Baltic Ice Lake - Formation

Formation

The edge of the retreating Weichselian glacier departed from the Lake Gardno end-moraines of northern Poland at around 14,000 BP and reached the southern shore of the Baltic Sea in the time window, 13,500/13,000 BP. In the next several hundred years, closed fresh water pools formed in the southern Baltic region from melt water as the ice retreated northward. These were about 40 m (130 ft) above the current sea level.

By 12,000 BP the edge of the glacier was at a line across southern Sweden to the northern shore of the Baltic countries. A connected body of water, the Ramsay Sea, stretched from the Danish islands region to the shores of Estonia. The Gulfs of Bothnia and Finland were still glaciated. In the Allerød warm period, rising land in the Denmark region created the Baltic ice lake. It egressed through a small channel in the Strait of Øresund. The lake was higher than sea level (which itself was lower than the present-day sea level) by some tens of metres. Lake Ladoga was part of it.

Emergence of the land then closed the channel through the Strait of Öresund. The lake rose until at about 11,200 BP it broke through a narrow corridor in the region of Mount Billingen in present-day south-west Sweden; this used to be described by quaternary geologists as a massive, single tap of Niagara-like force but it is now considered more likely that it happened in several steps over a limited period, perhaps a century, and along different local troughs and passages. By 10,800 BP, the lake had dropped 55 m (180 ft). At that point the climate reverted into cooling and during the Younger Dryas cold climate period, the glacier advanced again over the central Swedish exit. The lake was blocked again, rose about 25 m (82 ft) and broke through the Strait of Oresund. By now, the Gulf of Finland had been deglaciated.

At the peak of this high water phase, most of Finland was under water, including Helsinki, at a depth of 115 m (377 ft); only southern Sweden was free of ice. The Danish Islands were all connected west of the Strait of Oresund. Around 10,500 BP the climate became warmer, the ice retreated to the north of Mount Billingen, and the waters broke through central Sweden again, providing a second egress. Water level dropped 25 m (82 ft) to the sea level of that time.