Landscape Evolution Slides

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
First - time Visitors: Please visit Site Map and Disclaimer. Use "Back" to return here.

Effects of Erosion

	A polished outcrop created by stream erosion.
	Water in eddies often swirls pebbles around, eventually carving potholes like these. Note the overhang at the water line due to chemical weathering where the rocks are continually damp.
	During the Ice Age, sudden influxes of melt water caused huge floods to spill down the St. Croix River, creating huge potholes like these at Interstate Park in Taylors Falls, Minnesota. Water depths in the valley exceeded 100 meters and current velocities approached 100 km/hr.

Drainage Systems

	The most important drainage divide in North America is the Continental Divide, seen here in Colorado. The divide separates streams that flow to the Atlantic from those that flow to the Pacific.
	The river that did this ....
	....looks like this near its source in Rocky Mountain National Park, Colorado.
	The Colorado River starts out small, like all rivers.

The Classical Concept of Landscape Evolution

	A typical young landscape in southern Utah.
	A young landscape, bordering on mature, in the San Bernardino Mountains of California. The San Andreas Fault is a few miles away along the base of the mountains.
	A mature landscape in western Pennsylvania
	This landscape in central Tennessee is probably a fairly good example of an old mature landscape, far enough inland not to have been affected much by sea level changes and beyond the reach of the Pleistocene glaciers.

"Old Age" - Sometimes Real, Sometimes Not

	About where Brazil, Paraguay and Bolivia meet. This is probably a truly ancient landscape, so far inland it has not been affected by sea level changes and in an environment that has probably been stable for millions of years. Only a few resistant ridges stand up above the landscape. From seven miles up, there is not a sign of human presence. The lake is Laguna Mirin, Bolivia, 17 45' S, 57 48' W
	Resistant hills that stand up above ancient land surfaces are called monadnocks after a mountain in New Hampshire. This one is in Colorado.
	Two monadnocks seen across Moosehead Lake, Maine.
	Once, this would have been considered a landscape beginning to enter old age. The river is beginning to meander and has a wide flood plain. But the landscape on either side is youthful; V-shaped valleys and wide flat stream divides. Actually, this river in Indiana deepened its valley when Pleistocene sea level fell, then filled it in again as sea level rose. It probably also widened and streamlined its valley by carrying huge amounts of glacial melt water.
	This river in Nebraska has the classic meanders of "old age", but the landscape on either side is young to mature. This area wasn't glaciated, but the valleys were probably deepened and then filled in during Pleistocene sea level changes.
	A classic old age meander in central Wisconsin, except that the flat land was the bed of a glacial lake only 12,000 years ago. This "old age" landscape is only 12,000 years old! Rivers meander when the land is flat. One reason the land may be flat is that the landscape is very ancient, but some very young surfaces can also be flat.

Rejuvenation

	The San Juan River in Utah is a classic example of rejuvenation. The river must have been meandering on a flat landscape and then begun cutting downward.
	Landscapes can be rejuvenated at any time. Here at Machu Picchu, Peru, the mountain crests reveal a young mature landscape ....
	But the valley bottoms are so young that valley widening has scarcely occurred. This site is about 300 km from the Pacific but the river, the Urubamba, flows via the Amazon to the Atlantic, 5000 km away.

Antecedent Drainage

	The Delaware River cuts right through a ridge. This is the Delaware Water Gap. New Jersey is on the left, Pennsylvania on the right. Note how flat the ridge crest is.
	Another water gap seen from the ground. Note the very flat ridge crest, and that the distant ridge is about as high as the nearer one. The ridge crests are interpreted to mark the original land surface before the Appalachians were gently uplifted perhaps 10 million years ago.
	The ridge on the skyline is the Cumberland Mountains, an impassable barrier in colonial days and still formidable. The picture is taken in Virginia, and the ridge is the Kentucky state line.
	When this was discovered in the 1700's, it was a major event. This is the Cumberland Gap, one of the most important routes across the Appalachians. The stream that cut the gap was diverted when the relief was about half its present height. Parts of three states are visible here. The picture is taken from Tennessee, the middle distance is the extreme western tip of Virginia, and the skyline is the Kentucky state line.

In this panorama in southwestern Colorado, a stream flows from the right across an uplift (anticline) in the rocks. As soon as the stream enters the uplift, its canyon becomes deep. Note the entrenched meanders, a couple of which were cut through and abandoned when the canyon was about half its present depth. As soon as the river exits the uplift, the canyon once again becomes shallow. Clearly, the river was there first and the rocks arched upward across its course.

	An aerial view of the eastern end of the Grand Canyon shows that the Grand Canyon is the same thing on a larger scale. The river was there first and the crust arched upward across the course of the river.
	Devil's Gap, Wyoming, is one of the most remarkable examples of antecedent drainage in the world. A deep slot has been cut in the end of a ridge. Had the river flowed a mere quarter-mile further south, it could have missed the ridge entirely.
	From only a short distance away, Devil's Gap is all but invisible. It first becomes visible when the road drops into the valley. The soft sedimentary rocks along the road here once buried the ridge of Precambrian crystalline rocks completely. As the river cut its valley, it cut down into the buried ridge

The Rio Grande at Albuquerque (taken in 1970 before extensive development). A typical braided stream.

Small deltas in the Gulf of Corinth, Greece. The bare soil hints at overgrazing and overfarming. The deltas are probably due to very recent enhanced erosion from overuse of the land.

Landscapes of two ages in Utah. A younger, more angular landscape at right is encroaching upon an older, more vegetated and rounded landscape at left.

Yosemite Falls, California. A July photo with only a trickle going over the falls.

Floods

	Some parts of the world, like this coastal plain in Ecuador, flood regularly.
	In June, 1990, Green Bay got five inches of rain in a day and widespread flooding resulted.

Catastrophic Floods

	Satellite view of the Channeled Scablands, Washington. Spokane is at upper right and the Columbia River winds in and out of the top left edge.
	Many aspects of stream flow are independent of scale. In this picture there are virtually no size clues to show whether the eddies are centimeters or meters high. Many features of the Scablands floods are vastly scaled-up versions of smaller stream erosion features.
	Streams that flow over rocky bottoms pluck the rocks to create irregular beds like this in the Kennebec River, Maine.
	Plucking in the Scablands had similar effects, but on a far larger scale. This scoured channel is in Oregon, 150 meters above the Columbia River. The Columbia River filled its valley 150 meters deep and the overflow was still capable of doing this.
	Streams that flow over unconsolidated sediments produce smoothly-curving streamlined shapes.
	In the Scablands, stream bars are enormous. The hill in the center of the valley is a gravel bar that formed in the lee of a rocky outcrop.

Arid Landscapes


	Monument Valley, Arizona. A hard cap rock protects softer rocks beneath. Undermining of the soft rocks by groundwater sapping and chemical weathering causes the cliffs to retreat, leaving mesas and buttes (isolated hills). Butte is a generic term for a steep, isolated hill and has no specific geologic meaning.

	In old arid landscapes, mountain fronts retreat until opposing pediments join to form pediment passes. Isolated remnant masses of rock are termed inselbergs (German: island mountain).
	Water brings dissolved salts into closed desert lakes, where they cannot escape. The lakes eventually become saturated with dissolved salts and form salt flats like these around Great Salt Lake in Utah. The purplish color in the water is due to microorganisms that can live in hypersaline waters.
	The small lake surrounded by mineral deposits is Deep Springs Lake in California, a typical playa. The steep mountain scarp on the left and the Sierra Nevada scarp in the distance are both fault scarps.

Access notes on Landscape Evolution
Return to Physical Geology Index
Return to Professor Dutch's Home Page

Created 16 July 1998, Last Update 16 July 1998

Not an official UW Green Bay site