The dissolving mountains in the Catalan Pyrenees, the Aigüestortes i Estany de Sant Maurici National Park is defined by water and rock.%%CITE_1%%%%CITE_2%%%%CITE_3%% Nearly 200 lakes are set among jagged peaks formed from granite and slate pushed up from the sea during the Alpine orogeny.%%CITE_1%% These granitic rocks, cooled from magma deep underground around 300 million years ago during the Hercynian orogeny, are composed of minerals like feldspar, quartz, and mica.%%CITE_4%%%%CITE_5%%
Normally, these hard rocks weather very slowly. Natural rainwater, made slightly acidic by atmospheric carbon dioxide, reacts with minerals like feldspar in a process called hydrolysis. This chemical reaction slowly breaks down the feldspar into clay minerals, releasing various ions and leaving behind the highly resistant quartz as sand. In the pristine environment of the high Pyrenees, this process unfolds over geological timescales. However, the chemistry of the rain has changed.
Pollutants such as sulfur dioxide and nitrogen dioxide from industrial regions can travel long distances, reacting with water in the atmosphere to form sulfuric and nitric acid. This acid rain falls on the Pyrenees, drastically lowering the pH of the water interacting with the rock. Studies in the Pyrenees show that lakes in granitic basins are highly sensitive to acidification because they lack the limestone (calcium carbonate) that would otherwise neutralize the acid. The increased acidity accelerates the chemical weathering of the granite, dissolving the rock's mineral structure at an unnatural rate.