The history of the Danube dates back to the Upper Miocene (approximately 5–10 million years ago). At that time, the formation of the Alps, caused by the collision of the European and the African-Adriatic tectonic plates, was well advanced. North of the rising mountains, the Molasse Basin (Learn more) had formed — a depression that filled with sediments from the Alps (Learn more).
In the region of today’s Swiss Plateau and the southern German Alpine foothills, further uplifts occurred that repeatedly altered the courses of rivers and their drainage basins. It was here that the precursors of today’s river systems — the Rhône, Aare, Doubs, Rhine, and Danube — developed.
With the further uplift of the Jura Mountains (Learn more) (approx. 7–3 million years ago), a barrier was formed that redirected water flow eastward — giving rise to the Ur-Danube (ancient Danube). Its source was likely in the Aarmassif (Learn more); the upper Rhône may also have flowed into it.
Millions of years ago, the source river of the Danube likely lay in the area where the Aare originates today. This is what the area above the Oberaarsee in the Bernese Alps looks like today. In the center of the photo is the Oberaarsee, with the Oberaar Glacier behind it. To the right of the saddle is the Oberaarhorn (3,631 m), and further right (partially in clouds) the Finsteraarhorn (4,274 m). During the Upper Miocene and early Pliocene, the Alps had already formed into a high mountain range, even if the landscape’s relief may have differed in detail from today’s. However, it is likely that there were no glaciers at this elevation back then.
Significant tributaries at the time included the Alpine Rhine, which still flowed into the Danube at that point (Learn more), as well as the „Feldberg Danube“, which originated further north in the Black Forest. Feldberg is the name of the highest peak in the Black Forest.
In the later Pliocene (5–2.6 million years ago), further tectonic uplifts altered the Danube’s drainage basin. Around 3.5 million years ago, the Aare began to erode the southern Molasse Basin more intensely. The uplift of the Black Forest and its southeastern foreland blocked its original northeastward flow. Near Waldshut, it found a new outlet to the west, merged with the Ur-Doubs, and flowed into the Mediterranean via the Rhône — the so-called Aare-Sundgau system (also known as the Aare-Doubs system).
As a result, the Ur-Danube lost large parts of its drainage area. Its main tributaries now became the Alpine Rhine and the Feldberg Danube, the latter becoming the Danube’s new source river.
The Danube in the Pleistocene
With the beginning of the Pleistocene, 2.6 million years ago, the course of the river changed once again: due to the continued subsidence of the Upper Rhine Graben, the Aare now flowed northward into the Rhine — and thus into the North Sea.
Whereas tectonic processes had mainly shaped river courses up until then, it was now — starting with the onset of glacial–interglacial cycles (Learn more) — climate-driven changes that became dominant. The Rhine Glacier, which formed in the Alpine foreland, dammed western tributaries such as the Thur around 1 million years ago. During cold periods, meltwater flowed across the watershed into the Aare-Rhine system; during warm periods, drainage into the Danube was at times possible again.
With the carving of meltwater channels and the last tectonic movements, the Alpine Rhine permanently shifted westward. Around 450,000 years ago, the Danube lost this tributary for good. The Alpine Rhine now belonged fully to the Aare-Rhine system. The watershed between the North Sea and the Black Sea shifted further east; the Feldberg Danube remained as the most important source river of the Danube.
The formation of the Wutach Gorge
A particularly dramatic change occurred around 18,000 years ago during the last major glaciation. The Wutach, a tributary of the Upper Rhine, carved its way northward toward the Feldberg Danube through headward erosion. This process was aided by the steep gradient of the Wutach, as the Upper Rhine had already deeply incised into the landscape.
When the erosion front reached the watershed — intensified by dammed meltwater — a sudden breakthrough occurred, possibly lasting only weeks or months. The Feldberg Danube was diverted into the Wutach Valley and thus southward to the Upper Rhine. This led to the formation of the nearly 200-meter-deep Wutach Gorge and the characteristic „Wutach Bend“ (Wutachknie) near Blumberg.
This panoramic photo, taken from Buchberg above the Wutach Bend, provides a vivid impression of the region’s topography (Learn more).
This event may have taken place in the presence of early humans (Learn more).
Today, the Danube rises near Furtwangen at an elevation of around 1,100 meters on a high plateau in the central Black Forest. Here is a night-time photo of this remote location:
Today, the source of the Danube is no longer in the Alpine High Mountains. Instead, it lies in this idyllic spot among the gentle hills of the central Black Forest (Kolmenhof, near Furtwangen).
In the photo, taken on a summer night facing north, the band of the Milky Way is visible, while the Andromeda Galaxy appears as a faint, misty spot in the upper right. This galaxy is the most distant object visible to the naked eye and is located about 2.5 million light-years away. That means the light we see from this stellar system today was emitted long before the source river of the Danube ever flowed here in this peaceful corner of the Black Forest (view the photo in higher resolution).
Even during the Holocene, the Wutach continued cutting into the bedrock — a process that continues to this day. It is one of the few remaining wild rivers in Germany and offers a striking example of the dynamic, living nature of a flowing body of water. In its upper course, this river has carved into a sequence of rock layers of varying ages (Learn more).
In the Gauchach Gorge, a Side Valley of the Wutach, in Spring. The wild forest with its moss-covered tree trunks bears witness to the untouched development within this nature reserve.
And What About the Future?
We’ve seen that the drainage basin of the Danube river system has steadily shrunk over time, and that the watershed between the North Sea and the Black Sea has gradually shifted further east. This process appears to be ongoing — and is likely to continue in the future.
One phenomenon that illustrates this shift is the Danube sinkhole near Immendingen. Here, water from the Danube disappears underground into karst rock and reemerges at the Aachtopf spring. From there, it flows as the Radolfzeller Aach into Lake Constance. This phenomenon highlights how the Rhine, due to its lower elevation and gradient, increasingly captures water from the Danube — a process known as river capture.
Additionally, a small stream currently draining into the Wutach near Blumberg — the Schleifenbächle (Learn more) — is expected, through headward erosion, to gradually carve its way northeast via the Aitrach Valley toward the Danube. This means that, in the distant future, the Danube could be diverted toward the Rhine near Geisingen (Learn more). By then, the city of Donaueschingen might need a new name...
If this development continues, the source of the Danube may shift even further east.
The Inn — which originates in the Alps and joins the Danube at Passau — could eventually become the Danube's primary source river, when measured from its mouth at the Black Sea (Learn more).
This would essentially be a return to conditions during the Pliocene, when the Aare-Danube system also originated in the Alps. An intriguing thought.
However, we must not overlook one crucial aspect: with the warming of Earth's climate, most Alpine glaciers will vanish within just a few decades (Learn more), and a return to cooler conditions is not expected for thousands of years (Learn more). Therefore, the Alpine region may eventually lose its importance as a source area for the Danube system. Climate change is fundamentally altering water availability in the Alps: glaciers are melting rapidly, and their contribution to the Danube is already declining.
This article was originally written in German. The English version was translated with the assistance of AI and subsequently revised for clarity and accuracy.
×The Molasse Basin was at times filled with seawater and formed a waterway connecting the Paratethys — a marginal sea of Eurasia that stretched from the region of today’s Eastern Alps to present-day Kazakhstan — with the Tethys to the southwest, the predecessor of today’s Mediterranean Sea. The Black Sea, Caspian Sea, and Aral Sea are remnants of the Paratethys.
×A mountain range northwest of the Alpine ridge and the Swiss plateau. It is divided into the French Jura and the Swiss Jura.
×The largest mountain massif of the Swiss Alps, consisting of crystalline basement rock. It covers parts of today's Bernese Oberland and the Glarus Alps.
×And it would have had to merge with the Danube somewhat southwest of present-day Ulm.
×The beginning of the Quaternary, around 2.6 million years ago, marks the start of a climatically cold phase in Earth's history, characterized by regular alternations between glacial periods and interglacial periods. During this time, there was an increased formation of ice, particularly in the Arctic. Since then, longer glacials and shorter interglacials have occurred cyclically. These glacial-interglacial cycles have been made possible by an overall cooler climate, in which periodic changes in Earth's orbital parameters – the so-called Milanković cycles – increasingly affected global temperatures, thereby favoring ice ages and their weakening.
×When looking at the image, one can understand how the source area of the upper Danube gradually shifted northward over millions of years. Originally – as described above – the ancient Danube originated in what is now Switzerland. The photo was taken facing west; therefore, south is to the left and north is to the right.
In the panorama, we see the Bernese Alps in the background to the left, behind which lies today's upper Rhône Valley.
Over time, the source of the Danube gradually moved northward to the southern Black Forest, which is visible in the foreground of the photo. In the background to the right, one can see the snow-covered double peak of Feldberg – the source region of the Pleistocene Feldberg-Danube.
About 18,000 years ago, this Danube source was redirected southward into the Wutach Valley, likely due to a sudden dam-break-like event – the Wutach Bend was formed. The source area of the Danube then shifted further northward (outside the right edge of the image) to the area around Furtwangen.
In the foreground of the image, the upper Wutach Valley is clearly visible. Far right is the village of Achdorf, below Buchberg, where the valley makes a distinct 90-degree bend – the namesake Wutach Bend. From there, the Wutach Valley flows southward (to the left) toward the High Rhine and the Swiss border. To the left in the foreground, the valley continues downstream into the high plateau that it has cut into.
By the way, the image also shows the less common phenomenon of air reflections, which I have written about in detail in the following article
×There are no archaeological findings or written records that prove such an assumption. However, the caves and sites in the surrounding area, such as the Swabian Jura, are known for their prehistoric artifacts, which indicate the presence of humans in this region during the time of the last major ice age. For example, artistic artifacts from the Upper Paleolithic have been found in the Swabian Jura, including the famous 35,000 to 40,000-year-old „Venus of Hohlefels“.
×In the upper course of the Wutach, gneisses and granites outcrop that date back to the Paleozoic era (older than 255 million years), while further downstream sedimentary layers from the Lower Jurassic (180 million years old) are exposed.
×This is located in close proximity to the viewpoint where the panoramic photo discussed in an earlier footnote was taken:
×Frank Herzer: Die Flussgeschichte der Donau, GRIN Verlag, 2010, S. 17.
×The consideration also depends on how one ultimately defines what the most important source river of a river system is. Hydrologically, the following criteria can be used: The most important source river is the one whose origin is farthest from the river mouth.
However, one can also define the most important source river as the one that carries the largest volume of water.
Additionally, the naming of rivers also dates back to times when there were no accurate maps, meaning that historical aspects must also be taken into account
×See Zekollari, H., Huss, M., and Farinotti, D.: Modelling the future evolution of glaciers in the European Alps under the EURO-CORDEX RCM ensemble, The Cryosphere, 13, 1125–1146, https://doi.org/10.5194/tc-13-1125-2019, 2019.
Depending on the applied RCP scenario, the scientists estimate:
„a glacier volume loss of about 65 %–80 % between the early 21st century and 2100 under a moderate warming (RCP2.6 and RCP4.5) and an almost complete disappearance of glaciers under warmer conditions (RCP8.5).“
RCPs (Representative Concentration Pathways) describe possible developments of greenhouse gas concentrations in the atmosphere until 2100 and beyond. They provide the additional radiative forcing (in W/m²) caused by human emissions, thereby determining the extent of global warming.
Radiative forcing, a measure of the change in Earth's energy balance, is influenced by factors such as altered solar radiation (due to Milanković cycles and changes in solar activity), aerosols, surface reflection (albedo), or the concentration of greenhouse gases in the atmosphere.
Compared to the pre-industrial period (from 1750 to 2022), the radiative forcing caused by humans through the increase in greenhouse gas concentrations is 2.72 W/m². In comparison, the radiative forcing caused by altered solar radiation during the same period is 0.06 W/m².
Since the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC), climate scenarios are based on so-called SSP-RCP combinations.
The SSPs (Shared Socio-economic Pathways) describe possible societal and economic developments in the future – for example, regarding population growth, technology, or politics. The RCPs (Representative Concentration Pathways) indicate how much the Earth's atmosphere is heated by greenhouse gases (the so-called radiative forcing).
The new scenarios thus combine future visions of society (SSPs) with the corresponding emissions and climate impacts (RCPs)
×Here, measurements of carbon dioxide concentration in the atmosphere and reconstructions of global temperature over the last 20,000 years are compared with forecasts for the next 10,000 years. The forecasts are modeled for different emission scenarios (RCPs):
Clark, P., Shakun, J., Marcott, S. et al. Consequences of twenty-first-century policy for multi-millennial climate and sea-level change. Nature Clim Change 6, 360–369 (2016). https://doi.org/10.1038/nclimate2923 (Paywall).
„Temperatures will remain elevated above Holocene conditions for more than 10,000 years, with gradual recovery reflecting the long timescales involved in the removal of emitted CO2 by mid term (thousands of years) carbonate dissolution and by long-term (tens of thousands of years and longer) seafloor deposition of the products of silicate weathering as calcium carbonate.“
