Iso-Naakkima

Infobox_lake
lake_name = Iso-Naakkima
image_lake =
caption_lake =
image_bathymetry = Iso-Naakkima (kraatteri).pngcaption_bathymetry = Lake Iso-Naakkima with the impact structure area in grey.
location = Southern Savonia
coords = coord|62|11|N|27|9|E|region:FI_type:waterbody|display=inline,title
type =
inflow =
outflow = Sahinjoki
catchment =
basin_countries = Finland
length = 4.9 km
width = 3.3 km
area = 11.14 km²
depth =
max-depth =
volume =
residence_time =
shore =
elevation = 111.2 m
islands =
cities =
reference = [http://www.ymparisto.fi/default.asp?contentid=116972&lan=fi www.ymparisto.fi - Iso-Naakkima ] ] [http://kansalaisen.karttapaikka.fi/kartanhaku/paikannimihaku.html?cx=3508688&cy=6897884&scale=16000&tool=siirra&lang=en-GB Citizen´s MapSite] ]

Iso-Naakkima is a lake in Southern Savonia, Finland, about 10 km south of the town of Pieksämäki. It is notable having an eroded impact crater under the northwestern part of the lake. The crater is one of the oldest known, about 1200 million years old (900–1200 Ma, Mesoproterozoic). At the time of the impact event the continent of Baltica (modern northeastern Europe) was located near the equator. The crater is filled by recent (Quaternary) sediments and is not visible to the surface. Its existence was revealed by strikingly circular geophysical anomalies which are concentrated in a region 3 km in diameter; the actual remnant is about 2 km wide and 160 m deep. Its existence was later confirmed by drilling results. The discovery was made in 1989 and therefore Iso-Naakkima is the fourth known impact structure in Finland.

External links and references

* [http://www.unb.ca/passc/ImpactDatabase/images/iso-naakkima.htm Earth Impact Database]
* [http://www.somerikko.net/old/geo/imp/isona_e.htm Iso-Naakkima impact structure]
* [http://www.geophysics.helsinki.fi/tutkimus/impacts/isonaakkima.php?lang=eng Iso Naakkima impact structure — Division of Geophysics, University of Helsinki]
*cite journal | author=Pesonen, L. J., Järvelä, J., Sarapää, O., & Pietarinen, H. | title=The Iso-Naakkima Meteorite Impact Structure: Physical Properties and Paleomagnetism of a Drill Core | journal=Meteoritics & Planetary Science | year=1996 | volume=31 | issue= | pages= A105 – A106 | url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996M%26PSA..31S.105P&db_key=AST&data_type=HTML&format=&high=4172e8435400399