1.7 billion Years #17
by Eric Rundle
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Title
1.7 billion Years #17
Artist
Eric Rundle
Medium
Photograph - Photographs
Description
When you visit the Black Canyon of the Gunnison River National Park you cannot help to wonder how this place came to be.
The extreme steepness and depth of the Black Canyon formed as the result of several geologic processes acting together. The Gunnison River is primarily responsible for carving the canyon, though several other geologic events had to occur in order to form the canyon as it is seen today.
Precambrian
The Precambrian gneiss and schist that makes up the majority of the steep walls of the black canyon formed 1.7 billion years ago during a metamorphic period brought on by the collision of ancient volcanic island arcs with the southern end of what is present-day Wyoming. The lighter-colored pegmatite dikes that can be seen crosscutting the basement rocks formed during this period as well.
Cretaceous - Tertiary
The entire area underwent uplift during the Laramide orogeny between 70 and 40 million years ago which was also part of the Gunnison Uplift. This raised the Precambrian gneisses and schists that make up the canyon walls. During the Tertiary from 26 to 35 million years ago large episodes of volcanism occurred in the area immediately surrounding the present day Black Canyon. The West Elk Mountains, La Sal Mountains, Henry Mountains, and Abajo Mountains all contributed to burying the area in several thousand feet of volcanic ash and debris.
The modern Gunnison River set its course 15 million years ago as the run-off from the nearby La Sal and West Elk Mountains and the Sawatch Range began carving through the relatively soft volcanic deposits.[
Quaternary
With the Gunnison Rivers course set, a broad uplift in the area from 2 to 3 million years ago caused the river to cut down through the softer volcanic deposits. Eventually the river reached the Precambrian rocks of the Gunnison Uplift. Since the river was unable to change its course, it began scouring through the extremely hard metamorphic rocks of the Gunnison Uplift. The river�s flow was much larger than currently, with much higher levels of turbidity. As a result the river dug down through the Precambrian gneiss and schist at the rate of 1-inch (25 mm) every 100 years. The extreme hardness of the metamorphic rock along with the relative quickness with which the river carved through them created the steep walls that can be seen today.
A number of feeder canyons running into the Black Canyon slope in the wrong direction for water to flow into the canyon. It is believed that less-entrenched streams in the region have shifted to a more north-flowing drainage pattern in response to a change in the tilt of the surrounding terrain. The west-flowing Gunnison, however, was essentially trapped in the hard Precambrian rock of the Black Canyon and could not change its course.
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February 7th, 2013
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Viewed 386 Times - Last Visitor from Wilmington, DE on 03/25/2024 at 12:13 PM
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Comments (35)
David K Small
Before moving east, this was my "back yard" for almost a decade, and it still amazes me to view such images.
Malcolm Suttle
Now that's just stunning Eric!! What good luck you were there before it all changes :0) V