63.2, 23.7
Lappajärvi is a lake in Finland, in the municipalities of Lappajärvi, Alajärvi and Vimpeli. It is formed in a 23 km (14 mi) wide, partly eroded meteorite impact crater. The lake is part of Ähtävänjoki (Swedish: Esse å) basin together with Lake Evijärvi that is located downstream (north) of it.
The Lappajärvi impact structure is estimated to be 77.85 ± 0.78 million years old (Campanian age of the Late Cretaceous time period). Experts working on Finland's Onkalo spent nuclear fuel repository 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) found there, locally called Kärnäiitti.Nearby towns include Lappajärvi and Vimpeli and the nearest major city is Seinäjoki.
In September 2023, UNESCO accepted the Lappajärvi area's "Impact Crater Lake" Geopark application as one of the possible recipients of Geopark status for 2024.