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Why are the coasts of Sweden and Finland rocky and irregular?

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Map showing the physical features, major cities, and national boundaries around the Baltic Sea, North Sea, and English Channel regions of northern and western Europe. The map highlights coastal countries including the United Kingdom, Norway, Denmark, Germany, the Netherlands, Belgium, France, Sweden, Finland, Estonia, Latvia, Lithuania, Poland, and Russia, with sea depths indicated and key islands, peninsulas, and underwater trenches labeled. — Baltic Sea The Baltic Sea, the North Sea, and the English Channel.

The coasts of Sweden and Finland are highly irregular and rocky primarily due to the ancient geological structure of the Baltic Shield and the profound impact of Pleistocene Epoch glaciation.12

The underlying bedrock of these regions consists of ancient crystalline rocks, such as granite, which outcrop along the northern Baltic coasts. During the Ice Age, the weight of massive ice sheets depressed the Earth's crust and scoured the landscape. As these glaciers retreated, they left behind glacial drift and marine deposits that, combined with the exposed bedrock, created the characteristic "fretted" or indented coastline.312

This rugged terrain is often fringed by a "skerry guard"—a multitude of low, rocky islands—which are particularly numerous off the southwest coast of Finland and between Stockholm and the Gulf of Bothnia. Furthermore, because the Earth's crust is still rebounding from the removal of the glaciers' immense weight, the land continues to rise, gradually altering these coastal features over time.312