Thermokallio

Thermokallio is a dark-sand crater lake located on the island of Åland in the Baltic Sea, Finland. The lake is situated on the island of Långö, which is part of the municipality of Kökar.

Thermokallio is unique due to its high iron oxide content, which gives the lake its characteristic dark color. The lake's water is also cold, with a temperature ranging from 1 to 3 degrees Celsius. This contrasts with the name, "thermokallio," which is Finnish for "hot sounding or hot sounding gorge." The contrast between the cold water and the name suggests that the name may have originated from the sounds of heat or steam emitted by the geothermal activity in the area.

Geologically, Thermokallio is a tectonic depression that formed on the Baltic Shield, a region of the Earth's crust where the bedrock has been shaped by over 180 million years of tectonic activity. The rocky floor of the lake is composed of marble, which suggests that the lake is relatively young and formed from a combination of geological and fluvial processes.

Thermokallio is a mesotrophic lake, meaning that it has moderate nutrient levels and supports a range of organisms, including phytoplankton and zooplankton. The lake is also home to several fish species, including perch, pike, and eel. The combination of the lake's unique chemical composition and its location in the geologically violent area where the Baltic Shield meets the margin of the Fennoscandian shield make Thermokallio an interesting subject of study for scientists.