Lappajärvi

Video below tells you how Lappajärvi was formed.

Geologia

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Mittasuhteet Lappajärven synnyttäneen meteoriitin koosta.

76 million years ago, western Finland had been eroded to a flat continental region. The dinosaurs still
ruled the Earth.
One day, the orbit of an ordinary stony asteroid took
it from the asteroid belt between Mars and Jupiter
and put it on a collision course with the Earth. Its
speed was over 60,000 km/h and it had a diameter of
about 1.6 km. The impact released energy equivalent to that of over 17 million atomic bombs like the one that destroyed the city of Hiroshima. The depth of the newly-formed Lappajärvi crater was about 750 m and its diameter was about 22 km.

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If the Lappajärvi impact occurred today, it would affect all of Finland. The towns of Lappajärvi and Vimpeli would disappear and the town of Alajärvi would be covered by 50 m of ejected rock debris. One hundred km due west, in the city of Vaasa, heat
from the fireball would ignite forests and cause third degree burns. A magnitude 8 earthquake would collapse the buildings. About 50 cm of ejecta would cover the ruins. The air blast, arriving 5 minutes after the impact, would flatten anything that was still standing.

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In Helsinki, some 340 km away, the fireball would cause second degree burns, dust-like ejecta would amount to a layer 1 cm thick, and the earthquake would cause moderate damage to buildings. The hurricane-strength air blast would arrive in 15 minutes, tearing off the roofs and toppling 30% of the trees.

A unique combination: the rim, the central uplift, and the impactites

The Lappajärvi crater is surrounded by an uplifted rim, which can still be experienced on the hiking trails of Lakeaharju and Pyhävuori. In addition to the rim, the centre of the crater was also uplifted. Nowadays this central uplift is known as Kärnä Island. A new melted and mixed rock type created in the impact – kärnäite – has protected Kärnä Island from subsequent erosion. Kärnäite can be found in outcrops as well as countless boulders on the island.

Another type of impact rock or impactite, known as suevite, is a fragile mixture of crushed and melted fragments of the ancient bedrock. Suevite can only be found
as boulders on the southern and southeastern sides of the crater.

Lappajärvi is a magnificent place

Impact crater researchers around the world are well-aware of the exceptional nature of
the Lappajärvi crater. Impact craters are so rare on the Earth that each of the about 185 identified impact craters is unique in its own way. However, most of them are so old, eroded, covered, or remote that hardly anything is known about them. Instead, much is known about the youthful Lappajärvi, although for example Kärnä Island and the crater rim still possess a number of secrets. Impact craters that provide beautiful views, such as that of Europe’s largest impact crater lake in the rim region in Lakeaharju and Pyhävuori, are rare indeed. Also, where other than in Lappajärvi can one drink ground water that originates from the crushed bedrock of the floor of an impact crater?

Globally, nature- and geotourism are on the rise. While rambling the craters of the world, I have encountered much lesser holes in the ground where the impact has been
embraced as the unifying theme in the region and utilized in sustainable geotourism projects. I believe it’s now time to make the unique history and the natural beauty
of Lappajärvi much more widely known, not only throughout Finland, but also globally.

Text written by Teemu Öhman impact crater researcher. Used here with permission of the author.