"The morning of this sorrowful day begun with strong rain, which became less and lesser until at midday it stopped. Already in the early morning there were fissures in the earth and cracks in the meadows visible."
The Swiss physician Dr. Carl Zay, who witnessed the landslide of Goldau and in 1807 published a detailed report about the catastrophe, considered today the first naturalistic documentation of a landslide.
September 2, 1806 the Swiss village of Goldau was destroyed by a landslide, with an estimated volume of 40 million cubic meters, coming from the Rossberg. 457 people were killed - one of the greatest natural disasters in the Alps in historic times.
The Rossberg is a 1.574m high mountain situated north of Goldau. Old legends tells that a landslide destroyed the surroundings of the mountain already 2.000 years ago, in the 14th century a river was dammed up and in 1354 the ancient village of Rthen mysteriously disappeared. On the mountain rockfall and various large fissures, often filled with water, were noted by the locals years before the catastrophe. However these phenomena were not considerer threatening, as the village was considered distant enough from the endangered area.
The pastor G. Ott remembers 100 years later in his 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. Almost 500 persons found their eldritch 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 piously pilgrim searched for a path between rocks and debris, now the stranger encounters a whole new Goldau, with new traffic, with new streets, homes and a new population."
Thanks' to newspapers and the meticulous work of many naturalists the destruction of Goldau became widely known in Europe. It was the first time that a naturalistic approach to a geological catastrophe was chosen instead of the assumption that the landslide was a divine punishment. There exist various eyewitness reports and even paintings of the landslide and its aftermath and we can reconstruct in great detail the catastrophe.
Dr. Carl Zay describes in fanciful words in his book "Goldau und seine Gegend" how the landslide buried the village and plunged into Lake "Lowerzer", generating a tsunami that devastated the shores of the lake.
"The soil appears to be peeled apart and turns his green in the brownish colour of the reversed earth, the forest moves slowly and the fir trees vacillate in a single mass. Some larger stones are already rolling down the mountain, smashing houses and trees, and throwing themselves down in 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 into the depths. All detached and mobile, forest, earth, stones and rocks fall and slide, speeding up and finally falling down fast as a lightening.
Terrible roar is heard; whole sections of soil are torn up, 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 stormy wind.
Mountain and valley are shaken, people freeze at the sight, birds...plunge 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 from a cannon.
The flood of Lake Lowerzer, startled from their quiet, rears up and causes like a storm 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.1. Painting by Swiss artist Xaver Triner (1767-1824) of the Rossberg with the scar of the landslide and the buried village of Goldau in the foreground, work commissioned by the Government of the Canton Schwyz.
The notes and description of Zay help to understand the causes and the dynamics of this supposed "Trmmerstrom". A Trmmerstrom - or debris avalanche - consists of large, rapidly moving rock masses with an almost liquid motion (see also this U.S.G.S. document for the dangers and classification of mass movements).
Video.1. Spectacular video that documents the "flowing" of the debris avalanche (2,5 million cubic meters) of the Thurwieser in the Tyrolean Alps in September 2004.
The Rossberg consists of a heterogenic succession of argillaceous layers, sandstone and 30m thick layers of conglomerate, inclined with 20 degrees in direction of the valley floor. Infiltrating water tends to wash out the fine sediments, destabilizing the entire succession. Water also reduces the friction between the various layers. This instable situation needed only a last trigger to cause a catastrophe.
The winter 1805-1806 had experienced large amounts of snowfall and the summer 1806 was rainy (especially July and August). As noted by Zay also September 2, 1806 was a rainy day and in the morning new fissures opened.
In the early afternoon in the forest the sound of breaking trees and roots could be heard. Rocks "jumped" out of the soil, squeezed by the accumulating stress, in the meadows small mounds formed by the deformation of the soil and rockfall occurred in the entire area. Then trees begun to move and birds and the cattle fled from the mountain. In the late afternoon, finally the landslide occurred.
The description of Zay shows that the landslide started as a single mass, which became fragmented during movement and like a debris flow rapidly overflow the valley and the village. Parts of the landslide even moved upwards, like a wave of a liquid, on the opposite mountain Rigi. The people looked astonished at the moving mountain, when first large boulders approached the village they didn't even try to escape - nobody realized the danger until it was too late.
The scar left by the landslide of Goldau on the Rossberg is still visible today.
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