2 September, 1806: The landslide of Goldau

On September 2, 1806, the village of Goldau was destroyed by a landslide, coming from the mountain of Rossberg, killing 500 people. It was the first time that geologists investigated such a catastrophe.

Vicar G. Ott from Goldau writes in his 1906 book Goldau und der Bergsturz v. Rossberg 1806-1906:

"The 2. September 1806, the beautiful landscape of Goldau was buried by a landslide from the Rossberg. Approximatively 500 persons found there their ...  grave.
... But how in 100 years this Goldau has risen from the ruins! Where in the first years this area remembered more a sea in rage, and just 50 years ago the quiet hiker or pious pilgrim searched for a path between rocks and debris, now the stranger encounters a whole new Goldau, with new traffic, with new streets, stately homes and a new population."

Just one year after the catastrophe the physician Dr. Carl Zay, from the nearby town of Arth, collected eyewitnesses' reports and published the first scientific publication about a landslide with the title "Goldau und seine Gegend".

The Rossberg is a mountain located north of Goldau and the village stands on ancient landslide deposits. Legend tells that a landslide destroyed the surroundings of the mountain nearly 2.000 years ago. In the 14th century a river was dammed up and forced from his old path and in 1354 the ancient village of Röthen mysteriously disappeared.
 
Before the landslide in September smaller rockfalls were observed, but not considered dangerous.

The Rossberg consists of a heterogenic succession of argillaceous layers, sandstones and up to 30m thick conglomerate layers, inclined with 20° in the direction of the valley floor. Infiltrating water tends to wash out the finer sediments, destabilizing the entire succession.

The winter 1805-1806 had large amounts of snowfall, and summer 1806 was wet, especially July and August were characterized by strong precipitation events. September 2 was a rainy day, and in the morning in the flanks of the Rossberg large fissures were noted. In the forests the sound of breaking trees and roots could be heard, stones "jumped" out of the soil, squeezed by the accumulating tensions, in the meadows small mounds formed, partly superimposed each on another.
In intervals of a quarter of an hour, rockfalls occurred distributed over the entire area. In the afternoon (14:00) the rockfall activity intensified. Rumours of impacting boulders could be heard and a brown dust rose. At the base of the mountain soil and boulders were pushed up.
At 16:00 trees begun to move, and birds and cattle fled from the mountain.
At 16:45 finally a part of the mountain begun to slide, accelerating and impacting on Goldau.
Fig.1. Painting by Xaver Triner (1767-1824), commissioned by the Government of the Canton Schwyz, see also the paintings by H. Keller. The scar left by the landslide on the Rossberg is still visible today, you can compare the past depictions and the modern appearance on Pathological Geomorphology !!

Dr. Carl Zay collected various eyewitnesses' reports to reconstruct the catastrophe:

"The soil appears to peel from of each other and turns his green in the brownish colour of the reversed earth, the lower forests move gradually and the fir trees in a countless mass vacillate. Some larger stones are already rolling down the mountain, smashing houses, barns and trees, and throwing themselves down in the direction of the valley in a speeding motion, as messengers of the soon following terrible mass.
Now suddenly the movement increases, whole rows of pine trees fall in disorder down and in the depths. All detached and mobile, forest, earth, stones and rocks fall slide away, speeding up and finally falling down fast as lightening.
Terrible roar is heard, whole sections of torn-up soil, rock pieces as large or larger than houses, whole rows of standing pine trees are thrown trough the air. A terrible red-brown dust raises, wrapping up the avalanche in darkness and running before it as a dark cloud chased by the storm wind.
Mountain and valley are shaken, people freeze at the sight, birds, hindered in their flight fall down on the site of the devastation. Houses, people and cattle are thrown above the earth and in the air faster than a cannonball shoot out of a cannon.
The flood of Lake Lowerzer, startled from their quiet, rears up and starts over like a storm its devastation. A large part of the shattered masses climbs up the steep foot of the Mountain Rigi and single trees and boulders of rock fly up even higher… in a period of 3 to 4 minutes" it was all over.

Fig.2. Historic painting of the 1806 AD catastrophe drawn by 16 years old eyewitness David Alois Schmid, who observed the rock avalanche from his hometown Schwyz. In the foreground, the swampy western shore of Lake Lauerzer is depicted. Schmid clearly illustrates that upon the impact of the rock mass the substrate of the swampy deposits was laterally ejected towards the lake in vegetated slices reaching heights of small houses. This process subsequently triggered the devastating water waves on Lake Lauerz (figure from BUSSMAN et al. 2010).

Bibliography:

BOLLINGER, D. (2006): Der Bergsturz von Goldau: Rückblick und Ausblick. Bull. angew. geol. Vol.11(2): 3-12
BUSSMANN, F. & ANSELMETTI, F.S. (2010): Rossberg landslide history and flood chronology as recorded in Lake Lauerz sediments (Central Switzerland). Swiss J. Geosci. 103: 43-59
HÖFLER, H. & WITT, G. (2010): Katastrophen am Berg - Tragödien der Alpingeschichte. Bruckmann Verlag: 144
THURO, K., BERNER, C. & EBERHARDT, E. (2005): Der Bergsturz von Goldau 1806 - Versagensmechanismen in wechsellagernden Konglomeraten und Mergeln: 303-308. In: Moser, M. (ed): Veröffentlichungen von der 15. Tagung Ingenieurgeologie, 6-9. April 2005, Erlangen: 482