Durango Bill’s
Ancestral Rivers of the World
Ancestral Rivers in
Europe
by
Bill Butler
Antecedence and superimposition are geologic processes
that explain how and why rivers can cut through mountain systems
instead of going around them. The examples here (including pictures)
are from Europe, but other examples can be found throughout the world.
Featured Areas
Danube River, Serbia / Romania
Fier River, France
Labe River (Elbe River), Czech Republic
Olt River, Romainia
Rhine River, Germany
Salzach River (Salzburg River), Austria
Unknown tributary to the Pechora River, Ural Mountains, Russia
Danube River, Serbia /
Romania
In Johann Strauss’ famous waltz, The Blue Danube,
the river is blue as outlined in the picture below. In reality, the
river is usually muddy as its geologic job is to transport sediment
from its headwaters to its delta.
In the view above the Danube River is flowing from
west to east (left
to right) through the southwest end of the Transylvanian Alps. (The
Transylvanian Alps are further subdivided into local mountain ranges.)
The river also forms the border between Serbia on the near side of the
river with Romania on the far side.
River elevations on the upstream (left) side of the
mountains are about 200 feet above sea level and about 100 feet above
sea level on the downstream (right side). The Transylvanian Alps
adjacent to the river are a little over 2,000 feet above sea level, and
thus the river gorge is about 2,000 feet deep.
The age of the Transylvanian Alps is not known, but
an eyeball estimate would put their entire uplift history in the last
30 million years. Google Earth shows several recent earthquakes (not
displayed in this more distant view) including a 1991 quake with a
magnitude of 5.7 just above and to the right of center. Thus the range
is continuing to undergoing a slow uplift at the present time.
As with most examples of rivers taking an
“illogical” path through a mountain range, the Danube is
another example of “antecedence”. When the Danube
originally established its course, the Transylvanian Alps did not
exist. If you could look at the area before the Transylvanian Alps were
uplifted, you would see a flat plain with the Danube flowing in its
present course across the lowlands.
The river’s elevation closely approximates what it
was 30 million years ago. Thus, it is not the river that has cut down
into the mountains. As the mountains rose the Danube played the part of
a stationary band and abraded a slice of rising material that kept
“getting in the way”. This is how the river has been able
to maintain its original course.
Fier River, France
The picture above looks west across the Rhone Valley,
France, some 25 miles southwest of Geneva, Switzerland. The Rhone River
itself enters from the right edge and flows south-southwestward off the
left edge. Of interest is the long, uplifted ridge that begins just
below the
center of the picture and continues off the left edge. The Fier River
has
“illogically” split this ridge instead of taking a nice
easy route around the right end. The split portions are the Montagne
des Princes to the right of the Fier’s gorge and Le Gros Foug on
the left. In between, the Fier has cut a 2,000-foot deep canyon.
The long ridge that has been cut by the Fier is at the
southern end of the Jura Mountains. The Jura Mountains in turn are the
place name for the Jurassic geologic time period as their core rock
layers date to ~144 to ~208 million years ago. Most readers will
associate the name “Jurassic” with the Jurassic Park movie
and immediately think of Tyrannosaurus Rex dinosaurs. There were a lot
of dinosaurs during the Jurassic, but T. Rex didn’t show up for
the party until nearly 100 million years later, and then he only
existed in western North America which is a long way from the Jura
Mountains.
Earthquake icons in Google Earth indicate mountain
building in this area is still in progress. There were two magnitude
4-5 earthquakes less than ten miles to the northeast of the gorge in
1996, and several dozen others (mostly smaller) within a 20 mile range.
The uplift history of the Montagne des Princes / Le Bros Foug ridge is
not known, but it looks very recent. The Fier River Gorge has very
steep sides indicating it is less than 5 million years old.
It seems probable that the gorge is another example of
antecedence. The Fier River was in place first. As the ridge rose, the
river played the part of a stationary band saw and eroded away the
rising mountain that kept trying to “get in the way”.
The Fier River is not the only river that has cut a gorge
through some of the ridges in the Jura Mountains. If you have Google
Earth, you will find other gaps in the mountain ridges - especially in
the area some 15 to 30
miles west-southwest of Geneva. Happy exploring.
Labe River (Elbe
River), Czech Republic
In the view above the Labe River flows north-northwestward
into two branches of the Ore Mountains. At Praha (Prague - capital of
the Czech Republic) which is some 35 miles to the south-southeast
(upstream and off the lower right edge of the picture) the river
elevation is about 600 feet above sea level. Where
the Labe River enters the mountains in the picture, it is about 480
feet
above sea level. The mountains typically rise to 1,500 to 2,000 feet
above sea level.
The uplift history of the Ore Mountains is not known.
“Eyeball” examination and the recent moderate earthquake
activity suggest a maximum age of about 10-15 million years. It is
assumed that the Labe River Gorge is another example of antecedence.
The yellow line in the distance marks part of the border
between the Czech Republic and Germany. Once inside Germany the
river’s name changes to the more familiar Elbe, and from there it
continues to the North Sea.
Olt River, Romainia
The view above looks toward the south where the Olt River
cuts through the Transylvanian Alps. The Olt enters from the lower left
edge, cuts through the mountains, and eventually joins the Danube
River. (Flows from right to left in the distance.)
The river is about 1,200 feet above sea level just before
it cuts through the mountains and about 600 feet above sea level on the
far side. The Transylvanian Alps rise to 6,500 to 7,500 feet within a
10-mile range of both sides of the river. Thus the canyon is about a
mile deep, which is roughly comparable in depth to Arizona’s
Grand Canyon.
The geologic history of the Olt River is somewhat similar to the
Danube in that it cuts through the Transylvanian Alps. However, the Olt
cuts through some 120 miles east-northeast of the Danube, and as seen,
the mountains are much higher.
Rhine River, Germany
If you have ever traveled on a Rhine River cruise, you
probably went through the
gorge where the Rhine River has cut through the Hunsruck Taunus
Mountains.
The view above looks east- northeast along an active
fault zone in western Germany. The fault itself runs from the bottom
edge (right of center) up to the top of the picture. The area to the
right of the fault is extensively farmed lowlands, and elevations near
the river are less than 300 feet above sea level.
To the left of the fault, the land has been uplifted to
form a plateau which varies from 1,000 to 2,000 feet above sea level.
We ask: Which direction does the river flow? By now, you
should “smell a rat”.
The Rhine River flows from right to left, from the
lowlands into the highlands where it cuts a gorge some 1,500 feet deep.
The Hunsruck Taunus Mountains are very young. The steep
sides of the gorge and relatively minor erosional pattern on top of the
plateau suggest a maximum age of about 10 million years.
If we turned the clock back 10 million years, the Rhine
River probably closely approximated its present path. The mountains
hadn’t been uplifted yet. Thus the Rhine followed the lowest
route across a relatively featureless plain.
The Hunsruck Taunus
Mountains have been uplifted over the last 10 million years. As the
mountains rose, the Rhine had enough erosion power to maintain its
original elevation. The river itself is about the same elevation above
sea level that it was 10 million years ago. As the mountains rose, the
river simply abraded away material that kept trying to get in the way.
Salzach River
(Salzburg River), Austria
The view above looks northward across northwestern
Austria. (Germany is to the left of the yellow line marking the
border.) The city of Salzburg is in the white area in the distance.
(Astronaut / satellite photographs are taken at different times of the
year which produces different colors.) Salzburg is famous as the
birthplace of Wolfgang Amadeus Mozart, and the city has been recounting
the story ever since.
The Salzach River also has a story to tell but this one
covers 30 million years of geologic history. The Alps are a young
mountain range and have been essentially uplifted from scratch over the
last 30 million years. There were ancestral rivers here before then,
included the portion of the Salzach River that splits the high
mountains in the center of the picture. The two mountains are over
7,000 feet high while the river elevation between them is about 1,600
to 1,700 feet above sea level. Thus the gorge is over one mile deep.
The story here is similar to that of the other ancestral
rivers, and is another example of antecedence. The river was in place
first, and as the mountain range rose, the Salzach had enough erosion
power to cut down as fast as the mountains rose. Thus it was able to
maintain its original course.
Unknown tributary to
the Pechora River, Ural Mountains, Russia
The picture above looks northward over the northern Ural
Mountains in Russia. An unknown and perhaps unnamed river has its
headwaters on the east (right) side of the core of the Ural Mountains.
The valley systems for 10 to 15 miles east of the mountains feed into
this unknown river which then cuts westward through the highest part of
the Urals.
Elevations where the river cuts through are about
700 to 800 feet above sea level while the highest part of the mountain
range varies from 3,000 feet to a little over 4,000 feet. When the
river gets some 55 miles
further to the west-northwest, it joins the northward flowing Pechora
which in
turn flows into the Arctic Ocean.
In contrast to the relatively young mountains in the Alps
system, the Urals are some 250 to 300 million years old. They were
formed as part of the Pangaea supercontinent assembly process when two
subcontinents collided.
The historical geology of the area is completely unknown,
but we can make a few intelligent guesses by comparing what we can see
here vs. a system that is known. The Salina Creek system in
Utah’s Wasatch Plateau looks very similar to what we see in the
Urals.
Salina Creek has its headwaters east of the highest
portions of the Wasatch Plateau, and then flows westward to cut a
canyon
through the highest part of the range. Up to 5.4 million years ago, the
ancestral Colorado River crossed the Wasatch at the current location of
Salina Creek. As the Wasatch Plateau was uplifted, the Colorado was
increasingly blocked by the rising mountain mass. 5.4 million years ago
it shifted its course southward to Arizona and started to carve the
Grand Canyon. However, areas near the highest portions of rising
Wasatch were also being uplifted, and hence local drainage near the
crest of the range continued to use the ancestral path of the Colorado.
This local drainage became Salina Creek. (More info at:
http://www.durangobill.com/Salina.html
)
The local river system in the Urals looks very similar to
the Salina example. It seems probable that up to 250 million years ago
a larger river system used the same westward path that this unknown
tributary is using today. As the Ural Mountains rose, it became
increasingly difficult for this ancestral river to continue its path.
If it had
had enough erosion power, it might have been able to maintain this
original path. However in this case, the mountains rose faster than the
river could erode downward, and eventually the ancestral river
relocated somewhere else.
A speculative guess for this ancient river would be the present Ob
River which appears to track northwestward toward this location, and
then it changes
direction to take another route to the Arctic Ocean.
However, as the core of the Urals was uplifted, nearby
areas were also uplifted. This would make it easier for local drainages
to continue their path toward the gap that we see today. What we see
today is the local drainage system, but 250 million years ago this
local drainage was part of the tributary system for a much larger river.
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