Today, the Amazon is the uncrowned king of rivers on our planet. But this has not always been the case. In fact, it's only since very recently that South America took the title from Northern Europe for supporting the biggest river system on the planet. Geologists call this ancient river the Eridanos. In Greek mythology, the Eridanos was beyond the river Po, famous for its islands of amber.
Looking at a map of Northern Europe, this first thing people will notice are the intricate systems of waterways in this part of the continent. It's easy to imagine looking at that same map, that millions of years ago, a river ran from the north of Lapland, down through the Gulf of Bothnia, through the southern Baltic. Further down its stream it would first be carving out the various straits between the Danish isles before reaching the Atlantic Ocean south of Rogaland in Norway. At later times, after Denmark lifted up in the Miocene, this river would flow through what is now Jutland and the German Bight, taking in the waters of the rivers Elbe, Rhine, Scheldt and Thames, before creating an enormous delta system in what's now the central North Sea and the Northern Netherlands. At this time in its history, the Eridanos was at its largest, carrying as much sediment as the modern Ganges, nearly as much water as the modern Amazon, and being as long as the modern Danube, draining virtually all of Europe north of the Alps.
The Ice Ages eventually spelled doom for this magnificent river. At first, the advent of the ice caps in northern Fennoscandia allowed for more glacial runoff. However, when the severity of the ice ages increased in the Mid-Pleistocene, more and more of the Eridanos basin got buried underneath glacial ice, and by 700.000 years BP, the entire river disappeared underneath the ice cap. The sheer weight of the ice depressed the northern part of Europe so much, that after the retreat of the ice, what was formerly the wide valley of the Eridanos, got filled in with water, creating the modern day Baltic Sea.
Some aspects of this great river's legacy remained, though; 90% of the world's extractable amber can be found near coasts and islands of today's Baltic Sea. Also, with Northern Fennoscandia rising faster than the current sea level rise, the Baltic essentially behaves like a giant river, even at this date; the flow is primarily north to south, with most of the salty water flowing out through the Kattegat, being constantly replaced with fresh water from the many rivers that feed it. As a result, the Baltic Sea is merely brackish in its main basin, and by some definitions, the Gulf of Bothnia and Gulf of Finland could be considered fresh-water bodies.
Further reading and sources:
De Ondergrond van Nederland, Wolters-Noordhoff, ISBN 90-01-60514-1
Image: Lake Kilpisjarvi in Lapland, the source region of the Eridanos
