L2 Geology & Landforms

GEOG 3BLand, Water & Life

GEOLOGY & LANDFORMS

Landforms

Topography & relief

Hypsometry

Structure of the earth

Plate tectonics

Earthquakes & volcanism

Minerals and Rocks

Summer 2008 1


LANDFORMS

Landforms (e.g. hills, valleys, plateus) and their

formative processes - determined by the complex

interactions of endogenic and exogenic processes Initially determined by Endogenic (internal) geological processes:

Rock Formation

Crustal Deformation

Modified by Exogenic (external) geomorphic processes:

Weathering

Mass Wasting

Erosion

Deposition

Summer 2008 2


TERRESTRIAL LANDSURFACE

Topography:The undulations and configurations, including it’s relief, that gives the earth

it’s texture

We can represent topography through maps, DEMs and

globes

Summer 2008 3

HYpsometry


TOPOGRAPHY

We can characterize topography in terms of: Contours (lines of equal height or altitude)

Hypsometry (the percentage volume of land below or above a certain

altitude)

Summer 2008 6

HYpsometry


FACTOIDS

Summer 2008 10

Elevations: Bimodal Distribution of Elevations on Earth

(Continents, Ocean Basins) Average Elevation of Continents: 0.8km high

Average Depth of Ocean Basins: 4.0km

Average Depth of Ocean Trenches: 7.5km-11km

Mountain Islands: up to 6km in Relief

Areas: Oceans (71%), Continents (29%), and

Continental Shelves (essentially parts of continents, 5%)

Ages: Orogenic (Mountain) Belts at Margins: 100-500M years old (much

younger than Earth itself)

Continental Shelves: less than 100M years old

Question: Why?


RELIEF

Summer 2008 11

Relative Relief concerns elevation variations on a

terrestrial landsurface Mountains: Relative relief of 600m or more

Plains: Relative relief of 100m or less and Slopes of 5 degrees or less

Order of Relief concerns the spatial scale of features on

a terrestial landsurface 1st Order: Continents and Oceans

2nd Order: Mountain ranges, plains, and lowlands

3rd Order: Individual mountains, cliffs, valleys, hills


STRUCTURE OF THE EARTH

Summer 2008 19

1. The Crust Two Types: Oceanic: Thin

Continental: Thick

Lower contact: Mohorovicic Discontinuity (Moho)

2. The Mantle Depth: to 2900 km Two layers: Brittle (+ Crust = Lithosphere), soft, partially melted

(Asthenosphere)

Key Point: Lithosphere forms plates that float on denser asthenosphere.

3. Liquid Outer Core: to 5100 km Liquid nickel-iron, source of magnetism (& magnetic reversals)

4. Solid Inner Core Depth: to 6370 km Solid nickel-iron


PLATE TECTONICS

The conceptual theory (and model) that encompasses

the ideas of continental drift, sea-floor spreading, and

related aspects of crustal movement. Nowadays, this theory is almost universally accepted as the foundation of

crustal tectonic processes.

Key Points: The world is made up of plates (8 major plates).

The plates are brittle and called the lithosphere (Crust+Upper Mantle)

The plates float on soft material called the asthenosphere (Lower

Mantle)

Continental lithosphere is thicker but lighter

A plate can be oceanic, oceanic & continental, or mostly continental in

composition

Plates interact along faults and mid-oceanic ridges

Antonio Snider-Pellegrini (1856) suggested this past configuration

Plate Motions through time


PLATE DYNAMICS

Summer 2008 28

Plates move laterally Rates: 50-100 km/million years

The direction of plate movement varies from one plate to the next

Plates move vertically Isostasy - Crust "rebounds" when material is removed

Convection in the Mantle

Sinking at Subduction Zones


PLATE DYNAMICS

Plates form at spreading centers (Divergent Margins) Rift Valleys

Oceanic Ridges

Plates are destroyed at subduction zones

(Convergent Margins) Ocean-to-Continent Boundary

Ocean-to-Ocean Boundary

Continent-to-Continent Boundary

Summer 2008 29


FAULT TYPES

Normal Faults (Extensional) Steep, young over old

Spreading

Reverse Faults (Compressional) Shallow, old over young

Compression, uplifting or subduction

Transcurrent Faults (Strike slip) Near vertical, right lateral or left lateral

Summer 2008 32


ACCRETIONARY TERRANES

Summer 2008 33

ACCRETIONARY TERRANE:

A landmass that has been added to anpther landmass through the collission of plates

Examples:

• California

• India


TRANSFORM FAULTS

Summer 2008 34

Transform faults:Zone of fractured crust

between two plates where one plate slides past the other plate.

Transform fault: San Andreas Fault


HOT SPOTS

Hot Spots:Zones of weakness in

the mantle (mantle plumes)

Summer 2008 35


CRUSTAL DEFORMATION

Three major forces: Tension

Compression

Shear

Summer 2008 37

Crustal Deformation: Tension

Crustal Deformation: Compression

Crustal Deformation: Shear


FOLDS

FOLDS: Anticline (Antiform)

Syncline (Synform)

Summer 2008 38


Summer 2008 39

GEOLOGIC MATERIALS

Earthquakes

Geological materials (concept)

Minerals and Rocks


Summer 2008 40

EARTHQUAKES

Theory: Seismic Waves set off by rapidly-occurring

deformations in Earth's Crust or explosions

Energy transferred between Rock Particles

Speed through rock proportional to Modulus (Stiffness)

and inversely proportional to Density, and related to

Temperature and Pressure

Four types of waves 2 types of body waves (P-waves, S-waves)

2 types of surface waves

waves can interact


Summer 2008 41

EARTHQUAKES

P-Waves (longitudinally polarized) involve compression/rarifaction

can move through Fluids

travel faster: 8km/sec

S-Waves (transversally polarized) involve up/down or shearing motion

cannot move through Fluids

travel slower: 4km/sec

Waves move away from Epicenter in all directions in time

proportional to distance; time between arrival of P-, S-

Waves proportional to distance from Epicenter


Summer 2008 42

EARTHQUAKES

Need three Seismographs to locate Epicenter (Why?)

Reflection/Refraction of Waves

Structure of Earth derivable from arrival patterns of

different types of waves, their reflection, and refractions

Can obtain information from Earthquakes or explosions

on/in Earth (including those caused by man)


Summer 2008 43

EARTHQAUKES

PROBLEM: How far away is an Earthquake Epicenter if

the first S-wave arrives 1 second after the first P-wave?

SOLUTION: the time taken by the S-wave (Ts) is one second longer than the time

taken by the P-wave (Tp), so Ts=Tp+1;

the time taken by the S-wave is twice the time taken by the P-wave, so

Ts=2Tp;

since 2Tp=Tp+1, the time taken by the P-wave, Tp, is 1 second;

the P-wave has travelled 8 km in 1 second


Summer 2008 44

GEOLOGIC MATERIALS

Geological Material : This concept relates to the

composition and structure of the earth materials which

underlie landforms.

The composition of Geological Material can be

represented by: Chemical Element

Mineral

Rock


Summer 2008 45

CHEMICAL ELEMENTS

Factoids: Earths Composition involves approximately 90 elements

8 elements form 99% of Geologic Material

Oxygen, silicon form 75% of Geologic Material

Lighter elements have moved towards surface over time

Question: Where did these elements come from?

Elements are still forming within Earth

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Summer 2008 47

MINERALS

Minerals are naturally-occuring, solid, inorganic

substances that usually possess a definite chemical

composition (e.g., SiO2) and characteristic molecular or

crystalline structure.

Over 3500 Minerals knownLess than 20 Minerals form over 95% Crustal Rocks

Minerals form under specific conditions of temperature

and pressure (e.g. salt HCl crystals from evaporation of

H2O at surface of Earth) and from various mixtures of

chemicals.

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Minerals & Rocks:(Clockwise from left)

•Quartz – silicon dioxide (SiO2)

•Pyrite – iron disulfide (FeS2)

•Chalcopyrite


Summer 2008 49

ROCKS

Igneous Rocks formed from cooling of molten materials

"original", oldest rocks, but still forming

18% of continents (granitic)

100% of Oceans (basaltic)

Sedimentary Rocks formed from broken up pieces of other rocks

form 74% of continents

evidence back to 3.9B years

Metamorphic Rocks: formed from temperature/pressure effects on other rocks

form 8% of continents

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5151

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Summer 2008 55

IGNEOUS ROCKS

Formed from solidification of molten materials (magma)

Channels in which magma flows from deep chambers

(1200-1500C), Igneous Rocks solidify at different depths Intrusive Igneous Rocks (below surface)

Extrusive Igneous Rocks (surface)

Successive cooling and changing mineral assemblages Reaction Series

different stabilities of Minerals in Series under different conditions of

Temperature/Pressure

larger Crystals with slower cooling

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Summer 2008 57

IGNEOUS ROCKS

Igneous rock composition (there are two basic classes of

Igneous Rock that depend on the composition): Felsic Rock (largely silicate minerals high in potassium, sodium or

calcium, lighter in color and density, e.g. quartz & feldzpars)

Mafic Rock (largely silicate minerals high in magnesium and iron, dark,

high density, e.g. basalt)

There are two basic classes of Igneous Rock

that depend on where they form (underground

or on the surface): Intrusive igneous rock (Dioritetrue, Peridotite, Granite, Gabbro, Diorite,

Granite)

Extrusive igneous rock (Basalt, Andesite, Rhyolite)

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Summer 2008 59

SEDIMENTARY ROCK

Most Sedimentary Rocks are formed from deposits in

relatively shallow seas (2m/year) to 5 km (1M years) They may also form in other locations (Where?)

Stratification of sedimentary rocks

The most common Sedimentary Rocks are Limestone,

Sandstone (15%), Shale (52%)

There are three major classes of Sedimentary Rocks: Clastic sedimentary rock (conglomerate, sandstone, siltstone,

mudstone, claystone, shale)

Chemically precipitated rock (Limestone, dolomite)

Organic sedimentary rock (coal, petroleum)

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Summer 2008 61

METAMORPHIC ROCK

All classes of Rocks (Igneous, Sedimentary, and

Metamorphic) maybe changed by applying enough

pressure and heat. The two major forms are: Contact Metamorphism and Regional

Metamorphism.

New minerals may form (atoms can actually diffuse) and

there are characteristic new Index Minerals (e.g. Garnet,

Staurolite). Many other minerals survive.

How do the appropriate pressure and heat changes

required to form Metamorphic Rocks occur in the Earth?

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Summer 2008 63

ROCK CYCLE

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L2 Geology & Landforms