LANDSCAPE DEVELOPMENT Grotzinger • Jordan Understanding Earth Sixth Edition Chapter 22: LANDSCAPE DEVELOPMENT © 2011 by W. H. Freeman and Company

Landscape Development Chapter 22 Landscape Development

About Landscapes Geomorphology is the study of landscapes and their evolution. Landscapes are the result of a competition between forces that raise the land surface and those that reduce it. Landscapes represent a balance between tectonic and climatic systems.

Lecture Outline Topography, elevation, and relief 2. Landforms: features sculpted by erosion and sedimentation 3. Interacting geosystems control landscapes 4. Models of landscape development

Topography, Elevation, and Relief ● Topography – configuration of the Earth’s surface ● Elevation – vertical distance above or below sea level ● Relief – difference in highest and lowest elevations

● Topographic map – shows the configuration of the Earth’s 1. Topography, Elevation, and Relief ● Topographic map – shows the configuration of the Earth’s surface using contours ● Contours – lines that connect points of equal elevation

1. Topography, Elevation, and Relief: Example – A Mountain Peak in Maine

1. Topography, Elevation, and Relief: Example – A River Valley in Wyoming

1. Topography, Elevation, and Relief: Digital Elevation Model of Topography

1. Topography, Elevation, and Relief: Regional Slope Map

1. Topography, Elevation, and Relief: Various Concepts of Relief

● rugged mountain slopes ● river floodplains ● desert dunes 2. Landforms: Features Sculpted by Erosion and Sedimentation ● Landforms: examples ● rugged mountain slopes ● river floodplains ● desert dunes

● elevated masses of rock ● to be a mountain, several 2. Landforms: Features Sculpted by Erosion and Sedimentation ● Mountains and hills ● elevated masses of rock ● to be a mountain, several 100 m of relief is required ● steepness and relief are usually related

Landscape with High Relief 2. Landforms: Landscape with High Relief

● Flat-topped landforms ● plateaus ● mesas ● tablelands 2. Landforms: Features Sculpted by Erosion and Sedimentation ● Flat-topped landforms ● plateaus ● mesas ● tablelands

2. Landforms: Landscape with Mesas Monument Valley, Arizona

Landscape with Sharp Peaks 2. Landforms: Landscape with Sharp Peaks southern Argentina

2. Landforms: Features Sculpted by Erosion and Sedimentation ● Structurally controlled ridges and valleys ● folded mountains ● River valleys and bedrock erosion ● fluvial erosion

Landscape with Folded Mountains 2. Landforms: Landscape with Folded Mountains

Development of Ridges and Valleys 2. Landforms: Development of Ridges and Valleys Tributary stream Resistant layers Anticline Soft layers Syncline Syncline Main valley stream

TIME 1 Tributary streams erode the slopes faster than main streams erode the valleys. Tributary stream Resistant layers Anticline Soft layers Syncline Syncline Main valley stream

Development of Ridges and Valleys 2. Landforms: Development of Ridges and Valleys Resistant layers Anticline Soft layers Syncline Syncline

TIME 2 Tributaries over the synclines cut through resistant rock layers and start to carve steep valleys over the anticlines. Resistant layers Anticline Soft layers Syncline Syncline

Development of Ridges and Valleys 2. Landforms: Development of Ridges and Valleys Resistant layers Soft layers Syncline Anticline Syncline

TIME 3 Valleys form over the anticlines and ridges capped by resistant strata are left over the synclines. Resistant layers Soft layers Syncline Anticline Syncline

Example of Ridges and Valleys 2. Landforms: Example of Ridges and Valleys

● Key processes in fluvial erosion ● abrasion by saltation 2. Landforms: Features Sculpted by Erosion and Sedimentation ● Key processes in fluvial erosion ● abrasion by saltation ● drag force (plucking)

The Balance Between Forces 2. Landforms: The Balance Between Forces Resistance to Erosional forces Erosional forces Increasing deposition Increasing erosion Resisting power Stream power Sediment size X Sediment volume River slope X River discharge Equals

Increasing sediment size, sediment volume, and bedrock hardness increase the resistance to erosion. Erosional forces Erosional forces Increasing deposition Increasing erosion Resisting power Stream power Sediment size X Sediment volume River slope X River discharge Equals

Increasing river slope and river discharge increase stream power. Resistance to Erosional forces Erosional forces Increasing deposition Increasing erosion Resisting power Stream power Sediment size X Sediment volume River slope X River discharge Equals

River Erosion in Humid, Steep Areas 2. Landforms: River Erosion in Humid, Steep Areas

In steep, wet terrain, stream power overcomes resistance to erosion In steep, wet terrain, stream power overcomes resistance to erosion. Bedrock hardness becomes the principal factor in resistance to erosion.

River Erosion in Humid, Steep Areas 2. Landforms: River Erosion in Humid, Steep Areas Yellowstone River, Wyoming

River Erosion Where Forces Balance 2. Landforms: River Erosion Where Forces Balance

Where slopes are gentler, sediment begins to be deposited Where slopes are gentler, sediment begins to be deposited. Stream power and resistance to erosion are in balance.

River Erosion Where Forces Balance 2. Landforms: River Erosion Where Forces Balance Snake River, Idaho

River Erosion in Flat, Low Areas 2. Landforms: River Erosion in Flat, Low Areas

Where slopes are much flatter, the streambed builds up and fills the valley with sediment.

River Erosion in Flat, Low Areas 2. Landforms: River Erosion in Flat, Low Areas Mulchatna River, Alaska

● Key factors in fluvial erosion ● stream power ● slope and discharge 2. Landforms: Features Sculpted by Erosion and Sedimentation ● Key factors in fluvial erosion ● stream power ● slope and discharge ● First stages in fluvial erosion ● gullies and badlands

Formation of Gullies (Badlands) 2. Landforms: Formation of Gullies (Badlands) Badlands National Park, South Dakota

● Structurally controlled cliffs ● cuestas ● hogbacks 2. Landforms: Features Sculpted by Erosion and Sedimentation ● Structurally controlled cliffs ● cuestas ● hogbacks

2. Landforms: Formation of a Cuesta Erosion-resistant sandstone Easily eroded shale

Erosion of weak shale undercuts sandstone. Erosion-resistant sandstone Easily eroded shale

2. Landforms: Formation of a Cuesta Dinosaur National Monument, Colorado

2. Landforms: Hogback Ridges near Roxborough, Colorado

3. Interacting Geosystems Control Landscapes ● Feedback between uplift and erosion ● negative-feedback process ● process slows when the driving forces diminish

3. Interacting Geosystems: Example of Negative Feedback

3. Interacting Geosystems Control Landscapes ● Feedback between uplift and erosion ● positive-feedback process ● isostasy and isostatic rebound

3. Interacting Geosystems: Example of Positive Feedback

3. Interacting Geosystems Control Landscapes ● Feedback between tectonics and climate ● high elevations enhance weathering ● low elevations slow down

3. Interacting Geosystems: Plate Tectonics and Climate

Thought questions for this chapter If you were to climb 1 km from a river valley to a mountaintop 2 km high in a tectonically active area versus a tectonically inactive area, which would probably be the more rugged climb? Describe the main landforms in a low-lying, humid region where the bedrock is limestone.

● Some long-standing concepts ● Davis: cycle of uplift and erosion 4. Models of Landscape Development ● Some long-standing concepts ● Davis: cycle of uplift and erosion ● Penck: erosion competes with uplift (supported by recent work) ● Hack: over time, landscapes achieve dynamic equilibrium

4. Models of Landscape Development: Davis’ Cycle of Uplift and Erosion

Penck’s Erosion Competes with Uplift 4. Models of Landscape Development: Penck’s Erosion Competes with Uplift

4. Models of Landscape Development: Hack’s Dynamic Equilibrium

● Some methods of dating landscapes ● Radioisotopic: carbon-14, etc. 4. Models of Landscape Development ● Some methods of dating landscapes ● Radioisotopic: carbon-14, etc. ● Cosmogenic: chlorine-36, etc. ● Chemical: tephrochronology ● Paleomagnetic: reversals, etc. ● Biological: dendrochronology

Thought questions for this chapter The summits of two mountain ranges lie at different elevations: range A at about 8 km and range B at about 2 km. Without knowing anything else about these ranges, could you make an intelligent guess about the relative ages of the mountain-building process that formed them? A young mountain range of uniform age, rock type, and structure extends from a far northern frigid climate through a temperate zone to a southern tropical rainy climate. How would the topography of the mountain range differ in each of the three climates?

Key terms and concepts Contour Cuesta Elevation Geomorphology Hogback Badland Contour Cuesta Elevation Geomorphology Hogback Landform Mesa Plateau Relief Stream power Topography