The Green Ring - Stage 1

THEMED HIKES

Nature reserve Gypsum Holes

Around 220 million years ago, during the Triassic period, the Oberlech area was close to the equator and had a very hot, dry climate.

The coastal area at that time con- sisted of many little lagoons. Floods deposited salt water in the lagoons, which then boiled in the burning heat. The concentration of salts in the solution consequently rose and sulphates (gypsum, anhydrite) were precipitated.

Since the gypsum formed 220 million years ago, the Oberlech area has since migrated northwards on a tectonic plate, which collided with the Euro- pean plate, causing the Alps to form and the former lagoon sediments to be raised up to a great height. The gypsum landscape which weath- ered quickly exhibits varying morphological phenomena. On the one hand, gypsum formation caused the ground to swell and hillocks to form.

Anhydrite, which is a sulphur mineral stable at greater depths, is trans- formed into gypsum at the surface by the absorption of water. This entails an increase in volume of up to 50%. Conversely, gypsum is dissolved, cre- ating gypsum holes. On average, per m 2 , around 3 kg of rock are dissolved and carried away every year.

The gypsum holes are also special in botanical terms because every hole becomes a special microclimate for plants.