Geology and how the archipelago came to a balance between natural forces, without human influence. A couple of thousand million years ago, you would have had 15 kilometres of mountains above you, right where you are now standing. Try to imagine it!
That mountain is now eroded, but the rock you are standing on is the roots of that mountain. Then the earth’s crust folded as its pieces collided—it was like a rug being pushed together into a pile. Over a hundred million years, this is how the Svecofennian mountain range was formed, a majestic mountain range similar to today’s Himalayas. The red granites here in the archipelago come from melts at the roots of the mountain range.
The mountain range has long been broken down, but the rocks and structures are still visible in the archipelago. Along this path, you mainly encounter three types of rock, all formed from melts: granite, granodiorite and diorite. As the path begins to find its way up the hill from the forest, you first encounter the darker and softer diorite and, higher up, the lighter and harder granodiorite and granite.
Since the ice age, about 11,300 years ago, the archipelago has been slowly rising out of the sea. The land is still rising, but the rate is slowing with rising sea levels. Most of the landforms we see in today’s archipelago were created by the Ice Age. Glacially abraded rocks such as the round outcrops have smooth stoss sides and steep lee sides, as the ice moved in a southeasterly direction.
The Salpausselkä ridge shows where the edge of the ice was stationary for a long time. At the edge of the ice, the glacial rivers have dumped rock material into the delta, which today forms ridges. Hitis, Rosala and Örö are part of the second Salpausselkä ridge, and the third Salpausselkä ridge rises out of the sea along a line from Jurmo to Helsingholmen and across Kimitoön.
Can you balance like this?
Did you know? The second Salpauselkä ridge runs from Örö in the Archipelago Sea via Päijänne, almost all the way to Finland’s other biosphere reserve in North Karelia.
Finland’s bedrock is 3,000–1,400 million years old and is among the oldest, thickest and most stable in Europe. Granite is our country’s most common rock, and it is Finland’s national rock.