How Ice Sculpted These Lands

Smooth rock surfaces that reveal bedrock patterns dating back billions of years. Glacial striations. Boulders in peculiar positions. These are some of the immediate evidence that meets our eye when paddling through the maze of islands. But the entire archipelago landscape, all of it, is completely shaped by the last ice age.

A thick ice sheet, spanning several kilometers in depth, blanketed the whole region of Scandinavia. The sheer weight of this ice, coupled with the horizontal forces from its movement, profoundly impacted the land. As the ice began to melt, melt rivers formed, carrying with them vast quantities of debris ranging from fine silts to large boulders. This meltwater carved valleys, deposited sediments, and formed unique landforms.

All these processes led to the creation of a mosaic of islands, skerries, and intricate waterways – what us Swedes today call "Skärgården" (The Archipelago).

The most distinctive feature is undoubtedly the smooth polished rock surfaces of all the islands and islets. Glaciers on the move acted like giant pieces of sandpaper, grinding down the bedrock below. In the process, they revealed geological events from the earth's early history when the crust was forming.

The bedrock in Saint Anna and Gryt consists of igneous rocks like granite and gneiss that formed approximately 2 billion years ago. Over time, cracks in these ancient rocks were filled by magma, which solidified to form younger, often darker, rock types. The processes of folding, fracturing, and weathering have created fascinating patterns and colors, especially visible in the middle and outer archipelago.

Glacial striations, linear grooves in the rocks, are also very prevalent. They were carved by rocks and debris embedded at the base of the moving glacier.

An interesting phenomenon you can find in a few places is the presence of massive potholes, or “kettle holes”. These were formed by whirlpools of melting ice-water and rocks. Often, you'll see a round “pestle” rock at the very bottom of the hole.

There are a few places to explore that are extra interesting, for example Alnholm on the northern tip of the large island Aspöja. The rocks here display very special and colourful folding patterns – winding dark bands of pyroxene-rich minerals meander in a snake-like pattern between layers of white and red marble (crystalline limestone). There is also a large kettle hole here.

The enormous weight of the ice sheet also pressed down the entire land. Once the ice thawed, the land began its slow rise, a process still ongoing today. Though the elevation was initially more rapid, the land continues to rise by 2-3 mm each year. The sea charts, of course, need to be corrected accordingly every decade or so.

A few hundred years ago, many water passages existed far inland and between islands, but now these are dry lands. As the land elevates, waves wash away sediments, revealing bare rock surfaces. Over time, this results in exposed rocks in higher locations, glacial debris (known as “moraine”) on slopes, and fine sediment in depressions and hollows.