1. Landscapes Shaped by Stream Erosion

2. Objectives
Outline effects of geologic structure, lithology, tectonics and climate on stream erosion
Introduce types of drainage networks and their origin
Examine cases of stream erosion overcoming control of geologic structure
Review major theories of long-term landscape development

3. Introduction Rivers erode landscapes—processes occur at same time
Widening and deepening of valleys
Slope modification
Mass movements
Exposure of buried
Stream modified landscapes more extensive than other types

4. Factors Affecting Patterns of Stream Erosion--Climate
Debate continues about role of climate in landscape evolution
Yet landscapes imprinted by past climate.
For example, glacial period
Rivers with great sediment load drained ice sheets

5. Factors Affecting Patterns of Stream Erosion--Lithology
Rocks have different hardness and resistance to weathering and erosion
Quartzites very resistant
Mount Monadnock
Shales/mudstone not resistant
Limestone resistant in dry climate but not in wet one

6. Factors Affecting Patterns of Stream Erosion--Geologic Structure
Modified by streams to form landscape
Hogbacks, Cuestas
Ridges & Valleys—Appalachian Mountains

7. Factors Affecting Patterns of Stream Erosion--Geologic Structure
Modified by streams to form landscape
Domes—Black Hills
Faults
Produce scarps
Uplifted blocks modified and valley s sediment –filled

8. Factors Affecting Patterns of Stream Erosion--Geologic Structure
Modified by streams to form landscape
Faults
Produce scarps
Uplifted blocks modified and valleys filled with sediment

9. Factors Affecting Patterns of Stream Erosion--Geologic Structure
Extrusive Igneous structures
Volcanic landforms
Mesas and buttes
Intrusive Igneous structures
Domes of granite

10. Tectonic Activity Produces high mountains
Accelerates erosion, available potential energy is greater
Himalayas show steep stream slopes
Appalachians also possess steep slopes

11. Drainage Patterns Influenced by structure and rock type
High drainage density related to high erosion rates
Badlands
Radial Drainage
Develop mostly on volcanic cones
Annular Drainage
Develops on domes
Trellis Drainage
Develops on parallel folded or dipping sedimentary rocks of differing hardness
Rectangular Drainage
Forms where joints or faults dominate
Dendritic Drainage
Forms on extensive batholiths or flat-lying sedimentary rocks

12. Overcoming Geologic Structure
Rivers may cut across geologic structure
Superimposed Streams
Stream present above buried mountain range
Erodes downward as overlying rock is removed
Stream maintains course regardless of lithology and structure
Antecedent Streams
Stream cutting across uplifted ridge
River keeps pace with uplift

13. Stream Capture Stream captures another stream
Develops through headward erosion
Example Upper Kafue River captured by Lower Kafue River

14. Long-Term Landscape Evolution
Davis proposed cycle of erosion
Elements include geologic structure, geographic process and time or stage
Rapid tectonic uplift of area
Uplifted areas shaped by erosion during long time periods
Most hills eroded away to form peneplain
Penck proposed uplift and erosion occur simultaneously not in sequence
Hack proposed dynamic equilibrium
Ruggedness of topography does not change