1. Harry Williams, Geomorphology(21)

2. Harry Williams, Geomorphology
Landforms Developed on Folded/Tilted Strata
Underlying geologic structure influences surface landforms in two ways:
1. determines outcrop pattern.
2. The relative elevation and/or slope of outcrops will vary, because different rocks erode at different rates (depends on RELATIVE hardness of rock, cementation strength (if sedimentary rock) and joint abundance). This is called DIFFERENTIAL EROSION.
cuesta
Strike valley
Resistant rock layers
Harry Williams, Geomorphology

3. Harry Williams, Geomorphology
Resistant rock is left standing higher than less resistant rock, forming various types of cliffs ("scarps” or “escarpments”), ridges or uplands. The actual feature formed depends on the dip of the strata. Mesas are wide flat-topped hills capped by a resistant horizontal rock layer (a “caprock”); buttes are similar, narrower hills; a cuesta is the combination of a dipslope and escarpment (or scarp); a hogback is a fairly sharp ridge; a razorback is a very sharp ridge (dip of the rock layer determines which will form). Softer rock layers are eroded lower forming STRIKE VALLEYS - valleys parallel to strike direction.
Harry Williams, Geomorphology

4. Harry Williams, Geomorphology
MARBLE DEFORMATION
Outcrop Patterns and Landforms On Geologic Maps.
Subsurface rock layers are usually exposed by downcutting streams and rivers.
Horizontal Strata
1. Outcrop pattern parallels valleys
2. Contacts between rock units parallel contours because strata are flat.
fracture
flow
Harry Williams, Geomorphology

5. Harry Williams, Geomorphology
3. Uplifted horizontal strata form plateaus like the Colorado Plateau.
4. Vigorous downcutting during/after uplift forms canyons like the Grand Canyon.
5. Resistant strata form steep cliffs; softer rock erodes to gentler slopes.
Harry Williams, Geomorphology

6. Harry Williams, Geomorphology
6. Prolonged erosion isolates blocks of rock, forming mesas, buttes and pinnacles – particularly where a hard caprock protects underlying softer rock.
Lava flow caprock on a mesa in west Texas
hills
mountains
cliffs
ridges
Harry Williams, Geomorphology

7. Harry Williams, Geomorphology
Tilted Strata
1. Outcrops are roughly parallel bands.
2. Law of V's - low dip angle -> larger V.
3. Older beds dip towards younger beds.
4. Differential erosion forms ridges, dipslopes, escarpments, cuestas, strike valleys.
Harry Williams, Geomorphology

8. Harry Williams, Geomorphology
4. Cuestas, hogbacks or razorbacks are formed by resistant beds; strike valleys formed by softer beds.
Harry Williams, Geomorphology

9. Harry Williams, Geomorphology
CUESTA
Dipslope
Scarp slope
Harry Williams, Geomorphology

10. Harry Williams, Geomorphology
Domes
1. Outcrops are concentric belts.
2. Oldest rocks are in the center.
3. Law of V's -> beds dip away from center.
4. Resistant beds form inward-facing scarps.
Harry Williams, Geomorphology

11. Harry Williams, Geomorphology
5. Core of dome determines relief; if resistant -> central upland; if soft -> central lowland.
Harry Williams, Geomorphology

12. Harry Williams, Geomorphology
Basins
1. Outcrops are concentric belts.
2. Youngest rocks are in the center.
3. Law of V's -> beds dip towards center.
4. Resistant beds form outward-facing scarps.
Harry Williams, Geomorphology

13. Harry Williams, Geomorphology
Folds
1. Erosion of plunging folds (most plunge) -> zigzag pattern.
2. Anticlines V down plunge; oldest beds at center. Law of V's -> beds dip away from center; resistant rocks -> inward-facing scarps.
3. Synclines V up plunge; youngest beds at center; Law of V's
-> beds dip towards center; resistant rocks -> outward-facing scarps.
ANTICLINE
SYNCLINE
ANTICLINE
Harry Williams, Geomorphology

14. Harry Williams, Geomorphology
4. Since most folds form at depth, fold outcrop patterns are typical in eroded ancient mountain belts such as the Appalachians. The folds have been exposed by erosion.
compression
Harry Williams, Geomorphology

15. Harry Williams, Geomorphology

16. Harry Williams, Geomorphology
Landforms Developed On Faulted Strata
1. Form sharp linear boundaries of uplands or valleys
Harry Williams, Geomorphology

17. Harry Williams, Geomorphology
2. Displacement -> fault scarps (300 m high in this example from Utah).
Harry Williams, Geomorphology

18. Harry Williams, Geomorphology
3. Recognized on geologic maps by abrupt displacement of structures or rocks.
Harry Williams, Geomorphology

19. Harry Williams, Geomorphology
4. Characteristic of young mountain belts -> fault block mountains
UPLIFT
Harry Williams, Geomorphology

20. Harry Williams, Geomorphology
5. Basin and Range Province
Caused by crustal stretching due to heat flow from subduction. Tilting of normal faults resulted in fault-angle depressions (tilted fault blocks).
Harry Williams, Geomorphology

21. Harry Williams, Geomorphology
Death Valley
Basin and range in Texas
Harry Williams, Geomorphology

22. Harry Williams, Geomorphology
Surficial Deposits
1. Unconsolidated (“loose” or uncemented) recent sediments e.g. river sands, glacial deposits, landslide deposits.
2. Usually form a thin cover on underlying bedrock.
3. Usually associated with process e.g. river deposits in present river valleys; landslide debris at base of cliff etc.
bedrock
Harry Williams, Geomorphology

23. Harry Williams, Geomorphology
Influence of Geologic Structure On Drainage Patterns
1. Streams that develop on "original surface" (e.g. emergent coastal plain) follow the regional slope = CONSEQUENT STREAMS
2. Continued erosion -> strike valleys occupied by SUBSEQUENT STREAMS
3. Tributaries to subsequent streams that follow regional slope = RESEQUENT STREAMS (REnewed conSEQUENT); tributary streams that flow in the opposite direction to consequent streams = OBSEQUENT STREAMS (Oppsite to conSEQUENT).
Consequent stream, following regional slope
Harry Williams, Geomorphology

24. Harry Williams, Geomorphology
Consequent stream
Resequent stream
Obsequent stream
Subsequent stream
Harry Williams, Geomorphology