Editing Lake Ladoga (section)

==Geological history==
{{see also|Geology of the Baltic Sea|Svecofennian orogeny}}
[[Image:Baltic History 7500-BC.svg|thumb|upright=0.8|[[Ancylus Lake]] around 7,000 BC.]]
Geologically, the Lake Ladoga depression is a [[graben]] and [[syncline]] [[structural geology|structure]] of [[Proterozoic]] age ([[Precambrian]]). This "Ladoga–Pasha structure", as it is known, hosts [[Jotnian|Jotnian sediments]]. During the [[Quaternary glaciation|Pleistocene glaciation]]s the depression was partially stripped of its [[sedimentary rock]] fill by glacial [[overdeepening]].<ref name=amantovetal>{{cite journal |last1=Amantov |first1=A. |last2=Laitakari |first2=I. |last3=Poroshin |first3=Ye |date=1996 |title=Jotnian and Postjotnian: Sandstones and diabases in the surroundings of the Gulf of Finland |url= https://www.researchgate.net/publication/259459569|journal=[[Geological Survey of Finland|Geological Survey of Finland, Special Paper]] |volume=21 |pages=99–113 |access-date=27 July 2015}}</ref> During the [[Last Glacial Maximum]], about 17,000 years [[before present|BP]], the lake served likely as a channel that concentrated ice of the [[Weichselian glaciation|Fennoscandian Ice Sheet]] into an [[ice stream]] that fed glacier lobes further east.<ref name=Stroevenetal2016>{{cite journal|author-last=Stroeven|author-first=Arjen P. |author-last2=Hättestrand|author-first2=Clas |author-last3=Kleman|author-first3=Johan|author-last4=Heyman|author-first4=Jakob |author-last5=Fabel|author-first5=Derek |author-last6=Fredin|author-first6=Ola |author-last7=Goodfellow|author-first7=Bradley W. |author-last8=Harbor|author-first8=Jonathan M. |author-last9=Jansen|author-first9=John D. |author-last10=Olsen|author-first10=Lars |author-last11=Caffee|author-first11=Marc W. |author-last12=Fink|author-first12=David |author-last13=Lundqvist|author-first13=Jan |author-last14=Rosqvist|author-first14=Gunhild C. |author-last15=Strömberg|author-first15=Bo |author-last16=Jansson|author-first16=Krister N. |author-link13=Jan Lundqvist |date=2016|title=Deglaciation of Fennoscandia|journal=[[Quaternary Science Reviews]] |volume=147|pages=91–121|doi=10.1016/j.quascirev.2015.09.016 |bibcode=2016QSRv..147...91S |doi-access=free|hdl=1956/11701|hdl-access=free}}</ref>

Deglaciation following the [[Weichselian glaciation]] took place in the Lake Ladoga basin between 12,500 and 11,500 [[Before Present|radiocarbon years BP]]. Lake Ladoga was initially part of the [[Baltic Ice Lake]] (70–80 m. above present [[sea level]]), a historical [[freshwater]] stage of [[Baltic Sea]]. It is possible, though not certain, that Ladoga was isolated from it during [[regression (geology)|regression]] of the subsequent [[Yoldia Sea]] [[brackish]] stage (10,200–9,500 BP). The isolation threshold should be at [[Heinjoki]] to the east of [[Vyborg]], where the [[Baltic Sea]] and Ladoga were connected by a strait or a river outlet at least until the formation of the River Neva, and possibly even much later, until the 12th century AD or so.<ref>{{Cite journal | author = Ailio, Julius | year = 1915 | title = Die geographische Entwicklung des Ladogasees in postglazialer Zeit | journal = Bull. Comm. Géol. Finlande | volume = 45 | pages = 1–159 }}</ref><ref name="davydova">{{cite journal | last1 = Davydova | first1 = Natalia N. | display-authors = etal | year = 1996 | title = Late- and postglacial history of lakes of the Karelian Isthmus | journal = [[Hydrobiologia]] | volume = 322 | issue = 1–3| pages = 199–204 | doi = 10.1007/BF00031828 | s2cid = 9631019 }}</ref>

At 9,500 BP, [[Lake Onega]], previously draining into the [[White Sea]], started emptying into Ladoga via the [[River Svir]]. Between 9,500 and 9,100 BP, during the transgression of [[Ancylus Lake]], the next freshwater stage of the Baltic, Ladoga certainly became part of it, even if they hadn't been connected immediately before. During the Ancylus Lake subsequent regression, around 8,800 BP Ladoga became isolated.<ref>{{Cite journal|last1=Saarnisto|first1=Matti|last2=Grönlund|first2=Tuulikki|last3=Ekman|first3=Ilpo|date=1995-01-01|title=Lateglacial of Lake Onega — Contribution to the history of the eastern Baltic basin|journal=Quaternary International|volume=27|issue=Supplement C|pages=111–120|doi=10.1016/1040-6182(95)00068-T|bibcode=1995QuInt..27..111S }}</ref>

Ladoga slowly [[transgression (geology)|transgressed]] in its southern part due to uplift of the [[Baltic Shield]] in the north. It has been hypothesized, but not proven, that waters of the [[Litorina Sea]], the next brackish-water stage of the Baltic, occasionally invaded Ladoga between 7,000 and 5,000 BP. Around 5,000 BP the waters of the [[Saimaa Lake]] penetrated [[Salpausselkä]] and formed a new outlet, [[River Vuoksi]], entering Lake Ladoga in the northwestern corner and raising its level by 1–2 m.<ref>Saarnisto, Matti (1970). The Late Weichselian and Flandrian history of the Saimaa Lake complex. ''Societas Scientiarium Fennicae. Commentationes Physico-Mathematicae'' 37.</ref>

The [[River Neva]] originated when the Ladoga waters at last broke through the threshold at Porogi into the lower portions of [[Izhora River]], then a tributary of the [[Gulf of Finland]], between 4,000 and 2,000 BP. Dating of some sediments in the northwestern part of Lake Ladoga suggests it happened at 3,100 [[Before Present|radiocarbon years BP]] (3,410–3,250 calendar years BP).<ref>{{cite journal | last1 = Saarnisto | first1 = Matti | last2 = Grönlund | first2 = Tuulikki | year = 1996 | title = Shoreline displacement of Lake Ladoga – new data from Kilpolansaari | journal = [[Hydrobiologia]] | volume = 322 | issue = 1–3| pages = 205–215 | doi = 10.1007/BF00031829 | s2cid = 42459564 }}</ref>
<gallery perrow="3" widths="250px" heights="150px">
File:Lake Ladoga as part of Baltic Ice Lake.jpg|Lake Ladoga as part of the [[Baltic Ice Lake]] (between 11200 and 10500 yr BP). The light blue line marks the margin of the ice sheet by 13300 cal yr BP. 
File:Lake Ladoga as part of Ancylus Lake.jpg|Lake Ladoga as part of the [[Ancylus Lake]] (between 9300 and 9200 yr BP). The dark green line marks the southern shoreline of Lake Ladoga during the [[Yoldia Sea|Yoldia stage]] of the Baltic basin.
</gallery>