1. Structural Control of Landforms
ESCI 307, Fall 2003, Lecture 3
Structural Control of Landforms
Mostly Chapter 12
Plus a review of folds and faults
Photo from Drury: Two distinct units.  One dendritic drainage pattern is sparsely vegetated.  Parallel contours suggest it is horizontal.  Other formation banded, with straight wooded ridges, controlled by steep dips. The boundary truncates the ridges. Horizontal unit lies unconformably on the steeply dipping strata (angular unconformity). 
The wide spacing of drainage in the younger unit suggests that it is a massive, coarse clastic rock.  The older unit comprises shales and limestones. From Steve Drury, Image Interpretation in Geology, adopted for this course
Some photos in this PowerPoint made available online, courtesy of Steve Dutch, click here
SAND, HOSES, Slickensided Rock, Pencil, Rubber bandGum, Foam sediments, Cardboard fault models, 2 Plastic boxes, Food Coloring ,Paper, wood, Ice
From our lab workbook Image Interpretation in Geology by Steve Drury

2. Erodability Relative Erodability Layered rocks = wide range
ESCI 307, Fall 2003, Lecture 3
Erodability
Relative Erodability
Layered rocks = wide range
Sedimentary
Volcanic
Massive rocks = narrow range
Metamorphic
Intrusive igneous
Erodability is not absolute but
typically shale > limestone > sandstone ~ gneiss
Canadian Shield. Pale granite and darker metavolcanic rocks, the granite having resisted glaciation best. Drury IIG

3. ESCI 307, Fall 2003, Lecture 3
Erodability
"… shale, limestone, marble and some types of [mica] schist are less resistant "valley-makers" in humid climates" …
"whereas [quartz] sandstone, quartzite, [quartz] conglomerate and various igneous rocks [ granite has ~20% quartz H= 7] are resistant "ridge-makers" ….
Easterbrook (1969) Principles of Geomorphology
[words in brackets added]

4. ESCI 307, Fall 2003, Lecture 3
Lithology/Climate
Erodability: shale > limestone > sandstone ~ gneiss
In humid areas, weathering and erosion are faster, slopes are more eroded,
gentler after the same duration of exposure to weathering

5. Horizontally layered rocks – outcrops parallel topographic contours.
ESCI 307, Fall 2003, Lecture 3
Horizontally layered rocks – outcrops parallel topographic contours. 
In arid terrains (a) the intermittent violent erosion develops steep-sided gullies and valleys. Note differential erosion
In humid climate the topography is more muted.
Monadnocks resistant rock ridges Colorado

6. Undisturbed Sediments showing differential erodability
ESCI 307, Fall 2003, Lecture 3
Undisturbed Sediments showing differential erodability
Dry Climate, intermittent strong storms

7. Vees are pointing in direction of dip
ESCI 307, Fall 2003, Lecture 3
Review: Stream Vees
Vees are pointing in direction of dip

8. In horizontal beds, rock outcrops
ESCI 307, Fall 2003, Lecture 3
Tablelands
In horizontal beds, rock outcrops
would follow contours

9. Tablelands: note horizontal layers, differential erosion
ESCI 307, Fall 2003, Lecture 3
In horizontal beds, rock outcrops
would follow contours
Butte chimney
Tablelands: note horizontal layers, differential erosion
mesa
Inselberg
Pediment (gentle slope < 5%,
erosional concave up surface
w thin veneer of gravel etc.)
Dry Climate, intermittent strong storms
Plateau>mesa>butte>chimney
Ratio surface area of top to height

10. Desert Landforms near Mountains
ESCI 307, Fall 2003, Lecture 3
Alluvial Fan
(often exposed bare rock with gravel veneer)
Rain-shadow desert in the lee of mountains
Mountains eventually erode away to Inselbergs

11. Compression, Tension, and Shearing Stress
ESCI 307, Fall 2003, Lecture 3
Compression, Tension, and Shearing Stress
Convergent Divergent Transform

12. Convergent Plate Boundaries and Folding
ESCI 307, Fall 2003, Lecture 3
Convergent Plate Boundaries and Folding
Subduction causes Arc: Under Ocean Lithosphere Japan,
Aleutians, Cent. Am.; under continent Andes, Cascades
Continent-Continent
collision forms
Fold and Thrust Mountains: Alps, Himalayans, Appalachians

13. Strike and Dip
ESCI 307, Fall 2003, Lecture 3
Map Symbols: Strike shown as long line, dip as short line. Note the angle of dip shown: 45o
Strike intersection w horizontal, dip perpendicular, angle from horizontal down toward surface

14. Tilted Strata Monoclinal folds, or one side (limb) of a fold
ESCI 307, Fall 2003, Lecture 3
Monoclinal folds, or one side (limb) of a fold
Name = f(dip angle)
Cuesta (moderate dip)
Hogback (steep dip)
Flatiron remnant of dissected Hogback w triangular face

15. Dip Slope vs. Scarp slope
ESCI 307, Fall 2003, Lecture 3
Dip Slope vs. Scarp slope
Cuesta
Hogback
Hogback dip slope greater 30° - 40° with near symmetric slope on each face

16. Ridges Dip of Cuesta < Hogback
ESCI 307, Fall 2003, Lecture 3
Ridges
Dip of Cuesta < Hogback
Copyright © J. Michael Daniels 2002

17. Folds are typical of convergence Folded Rock Before Erosion
ESCI 307, Fall 2003, Lecture 3
Folds are typical of convergence Folded Rock Before Erosion

18. Folded Rocks, Hwy 23 Newfoundland, New Jersey
ESCI 307, Fall 2003, Lecture 3
Folded Rocks, Hwy 23 Newfoundland, New Jersey
Note highest point
Adjacent Anticline and Syncline
Source: Breck P. Kent

19. Folded Rock After Erosion
ESCI 307, Fall 2003, Lecture 3
Folded Rock After Erosion
Eroded Anticline, older rocks in center. Syncline is opposite.

20. Topography may be opposite of Structure Anticline Before/After Erosion
ESCI 307, Fall 2003, Lecture 3
Topography may be opposite of Structure Anticline Before/After Erosion
Notice center rock oldest

21. Topography may be opposite of Structure Syncline Before/After Erosion
ESCI 307, Fall 2003, Lecture 3
Topography may be opposite of Structure Syncline Before/After Erosion
Notice center rock youngest

22. ESCI 307, Fall 2003, Lecture 3
Various Folds

23. ESCI 307, Fall 2003, Lecture 3
Various Folds (cont'd)

24. ESCI 307, Fall 2003, Lecture 3
Various Folds (cont'd)

25. Various Folds (cont'd) Axis
ESCI 307, Fall 2003, Lecture 3
Various Folds (cont'd)
Axis
Axial plane near axis should be close to horizontal

26. Plunging Folds and Nose Rules
ESCI 307, Fall 2003, Lecture 3
Plunging Folds and Nose Rules
Demo: Plastic box, water, paper folds Up
End
Down
End
Nose of anticline points direction of plunge, syncline nose in opposite direction

27. ESCI 307, Fall 2003, Lecture 3
Plunging Folds
Nose
Nose
Nose

28. Joints: Fractures – with no movement
ESCI 307, Fall 2003, Lecture 3
Joints: Fractures – with no movement
vs. Faults with relative movement
Sandstone, note no streams here, too many cracks
Source: Martin G. Miller/Visuals Unlimited

29. ESCI 307, Fall 2003, Lecture 3
Demo: Cardboard Models
Dip-Slip Faults

30. Continental Rift into Ocean Basin - Tension => Divergence
ESCI 307, Fall 2003, Lecture 3
Continental Rift into Ocean Basin - Tension => Divergence
Rift Valleys and Oceans are the same thing
Normal Faults

31. Normal Faults at Divergent Margins - Iceland
ESCI 307, Fall 2003, Lecture 3
Normal Faults at Divergent Margins - Iceland
A new graben, down dropped hanging wall block - Normal Fault – divergent zone MOR
Overhanging
Block
Footwall

32. Fault Line scarp (High-angle Normal Fault)
ESCI 307, Fall 2003, Lecture 3
Fault Line scarp
(High-angle
Normal Fault)

33. Convergent Margins Shallow Reverse Fault = Thrust Fault
ESCI 307, Fall 2003, Lecture 3
Convergent Margins Shallow Reverse Fault = Thrust Fault

34. Lewis Thrust Fault (cont'd)
ESCI 307, Fall 2003, Lecture 3
Lewis Thrust Fault (cont'd)
Same layer

35. Lewis Thrust Fault (cont'd)
ESCI 307, Fall 2003, Lecture 3
Lewis Thrust Fault (cont'd)
Source: Breck P. Kent
PreCambrian Limestone over
Cretaceous Shales

36. Geologists are frequently called upon to find the ore body
ESCI 307, Fall 2003, Lecture 3
Geologists are frequently called upon to find the ore body
Younger
This guy is rich
What phase of magma fractionation would result in the placement of this ore body?
Which formed first, the ore body or the fault?
What common mineral is mostly likely in the ore body?
Reverse
Miners pay geologists to find their lost orebody
One friend earned enough to buy a house
Normal
This poor guy is out of luck

37. Horizontal Movement Along Strike-Slip Fault
ESCI 307, Fall 2003, Lecture 3
Horizontal Movement Along Strike-Slip Fault

38. Landscape Shifting, Wallace Creek
ESCI 307, Fall 2003, Lecture 3
Landscape Shifting, Wallace Creek
San Andreas Fault

39. Normal Fault Quake - Nevada Reverse Fault Quake - Japan
ESCI 307, Fall 2003, Lecture 3
Normal Fault Quake - Nevada
Reverse Fault Quake - Japan
Divergent
HW Down
Convergent
HW Up
Transform
Strike Slip Fault Quake - California

40. Fracture Zones and Slickensides
ESCI 307, Fall 2003, Lecture 3
Fracture Zones and Slickensides

41. Part 2 Structural Control of Streams mostly Ch. 12
ESCI 307, Fall 2003, Lecture 3
Part 2 Structural Control of Streams mostly Ch. 12
Consequent streams follow slope of the land over which they originally formed.
Subsequent streams are streams whose course has been determined by erosion along weak strata.
Resequent streams are streams whose course follows the original relief, but at a lower level than the original slope
Obsequent streams are streams flowing in the opposite direction of the consequent drainage.

42. resequent streams (original slope but lower level)
subsequent (s along weak)
ESCI 307, Fall 2003, Lecture 3
consequent (c follow slope)
Insequent (random dendritic)
obsequent (o opposite main slope)
resequent streams (original slope but lower level)

43. Insequent Streams= Initial Consequent
ESCI 307, Fall 2003, Lecture 3
Insequent Streams= Initial Consequent
Almost random drainage often forming dendritic patterns.
Typically tributaries - developed by headward erosion on a horizontally stratified rocks, or a substrate with ~ constant composition.
NOT controlled by the original slope of the surface, its structure or the type of rock.
Headward Erosion

44. ESCI 307, Fall 2003, Lecture 3

45. Drainage Patterns with and without structural control
ESCI 307, Fall 2003, Lecture 3
Drainage Patterns with and without structural control
None Joints fold limbs
Volcano, exposed pluton, diapir

46. Dendritic Patterns
ESCI 307, Fall 2003, Lecture 3
Underlying bedrock has no structural control over where the water flows.
Characteristic acute angles
No repeating pattern.

47. ESCI 307, Fall 2003, Lecture 3
Trellis Patterns
Form where underlying bedrock has repeating weaker and stronger types of rock.
Streams cut down deeper into the weaker bedrock
Nearly parallel streams
Branch at higher angles.

48. Rectangular patterns Branching of tributaries at nearly right angles
ESCI 307, Fall 2003, Lecture 3
Rectangular patterns
Branching of tributaries at nearly right angles
Form in jointed igneous rocks or horizontal sedimentary beds with well-developed jointing or intersecting faults.

49. ESCI 307, Fall 2003, Lecture 3
Parallel Erosion
Form on unidirectional regional slope or parallel landform features. Small areas.

50. Radial Erosion Flow of water outward from a high point
ESCI 307, Fall 2003, Lecture 3
Flow of water outward from a high point
Down a volcano cone
or an intrusive dome, or
down an alluvial fan.

51. Annular patterns form on domes of alternating weak and hard bedrocks.
ESCI 307, Fall 2003, Lecture 3
Annular patterns
form on domes of alternating weak and hard bedrocks.
The pattern formed is similar to that of a bull's-eye when viewed from above
weaker bedrocks are eroded and the harder are left in place.

52. Centripetal patterns
ESCI 307, Fall 2003, Lecture 3
Form where water flows into a central location, such as a round bowl-shaped watershed, or a karst limestone terrain where disappearing streams flow down into a sinkhole and then underground.

53. Structural Control of Drainage
ESCI 307, Fall 2003, Lecture 3
Structural Control of Drainage
Contorted
Folded Rocks

54. ESCI 307, Fall 2003, Lecture 3
Stream Capture
Headward Erosion

55. Stream Capture vs. Structural Control
ESCI 307, Fall 2003, Lecture 3
Stream Capture vs. Structural Control
Susquehanna captures headwaters of Beaverdam Creek, diverting upper Beaverdam trunk to Susquehanna channel.
Subsequent Susquehanna does not reach Beaverdam Creek flowing through water gap

56. Stream Capture Dry Valley Elbow of Capture Brodhead Creek
ESCI 307, Fall 2003, Lecture 3
Dry Valley
Elbow of Capture
Brodhead Creek
Godfrey Ridge
Headward erosion from Water Gap area cut through Godfrey Ridge and captured Brodhead Creek which was flowing east behind Godfrey Ridge
Stream Capture

57. 1. Old river meanders across floodplain
ESCI 307, Fall 2003, Lecture 3
Terraces 1
1. Old river meanders across floodplain
2. Base level drops (how?), or region uplifts. Area now much higher above sea level than before.
Potential energy increases, water flows faster, better erosion, stream straightens and cut down to base level, less floodplain width and cut lower.
3.Terrace forms from previous floodplain. Further incision cuts another terrace
Next time Terraces 2 and 3: Isostatic Rebound and high water shorelines as glaciers melt
Potential rgh to Kinetic Energy 1/2mV2

58. A flight of river terraces
ESCI 307, Fall 2003, Lecture 3
A flight of river terraces

59. River is older than uplift
ESCI 307, Fall 2003, Lecture 3
Antecedent Streams and Superimposed Streams
Meanders in steep, narrow valleys
Caused by a drop in base level or uplift of region
Delaware Water Gap
Incised (entrenched) meanders
River is older than uplift

60. ESCI 307, Fall 2003, Lecture 3
"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 [incised] 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." Steve Dutch
Some photos in this PowerPoint made available online, courtesy of Steve Dutch, click here

61. Pediments and Alluvial Fans
Alluvial fans typically develop at the exits of intermittent streams draining arid mountainous regions. 

62. And on Mars …
Link courtesy Melissa Hansen

63. An example of a v-shaped stream, with fairly constant slope and cross section

64. Conservation of Energy with frictional losses
An example for the homework calc.
A stream channel has been uplifted to 300 meters above base level. It’s cross sectional area, slope, and water depth is close to constant. The stream is full of large boulders. At 300 meters it flows out of an alpine lake, where it has an average velocity of meters/sec, that is, it has mostly potential energy. At base level it has a velocity of 15 meters per second (so all kinetic energy, plus frictional losses on the way down. Estimate the percent energy lost to friction.