The shapes and substrate of the Baltic Sea’s seafloor are everything but dull. The underwater world has a big selection of hills, ridges, plains and deeps.
Where the seafloor is hard, it is covered either by boulders, rocks or gravel. Soft areas of the seafloor floor are in turn covered with sand, clay or mud. In certain places, the seafloor is formed of bedrock that can be up to two million years old. In the softer parts, the seafloor can be formed from substrate that has sunk to the bottom very recently.
If you sunk the tower of the Helsinki Olympic Stadion in a pool that is 54 metres deep – the average depth of the Baltic Sea – you would still have 18 metres of tower over the surface. The deepest point of Finland’s sea areas is in the Bothnian Sea. It is 293 metres deep, which means you could sink the Eiffel Tower in it.
The deepest point of the whole Baltic Sea is 459 metres deep. It is located in the Landsort Deep, in the Swedish sea area between Stockholm and Gotland. It is deep enough that you could sink the Eiffel Tower and stack two of the Helsinki Olympic Stadium’s towers on top of it. That’s pretty deep! However, the average depth of the great oceans – a whopping 4,000 metres – would hold a bit over 13 Eiffel Towers. That is why the Baltic Sea competes in a completely different race than the great oceans, when looking at how much water is in it (21,000 m3).
Bar chart on average depth: The Baltic Sea (54 m), tower of the Helsinki Olympic Stadium (72 m), the Eiffel Tower (300 m), the Mediterranean sea (1500 m) and the World Ocean (4000 m).