How many islands are in the Finnish archipelago?

It depends on how small a rock you count, but the Archipelago Sea between Turku and Åland has tens of thousands of islands and skerries. Finland as a whole has about 179,000 islands in the sea and in lakes.

Why are the rocks so smooth and rounded?

They were ground down and polished by the ice sheet that covered Finland during the last ice age. Stones frozen into its base scraped the bedrock smooth and left fine scratches showing which way the ice moved.

Is the land in Finland really rising?

Yes. Freed from the weight of the ice, the crust is still slowly rebounding, by a few millimetres a year in the Archipelago Sea and around 8 millimetres a year in the Kvarken further north.

Is the Baltic Sea salty?

Only slightly. It is brackish: in the Archipelago Sea about a fifth as salty as the open ocean, because rivers add fresh water and salt water enters only through the narrow Danish straits.

Kallio is the Finnish word for bare bedrock, the smooth granite outcrops that cover much of the archipelago and the Finnish landscape.

Can I explore the Finnish archipelago in the app?

Yes. You can land on a granite skerry in the Turku Archipelago in interactive 3D, walk the rock, swim and dive between the islands and try different skies, including the northern lights.

Tens of thousands of ice-polished granite islands in the calm, brackish Baltic

Archipelago

3D landscape · Turku Archipelago, Finland

Land here and explore →

The Archipelago Sea between Turku and Åland is a maze of islands, islets and bare rock skerries scattered across shallow, sheltered water. Depending on how small an island you count, there are tens of thousands of them, which makes it one of the largest archipelagos in the world by number of islands. Most are low and rounded, made of ancient pinkish-grey granite and gneiss polished smooth by ice. In this app you can land on a skerry near Nauvo (Nagu), walk the bare rock — kallio in Finnish — and swim in the Baltic between the islands in interactive 3D.

The landscape changes as you head out to sea. Inner islands are large and forested, with farms, meadows and summer cottages. Further out, trees give way to junipers, heather and crowberry growing in the hollows of the rock, and the outermost skerries are bare granite washed by waves, home to seabirds and grey seals. The whole area is still rising after the weight of the ice was lifted, so new skerries keep slowly emerging from the sea.

Key facts

Model setting: Turku Archipelago, south-west FinlandA skerry near Nauvo (Nagu), about 60.2°N
Islands and skerries: Tens of thousandsThe count depends on how small a rock is included
Finland's islands: About 179,000Sea and lakes together, in a national count from 2015
Bedrock: Precambrian granite and gneissMuch of it around 1.6 to 1.9 billion years old
Last ice sheet left: About 11,000 years agoLeaving rock polished and scratched by moving ice
Land uplift: A few millimetres a yearFaster further north, up to about 8 mm a year in the Kvarken
Water: BrackishRoughly a fifth as salty as the open ocean
National park: Archipelago National Park, 1983Part of a UNESCO biosphere reserve since 1994

Rock polished by ice

During the last ice age a sheet of ice several kilometres thick lay over Scandinavia and Finland. As it slid slowly towards the south-east, it scraped away loose soil and ground down the bedrock with the stones frozen into its base. When the ice melted, around 11,000 years ago in this region, it left behind the smooth, rounded rock surfaces that define the archipelago today. Geologists call these streamlined knobs roches moutonnées or whalebacks: gently sloping and polished on the side the ice came from, rougher and steeper on the side where it plucked rock away.

Look closely at the bare rock and you can often see glacial striations, fine parallel scratches carved by stones dragged along under the ice, which show the direction it moved. The rock itself is very old. Much of south-west Finland's bedrock formed between about 1.9 and 1.6 billion years ago, and the reddish rapakivi granite of Åland and the nearby coast is famous among geologists worldwide.

Land that is still rising

The ice was so heavy that it pressed the Earth's crust down by hundreds of metres. Since it melted, the land has been slowly springing back, a process called post-glacial rebound or land uplift. In the Archipelago Sea the ground still rises by a few millimetres a year, and further north, in the Kvarken archipelago, by around 8 millimetres a year, one of the fastest rates in the world.

Over a human lifetime the change is visible. Shallow bays turn into lakes and meadows, channels become too shallow for boats, and new rocks appear above the water. The Kvarken Archipelago and Sweden's High Coast are a joint UNESCO World Heritage Site because they show this process so clearly.

From inner islands to outer skerries

Scientists and locals divide the archipelago into zones. The inner archipelago has large, sheltered islands with mixed forest, fields and villages. In the middle zone the islands grow smaller and rockier, with pine and birch in the sheltered dips and stretches of bare rock between. The outer archipelago faces the open Baltic: low skerries of bare granite, wind-bent junipers and pines, and heather, crowberry and lichens clinging to cracks and hollows where a little soil can collect.

Much of the vegetation follows the rock. Water and soil gather in cracks and depressions, so plants grow in lines and patches across the otherwise bare kallio. Alder often lines the shores of the larger islands, while rowan, birch and aspen form dense thickets in sheltered places. In early summer the rocks are bright with flowering stonecrops and thrift.

A sea that is neither fresh nor salt

The Baltic Sea is one of the largest bodies of brackish water in the world. Rivers pour fresh water into it, while salty water from the North Sea can only enter through the narrow Danish straits. In the Archipelago Sea the water is only about a fifth as salty as the open ocean. That makes life difficult for both marine and freshwater species, and many live here at the edge of their tolerance: bladderwrack seaweed, blue mussels and Baltic herring alongside freshwater fish such as pike and perch.

The Archipelago Sea is also shallow, with depths of a few tens of metres in most places, so it warms quickly in summer and often freezes in winter. Its sheltered, nutrient-rich water makes it sensitive to eutrophication, the overgrowth of algae caused by nutrients washing in from land.

Archipelago wildlife

The skerries are important nesting grounds for seabirds. Common eiders, Arctic and common terns, gulls, black guillemots and velvet scoters breed on the outer islands, while white-tailed eagles, which nearly vanished from Finland in the 1970s, have made a remarkable recovery and are now a common sight. Grey seals haul out on the most remote rocks.

The water between the islands holds a mix of marine and freshwater fish, and in spring and autumn huge numbers of migrating waterfowl pass along the coast. The Archipelago National Park, founded in 1983, protects many of the outer islands, and the wider Archipelago Sea area became a UNESCO biosphere reserve in 1994.

People of the islands

People have lived in the archipelago for centuries, fishing, farming small fields, keeping cattle and sheep on the islands and sailing between them. The region is bilingual, with many Swedish-speaking communities, and villages are linked by bridges and small ferries. A popular route known as the Archipelago Trail loops through the islands by road and ferry.

Today many islands are dotted with summer cottages and saunas, and sailing, kayaking and island-hopping are a big part of Finnish summer life. Thanks to the right of public access, everyone may move through nature and land on most uninhabited shores, as long as they respect wildlife, nesting seasons and private yards.

Surprising facts about Archipelago

The archipelago is still rising: some rocks you can stand on today were under water when your grandparents were young.
The smooth rounded rocks were shaped by an ice sheet several kilometres thick.
Scratches on the rock show which way the ice moved, more than 10,000 years ago.
The Baltic is so weakly salty that pike and perch live alongside sea mussels and seaweed.
White-tailed eagles almost disappeared from Finland in the 1970s and are now common in the archipelago again.
Finland has around 179,000 islands, counting those in lakes as well as the sea.

Frequently asked questions

How many islands are in the Finnish archipelago?: It depends on how small a rock you count, but the Archipelago Sea between Turku and Åland has tens of thousands of islands and skerries. Finland as a whole has about 179,000 islands in the sea and in lakes.
Why are the rocks so smooth and rounded?: They were ground down and polished by the ice sheet that covered Finland during the last ice age. Stones frozen into its base scraped the bedrock smooth and left fine scratches showing which way the ice moved.
Is the land in Finland really rising?: Yes. Freed from the weight of the ice, the crust is still slowly rebounding, by a few millimetres a year in the Archipelago Sea and around 8 millimetres a year in the Kvarken further north.
Is the Baltic Sea salty?: Only slightly. It is brackish: in the Archipelago Sea about a fifth as salty as the open ocean, because rivers add fresh water and salt water enters only through the narrow Danish straits.
What is kallio?: Kallio is the Finnish word for bare bedrock, the smooth granite outcrops that cover much of the archipelago and the Finnish landscape.
Can I explore the Finnish archipelago in the app?: Yes. You can land on a granite skerry in the Turku Archipelago in interactive 3D, walk the rock, swim and dive between the islands and try different skies, including the northern lights.

Keep exploring

The landscapes in Ember’s Universe are procedural 3D scenes modelled on real places. The landforms, plants and light follow the real thing, but the details are generated, not mapped.

Sources