Harry Williams Geomorphology21 1 Harry Williams Geomorphology21 2

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Harry Williams, Geomorphology(21) 1

Harry Williams, Geomorphology(21) 1

Harry Williams, Geomorphology(21) 2

Harry Williams, Geomorphology(21) 2

Landforms Developed on Folded/Tilted Strata Underlying geologic structure influences surface landforms in two ways:

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

Resistant rock is left standing higher than less resistant rock, forming various types of

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

MARBLE DEFORMATION Outcrop Patterns and fracture Landforms On Geologic Maps. flow Subsurface rock layers

MARBLE DEFORMATION Outcrop Patterns and fracture Landforms On Geologic Maps. flow 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. Harry Williams, Geomorphology 5

3. Uplifted horizontal strata form plateaus like the Colorado Plateau. 4. Vigorous downcutting during/after

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

6. Prolonged erosion isolates blocks of rock, forming mesas, buttes and pinnacles – particularly

6. Prolonged erosion isolates blocks of rock, forming mesas, buttes and pinnacles – particularly where a hard caprock protects underlying softer rock. Lavahills flow caprock on a mesa in west Texas mountains cliffs ridges Harry Williams, Geomorphology 7

Tilted Strata 1. Outcrops are roughly parallel bands. 2. Law of V's - low

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

4. Cuestas, hogbacks or razorbacks are formed by resistant beds; strike valleys formed by

4. Cuestas, hogbacks or razorbacks are formed by resistant beds; strike valleys formed by softer beds. Harry Williams, Geomorphology 9

CUESTA Dipslope Scarp slope Harry Williams, Geomorphology 10

CUESTA Dipslope Scarp slope Harry Williams, Geomorphology 10

Domes 1. Outcrops are concentric belts. 2. Oldest rocks are in the center. 3.

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

5. Core of dome determines relief; if resistant -> central upland; if soft ->

5. Core of dome determines relief; if resistant -> central upland; if soft -> central lowland. Harry Williams, Geomorphology 12

Basins 1. Outcrops are concentric belts. 2. Youngest rocks are in the center. 3.

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

Folds 1. Erosion of plunging folds (most plunge) -> zigzag pattern. 2. Anticlines V

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 -> inwardfacing 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

4. Since most folds form at depth, fold outcrop patterns are typical in eroded

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 16

Landforms Developed On Faulted Strata 1. Form sharp linear boundaries of uplands or valleys

Landforms Developed On Faulted Strata 1. Form sharp linear boundaries of uplands or valleys Harry Williams, Geomorphology 17

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

2. Displacement -> fault scarps (300 m high in this example from Utah). Harry Williams, Geomorphology 18

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

3. Recognized on geologic maps by abrupt displacement of structures or rocks. Harry Williams, Geomorphology 19

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

4. Characteristic of young mountain belts -> fault block mountains UPLIFT Harry Williams, Geomorphology 20

5. Basin and Range Province Caused by crustal stretching due to heat flow from

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

Death Valley Basin and range in Texas Harry Williams, Geomorphology 22

Death Valley Basin and range in Texas Harry Williams, Geomorphology 22

Surficial Deposits 1. Unconsolidated (“loose” or uncemented) recent sediments e. g. river sands, glacial

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

Influence of Geologic Structure On Drainage Patterns 1. Streams that develop on "original surface"

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 con. SEQUENT); tributary streams that flow in the opposite direction to consequent streams = OBSEQUENT STREAMS (Oppsite to con. SEQUENT). Consequent stream, following regional slope Harry Williams, Geomorphology 24

Consequent stream Resequent stream Obsequent stream Subsequent stream Harry Williams, Geomorphology 25

Consequent stream Resequent stream Obsequent stream Subsequent stream Harry Williams, Geomorphology 25

YOU WILL NEED A RULER, CALCULATOR, PENCIL, ERASER FOR LAB 2. Harry Williams, Geomorphology(21)

YOU WILL NEED A RULER, CALCULATOR, PENCIL, ERASER FOR LAB 2. Harry Williams, Geomorphology(21) 26