Lake Lappajärvi
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Lappajärvi is a lake in Finland, in the
municipalities A municipality is usually a single administrative division having municipal corporation, corporate status and powers of self-government or jurisdiction as granted by national and regional laws to which it is subordinate. The term ''municipality' ...
of
Lappajärvi Lappajärvi is a municipalities of Finland, municipality in Finland's Southern Ostrobothnia region. It is located from Seinäjoki, from Kokkola and from Vaasa. The municipality has a population of () and covers an area of of which , or near ...
,
Alajärvi Alajärvi (; ) is a town and municipality of Finland. It is located in the South Ostrobothnia region. The town has a population of () and covers an area of of which is water. The population density is . The town is unilingually Finnish. The mu ...
and
Vimpeli Vimpeli (; ) is a municipality of Finland. It is located in the South Ostrobothnia region, northeast of Seinäjoki and northwest of Jyväskylä. The municipality has a population of () and covers an area of of which is water. The population de ...
. It is formed in a wide, partly eroded
meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...
impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...
. The lake is part of Ähtävänjoki () basin together with
Lake Evijärvi Lake Evijärvi is a lake of Finland in Evijärvi, Southern Ostrobothnia region. The lake is part of Ähtävänjoki () basin. See also *List of lakes in Finland Most lakes in Finland are small, but there are 309 lakes or reservoirs with a ...
that is located downstream (north) of it. The
Lappajärvi Lappajärvi is a municipalities of Finland, municipality in Finland's Southern Ostrobothnia region. It is located from Seinäjoki, from Kokkola and from Vaasa. The municipality has a population of () and covers an area of of which , or near ...
impact structure An impact structure is a generally circular or craterlike geologic structure of deformed bedrock or sediment produced by impact on a planetary surface, whatever the stage of erosion of the structure. In contrast, an impact crater is the surface e ...
is estimated to be 77.85 ± 0.78 million years old (
Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...
age of the Late
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
time period). Experts working on Finland's
Onkalo spent nuclear fuel repository The Onkalo spent nuclear fuel repository is a deep geological repository for the final disposal of spent nuclear fuel. It is near the Olkiluoto Nuclear Power Plant in the municipality of Eurajoki, on the west coast of Finland. It will be the wo ...
project have studied Lake Lappajärvi to help them project how Finnish landscapes might look one million years in the future and beyond. An island in the middle of the lake, Kärnänsaari (Kärnä Island), gives the name to the black impact melt rock (
impactite Impactite is rock created or modified by one or more impacts of a meteorite. Impactites are considered metamorphic rock, because their source materials were modified by the heat and pressure of the impact. On Earth, impactites consist primarily ...
) found there, locally called ''Kärnäiitti''. Nearby towns include
Lappajärvi Lappajärvi is a municipalities of Finland, municipality in Finland's Southern Ostrobothnia region. It is located from Seinäjoki, from Kokkola and from Vaasa. The municipality has a population of () and covers an area of of which , or near ...
and
Vimpeli Vimpeli (; ) is a municipality of Finland. It is located in the South Ostrobothnia region, northeast of Seinäjoki and northwest of Jyväskylä. The municipality has a population of () and covers an area of of which is water. The population de ...
and the nearest major city is
Seinäjoki Seinäjoki (; "Wall River"; , formerly ) is a city in Finland and the regional capital of South Ostrobothnia. Seinäjoki is located in the western interior of the country and along the Seinäjoki (river), River Seinäjoki. The population of Sein ...
. In September 2023, UNESCO accepted the Lappajärvi area's "Impact Crater Lake" Geopark application as one of the possible recipients of
Geopark A geopark is a protected area with internationally significant geology within which Sustainability, sustainable development is sought and which includes tourism, conservation, education and research concerning not just geology but other relevant s ...
status for 2024.


Impact crater

Lappajärvi is the largest or second-largest meteorite crater in Finland, and it is also the youngest and the first meteorite crater discovered in Finland. The diameter of the crater, which was formed in Lappajärvi, was approximately 22-23 kilometers, with a depth of 750 meters. It was caused by an asteroid estimated to be about 1.6 kilometers in size, around 77.85 ± 0.78 million years ago. According to current estimates, it is believed to have been formed during the intensified meteorite and asteroid bombardment in the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
epoch. The asteroid is thought to have been a common H-type chondrite. The cooling of the bedrock is estimated to have taken place over a period ranging from one hundred thousand to one million years. Below the Kärnänsaari island in the middle of the lake, there is impactite known as kärnäite. Kärnänsaari has been suspected to be the central uplift of the impact crater, although it could also be a mere erosional remnant shaped by glacial activity. The southeastern edge of the crater is surrounded by an elevated rim, now known as Lakeaharju and Pyhävuori. Typical rocks found in meteorite craters, such as
breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...
, as well as impact diamonds and minerals like
suevite Suevite is a rock consisting partly of melted material, typically forming a breccia containing glass and crystal or lithic fragments, formed during an impact event. It forms part of a group of rock types and structures that are known as impact ...
and
coesite Coesite () is a form (polymorphism (materials science), polymorph) of silicon dioxide (silicon, Sioxide, O2) that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first ...
, have been discovered in Lappajärvi. The shattered bedrock resulting from the meteorite impact has created favorable groundwater areas in Lappajärvi. Iso-Räyrinki Lake in Alajärvi has been suggested as a secondary crater of the Lappajärvi meteorite, thought to have been formed by a moon orbiting the Lappajärvi meteorite.


Discovery

The research history of Lappajärvi is considered to have started in 1858 when Henrik Holmberg mentioned in his book "''Materialier till Finlands geognosi''" a volcanic rock found in Lappajärvi. In 1916, geologist Eero Mäkinen analyzed the rock and identified it as
dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...
, a type of
lava rock Volcanic rocks (often shortened to volcanics in scientific contexts) are Rock (geology), rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into Subv ...
. After his studies on
Lake Yanisyarvi Lake Yanisyarvi (; ) is a lake in the Republic of Karelia, Russia, located north of and draining to Lake Ladoga. The basin of this somewhat circular lake was formed by meteorite impact 700±5 million years ago during the Cryogenian period. The ...
in Karelia in 1920, geologist
Pentti Eskola Pentti Elias Eskola (8 January 1883 – 6 December 1964) was a Finland, Finnish geologist who specialised in the petrology of granites and developed the concept of metamorphic facies. He won the Wollaston Medal in 1958, the Vetlesen Prize in 19 ...
became convinced that Lappajärvi was also a
volcanic lake A volcanogenic lake is a lake formed as a result of volcanic activity. They are generally a body of water inside an inactive volcanic crater (Volcanic crater lake, crater lakes) but can also be large volumes of molten lava within an active volcan ...
. In the summer of 1926, Eskola visited Lappajärvi and confirmed that the kärnäite rock was volcanic in origin. Lappajärvi was long believed to be the remnant of an ancient volcano, and as late as 1964, Professor Ahti Simonen wrote about the lake's ancient volcanic activity. In the spring of 1967, after studying the Nördlinger Ries crater in Germany, Professor Thure Georg Sahama began to suspect that Lappajärvi was also a meteorite crater and suggested that Martti Lehtinen investigate it. In 1967, Swedish researcher Nils-Bertil Svensson observed that quartz in kärnäite was fragmented in the same way as in other craters on Earth. Svensson's findings were published in ''
Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...
'' in February 1968. In 1967, Martti Lehtinen started his investigations of the crater and discovered suevite in the Hietakangas gravel pits in July 1967. In the summer of 1968, he found coesite in Lappajärvi. His licentiate thesis on the research was completed the following year. In 1976, Lehtinen published an English-language doctoral dissertation on the meteorite theory, which included evidence of quartz transformations in certain rock samples that could not have resulted from volcanic activity. The dissertation is considered the final confirmation of the meteorite theory. Gravity measurements conducted in the same year also supported the meteorite theory, as a gravitational anomaly was detected within a 17-kilometer diameter area. In 1980, German researchers Elmar Jessberger and Uwe Reimold used the
argon–argon dating Argon–argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede Potassium-argon dating, potassiumargon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measur ...
method to determine the age of the crater to be approximately 77.3 million years. From 1988 to 1990, the Geological Survey of Finland conducted drilling studies, with the first one reaching a depth of 217.75 meters in Härkäniemi, where kärnäite was found to extend from the surface to the depth of 145 m, followed by a suevite layer and a breccia layer. The second drilling reached a depth of 165.75 meters in Pokela, Vimpeli. The fourth drilling reached a depth of 275 meters in the intermediate island between Kärnänsaari and Matalasaari, but no kärnäite was found. In 1992, paleomagnetic methods estimated the age of the crater to be around 195 million years. In 1997, small impact diamonds were discovered in suevite boulders from Lappajärvi. In 2001, uranium-lead dating by the Geological Survey of Finland estimated the age of the crater to be around 73.3 million years, with a margin of error of five million years, confirming that Lappajärvi was formed during the Late Cretaceous epoch. In a study published in 2013, argon–argon dating yielded an age of 76.2 million years for the crater. The study also revealed that some minerals were approximately one million years younger, suggesting that the cooling of the crater took place over a period ranging from one hundred thousand to one million years. In the summer of 2018, researchers proposed an age of 77.8 million years based on uranium-lead dating. After peer review, the age was revised to approximately 77.85 (± 0.78) million years.


Gallery

File:Lappajärvi.jpg, Lake Lappajärvi File:Lappajärvi, july 2014.JPG, Lake Lappajärvi File:Lake Lappajärvi 2015-02-15.JPG, Frozen in winter File:Northern lights Lake Lappajärvi 20180315.jpg, Winter with northern lights File:Метеорит Шаттеркон.jpg, Lappajarvi impactite


See also

*
Impact craters in Finland As of June 2018, 12 confirmed impact structures have been found in Finland. They are listed below, sorted by original diameter. Note 1: The "original" crater dimensions are coarse estimates. Original depths were calculated using the given original ...


References


External links

*
Lappajärvi impact structure

Lake Lappajärvi, a meteorite impact site in western Finland by Martti Lehtinen (1976)
{{DEFAULTSORT:Lappajarvi, Lake Impact craters of Finland Cretaceous impact craters
Lappajärvi Lappajärvi is a municipalities of Finland, municipality in Finland's Southern Ostrobothnia region. It is located from Seinäjoki, from Kokkola and from Vaasa. The municipality has a population of () and covers an area of of which , or near ...
Vimpeli Impact crater lakes