As of June 2018, 12 confirmed impact structures have been found in Finland. They are listed below, sorted by original diameter. + List of identified impact structures in FinlandStructure nameCrater typeDiameter (km)Depth (m)Age (Myr)Geologic period (epoch)LocationMunicipalityImpact origin shown [Note 3]NotesOriginal (estimate) [Note 1]CurrentOriginal (estimate) [Note 1]Current (buried structure)Current (solid surface) [Note 2]MinMaxBest fitKeurusselkäComplex3014820N/A114111611150StenianKeuruu / Mänttä-Vilppula2004 2010Heavily eroded, only remnants of central peak remain.LappajärviComplex201773013777.0778.6377.85Cretaceous (Late)Lappajärvi / Alajärvi / Vimpeli1968 1970
1976 Preserved well, rim outside lake largely intact.PaasselkäComplex?1059074229.2232.8231.0Triassic (Late)Savonlinna / Kitee1999 2003
2008Bay of Orivesi lake in Greater Saimaa.LumparnComplex99 - 105704501250580Ectasian to OrdovicianJomala / Lemland / Lumparland / Sund1993 1997Bay of the Archipelago sea.SöderfjärdenComplex, polygonal (hexagonal)6.66.652055520 - 640Cambrian (Early)Vaasa / Korsholm / Malax1978 1985
2013Extremely well preserved; rim nearly entirely intact, buried soon after impact, later exhumed. Dried bay of Kvarken.SääksjärviSimple?54.5 - 54809.1544576560EdiacaranKokemäki1969 1980
1997Central part of the Sääksjärvi lake.Suvasvesi NComplex?445079.788.185Cretaceous (Late)Kuopio / Leppävirta1995 1996Kukkarinselkä; open water in the Suvasvesi lake.Suvasvesi SSimple?
Complex?~4450679727710Cryogenian, possibly but unlikely TonianKuopio / Leppävirta2001 2002 2003Haapaselkä; open water in the Suvasvesi lake.Iso-NaakkimaSimple< 42 - 3450 - 600160N/A9001200Stenian or TonianPieksämäki / Mikkeli1993Buried, only partly under the Iso-Naakkima lakeSaarijärviSimple?3.41.5 - 24200541Cambrian to QuaternaryTaivalkoski1997 1998
2013Central part of the Saarijärvi lake.SummanenSimple?2.6640200412.5881910Orosirian to NeogeneSaarijärvi2007 2018Central part of the Summanen lake.KarikkoselkäSimple31.364026 230260 - 458(Late) Ordovician to (Early) TriassicPetäjävesi1996 1999
2000Open water in Petäjävesi lake Note 1: The "original" crater dimensions are coarse estimates. Original depths were calculated using the given original diameter using the Impact: Earth! program.
Note 2: "Current solid surface" topography is calculated from the deepest floor (regardless whether it is underwater or on dry land) to highest rim crest; other depth values give the depth of the floor in relation to the original terrain, thus excluding the rim and/or central uplift.
Note 3: Evidence for impact origin for a given structure is often provided in several publications. The year column includes some publications where some evidence of impact origin was provided even though an impact was not necessarily suggested by the authors; somewhere an impact was suggested even though the proof wasn't conclusive; and somewhere definite proof was provided.
General note 1: Crater sizes and shapes vary according to local differences. For example, depending on where you measure the crater diameter the result may vary (craters are seldom perfect circles). This is affected by, e.g., impact angle (low < 5-10 degree impact angles cause more elliptical craters) and local zones of weakness (may cause the crater to become polygonal).
General note 2: On Earth the (theoretical) transition diameter between simple and complex craters is 2 – 4 km. Such small craters may be either end member or some intermediate form, and thus the given dimension estimates may be off. The depth may be off by ~50 %.
References
Suomen kraatterit, Finnish impact craters, https://kraatterit.wordpress.com/2015/09/01/perustietoa-montako-kraatteria-suomesta-loytyy/