Geography Notes 1

7/29/2019 Geography Notes 1

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See Q. Sampler on packet, pages 12-15

1st

Lecture Exam on Tuesday, October 2nd

(Multiple Choice)

EVOLUTION OF THE UNIVERSE: GALAXIES- Milky Way

o Democritus (450-370 BC) gave the first notion of the milky wayo Galileo (1610 BC)

First to really develop the telescope First to really look at space and the milky way

o Georges Lemaitre (1927) Came up with the idea of the big bang

o 20-15 BYA: Big Bango EP Hubble (1924)

Looked at the milky way and discovered that there were billions ofgalaxies beyond the MW

o G. Gamow (1940s) Looked into the evolution of protogalaxies

o Expansion: atomic fusion & coolingo Gravitational attraction = galaxies formed

- Solar Systemo Nebular Theory [Pierre Simon Marquis de LaPlace(1815)]

Matter became clustered in stars with the outer eddies condensed inchunks

A hypothesis concerning the origin of the solar system according to whicha rotating nebula cooled and contracted, throwing off rings of matter thatcontracted into the planets and their moons, while the great mass of the

condensing nebula became the sun.- Earth

o Earth is about 4.6 billion years oldo All planets circle sun in same direction and their orbits lie on the ecliptic planeo Earths formation:

Planetesimal (chunks of matter) accretion by coalescence Internal melting due to

Gravitational compression Impact heating Radioactive decay

Differentiation into layers Light material rises to the top (surface) Heavy material sinks to the center (core)

4.2 to 3.7 billion years ago, crustal cooling & thickening start andcontinued until 1,000 million years ago, when crustal plates break up &begin migrating, initial mechanisms of plate tectonics

Sea-floor spreading Subduction


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By 600 million years ago, the earth already reached the structure of how itis today

o 4 concentric layers of Earth Inner core: 1250 km Outer core: 2250 km

NiFe = HighDensity

5500 degreesCelsius? Molten?

Mantle: 2900 km Si, Mg, Fe: High

Density

2800 degreesCelsius

Lower mantle isrigid** (under

pressure)

Upper mantle isplastic** (100-700km): Asthenosphere

Crust: 10-40 kmo It actually moveso Behaves differently from the lower mantle

Differentiated into oceanic and continental crust Oceanic crust:

o Basaltic (SIMA)o Heaviero Younger

Continental crust:o Less dense (lighter)o Granitic (SIAL)o Doesnt subducto Thicker

Gutenberg discontinuity: lies at mantle base between mantle andouter core

o Beno Gutenberg (1913) Mohorovicic discontinuity: lies right below the crust base between

the crust and the mantle

o Andera Moho Mohorovicic (early 20th century)o

Made of Basaltic Rocks (Sima) Lithosphere = crust & uppermost mantle

o Earths crust is thicker under continents Upper crust (SIAL) is lighter (density: 2.65 g/cc) and discontinuous,

so its only found under the continents Lower crust (SIMA) is denser (about 3.0 g/cc) than continents and

continuous, so its found over the whole planet (therefore, only this crust

type is present below oceans

Continents float on a heavier (about 13% more) crust layer SIAL: aluminum silicates


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SIMA: magnesium silicateso Crust under mountains are thicker than any other areas (called mountain roots,

allows crust of the continents to extend deeper through the mantle)

Rocks Formation, Classification, and Relationships

Pockets of magma approach surface and cool -> Igneouso Weathering: process of breaking down rockso Transportation: moves downhill usually and clumps up

Sediments stack up and the bottom layers become compacted from high pressure(lithification) -> Sedimentary

Heat and pressure create Metamorphico Deformed rocks from some previous cycle (magma)o Melting allow the process to start over

Rock Formation

+/- 100 elements -> 2000+ minerals -> combine to form rockso Physical propertieso Chemical propertieso Origin, processes formation

Rock Genesis

3 basic groups and 6 sub groups Igneous (Intrusive aka plutonic or extrusive aka volcanic) Sedimentary (Detrital aka clastic or chemical) Metamorphic (foliated or non foliated)

Definitions

Intrusive (igneous): form inside the crust of the earth = plutonic Extrusive (igneous): form on surface of earth = volcanic Detrital: chunks of rock from weathering and breaking down that clump up eventually Chemical: non chunks Foliated: cleavage, parallel lines

Igneous Rocks Crystalline structure (even during cooling and solidification) Location (internal/external) Temperature (cooling rate) Speed of formation Size of crystals -> strength Igneous intrusive rock (plutons, a lot of plutons = batholith) Dike: vertical structure Sill: horizontal structure


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Laccoliths: dome shapeVolcanic Rocks

Lava: magma at earths surface and flows, differ in chemical and physical, properties:basaltic and silicic. Pyroclastic material: broken by fire, ejected, travel through air. Allsizes, from ash/cinder to volcanic bombs.

Mica is a very common mineral found in

rocks.

SEDIMENTARY ROCKS

- - Sedimentary environments are justwhere materials have been collected

-

- Deposition below slopes are calledcolluvial sediments

- Arranged in layers and develop insedimentary environments

- Only 5% of the earth, but 75% of alloutcrops!

- Contain fossilssedimentary rocks arethe only ways we can preserve fossils

- Economically important- Nicholas Steno published

Sedimentology (1669)

o Law of Superposition: inundeformed sequences, theolder beds are on the bottom

o Law of Original Horizontality: if beds are tilted, they must have been moved intothat position after their deposition

- Sedimentary rocks have beds andbedding planes

- Conglomerates are very common formsof sedimentary rocks

Rock formation sequence:

Weathering Transport (Erosion)

Deposition (end of sedimentation) Internalchanges

What leads to a rock?


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- Burial causes compaction- Pressure solution along grain contacts- Deposition of dissolved materials in percolating water and grain residues

Two possible components:

1) Rock Particles (grains)2) Intergranular cement (also called matrix)*Their strength and other properties may be different from one another and may affect

further weathering, infiltration, water storage, etc.

Two Sedimentary Rock Types:

1) Detrital (aka Clastic): with rock fragments/grains and cement2) Chemical: with soluble materials

- These may be precipitated by inorganic or organic (biological) processes- Organic example: Coral limestone, coal

Detrital Inorganic

Sedimentary

Chemical Organic

METAMORPHIC ROCKS- Metamorphic rocks have been subjected to processes of metamorphism (e.g. heat,

pressure, chemical fluids)

Contact metamorphism: in close proximity to magma masses, lots of heat Regional metamorphism: occurs over extensive areas, especially along

subduction zones

Hydrothermal metamorphism (least common): contact with thermal waters*For diagrams of the forms of metamorphism, see textbook

- Metamorphic rocks are also divided by INTENSITY of metamorphism processes Low grade metamorphism (minimal alternation) High grade metamorphism (significant change)

Metamorphic Rocks

1. Metamorphic rocks are classified by Presence of Foliation Foliation

- Cleavage Plains Foliated

- Mineral crystals are visibly aligned, rock displays a banded aspect (2+minerals must be present.)

1. Mainly produced by Compressive Stress Non-foliated

- Rocks have one single mineral, and/or have minimal deformation (low-grade), and minerals have equidemensional crystals (i.e.+- equaldimensions.

2. Metamorphism Results in Specific Types of Rock (know this)


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Limestone----Marble Sandstone----Quartzite Granite-----Gneiss Coal----Anthracite Shale---- Schist, Slate

Metamorphism of metamorphic rock

(Met) Schist, Gneiss-----Migmatite (Met) Phyllite-----Schist

3. Final Possibility in the Rock Cycle Rocks may be so completely melted and thoroughly deformed, that the may

revert to molten Magma, thus cycle is completerand new igneous rocks may

form

Rock Weathering

1. 2 types of weathering Physical

o Involves physical changes, mainly fragmentation of rocks, down to siltsize (>.01 mm)

o Major Components Frost wedging

- Expansion up to 9%, up to 125 kg/cm pressure- Intensity vs. Frequency- Most common at high latitudes and high altitudes

Salt (Crystallization) Weathering- First, water dissolves mineral: Solution- Then water evaporates- Solutes precipitated left behind- Then, solutes fill cavities of rocks creating pressures up to

125 kg/cm- Produces small cavities called Tafonio Many Tafoni result in honeycomb pattern

- Common in areas where salt is abundant, with hightemperatures and in deserts

Pressure Release- Occur over Long time periods- Best seen in Plutons, as igneous rocks slowly expand as

pressure above gradually decreases (due to slow landscape

erosion)

- Cracks, Fracture planes result-

The Process is Exfoliation. The resulting landforms areexfoliation domes

Insolation (=ThermalWeathering)

- Due to temperaturechanges


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- Caused by solar radiation, fires, or even raino Rain causes sudden rock cooling

- Occurs in areas with hot days and colder nights- Rock expansion during heating (day), then pronounced

contaction during cooling (night), when rock breaks down(splits)

- Most common in deserts and hot/dry areas Plant (root) pressure

- Induced by plants- Lichens & larger plants (shrubs, trees, etc.)

o Lichens can break down rocks that ultimatelyaccumulate to create soil

o Lichens grow everywhereo Larger plants can pry apart layers/slivers of rock,

due to the gradual growth and expansion of roots

- Root growth (thickening, elongation) & increase inpressure against rocks

**ABRASION: weathering that can be done by wind, water and gravity

Chemicalo Associated with chemical changes

Rock materials are altered; new chemical compounds may beformed and released, including clays

o Major Components Solution (Very Important)

- Affects ALL minerals and elements, but some are moresoluble than others

Carbonation- Calcium Carbonate (CaCO3) dissolves, and it is faster

when Carbon Dioxide (CO2) is present Chelation

- Organic acids from decomposing plants; acids are catalystsand speed up mineral solutions

Hydration (water absorption)- Water is a POLAR liquid, with + charges on one end and

charges on the other


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- Water is attracted to mineral particles; these havenegatively charged particles

- Water molecules also attach to other water molecules- Many water layers attach on mineral particles- Water layers act like wedges, pushing apart mineral

particles. Minerals in rocks are altered and weathered

o Expansion when wet, contraction when dry Hydrolysis

- Water molecule splits into 2 ions- H2O = HO + H- These ions then combine with minerals- Occurs more frequently at high temperatures

Oxidation and Reduction- Minerals react in the presence or absence of oxygen- Oxidation: occurs in aerobic (O-rich) environments

o Produces red/yellow/orange colors- Reduction: occurs in anaerobic (O-deficient) zones

o Produces gray/dark brown/black colors Weathering is needed for the development of different sediments and soils Main elements in Earths crust

o Oxygen (O)o Silicon (Si)o Aluminum (Al)o Calcium (Ca)o Magnesium (Mg)o Sodium (Na)o Potassium (K)o Iron (Fe)

(SiAlOCaFeKNaMg)

- Order of relief: difference of elevationo First-Order landforms

Oceans and landscapeso Second-Order landforms

Features: Major oceans or continent subdivisions Examples: mountain ranges, large river valleys, deltas, ocean basins,

marine fans

Second order includes third ordero Third-Order landforms

Examples: mountains, glaciers, domes, streamso Fourth-Order landforms

Miniature relief: an area with Tafoni, a rock Pedestal, a group ofexfoliated blocks

*Orders ofrelief includes one another (fourth falls in third, which falls in second)

* 1st

and 2nd

order landforms (continents, oceans) are caused by global dymanics (platetectonics) over long time periods

* 3rd and 4th order landforms caused by erosion and deposition of materials over shorter

time periods


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CONTINENTAL DRIFT AND PROCESSES OF PLATE TECTONICS

- Alfred Wegener came up with the idea of the continental drift- Early Jurassic, ~200 million years ago [MYA]

o Pangaea continent, surrounded by Panthalassao ~750 MYA: Rodinia started splitting

- Late Jurassic, ~150 MYAo Starts separation into Laurasia (North) and Gondwana (South)o 250 MYA: Gondwanas glactiation occurred

- Cretaceous, ~90 MYAo Gondwana breaks apart into South America, Africa, India, Australia, Antarctica

- Early Cenozoic, ~50 MYAo Laurasia breaks apart into Eurasia, North America, and Greenland

- Late Cenozoic, ~20 MYAo Separation into Atlantic and Gulf Coasts, Pacific Coast

- 20 last MYA to presento Gulf of California, Red Sea opens up, Panama Isthmus forms

- Possible Futureo North and South America move further, West Africa and Europe might collide,

Australia crosses the Equator moving north

Processes of Plate Tectonics1. Plate divergence

-

- Leads to continental break-up and seafloor spreading- If the split is at a slow rate, the geography piles up- If the split is at a fast rate, the geography doesnt have time to pile up and is

more flat- Ex: East African Rift Zone, Mid-Atlantic Ridge, East Pacific Rise

Processes of Plate Convergence (collisions)

2. Continent/Ocean collision (C/O)- Subduction: oceanic plate goes under continent and melts away into the

mantle

- Many ocean trenches are around the ring of the Pacific- Ex: Western South American and the Andes)

3. Ocean/Ocean collision (O/O)- Formation of (Oceanic) volcanic islands

Perpendicular to (main)

Divergent Boundary

Plate Boundaries


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- Ex: Guam-Marianas Islands and Marianas Trench, in the Western PacificOcean, Puerto Rico Trench

4. Continent/Continent collision (C/C)- Formation of folded mountains- Ex: India and the Himalayas

Additional processes

1. Hot Spot interactionplates poke through the crust (like a bubble rising through themantle from the core)

- Eventually reaches the surface of the planet, creating flood basalts- The plates are moving, so the stationary hot spot plume creates an island chain- The Hawaiian Islands are a perfect example of how islands are created by hot

spots

- Ex: Hawaii, Galapagos, Canary Islands

VOLCANIC PROCESSES & LANDFORMSVolcanism: related to tectonicplate boundaries (subduction, seafloor spreading) and hot spots

Magma sources & types define:- Nature of the eruption- Types of landforms created

Basaltic vs. Silicic Volcanism

- Basaltic magmao Calm eruptionso From upper mantle (new magma)o Main sources: mid-oceanic ridges, areas of crustalrift & hotspotso SIMA with low silica %o Very hot = ~1,200 degrees Co Very low gas %,

Include water vapor (most abundant) Gases remain dissolved in the melt

o Low viscosity = high fluidity (due to low SiO2% and high temperature)o Little or NO explosive activityo Volcanic products: fluid lava

Main type: Pahoehoe = travels far- Silicic magma

o From melting of subducted rocks Main sources: subduction zones @

continental edges & island arcs

o SIAL, with high silica %o Lower temperatures = ~900 degrees Co **High gas %, mostly water vapor

Gases separate below surface, when stillunder high pressure

o High viscosity = low fluidity (due to high SiO2% & low temperature)


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o Extremely explosive activity Chain reactions due to gas pressure Gas bubbles (lava vesicles) are produced

o Numerous volcanic products: Viscous Lavas, main type: AA, with a broken, blocky, jagged surface Pyroclastic (which means broken by fire) material: ASH, cinder,

pumice, volcanic bombs, tephra

Gases: H2O, CO2, CO, S, N, Cl, H

o Fissure Eruption on Shield volcano Lava fountaining Basaltic lava flows Fissure

Volcanic Landforms

- Basaltic: Shield volcanoes(flood) lava plateaus

- Silicic (aka Andesitic): Composite (strato-)volcanoes, calderas, and plug domes

o Collapse calderas (indentation/depressionin the middle of volcano)

o Collapse of Mt. Mazama (~7700150years B.P.) Formation of crater lake

(Caldera)

Collapse of mountain into magmachamber

o Plug dome Always associated with silicic lava

with very high content of SiO2(~70-80%)

Produced by highly silicic lavasthat flow slowly and solidifyquickly

All the previous plug domes areformed of dacite

- Cinder coneso Steep conical hill of tephra (volcanic

debris) that accumulates around and

downwind from a volcanic vent

o Made of pyroclastic materialo Magma exploded into the air and cooled quickly to form cinder cones


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4 Zones of Vulcanism1) Seafloor spreading2) O/C subduction3) O/O subduction4) Hot spots

Summary of Volcanic Landforms:

- Basaltico Shield volcanoeso Lava plateaus

- Silicic (Andesitic)o Composite (strato-) volcanoeso (collapse) Calderaso Plug domes

Plus: Cinder Cones (present in basaltic, but more common in silicic volcanic areas)

Geography Notes 1

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