GEO 306 Environmental Geomorphology Exam 1 Study Guide

Geomorphology – the study of landforms. (‘Geo’-earth; ‘morph’-formed; ‘ology’ – study)

-Description, Analysis, and Understand the landscapes & processes that changed/formed them.

WHY STUDY GEOMORPHOLGY?

1.) “Hydrological Reasons” (some landforms transmit water, some do not)

2.) All “Land Uses” are on the same kind of landform

3.) Many landforms are “Economically Valuable”

CUP Model C haracterize the subjects of study (landforms).

U nderstand the PROCESSES that govern their distribution, occurrence, and behavior.

P redict future occurrences and behavior of the landforms, to help us better manage/use them (modeling).

Naming Landforms

- Non-Genetic Names (Plain, Mountain, etc.)

- Genetic Names (Esker, Drumlin, Kettle, etc.)

SEDIMENT vs. SURFACE (Geomorphic Surfaces)

Geomorphic Surface – commonly named, must be mappable, relationships to adjoining surfaces

with respect to age, lithology, development, etc., are known/can be discovered, formed by one/more

surfacial processes. Surfaces – STABLE , ERODING, AGGRADING (accumulating/buried), PLAIN, STEPPED SURFACES (Terraces)

Slope Curvature – ways to view the world.

-“PLAN” – from above

-“PROFILE” – from the side

Pediment – slope of transportation, at the base of eroding slopes (free faces & debris slopes).

Slopes effect on Soils

1.) Sediment Transfer (downslope)

2.) Watertable Effects

Clay is thickest at lower slopes (more water, not

washed away like soils on slopes, moves down

thorough the profile).

Slope Gradient – (angle of the slope in respect to the horizontal.

-100% slope = 45 degree angle

Principles of Geomorphology

1.) Principle of Original Horizontality (everything is working toward horizontal)

2.) Principle of Superposition (layers; oldest bottom, youngest top)

3.) Principle of Lateral Continuity (layers are continuous)

4.) Principle of Cross-Cutting (something that cross-cuts is younger than what it cuts)

5.) Principle of Catastrophism – most of the erosional/depositional work on earth happens due to

catastrophic events.

o Magnitude – Frequency

o UNIFORMITARIANISM (Hutton)

Laws of nature are time-invariant

Similar processes prevailed in the past as prevail today (rates may have changed)

Present is the key to past (things aren’t the same!)

Change takes place gradually/progressing by relatively small-scale events

Opposing Processes

UPLIFT – Epirogenic (broad, regional)

Endogenic (volcanoes, mnt building, plate boundaries)

“DIASTROPHISM”, “TECTONISM”, “VULCANISM”

Tectonics – process associated with the movements of the Earth’s

crustal plates.

Volcanism – processes associated with the movement of molten

Material within & ontop of the earth.

WEARING DOWN –

“WEATHERING”, “EROSION”(Denudation)

Deformation of the earth’s crust (FOLDING & FAULTING)

Weathering – the breakdown of rocks & sediments at or near the

earth’s surface (Biological, Chemical, Physical).

Erosion – downslope displacement of solid sediment, usually by

Wind, water, or ice.

Denudation – combined effect of WEATHERING & EROSION,

Leading to an overall “REDUCTION of LANDSCAPE”.

Models of Landscape Development

WILLIAM MORRIS DAVIS (Geography Prof. @ Harvard)

- Geographic Cycle (Cycle of Erosion)

o 1.) UPLIFT, 2.) DENUDATION, 3.) CONTINUES, 4.) BASE LEVEL

- STAGES

o 1.) YOUTH, 2.) MATURITY, 3.) OLD AGE (“PENEPLAIN”)

UPLIFT – flat Peneplain, high block of land that water runs off of.

- Deep “V” shaped valleys, flat uplands….. (YOUTH) - Flood Plains, increased meanders, less ‘V” Shaped….. (MATURITY)

o Getting closer to base level = looses energy o RELIEF IS MAXIMUM (closer to base level, still high topography) o GRADED STREAM – can carry all the sediment that is delivered to it.

- Getting close to base level, flatter topography, builds up sediment in flood plain…. (OLD AGE) o Broad, Flat, Swampy, Flood Plains, Excess SEDIMENT

Steep – rapidly flowing streams, can carry away all sediment load (V-Shaped Valleys)

Moderately – rapidly flowing streams, plus maximum slope = lots of sediment load. Rivers store excess in ‘Floodplains’ (Maturity = excess sediment)

Low – amounts of load delivered, but sluggish streams cannot carry it all away. (Broad floodplains develop, Old Age).

MONADNOCKS – (named; Mt. Monadnock, New Hampshire) resistant hills either far from river systems or geologic bedrock. (Found in the Amazon, Australia, Old Tropical Landscapes)

1.)Rapid initial uplift, 2.) Slope decline (Down-Wasting), 3.)Decreasing relief overtime, 4.) Ends with a

‘Peneplain’ with ‘Monadnocks’

Penck- Arid Climates

- Not much ‘Down-Wasting’ (Steep Slopes)

- ‘Backwastage’ = ‘Pediplain’

- ‘INSELBERGS’ – island rock, isolated rock in arid landscapes.

- Slow uplift at first, then more rapid, then slows fast! (Creates ‘CONCAVE’ features)

DATING

In Geomorphology, we are often interested in dating “Surfaces”. Surface Dating – can date ‘erosional’ events & ‘burial’ events. Subaerial – sediment exposed to the air, hence “aerial” …. STABLE – Soil Forming UNSTABLE – Eroding (soils eroded)/Aggrading (soils buried) Surface Age - “ALWAYS” Younger than or equal to sediment age…. Erosion Surface – Younger than the youngest surface cut/s.

Surface Age = Sediment Age (Aggradation Surfaces), ‘Younger’ than sediment age (Erosional Surfaces)

Maximum Limiting Date = Oldest an object can be. Minimum Limiting Date = Youngest an object can be. Time-Transgressive = Surfaces that change over an area.

Surface Exposure Dating (SED) – done by examining Post-Depositional Modifications (PDM’s) to the surface.

- Relative Dating – estimates the numerical age of an undated surface by extracting from numerical ages other than the surfaces.

o Older vs. Younger o Sequence (1,2,3,ect.) o Magnitude (A is 3 times older than B) o Calibrated Age Dating

- Find common info like; rock erosion, sediments, etc. and compare!

- COMMON PDM’s o Geomorphology – ‘sharpness’ of landforms (rounded or sharpness) o Changes to rocks on the surface (Formation of “DESERT PAVEMENT”)

DESERT PAVEMENT- (Lag Concentrate) 1.)Sands blow into the desert environment 2.)Rainfall pushes the sand particles under the rocks 3.) Sands accumulate under the rocks 4.)Soil wetness ‘expands’ moving the rocks ‘upward’

DESERT VARNISH – (turns brown/blackish; hundreds of Thousands of years) smooth, tightly adhered to the rock, few mm thick. 1.)Dust Deposition 2.)Rain brings in carbonic acid (H2CO3) 3.)Manganese(Mn); black color, separates from Fe 4.)Oxidizing conditions concrete Mn cemented to varnish 5.)Cycle repeats Mn builds up with bacteria, bacteria dies after eating, enhances red color! -Makes more layers (thicker during wetter climates) Radio-carbon dates bacteria between rinds (lowest layer of varnish). Weathering Rinds – rocks weather (get rinds), cracked, porus from the outside in, thicker with age. How old is a rind? Rinds flake off, making it hard to get an age! Lichenometry – “Thallus” or “Thalli” Lichen body (thallus) gets bigger with time (Rapid Growth = Great Period; Then Slows = Linear Phase) -Dependant on lichen type/conditions/search area -Look for the biggest lichen (1st there) = minimum age of feature. (Take AVERAGE of BIGGEST lichens) -Best for ALPINE regions (slow growth, plant competition is low) -Limit of 4,500 years

COMMON PDM’s Changes to soils on the surface (Soil Development)

- Can always use them, best tool (Stable) - ‘Older’ soils have ‘more horizons’ - Thicker Solum (A & B) in Michigan = 1 meter (young) - “RUBIFICATION” – redder with time (unless wet) Rainforests

o More Clay in Humid Climates = older o ‘Dust’ = more carbonates in Arid Climates = older

“Increased” weathering of various minerals….. -Weatherable Minerals: amphibules, biotite mica, plagioclase feldspar -Resistant Minerals: Quartz, Zircon, Tourmaline Ratios: Resistant / Weatherable Raito = WEATHERING GOES UP WITH AGE

NUMERICAL DATING GEOCHRONOMETRIC TECHNIQUES -Read the ‘Natural Chronometer’ built into the geologic system -Usually easier to date sediment, NOT SURFACE sediement Paleomagnetism – determines ‘Remanent Magnetism’ in sediment. Shows at which magnetic field (Normal “now” vs. Reversed Polarity)

- Magnetostratographic Markers - Poor Precision (provides two baselines = 770,000 & 2,500,000 Ka) - Water/Ocean sediments, loess, volcanic deposits, till

Tephrochronology – dating volcanic ash deposits (usually river valleys)

- 2 advantages = ash layers span large areas & small time scale; 1 event! - Ash = glass shards dateable (K-Ar, Fission Track, Luminescence) - “Chronostratigraphic Units” - layer with known date

Cosmogenic Isotopes – Stable vs. Unstable (decay at a known rate) -26Al & 10Be (Beryllium) best for dating -Cosmic Rays (Sunshine) bombard 14N to create 14C and 10Be -14C taken up by plants in 14C -10Be delievered to SFC in; “Precipitation” –fallout 10Be ‘garden variety’ “Situ” – in rocks Precipitation - Fallout -Relatively non-mobile in soils (highest in B Horizon) decreases with depth (problems in sand) 1.)Constant deposition rate (varies slightly with rainfall/climate) 2.)Loss of 10Be from soil is minimal (holds in most nonacid soils) Biggest Problem; Doesn’t work in sand 3.)Little or no SFC erosion 4.)Amount of ‘inherited’ 10Be can be determined (from parent material) -Exposure time (of SFC) = 10Be concentration in soils/delivery rate

In Situ -Formed in quartz (surface; sun has to hit it) in rocks, at the SFC Only way to lose 10Be in quartz is decay -Rocks below 2 m are shielded -Rocks accumulate 10Be as a function of exposure time, and depth -Quartzite (has quartz and isn’t easily weatherable) Problems: Previously exposed history(could have been sun exposed before) ,Can fix by looking in deeply buried soils or looking for rocks exposed recently (erosion).

Luminescence – “dates sediments” Establishes the last time sediment was exposed to sunlight. Thermoluminescence (TL) Optically Stimulated Luminescence (OSL) ‘Luminescence’ refers to light emitted from mineral grains when ‘heated’ or ‘exposed to light’. OSL – 1.)Mineral grains have crystalline (quartz) defects. 2.)Defects ‘trap photons’ from radioactive decay of nearby minerals 3.)Photons released from traps as ‘luminescence’ when exposed to light in the lab. -The longer time since the minerals were last exposed to light, the more luminescence they have. Dose Rates – rate at which photons are emitted from surrounding sediment. (40-120,000 years until full) -Exposed to light (in lab/sunlight) releases the elements! -Radioactivity of the surrounding sediment. -Quartz & Feldspar uses (dune sand, loess, shallow water environments)

AGE (years) = EQUIVANLENT DOSE / DOSE RATE

Radiocarbon – 14C (very small portion of earth’s carbon; <0.01%) Half Life of 5,730 +- 40 years Radiocarbon Date – is an estimate of the time since the death of the plant or animal. -It is a statistical approximation (error term)

-12,350+- 105 radiocarbon yrs BP -12,350 (most probable age)

+- (“actual age” has a 68% probability of falling within that range) 68% = 1 Sigma Age (2 Sigma Age = 2 Standard Deviations)

105 radiocarbon yrs BP (Before Present; 1950) What can we date? ANYTHING ONCE ALIVE! -Wood, Bones, Peat, Hair, Organics in Soils, Seeds, etc. -Anything that has accumulated CaCo3 (calcium carbonate) -Caves, Soils, Sea Water, Air-Bubbles in Glaciers -Limit = 55,000 years (fairly accurate) -Radiocarbon years vs. Calendar years (longer) 10,000 RC yrs = 11,475 C yrs (Start of Holocene) -14C years are usually calibrated to Calendar years.

Rocks & Minerals Lithosphere – solid part of earth, Silicates: 93.7 % oxygen minerals, 0.86% silicone minerals -Oxides: 6% (Aluminum, Iron, Sodium, Calcium, etc.) -Primary minerals are ‘Silicates’ (silicon & oxygen) -More weatherable at the surface than secondary minerals -Secondary minerals are ‘Clay minerals’ or ‘Oxides’ (surface/soil)

DARK (Ca,Mg,Fe) Low Silica Complex Structure

LIGHT (K,Na,Si) High Silica Simple Complex Resistant (hard to weather) SEDIMENTARY ROCKS WORLDWIDE -Shale = 45% -Sandstone = 32% -Limestone=22% -All others Sedimentary Rocks = 1% Shale erodes easily, we don’t notice it as much as others because it covered by dirt and vegetation.

Most of earth’s crust is CRYSTALLINE (90%!)

Landform Categories

1.) Bedrock Controlled (Erosional Landforms) 2.) In Unconsolidated Sediments (Constructional OR Erosional Landforms)

Sedimentary Rocks – The influence of “Lithology” & “Structure”

STRUCTURE – (DIP, STRIKE, JOINTING) Dip – angle at which rocks “plunge” Strike - the line formed by the “intersection of a horizontal”l

plane with the structure.

STRIKE VALLEY – Horizontal Valley paralleled by ridges of the tilted sediments called “cuestas”.

LITHOLOGY – mainly resistance to erosion (weak- valley, strong – ridges) -In bedrock controlled regions, the rock’s ‘resistance to weathering ‘determines the whethering of the rock valley or ridges. -Rock resistance to weathering is based on; -‘minerals’ within (their resistance) -‘cementation’ (packing of minerals) -‘climate’ (processes that are attacking the rock, WATER) -‘jointing/density’ (amount) -Rocks with equal resistance / same structure -‘Random’ hills & Valleys, Dendritic Erosion (Crystalline material at surface) -Resistance to erosion & weathering -Quartzite Other Metamorphic Rocks Other Igneous Rocks Sedimentary Rocks

- Granite is fairly weak (minerals that compose it erode easily)

Differing Resistances of “Sedimentary Rocks” to Erosion

Dolomite (Most Resistant)------------------------------------------------------(Least Resistant)Evaporites Diplomatic Sandstone Limestone Sandstone Shale RIDGES (Can Flip-Flop) VALLEYS

Humid Climates (WATER) Vegetated (can’t see rocks) Appalachian Mountains (Humid Climate)

‘Strike Valley’

Nevada (Arid Climate)

FLAT-LYING ROCKS (PLATEAUS)

MESA & SCARP TOPOGRAPHY

“STEPPED STRUCTURAL SURFACES” “BACK-WASTING” “Down-Wasting”

Anticlines are highly jointed, making them weak, bent, thus highly eroded. Synclines are compact, strong, making them resistant (Synclinal Mountains).

Escarpments – want to retreat! Variable resistance in dipping sedimentary rocks, leads to the formation of ‘CUESTAS’.

Dome & Basin Cuestas FLATIRONS

Cuestas in DOMES face away from the center. (Escarpments eroding outward) -Dome Cuestas have to have a stream carrying sediment out of the feature. Cuestas in BASINS face toward the center. (Escarpments eroding inward)

Michigan Cuestas -Cuestas in Michigan are covered in Glacial Drift. -All the Great Lakes sit in ‘STRIKE VALLEYS’ (Carved out by Glaciers) -Shales and Soft Sandstones were carved out in these strike valleys.

BADLANDS – dendritic drainage, dry climate, rapid erosion, weak parent material, flat rocks

EFFECTS OF ROCK STRUCTURES

JOINTING (Perpendicular Jointing: BRYCE CANYON)

Balanced Rocks Hoodoos Have a cap rock Pillar-Like rock feature

Balancing Act

Jointing Happens to pushed up Rock (Parallel Jointing) FINS at Arches National Park

“JOINTING FINS ARCHES”

WINDOWS