Huge landslide 50 years ago in the Tegernsee Alpbachtal: an expert explains where the dangers lurk

Created: 01/22/2022, 12:00 p.m

By: Gabi Werner

Uprooted trees marked the path of the landslide in the Alpbach valley at the end of 1971/beginning of 1972.

Old trees also fell victim to the rubble and mud masses.

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A massive landslide in the Tegernsee Alpbachtal caused a stir a good 50 years ago.

Could such a natural event happen again today?

An expert takes a stand in the interview.

Tegernsee

– A good 50 years ago, on December 30, 1971, a disaster was declared in Tegernsee.

A huge debris and mud avalanche had poured into the Alpbachtal from the Riedersteinwald.

At the time, the

spoke of around 70,000 cubic meters of material, but according to the Bavarian Environmental Atlas today it must have been well over 100,000 cubic meters that were moving here and taking old trees with them.

The Rosenheim water management office erected two barriers made of boulders, and volunteers from the Tegernsee fire brigade worked around the clock.

Fortunately, no one was injured in the slide.

We spoke to Andreas Holderer (53), the department head responsible for the district of Miesbach at the Rosenheim Water Management Office, about the events of that time and whether and where such dangers still lurk.

At the turn of the year 1971/1972, huge masses of mud and rubble started to move in Tegernsee and threatened the Alpbach valley.

An event that is specifically noted in your authority, Mr. Holderer?

Andreas Holderer:

We are of course aware of the events.

It's not like something like that disappears somewhere in one act and falls into oblivion.

At that time, a massive landslide pushed towards the upper reaches of the Alpbach.

As a result, a large dam was built there, which lets the water through, but is intended to stop such material if necessary.

We have to differentiate here between mudflow and landslide.

Can you please explain the difference?

Andreas Holderer:

The event in the Alpbachtal was a mass movement independent of the torrent.

This can happen if, for example, the soil on a slope is saturated with water.

The water then pools against an impermeable layer underground, and the unstable material above can slide on that layer.

Only when debris, rubble, wood and clay end up in the stream bed and are mobilized by precipitation or flooding does one speak of a mudslide.

To prevent this, the restraint system was built in the upper reaches of the Alpbach.

The dam still ensures safety today?

Andreas Holderer:

The dam is maintained by us and also regularly renovated.

Are there any signs that the slope above the Alpbachtal could slide again?

Andreas Holderer:

The situation in this area is relatively stable today.

So far we haven't been able to see anything moving again.

So there is currently no danger at this point.

But such landslides are a real risk elsewhere in the Tegernsee Valley, aren't they?

Andreas Holderer:

Yes, the landslide in the Alpbachtal was certainly not a unique event back then.

The Bavarian State Office for the Environment has a map of geohazards that everyone can see on the Internet.

And that is relatively colorful for the area around Lake Tegernsee.

That means: Due to the valley location and the special geology, a lot can be set in motion here.

The Leeberg in Tegernsee is one such example.

The mayor of Tegernsee has already announced that he will take up the issue in the future.

Andreas Holderer from the Rosenheim Water Management Office.

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Why is it that the danger of landslides is so great in our region?

Andreas Holderer:

This is due to the special, weather-prone layers of rock in the foothills of the Alps, the so-called flysch.

Smaller and larger landslides are unavoidable.

You have to live with that when you live in the mountains.

We can only fight the symptoms here, you can't get the real cause under control.

So what can you do to protect yourself from natural events like these?

Andreas Holderer:

We know pretty well where slope movements are currently possible. The most important thing is to avoid these danger zones and to plan and build responsibly. Land use planning plays an important role here, as well as in protection against other natural hazards. This is of course difficult in Tegernsee because there is only little space available for settlement. As the water management office, we also make sure to secure the torrents and install debris barriers. In some cases, it can also make sense to adapt the building – in other words, the side of a house that faces the mountain is built more sturdily than the rest of the building, for example. If the landslide is only superficial, a near-natural, species-rich mixed mountain forest can protect against landslides. The roots hold the structure together. When the slide is deepbut even a tree doesn't help anymore.

An article in our newspaper at the time said about the mud and debris avalanche from the Tegernsee Alpbachtal: The natural event had never threatened people and needed "no dramatization".

Andreas Holderer:

Such a landslide is actually normal in the Alps.

However, the event in the Alpbachtal was one of the most striking in the region in recent decades.

There was also a landslide in the Zeiselbach valley, but it wasn't that pronounced.

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