ACADEMIA The distinctive story of the Odra River Geology Focus on A River of Curiosities Sudetes, and so it drains most of the precipita- JURAND WOJEWODA tion in this region. Institute of Geology, In the Lower Silesian segment, the Odra University of Wrocław flows through a broad depression, sometimes Asst. Prof. Jurand Wojewoda is a geologist, sedimentologist, more than 20 km across, known as the ancient and cartographer, specializing in paleogeographical Proglacial Odra Valley. Three times along this reconstructions of the Czech massif and the Sudetes. A Humboldt scholar, one of the initiators of Poland’s Table depression, it encounters uprisings that it cuts Mountains National Park, and president of the Lower through, and each time it changes direction. At Silesian branch of the Polish Geographical Society, he is these locations, the valley is narrow and deep. currently head of the Section for Structural Geology and When river waters swell, the local towns face Geological Mapping at the University of Wrocław. the danger of flooding. The first such gorge is situated in the vicinity of Opole, where the Oder channel cuts through tectonically Its history began more than 10 million elevated calcareous rocks of the Triassic and years ago, back in the Tertiary period. Its Cretaceous age. The second cut, near Ścinawa, geographic position and structure already separates a strip of terminal moraine of the attracted settlers back in the middle Odra Stadial into two ranges: the Trzebnica Paleolithic. What is so special about the Hills to the east and the Dalkówskie Hills to Odra (Oder), Poland’s number-two river? the west (200-250 m above sea level). The third incision, east of Nowa Sola, separates the How turbulent is its story? Zielona Góra Hills from the Leszno Lakeland, BE&W The Odra flows out of the Odra Mountains, which are relicts of the terminal and ground a range in the Opava Mountains of the Czech moraines (respectively) of the Warta Stadial. Republic. The source of the river is considered to lie at an altitude of around 630-680 meters Cutting power above sea level, on the slopes of Mount Vysoká. Geologists studying the paleogeography In its upper course, after leaving the mountain- of the Sudetes agree that 10 million years ous region, the river turns northward and flows ago (back in the middle Miocene) the region through the Moravian Gate into the Sudeten from today’s Sudeten Foothills all the way Foothills. Near Koźle it turns to the northwest to the Great Poland Lowlands already had and maintains that bearing all the way to rivers flowing across it from sources in the where it meets the Lusatian Neisse, after which zone of today’s southern Poland. The largest it again heads north, directly to the Baltic Sea. of those, the ancient Odra (or “pre-Odra”), Running 854 km, it is the second-longest flowed from the area where the Sudeten river in Poland (after the Vistula) and also the mountain range then started forming. We second-longest river flowing out of the Sudetes should point out here that the geological (after the Elbe). Interestingly, the catchment sense of the term “mountains” does not al- areas of the two Sudeten rivers are compa- ways coincide with the geographical sense. rable (at 118,861 km2 and 144,055 km2, The rocks that the Sudetes are made out of respectively). However, they differ greatly in are currently part of the geological struc- terms of their source elevation – the source of ture of Europe and were created between the Elbe lies at about 1380 meters above sea 500 million and 60 million years ago. Most level, as does that of the third-largest Sudeten of them were formed during a time known river, the Morava (around 352 km, a tributary as the Variscan orogeny and immediate- of the Danube, draining into the Black Sea). ly thereafter, that is to say between 320 The Odra is also distinct in that its catchment million and 180 million years ago. In the basin includes nearly the entire area of the paleogeographic sense, on the other hand, 18 No. 1 (45) No. 2015 ACADEMIA Panorama Geologia the Sudetes are a set of mountain ranges, This occurred along the line of one of the most For the residents of valleys, and basins of very diverse origins. important tectonic faults in Lower Silesia – Wrocław, whose day-to- In the late Miocene, around 8 million to the Sudetic Marginal Fault. Some of the new day lives involve crossing 5 million years ago, the area of the Sudetes Sudeten rivers in the ancient Odra basin began numerous waterways (the and Sudeten Foothills formed a compact and to flow in the opposite direction, northward, urban agglomeration alone moderate-sized massif, from which the first most likely the utilizing still-existing valleys. having more than 300 ancient rivers flowed in a radial pattern, in Somewhat later, the ice sheet advancing bridges and footbridges!), all directions. The largest at that time was un- from the north reached the front of the uplift- the presence of water doubtedly the pre-Morava. The mighty scale of ing Sudetes. The waters flowing out both from in the city is something that river is illustrated, for instance, by the fact the melting ice and from the region of today’s completely normal, that it cut through the emerging massifs of the Sudetes, which then formed a broad elevation, forming an integral part Carpathian orogeny, forming one of the larg- deposited material over virtually the entire area of Wrocław’s urban fabric est gorges in this part of Europe (the Morava of Lower Silesia and southern Great Poland. and landscape. But visitors Valley). We can assume with great likelihood The successive halting of the Scandinavian from outside are frequently that it was then that the system of valleys of the ice-sheet created bands of moraines, forming a astounded, getting the largest Sudeten rivers, including the pre-Odra, series of moraine hills after it retreated. During impression that the city is began to form. the Odra Stadial and immediately thereafter, “built on water…” It was not until relatively recently, in the the waters flowing from the ice-sheet and the Pleistocene (around 2 million years ago), before pre-Odra combined into a great river flowing the Scandinavian ice sheet advanced into the vi- west towards the broad German lowlands and cinity of the Sudetes (a time described as as the the North Sea. It carved out the broad ancient pre-glacial period), that the landscape changed Proglacial Odra Valley, part of which is used by radically, as a result of a process known as “in- the recent channel of the Odra. version.” The area of today’s Sudeten Foothills From the last glaciations to modern times, lowered, while the Sudeten range was uplifted. the Sudeten area has been uplifting, marking 19 1 (45) No. 2015 exten ine t of terminal mora (Warta Stadial) ACADEMIA The distinctive story of the Odra River t of te exten rmina dra S l m (O tadi or Geology Dalków Hills a a l) in e out a clear watershed for rivers emerging from Trzebnica Hills it. Some of them flow southwest to the Black Focus on Sea (the Morava and Danube basin), others Proglacial Odra Valley are tributaries to the Elbe, which flows into the North Sea. But the largest and most important river system emerging from the Sudetes is the Odra and its tributaries (the Biała, Eastern Nysa, Bystrzyca, Strzegomka, Kaczawa, Bóbr, Kwisa, and Lusatian Nysa) Red square - Wrocław Water Node sources of the Odra Age and structure sources of the Morava sources of the Labe Reconstructing the natural, original shape of the valley and channels of the Odra in the va segment between Oława and Brzeg Dolny is not pre-Bóbr Miocene an easy task, mainly because of centuries of Wrocław is the most ea basin S river regulation efforts for navigation purposes. important hydrographic h The urban region of Wrocław is particularly node in southwestern rt o N problematic, as there are no longer any natural Poland. Its main axis is of R E - S elements of the valley and most of the surface course marked the Odra, P U D E waters follow man-made channels. However, which has as many as T we have managed to approximately identify the 5 significant tributaries pre-Elbe E The outline of today’s S range of the original river valley based on exist- within the limits of the system of river valleys ing traces of the ancient Odra – mainly in the urban agglomeration: the in Lower Silesia already pre-Morava remains of preserved meander sandbars and Oława, Ślęza, Bystrzyca, began to emerge around former channels which today form oxbow lakes. Widawa and Dobra sin 20 million years ago, when Black Sea ba Valuable material was supplied by construction the Carpathians were work in connection with the renovation of basin Pliocene folding and at the same pre-Bóbr Wrocław’s floodway channels, which revealed ea S Pleistocene time upheaving in the the location of former river talwegs. Dating of southeast of Europe. In h deposited oak trunks which had previously t r the late Miocene, around o pre-Odra grown in the floodplains of the ancient Odra N 8-5 million years ago, (known as “black oaks”) enabled the age of rivers flowed from what PRE-SUDETES these paleochannels to be dated to from 1,500 is today’s Scandinavia, to 6,h000 BCE. pre-Neisse some of them flowing into pre-Elbe Along the segment under discussion, the the “Pre-Carpathian sea” Odra Valley takes the shape of a regular band in the south of today’s with an average width of around 4.8 km, gra- Poland.