Megadunes and their sedimentary successions on the proximal part of the Augustów Sandur, NE Poland

<p>Extreme geological processes include cataclysmic glacial floods often contribute to glacial landscape evolution. Based on the geomorphological research the unique glacial megaflood landforms were discovered on the proximal part of the August&#243;w Sandur, NE Poland (Weckwerth et al., 2019). First-order and second-order megaflood-related landforms were distinguished. The latter includes straight-crested (two-dimensional) megadunes located south of Suwa&#322;ki. The megadunes have mean heights on stoss slopes between 2.3 and 3.9 m and mean heights on lee slopes between 2.5 and to 4.5 m, while the maximum recorded megadune height is 8.5 m, and the maximum length is 420 m. Characteristic features of the 2D megadunes south of Suwa&#322;ki are elongated depressions occurring along megadune crests. Megadunes located in the vicinity of Wigry Lake originated from depositional processes related to the reduction in flow energy and competence in the area of the broad outwash plain. The width of this plain rapidly increases and thus creates an accommodation space (unconfined outwash plain) for the aggradation of mega-scale, superimposed bedforms (Weckwerth et al. 2020b). Their three-stage evolution was recognised as a result of sedimentological and geophysical investigations. The first stage represents foreset deposition on the lee side of the megadunes, while the second was deposition from 2D and 3D superimposed bedforms and longitudinal gravelly bars climbing downstream on a megadune stoss slope, which were locally separated by gravelly pavement and scour infills. During the third stage, the crestal depressions evolved as a result of the development of both north- and south-dipping normal faults oriented parallel to the megadune crest, representing syn- and meta-sedimentary deformations (Weckwerth et al., 2020a, b).</p><p>This study was carried out as part of the scientific project financed by the National Science Centre (NCN) in Poland, project no. 2018/31/B/ST10/00976 and Danish Council for Independent Research (FNU) grant DFF-7014-00156.</p><p><strong>References</strong></p><p>Weckwerth P., Piotrowski J.A., Wysota W., Krawiec A., Adamczyk A., Kali&#324;ska E., Chabowski M., 2020a. Mature and immature megadunes : insights from morphology and sedimentary successions of mega-scale bedforms south of Wigry Lake (NE Poland). [In:] Weckwerth P., Wysota W., Kali&#324;ska E. (eds), Glacial megaflood landforms and sediments in North-Eastern Poland. Wydawnictwo Naukowe Uniwersytetu Miko&#322;aja Kopernika, Toru&#324;: 99-107.</p><p>Weckwerth P., Wysota W., Chabowski M., Krawiec A., Kali&#324;ska E., Adamczyk A., 2020b. Morphology, geological structure and development of two-dimensional megadunes formed on an outwash plain in NE Poland. [In:] Weckwerth P., Wysota W., Kali&#324;ska E. (eds), Glacial megaflood landforms and sediments in North-Eastern Poland. Wydawnictwo Naukowe Uniwersytetu Miko&#322;aja Kopernika, Toru&#324;: 89-97.</p><p>Weckwerth, P., Wysota, W., Piotrowski, J. A., Adamczyk, A., Krawiec, A., D&#261;browski, M., 2019. Late Weichselian glacier outburst floods in North-Eastern Poland: Landform evidence and palaeohydraulic significance. Earth-Science Reviews, 194: 216&#8211;233.</p>