Editing Mälaren (section)

==Geology==
{{See also|Central Swedish lowland}}
[[File:La3-demis-malaren.png|300px|thumb|Mälaren details, with [[Stockholm urban area]] to the right in pink.]]
By the end of the last ice age about 11,000 years ago, much of northern Europe and North America was covered by [[ice sheet]]s up to {{cvt|3|km|1}} thick. At the end of the ice age when the glaciers retreated, the removal of the weight from the depressed land led to a [[post-glacial rebound]]. Initially the rebound was rapid, proceeding at about {{cvt|7.5|cm|2}} per year. This phase lasted for about 2,000 years, and took place as the ice was being unloaded. Once deglaciation was complete, uplift slowed to about {{cvt|2.5|cm|1}} per year, and decreased exponentially after that. Today, typical uplift rates are of the order of {{cvt|1|cm|2}} per year or less, and studies suggest that rebound will continue for about another 10,000 years. The total uplift from the end of deglaciation can be up to {{cvt|400|m|0}}.{{Citation needed|date=March 2007}}

In the [[Viking Age]], Mälaren was still a bay of the [[Baltic Sea]],<ref>{{Cite web |url=http://samla.raa.se/xmlui/bitstream/handle/raa/2222/1974_121.pdf?sequence=1 |title=Landhöjning och bebyggelse i nordligaste Uppland |access-date=2017-10-09 |archive-date=2017-10-20 |archive-url=https://web.archive.org/web/20171020135733/http://samla.raa.se/xmlui/bitstream/handle/raa/2222/1974_121.pdf?sequence=1 |url-status=dead }}</ref><ref>''Friman, Helena'', ''Söderström, Göran''. (2008). Stockholm: en historia i kartor och bilder.</ref> and seagoing vessels could sail up it far into the interior of Sweden. [[Birka]] was conveniently near the trade routes through the [[Södertälje Canal]]. Due to the post-glacial rebound, Södertälje canal and the mouth of [[Riddarfjärden]] bay had become so shallow by about the year 1200 that ships had to unload their cargoes near the entrances, and progressively the bay became a lake.<ref>{{Cite web |url=http://arne.ljungdahl.info/malaren/MALAREN.PHP |title=Om Mälaren |access-date=2017-10-09 |archive-date=2022-03-28 |archive-url=https://web.archive.org/web/20220328124627/http://arne.ljungdahl.info/malaren/MALAREN.PHP |url-status=live }}</ref> The decline of Birka and the subsequent foundation of [[Stockholm]] at the choke point of Riddarfjärden were in part due to the post-glacial rebound changing the topography of the Mälaren basin. The lake's surface currently averages {{cvt|.7|m|ft|1}} above [[sea level]].