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

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

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]

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

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

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

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

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

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

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

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

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

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

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

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

Ridges Dip of Cuesta < Hogback ESCI 307, Fall 2003, Lecture 3 Ridges Dip of Cuesta < Hogback Copyright © J. Michael Daniels 2002 http://www.alperry.com/coal/grand_hogback.html http://www.aureo.org/conference/boulderconference.html

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

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

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

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

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

ESCI 307, Fall 2003, Lecture 3 Various Folds

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Fracture Zones and Slickensides ESCI 307, Fall 2003, Lecture 3 Fracture Zones and Slickensides http://pangea.stanford.edu/~laurent/english/research/Slickensides.gif

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.

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)

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

ESCI 307, Fall 2003, Lecture 3

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

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.

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.

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.

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

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.

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.

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.

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

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

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

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

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

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

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

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

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

And on Mars … Link courtesy Melissa Hansen

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

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 0.01 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.