulted in the development of floodplain levels and terraces. Though climate and vegetation changes also simultaneously influenced the rivers' hydro-morphology, channel pattern changes were found just along the margin of the plain, and only meandering paleo-channels remained in the center of the GHP. During dry and cold periods, braided patterns appeared in the alluvial fans, most likely the result of abundant sediment supply and due to the inability of sparse riparian vegetation to stabilise the banks effectively. Based on paleo-discharge calculations, by the end of the Pleistocene the rivers of the GHP produced three to eight times more discharge than they do currently, and discharge levels continuously decreased during the Holocene. However, due to the long length of the rivers, there is a considerable time lag between the response rates of the different river sections, which makes creating paleo-hydrological reconstructions even more difficult.
The aim of the present study is to analyse the morphology, sedi-mentary structure and age of flood-free islands on the low-floodplain of the Lower Tisza in order to determine the date and causes of river incision. On the study area the identified 16 elevated surfaces were divided into two groups. The real or meander core floodplain islands appear in the northern and central units of the study area. They are characterized by steep slopes, elevated surface and small territory (2.1 km2 in average). The second type consists of elevated surfaces of point-bar systems and natural levees of paleo-channels, and they mostly appear in the southern unit. They have gentle slopes, smaller relative height and greater area (4.1 km2 in average). The spatial distribution of the two types refers to slow and slight tectonic uplift in the northern part of the study area, though in the south they refer only to the lack of sinking. The results of the sedimentological analysis on the meander core at Szegvár show that it originally belonged to the high-floodplain. Due to the slight tectonic uplift the meandering channel incised into the soft sediments, and as lateral erosion was possible, an ingrown-type meander developed, which later as a result of cut-off has become a meander core (or umlaufberg). Based on the OSL data the incision started at least 20.1±2.1 ka ago, and it terminated ca. 8-9 ka ago. The calculated bankfull discharge of the Szegvár paleo-meander is estimated to be 4000-7500 m3/s, referring to a considerably higher discharge than that of the present-day Tisza (800 m3/s). Similar planimetric meander parameters of paleo-channels on the high and low-floodplain suggest that the incision was not driven by climate, i.e. discharge change but primarily by tectonic movement. This is also supported by the height condition of the islands, as their surface is almost at the level of the high-floodplain.
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