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UNESCO World Heritage Site:
Swiss Tectonic Arena Sardona
A region with fundamental universal value
Thomas Buckingham
Simon Walker
Jürg Meyer
Harry Keel
Translation:
Lucy Fleming &
Thomas Buckingham
07.08.2013, v3.0
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TABLE OF CONTENTS
THE "MAGIC LINE" OF THE SARDONA
The Glarus Overthrust: a unique natural phenomenon
WHAT DOES " TECTONIC ARENA SARDONA " MEAN?
"Tectonic"
"Arena"
"Sardona"
WHY A WORLD HERITAGE SITE?
UNESCO - Guardian of the Peace
The Idea of World Heritage Sites
How did the Swiss Tectonic Arena Sardona become a World Heritage Site?
THE WORLD HERITAGE SITE
Situation and Location
The Geopark Sardona
THE MYSTERY OF LOCHSITE
The "wrong" rock sequence at the Swiss Tectonic Arena Sardona
SCHOLARS STRUGGLE FOR EXPLANATIONS
19th-century researchers and the development of the Thrusting Hypothesis
TOUGH WORK BEARS FRUIT
The geological exploration of the Alps and the current model of their formation
THE EARTH MACHINE: THE MOTOR OF MOUNTAIN BUILDING
The composition of the earth and the formation of mountains
UPLIFT AND EROSION
The Boosting Principle: the real story behind the mountains' formation
THE MYSTERY CONTINUES
Current research on the Glarus Overthrust
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THE "MAGIC LINE" OF THE SARDONA
The Glarus Overthrust: a unique natural phenomenon
In the picture below, taken in the border area of the Glarus, St. Gallen and Graubünden
cantons, one can see a razor sharp line running along mountain slopes in the Swiss Tectonic
Arena Sardona. What is it? A secret military road? An exposed trail?
No, it is a natural phenomenon. This "magic line" is actually a section of the long-lost
surface shown in Figure 2 (at right). It runs, curving like a dome, through the mountains.
Geologists call it the Glarus Overthrust. It climbs steeply from the Rhine Valley to the south,
reaches its peak under the Piz Sardona and then descends less steeply to the north. It is
visible one final time at the entrance to the Sernf Valley at Lochsite near Schwanden / Sool.
Fig. 1: Aerial view of Ringelspitz, with the "magic line" of the
Glarus Overthrust very visible.
Fig. 2: Aerial view of Ringelspitz,
Ringelspitz, showing graphic
representation of the "lost" surface.
Clearly, other rocks above this magic line are present, as below. One can see dark, massive
rocks forming rough rock walls in the Pizol area, on the Tschingelhörner, on Kärpf, on
Foostock or on Ringelspitz. Under the surface are softer, often foliated rocks.
Today we know that the "magic line" is actually a "thrust surface", where the upper rock
sequences have been pushed during the formation of the Alps on the bottom sequence, at
least 40 kilometers (24 miles) from south to north. These rock sequences above and below
the thrust are are called "nappes"
nappes". The Alps are a mountain range full of such nappes. But
nowhere else in the Alps - in fact, nowhere in the world - is such a nappe contact so clear and
visible in three-dimensions!
The first Alpine geologists were already fascinated by this natural phenomenon. But they did
not yet know that the rifting of the continents causes mountains to form. Such a huge thrust
of rock sequences was beyond their imagination. So, they tried other explanations. However,
after an epic scientific battle, it was clear from the evidence in the Glarus Overthrust that
thrusting was truly the answer. In this way, the Glarus Overthrust played a role in the history
of science.
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"overthrust"??
What is an "overthrust"
"Thrusting" is an important mechanism in
in the formation of mountains. Through this mechanism,
formerly adjacent rock layers break through enormous compressive forces and are stacked along a
parting surface. This separation surface is called the "thrust surface" or simply “overthrust”.
“overthrust” The
stacking causes, that along this overthrusts,
overthrust old rocks come to lie directly on younger
younge ones.
Fig. 3. Schematic diagram of an
an
overthrust formation.
formation.
The separated and pushed rock sequences are called "nappes" and can
n be several kilometers thick; the
t
transport route along the thrust surface may well be tens of kilometers.
The collision of continental plates createss
creates entire nappe complexes. A similar thing happens when snow
is plowed in the winter. The earth's crust is therefore thickened by thrust faults and nappe stacking and
at the same time eroded by climate.
Fig. 4. Schematic diagram of nappe
stacking similar to a "snow plow"
All these processes take place deep in the earth's crust. The thrusting process at the Glarus Overthrust
occurred approximately 10-15
15 km beneath the earth's surface and lasted several million years. Only
through the continuous uplift and the
t simultaneous erosion of the mountains did the thrust sheet at the
surface become visible. The Glarus thrust is no longer active
acti - it has been "frozen" during uplift. But
new thrust sheets are forming deep
eep in the earth's crust through the ongoing collision of Africa and
Europe.
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The Alps: A Product of Continental Collisions
Figure 27: Here, where continental plates drift
and collide against
against each other , mountain
ranges like the Alps or the Himalayas are
formed. The Alps are the result of
of a collision
between Europe, Africa and a few smaller
plates.
First, the continental plates collide (A - C). The
overthrusting
overthrusting process takes place over a
distance of more than 40 km (25 miles),
miles), but at
a speed of a few millimeters per year. This
means the process lasts several million years in
total. The plate collision leads to a thickening of
the crust followed by uplift of the entire
mountain range.
SouthSouth-toto-north movement continues to this day.
day.
The Glarus Overthrust is not active anymore, but
new thrust surfaces are formed deep in earth’s
crust (D).The star represents the position of a
rock body over the past 2020-40 Mio years
nowadays exposed at the surface.
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How does the Glarus Overthrust compare?
The Glarus Overthrust received an assessment of "outstanding universal value" from structural
geologists Prof. A. Pfiffner (Bern), Prof. St. Schmid (Basel) and Prof. M. Burkhard († Neuchâtel) in a
study called "Comparative Study on Thrust Faults". This very comprehensive study compares the major
thrusts worldwide through assessing the scientific, scenic, geomorphological and educational
uniqueness of each.
In a global comparison with other thrusts, the Glarus Overthrust stood out in all categories. Various
internationally respected and independent experts and Swiss institutions agree with this view and have
expressed their support for its conservation.
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WHAT DOES " TECTONIC ARENA SARDONA " MEAN?
MEAN?
"Tectonic"
Tectonics is a specialized field of geology that deals with the structures of the earth, the
movements in its interior and on the surface as well as the mechanisms and forces that drive
these movements.
In the area of the UNESCO World Heritage Sardona Tectonic Area, the Glarus Overthrust is
the defining and central tectonic element. In addition, however, a variety of other tectonic
processes, such as folds and fractures alongside the deep valleys, can be observed in this
area.
"Arena"
At the peaks around the Piz Sardona, the Glarus Overthrust is visible in three dimensions. In
some places, such as on the Fil de Casson, on the Segnes- or the Heidelpass, visitors have the
feeling of standing in the middle of an arena.
"Sardona"
The Piz Sardona is not the most impressive peak of this region of the Alps, standing at 3056
m (10026 ft). Why does the entire 330 sq km (124 sq miles)area take its name from such
this mountain? There are three reasons. First, the Piz Sardona is in the center of the region.
Second, its status as a border mountain between the three World Heritage-participating
cantons of Glarus, St. Gallen and Graubünden makes it a symbol of cross-border cooperation,
across cantons and across the world. Third, the Glarus Overthrust is visible from all sides of
the Piz Sardona's summit.
Therefore:
The Swiss Tectonic Arena Sardona describes the unique area around the Piz Sardona in which
the processes of mountain building are especially visible.
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Fig. 5.1:
.1: The Piz Sardona (3056 m/10026ft
m/10026ft)
/10026ft) on the left in an aerial view from the north. This peak marks the center
of the eponymous World Heritage Area. The thrust is clearly visible.
Fig. 5.2:
5.2: Again Piz Sardona (3056 m/10026
m/10026 ft)
ft) in the front on the left in an aerial view from the north. In the
background Ringelspitz. The thrust surface has been visualized – this is what a geologist sees when walking through
the region.
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WHY A WORLD HERITAGE SITE?
SITE?
UNESCO - Guardian of the Peace
"Since wars begin in the minds of the people, the peace of mind of the people must be
anchored." That's the guiding principle of UNESCO, the United Nations Organization for
Education, Science and Culture, which was founded in 1945. Its primary objective is the
preservation of peace. It also manages the world heritage of mankind, consisting of world
cultural and natural World Heritage Sites. Some things are so valuable, that all mankind has a
duty to: unique and beautiful cities, landscapes and cultural history. And, of course, peace.
The Idea of World Heritage Sites
In 1972, UNESCO adopted the Convention for the Protection of the World Cultural and
Natural Heritage. The idea of World Heritage Sites is to foster the preservation of unique
natural and cultural values for future generations. Switzerland signed in 1975. The central
prerequisite for a World Heritage Site is the global uniqueness of the so-called "exceptional
universal value" (OUV = outstanding universal value). In addition to this singularity, UNESCO
World Heritage Sites are also characterized by authenticity and integrity. Worldwide, there are
now about 725 World Cultural Heritage Sites and 180 World Natural Heritage Sites. In
Switzerland, there are currently eight Cultural Sites and three Natural Heritage sites (as of
2011).
How did the Swiss Tectonic Arena Sardona become a World Heritage
Site?
Unique visibility of natural mountain-building phenomena, exemplary history of research, and
continuing importance for geological research in this cross-cantonal area contributed to its
receiving, in 2008, status as a World Heritage Site. As such, the Sardona is in the same
league as the Grand Canyon, the Galápagos Islands, the Great Barrier Reef and the volcanic
islands of Hawai'i. A great honor - but also a great obligation for the three cantons and the
thirteen World Heritage communities to care for the area long-term.
Figure 6: Logo of the UNESCO World Heritage Site Swiss Tectonic Arena
Sardona
The logo is kept in brown colors of the predominant Verrucano rocks.
rocks. The
different
fferent rocks above
mountain sketch shows the Glarus thrust in white, with di
and below. The UNESCO World Heritage logo, shown at the top, illustrates
the relationships between culture and nature. The central square symbolizes a
manman-made form, while
while the circle represents natural forms.
forms. Both forms closely
intermesh, with the curves depicting
depicting both the earth's shape and the curvature
of protection.
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THE WORLD HERITAGE SITE
Situation and Location
The Swiss Tectonic Arena Sardona is located on the border of the cantons of St. Gallen,
Glarus and Graubünden. It includes the Ringelspitz mountain chain, Calfeisental, the Pizol
area, the Foostock and southern Weisstannental, the Flumserberg, southern Murg Valley, the
southern Kerenzerberg area, the Mürtschen group, the Mülibachtal, the northern Chrauchtal,
the Tschingelhorn, the Piz Sardona and Piz Segnas group and the Crap da Flem
(Flimserstein). The deepest point is in Ennenda (GL) to nearly 540 meters (1772 ft) above
sea level, while the highest point is 3,247 m (10653 ft) above sea level at the Ringelspitz.
The World Heritage perimeter follows mainly topographical elements such as water, valleys,
mountain ranges, forest boundaries and roads. Often it is identical with the boundaries of
existing protected areas. The total area of the region covers more than over thirteen
municipalities: Bad Ragaz, Flums, Mels, Ragaz, Quarten, Vilters-Wangs, Flims, Laax, Tamins,
Trin, Glarus, Glarus Nord, and Glarus Süd.
The Geopark Sardona
Since 1999, the Swiss Tectonic Arena Sardona has formed the core of the Sardona Geopark.
This area encloses the UNESCO World Heritage Site on all sides. The Geopark Sardona
Association was essential in securing UNESCO World Heritage status for the region.
As a network of diverse geological areas, the Geopark Sardona is a perfect addition to the
UNESCO project. The Sardona Geopark Association promotes and supports activities in the
fields of geology, underground construction, mining and stone processing, and is committed
to strengthening the experience of educational tourism, the expansion of research facilities
and the support of stone- and earth-enterprises.
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Fig. 7: Map showing the perimeter of the UNESCO World Heritage Site Swiss Tectonic Arena Sardona (gold)
and the Geopark Sardona (green). The numbers represent the geological attractions of the Geopark Sardona.
Sardona.
THE MYSTERY OF LOCHSITE
The "wrong" rock sequence at the Swiss Tectonic Arena Sardona
Near the town of Schwanden, where today a footbridge crosses the road, lies one of the most
famous rock outcrops in the Alps. An inconspicuous slope in the forest, a cliff of 50 m long,
40 m high: Lochsite. This area is a kind of "holy grail" for Alpine geologists. Here the "magic
line" visible high in the mountains can be conveniently studied, even touched with one's
hands.
This remarkable outcropping is known to geologists for 200 years. It was first described by the
famous Hans Conrad Escher von der Linth in 1807. He noted, "Below is a slate-like rock at
the base of the cliff. Above it is an overhang of a much firmer and harder, much older
sedimentary rock consisting of many small rock fragments, sandwiched between a 30-50 cm
(12-20 in) layer of calcite rich rock, with wild kneading and folding structures." This
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substance was called "Lochsite calc-tectonite " by later geologists. But the mystery remained:
How did an older deposit come to lie above a younger one?
Figure 8:
Sketch of outcrop Lochsite of Arnold Heim, as found in many
publications.
1 Slate - Flysch rocks;
rocks;
2 Lower and upper segments of Lochsite calccalc-tectonite;
tectonite;
3 Razor sharp surface, the youngest structure (so(so-called septum);
4 Verrucano rock, deformed;
5 Verrucano rock, hardly deformed
Geologists soon realized that these "wrong" sequences in the Glarus region of the Alps always
occurs at the prominent "magic line" accessible on the Foostock and the Segnespass, and also
very visible at the Tschingelhörner.
Fig. 9: Rocks on the Glarus Overthrust;
Overthrust; older rocks lie on top of younger ones.
Ever since Escher's time, geologists have made pilgrimages to Lochsite. All Swiss geology
students visit Lochsite at least once during their study. In fact, this outcrop is so crucial to
geological research and understanding of Alpine orogeny, that the renowned American
Museum of Natural History in New York has a faithful replica of Lochsite itself! Today we
understand much more - for example, how the "wrong" sequence occurred, but Lochsite still
possesses many riddles for contemporary geologists.
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Upside--Down
Turning Superposition Theory Upside
Two important laws for geological sedimentary rocks were formulated in 1670 by the Danish polymath
Nicolaus Steno. They now seem almost self-evident,
self
although back then they were a fundamental step
forward in the direction of modern geology:
1 Sedimentary rockss are deposited horizontally. When they are found in a different position (stacked
steeply, slated,, broken), this must be the result of a tectonic event.
Fig. 10: Horizontal calciteand
calciteand marl layers on Mürtschenstock.
Fig. 11: Layered and sheared limestones
limestones found on the south
side of Ringelspitz.
2. The deposition of sedimentary rocks follows layer upon layer. Thus, in an undisturbed sequence of
layers, the upper layers are younger than the lower. Along the Glarus thrust, this second law is defied and therefore
erefore produced a lot of headaches for geologists!
geolo
Figure 12: The undisturbed sequence of sedimentary layers in
the Churfirsten (lower to middle Cretaceous).
Figure 13: The inverted rock sequence at the Glarus
Overthrust, with older Verrucano over younger Lochsite calccalctectonite and Flysch.
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Portrait:: Hans Conrad Escher von der Linth
Portrait
1767 – 1823
This great polymath was a descendant of a wealthy
merchant family in Zurich and was involved in the
sciences while holding various offices.
Escher's main work was the regulation of the river Linth
- hence his aristocratic title. His scientific interest was
primarily in geology. His observations he recorded in
"Fragments on the Natural History of Helvetia," and in
over 900 watercolor mountain views and panoramas.
H.C. Escher was the first to describe, 200 years ago,
the "wrong" lying rock strata in the Glarus mountains.
However, he doubted the correctness of his
interpretation. At that time, the possibilities of relative
age determination were not yet fully developed. Still, he
can be seen as the "father" of research in the Swiss
Tectonic Arena Sardona.
Fig.
Fig. 14: Hans Conrad Escher von der Linth
SCHOLARS STRUGGLE FOR EXPLANATIONS
19th-century researchers and the development of the Thrusting
Hypothesis
The study of the Glarus overthrust is a prime example of how science struggles to produce an
explanatory model. The great scholar Hans Conrad Escher von der Linth (see above) suspected
in 1800 that in the Glarus Alps, the usual rock sequence "older below, younger above" was
not true. He suggested this to the distinguished German geologist Leopold von Buch, who
challenged the Evidence at the scene and interpreted the rocks rather differently. He stuck to
the old anthem: What can not be, must not be ...
Arnold Escher, the son of Hans Conrad and first professor of geology in Zurich, was sure that
younger rocks lay under older ones in the Glarus region. He even theorized about a "colossal
overthrust" - an idea that eventually proved to be the only explanation. In 1848, Escher
brought Roderick Impey Murchison, then a leading geologist, to the Glarus Overthrust.
Murchison was amazed by the "wrong" layers they found, and agreed with Escher's
interpretations. But he still flinched away from publishing, believing that the results would
shock the geological world too much. "No one would believe it," he maintained. "People would
think me a fool."
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In the mid-19th century
entury came to the contraction hypothesis, according to which the earth
shrinks due to cooling and thus the layers are thrown into folds at the surface (the
(
"Shrinking
Apple model"). This Escher formulated after several previous attempts to explain the Glarus
Alps in terms of a complicated folding model, the "Glarus double fold," designed by Escher's
student, the great Alpine geologist Albert Heim. The double fold consists of two horizontal
folds, one from the north and from the south, which lock together like a leather pouch.
Fig. 15: Heim's "double fold' model (1878, 1891), seen similarly to a leather pouch (Source: http://arthttp://art-ofof-craftscom)
By the turn of the century, the evidence irrefutably pointed towards the thrusting model - that
the Alps are primarily a range full of nappes and not constructed primarily of folds. But Heim
vehemently defended his double-fold
double fold model with all the weight of his academic authority until
he finally had to admit that he was wrong. However, he not only embraced the new thrust
explanation, but developed
ed it enthusiastically. In his famous 1921 textbook Geology of the
Alps, he wrote, "Those who still doubt the great thrust need only look at Lochsite..."
Fig. 16: The overthrust according to Heim (1921). GL = Glarus Overthrust, Mü = Mürtschen Thrust (a smaller thrust
above the Glarus Overthrust)
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The good accessibility and visibility of the significant geological phenomena of the Glarus
thrust became a major key research area of the new overthrusting and nappe formation theories.
Since then, many other geologists have visited the outcrops around the Glarus thrust and worked
intensively with exact mapping, sequence composition and age of sedimentary rocks and the local
structures. The Glarus Alps and the Swiss Tectonic Arena Sardona are in this respect one of
the most studied areas in the world.
The earth as a "Shrunken apple" - the old vision of the world
The shrunken apple is symbolic of an explanatory model of the earth developed in the middle of the
19th Century and persisting through to the 20th century. Scientifically, it is known as the contraction
model (or cooling or shrinkage theory). The theory was developed to explain the large-scale processes in
the earth's crust.
The central idea was that the earth was molten-hot at the beginning and cooled with time. This body of
the earth shrank slowly but unevenly because not all areas of the surface and underlying layers cooled
equally fast. These different cooling speeds generated at the surface and in the interior of the earth led
to earthquakes, cracks, folds and depressions in the earth's crust.
Many textbooks compared to the contraction of the earth with an apple, which forms wrinkles as it dries
out by the loss of water in the interior.
Fig. 17: ThreeThree-dimensional sculpture of the
Shrinking Apple Model from the Glarus Visitor
Center at the Elm location
Knowledge gained since the 1800s about the earth's interior and the structure and rocks of the
mountains meant that the "Shrunken Apple model" had to be abandoned. The earth cools down only
very slowly because in its interior heat is continually produced. Today we know that mountains caused
by the drift of tectonic plates on the viscous mantle (more on this in the chapter "The Earth Machine the engine of mountain building"). The theory of plate tectonics, finally, shows the relationship between
large tectonic movements and the observed phenomena thrust and thus underpins the nappe theory.
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Portrait: Albert Heim
1849 – 1937
"Those who still doubt the great thrust
need only look at Lochsite..."
This exceptional researcher contributed
greatly to the geological exploration of the
Alps. The Glarus Geology employed him
especially his scientific career and
influenced decisively. He further developed
the double-folds hypothesis theorized by A.
Escher and helped it to gain broad
scientific recognition. This model of
explanation then increasingly came under
fire and he acquiesced that it was no
longer tenable, which must have been a
difficult experience for such a strong
personality. It is to Heim's credit that he
did take up the new nappe theory quickly
and enthusiastically worked with it .
Fig.
Fig. 18: Albert Heim
TOUGH WORK BEARS FRUIT
The geological exploration of the Alps and the current model of their formation
What we know today about the geological origin and tectonic construction of the Alps is all
based on tremendously tough and costly field work done by the geologists of the last 200
years. Imagine for a moment what it took for the "Stone Doctor" Jacob Oberholzer (1862 1939) to publish his geological maps of the Glarus Alps: he had to essentially traverse every
square meter of the area and record the rocks occurring there. This involved many years of
field work and thousands of meters of altitude.
Even after field surveys are complete, the work is not finished. The rocks must be described,
analyzed and related to each other, the construction conditions (tectonics) interpreted. This
usually happens with engineered profile sections. Numerous tunnels and man-made
constructions (transport, hydropower) and boreholes have further refined the geological
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picture of the Alps. In the last few decades, geologists can even inspect large, inaccessible
depths using seismic wave technology.
Thanks to this work, the modern image of the Alps' construction has arisen as we know it
today. We recognize the Alps as a gigantic "crush zone" between the interlocking edges of the
European and African continental plates, which has been in turmoil for about 100 million
years. This collision has created a highly complicated structure of pushed, thrusted and
folded rocknappes.
Fig. 19: Tectonic profile of the entire Alps range. Such a tectonic profile can be imagined as a slice made by a knife through a
pie. Here we see the Glarus Overthrust. It is only one of countless other thrused
thrused nappes.
nappes. This diagram (from 2005) brings
together the careful work of hundreds of researchers over the past 200 years.
Still, the concept of "Alpine folding" stubbornly persists. Why? Because rock folds are very
striking, especially for laypeople. With the exception of something as obvious as the Glarus
Overthrust, the shifting and folding is not as clearly visible in the landscape.
The Alps are primarily a mountain range full of nappes, characterized by a large number of
superimposed rock layers. These nappes can be enormous, and pushed for over 100 km (62,
1370 mi). Folds are formed in the course of this thrusting. So: it's better to think of the Alps
as thrusting rather than folding!
It's also important to remember that the most modern alpine geology still begins in the field.
Even the most accurate laboratory measurement of the most elaborate computer model must
be able to stand before the observations encountered in nature. That's the beauty and
fascination of being a geologist.
The tools of the geologist
Geological field work requires only a few tools:
1. Field geologists identify with their hammer
hammer.
2. A magnifying glass is and will remain very important for proper identification and description of
rocks in the field.
3. With the geologist's compass
compass, the geologist can detect the location of geological structures such as
stratification and foliation surfaces, fold axes, fractures, stretching lineations, etc. In addition to the
compass this requires a bubble level in the device as well as a mechanism for applying the compass to
the rock structures.
4 The field book is the most important thing for the field geologist. All observations are written in it,
including sketches and views, records of rock samples, and hypotheses. The loss of a nearly-full field
guide is the geologist's nightmare!
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Fig. 2020-23: The important tools of the geologist.
Today, electronic devices bring significant simplification and additional options. A tablet PC or
smartphone is many things in one: base map with exact location determination using GPS, geological
compass, camera, database, field book. New applications allow recently three-dimensional
representations of geological findings, which bring tremendous advantages. However, such devices
cannot replace the trusted hammer and magnifying glass.
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Jacob
Jacob Oberholzer
1862 - 1939
"Dealing with my stones and geological
problems,, I perhaps alienated myself from the
problems
psyche."
student psyche
."
J. Oberholzer, the son of farmers in Tösstal, had
his career start as a hireling, but he acquired an
education and was hired as a teacher in 1887 in
Glarus. His love was the sciences and soon he
focused entirely on the geology of the Glarus
Alps.
The basis of his precise knowledge of the Glarus
geology lay in his almost 40 years of self-taught
geological field work. For the mountain farmers
he was only the "Stone Doctor," but in 1910 he
laid out the "Geologic Map of the Glarus Alps."
In 1917, "in recognition of his outstanding
service to the geological exploration of the
Glarus Alps," he received an honorary doctorate
from the University of Zürich.
Fig.
Fig. 24:
24: Jakob Oberholzer
By 1930, he had completed a 1,000-page manuscript named Geology of the Glarus Alps, neatly
written by hand and accompanied by print-ready drawings. It was published in 1933.
THE EARTH MACHINE: THE MOTOR OF MOUNTAIN BUILDING
The composition of the earth and the formation of mountains
Why we are surrounded by mountains in the Alps? The reason for this is found in the ironnickel core of the earth. There, the crystallization of molten iron - about 1 million kg (2.2
milion lbs) per second! - as well as radioactive decay reactions permanently generate gigantic
amounts of heat. This heat flows from the bottom to the viscous mantle, the 3,000 km (1864
mi) thick covering of the earth's core, which has temperatures of well over a thousand
degrees. The heat supplied from below the core generates heat convection by which the
energy is conducted to the outside, similar to the slow simmer of soup over the hot stove,
though the simmering currents of the mantle are much slower than in a cooking pot. The
plastic rock material flows only about 10-20 cm (4 -8 in) per year
The outermost solid layer of rock of the earth, the "lithosphere," is only about 100 km (62,
1370 mi) thick. It is divided into twelve large and numerous small plates that drift around on
the plastic upper mantle, with speeds of 1 - 10 cm (0.4 – 4.0 in) per year. The consequences
are obvious: there are zones where plates move apart, those where they scrape past each other
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and others where they approach each other. These "plate tectonics"" conclusively explain so
many geological phenomena, yet the theory of plate tectonics has been generally recognized
only for about 50 years!
Figure 25: Schematic cross
core to the solid
cross section of the earth. Complex thermal currents bring the heat of the Earth's core
rock of the surface plates.
Until recently it was assumed that there are relatively regular thermal convection currents in
the mantle that move the tectonic
tecto
plates. The
he rising convection cells were thought to lie below
mid-ocean
an ridges, where new lithosphere is formed by basaltic pillow lava emerging from the
seabed. Today we know from seismic tomography data that convection cells are much more
complex. Thee tectonic plates are not only driven by the heat convection currents, but cooler
and heavier plates can start pulling down the rest of the plate in subduction zones (the "slap"slap
pull" hypothesis). Also new is evidence that the subducted lithosphere can sink down to the
core-mantle boundary.
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Eduard Kissling
b. 1953
"For a better understanding of the Alps we
must also view from below."
Based on the computed tomography in
medicine, the seismic tomography was
developed in the 1980s. This method allows
a three-dimensional analysis of deep
structures.
Eduard Kissling was fascinated by the Alps
since his childhood. He wrote his doctoral
thesis on crustal structure and isostasy in
Switzerland at the ETHZ. After that, he
worked on the development of seismic
tomography and began to apply them to the
Alps. Today he is Professor of Geophysics at
ETH Zürich. Thanks to his research, a new
picture of the Alps up to several hundred
kilometers' depth has been produced. This
has greatly changed and developed the
interpretation of its formation.
Fig.
Fig. 26:
26: Eduard Kissling
22
UPLIFT AND EROSION
The Boosting Principle: the real story behind the mountains' formation
When two continental masses collide due to the drift of plates - as happened approximately
35 million years ago between Africa and Europe - the edge of one plate is pressed under the
rim of the other. Both edges are chipped in the process, and remnants of once-existing oceans
are sheared, thrusted and stacked ontop of each other. They become the rock nappes from
which mountains will be formed. Such was the origin of the Glarus Overthrust: a stack of old
Verrucano rock was pushed over much younger Flysch rocks. All of these processes played out
several kilometers/miles underground.
The various thrusted nappes lead to a thickening of the crust in the collision zone. This
results in a higher load on the two lithospheric plates that are pressed as a result into the
viscous mantle. This thickened crustal root leads to the actual uplift of the mountain chain,
according to the Archimedes buoyancy principle: the thicker the floating stacked lithosphere
on the mantle area, the lower the crustal root level in it. Because of a sinking of the
lithosphere into the specific heavier, viscous mantle due to buoyant forces the entire range
will be uplifted.
Fig. 28: (A) In the collision zone, the crust is thickened by the formation of thrust faults. (B) The thickened crustal root
sinks under the additional burden into the mantle. (C) as a consequence of buoyant force the entire mountain range is
uplifted.
uplifted.
Thus, the nappe structure of the Alps began to slowly uplift about 40 million years ago. Once
the rock was lifted above the sealevel, erosion immediately set in, and a "race" began between
uplift and erosion.
Whichever force "wins the race," a mountain can never grow "to the sky" because after a few
thousand meters it starts to slide laterally from its own weight. Such slippages can also be
found in the Alps. We know that the Alps were never significantly higher than today.
In the last 2.6 million years, the ever-advancing Ice Age glaciers created the outline of the
Alps we know today. Although weathering and erosion continually eat away the mountains
and valleys of the Alps, they are still "growing."
23
growing??
The Alps are growing
The rate of uplift in the Alps is still a bit higher than the erosion rate, which gently increases
the mountains' height. But geologists believe that in the near future this is likely to change; a
net removal process will slowly flatten the mountains.
Figure 29: Lines of equal uplift rates in mm / year to the present time, registered to a height relief. The
present rate of uplift in the
the Alpine region is between 0.5 - 1.6
1.6 mm (0.02 – 0.06 in) / year. The
distribution is characterized
characterized by striking "highs"
"highs" and "lows.
"lows." The area around Elm stays at a rate of
around 1 mm (0.04 in) per year. (All
(All figures are gross without erosion.)
erosion.)
Figure 30: Erosion
Erosion rates, determined from discharge measurements of Alpine rivers for their catchment
area. They vary from 0.15 to about 0.5 mm (0.006 – 0.02 in) per year.
year.
24
Adrian Pfiffner
b. 1947
thrustss without folds
folds."
"There are no thrust
."
Adrian Pfiffner, Professor of Geology at
the University of Bern since 1987, is the
doyen of the Swiss Tectonic Arena
Sardona. He was principal author of the
application to UNESCO and Chairman of
the Scientific Advisory Board of the
Sardona. He conducts research on the
construction of the Alps and the
mountain building processes, especially
about the relationships between folds and
thrust. To him we owe the current
tectonic profiles of the Glarus Alps and a
structure map of the entire Helvetic zone.
Fig.
Fig. 31:
31: Adrian Pfiffner
Pfiffner was instrumental in the seismic
exploration of the Alps, thanks to which
we know much more about the deeper
structures of the Alps. Today he
investigates the still ongoing mountain
formation as well as the rock deformation
at the atomic level, for example with
Lochsite calc-tectonite.
THE MYSTERY CONTINUES
Current research on the Glarus Overthrust
For a while everything seemed so clear. One may consider as well-substantiated scientific fact
today that there is a overthrust at Sardona's "magic line." But as so often in the sciences, new
generations bring new questions and are curious to replace these questions with answers.
Such is the case with the Glarus Overthrust.
Today's questions revolve around the mechanisms of this huge ceiling overthrust. How is that
mechanically possible? What types of deformation occurred? What role did deep groundwater
play? How quickly did the structures form? And what is the true nature of the Lochsite calctectonite - a real limestone, a rock formed by the thrust, or both?
Even after 200 years of geological research, the Glarus Alps remain a hot topic for the modern
Earth Sciences - one of the reasons for the area's recognition as a UNESCO World Heritage
Site!
25
Joseph Mullis
b. 1945
"The Verrucano rocks were pushed as on a
cushion of air of methane, carbon dioxide
and water via the Flysch and limestone."
J. Mullis, a professor at the University of
Basel, examines microscopically small
fluid inclusions in minerals. These provide
information on pressures, temperatures
and compositions of deep groundwater in
geologic processes. Thanks to his research,
we now know more about the Alpine
metamorphism and the role of deep water
in the rock deformation.
He showed that much methane was below
the Glarus thrust at very high pressure,
which was converted to the base of
Verrucano to carbon dioxide. This meant
that lime cement was dissolved in the
underlying flysch and precipitated on the
overthrust area through Lochsite calctectonite
Fig.
Fig. 32
32: Josef Mullis
Lochsitee-calc tectonite - "grease" of the Glarus Overthrust?
The Lochsit
Under conditions at the surface, all rocks respond to deformation by brittle fracture. At depths greater
than a few kilometers, where the pressures are more than 1,000 bar (100 Kpa)and temperatures above
230° C (446 °F), limestones begin to deform into a plastic state. The Glarus Overthrust formed at a
depth of approximately 10-15 km (6.2-9.3 mi)and temperatures of 230-340 ° C (446-664 °F). Under
these conditions, rocks literally flow due to recrystallization and crystal lattice displacements at the
atomic level.
Does this mean that rocks are not completely dry? Our intuition is misleading: without water hardly
anything would ever happen to rocks. At great depths, groundwaters are present. Due to the high
temperatures and pressures in these areas, the rocks behave as "fluids" behave and interact with the
water in many ways. Fluids can strongly influence the plastic deformation of rock: the more fluids, the
easier the deformation proceeds. The study of fluid inclusions in rocks and minerals provides important
information about the processes of rock formation.
26
Figure 33: Polished rock sample of the Glarus' Overthrust's famous Lochsite calccalc-tectonite.
tectonite. Researchers are still examining this
type of rock, and its formation is disputed. Most scientists agree that deep groundwater was decisive.