Most of the bay fills a nine kilometer wide
impact structure. The structure is estimated to be about 1000 million years old (
Proterozoic). The depression was originally believed to be a
rift. Extraterrestrial origin was first proposed in 1979, but not until 1993 was the impact structure finally confirmed. Long
shatter cones have been discovered in the southwestern part of the bay. The remains of the crater are filled with sediments. Between
Pleistocene sediments and crushed
rapakivi granite bedrock there is a layer of
Paleozoic (
Ordovician)
limestones. This makes Lumparn one of the few places in Finland where
fossils have been found. The bay has also previously been referred to as
Lumpari in some
Finnish documents, though the
Research Institute for the Languages of Finland does not list
Lumpari as in current usage. == Gallery ==