If you get the smell of rotten eggs on a hike on the Hoher Meißner, then the "Stinksteinwand" is not far away.

Lignite has been smoldering in the former Kalbe opencast mine on the eastern slope of the highest mountain in north-east Hesse for centuries.

"The name of the wall is due to the resulting sulfur gases, which escape from the seams underground through cracks in the ground," says Diethard Lindner from the Geo-Nature Park Frau-Holle-Land, where the Hoher Meißner is located.

Beneath the basalt cover of the mountain in the Werra-Meißner district lies a lignite seam up to 60 meters thick, which was first mined underground and later also in opencast mining.

Coal can self-ignite

“The coal contains marcasite, a mineral that breaks down when exposed to oxygen and moisture.

In the process, so much oxidation heat is released that the coal can self-ignite,” Lindner explains the seam fire phenomenon.

In certain weather conditions, the smell of sulfur can be heard hundreds of meters away, reports the geologist.

Sometimes you can also see clouds of smoke rising from the stink stone wall.

The fires in the legendary massif - Frau Holle is said to have worked there - have been smoldering for at least 400 years.

Lindner knows that mining has been going on on the east slope of the Hoher Meißner since 1578, when attempts were made to extinguish it by walling off the tunnels.

In 1929, coal mining at the Meißner was stopped, resumed in opencast mining after the Second World War and finally ended in 1974.

A total of 9.5 million tons of lignite were mined during this period.

After the end of mining, the deposit was covered with overburden.

But that doesn't stop the charcoal from smoldering.

The fires cannot be extinguished, says Matthias Dumm, head of the Hessisch Lichtenau forest office responsible for Meißner.

“This area of ​​the Hoher Meißner is interspersed with numerous old tunnels that have been driven into the mountain since the 16th century and are no longer accessible today.

This fractures the mountain, allowing air and therefore oxygen to circulate, which keeps fueling the fire,” he explains.

Fires on many square kilometers

Seam fires are not uncommon in coal mining areas.

"Most of them are currently in China, the USA and Australia," explains Dumm.

There, however, the fires are mostly much larger, some of which extended to many square kilometers.

In contrast, the phenomenon on the Stinksteinwand is limited to a very small area.

"I estimate the total size of the subterranean area, in which it probably smolders in various smaller places on the Meißner, to be a maximum of 10,000 square meters."

The area around the wall is cordoned off and entering is forbidden.

It can only be visited during guided hikes in the geo-nature park.

Because there is a risk that burnt-out cavities will collapse.

This is how it happened in 2001: At that time, a jogger discovered large clouds of smoke over the eastern slope.

The exposed up to 1000 degrees hot embers near the surface threatened to ignite a forest fire.

Trees were cleared and the cavities and crevices that fanned the subterranean fire like a chimney were covered with 150 truckloads of earth.

This has succeeded in reducing the smoke development back to the level that has existed for centuries, says Dumm.

The fire gases continue to escape.

A risk assessment carried out at the time showed that they were already so severely diluted directly above the exit point that it was unlikely that people would be endangered, explains the head of the forestry office.

Danger to life but from impending landslides.

“The basalt wall is fragile.

The mountain is in motion,” explains geologist Lindner.

"A natural consequence of mining, promoted by water in the slope." Again and again, chunks came loose and slid off.

The sea of ​​rubble at the foot of the wall bears witness to this.

"On the one hand, there has been erosion and demolition at the edge of the covering basalt plate for thousands of years, and on the other hand, the Meißner was a mining area for over 450 years," explains Dumm.

"Not only tunnels were dug, but also heaps of overburden were heaped up, which from the outset did not have the stability of natural geological structures." During more detailed investigations in recent years, slope movements were found in the area of ​​the old Schwalbenthal mining settlement below the massif, reports Dumm.

A concept for stabilization is currently being developed.

The mountain slipped earlier.

After a landslide in 1907, the mining village of Schwalbenthal had to be demolished because the houses were in danger of collapsing.

Only the former mining authority and later Gasthaus Schwalbenthal survived the incident.

However, the restaurant has been closed since 2010 because it can hardly withstand the pressure of the mountain.

In 1988 there was another landslide, which badly damaged a ski home below the Schwalbenthal.