Bod záujmu
Purple Lake
A flooded working of the Nadzieja mine, where pyrite extraction left acidic water and iron compounds that give the lake its characteristic colour.
Jazyk obsahu
The water in Purple Lake remains in contact with rock exposed by the former Nadzieja mine, known in German as Hoffnung. The mine opened in 1785. Extracted material was sent to a plant producing sulphuric acid. The lake now occupies an elongated working at around 560 metres above sea level, surrounded by steep rock walls.
Iron compounds account for its characteristic colour. Pyrite within the schists oxidises, and the products of these reactions enter the water. This creates conditions known as acid mine drainage: the effects of exposing a deposit continue long after the miners have left. Measurements in September 2011 recorded a pH below 3, indicating strongly acidic water. Iron and sulphate concentrations increased with the depth at which samples were taken.
Shallow water and exposure to sunlight encourage evaporation, which concentrates dissolved substances. The purple surface is thus the visible part of a process also taking place in the rocks, sediments and deeper layers of water. Its colour and water level may differ after rain and after a long dry spell.
Otázka 1 z 2
Compounds of which element give Purple Lake its characteristic colour?
- Poloha
- Former mine workings on the northern slope of Wielka Kopa