Geology Final

Definition of a mineral

A naturally occurring inorganic solid that has a specific elemental composition and a specific arrangement of atoms.

Composition of intrusive rocks and their extrusive equivalents

Silicic - (Granite-intrusive, Rhyolite-extrusive)

Intermediate - (Diorite-intrusive, Andesite-extrusive)

Mafic - (Gabbro-intrusive, Basalt-extrusive)

Ultramafic - (Periodotite-intrusive, Komatiite-extrusive)

Partial Melting

When a given mass of rock within the Earth is subjected to conditions that cause melting, the minerals with the LOWEST melting points melt first (Bowen's Reaction Series)

Bowen's Reaction Series

High Temp: Olivine (first to crystallize)
Pyroxene
Amphibole
Biotite
Potassium Feldspar
Muscovite
Low Temp: Quartz (Last to crystallize)

Intrusive Igneous Rock

A rock that forms from cooled Magma.

Extrusive Igneous Rock

A rock that forms from cooled Lava.

Magma

Molten rock below the earth's surface.

Lava

Molten rock above the earth's surface.

How and Where Magma forms.

Forms by Partial Melting in...
1) Subduction Zones: Oceanic Lithosphere is forced into mantle.
2) Dewatering of the down going slab: Water is released from the subducted plate and goes into the mantle wedge/asthenosphere
3) Decompression Melting: Rocks rising to fill space decompress, and remain warm, but lower pressure at shallower depths lowers their melting point.
4)Hot Spot volcanoes

Definition of Soil

Where the atmosphere, hydrosphere, lithosphere, and biosphere interact.

Assigning names to detrital sedimentary rocks.

Names based on Clast Size, median diameters larger than 2 mm, clast shape

Breccia: Angular Clasts, closest to source than conglomerate

Conglomerate: Round Clasts

Implications regarding depositional environment of clast size and clast shape

Shear traction at channel bottom determines size of largest clast that will be transported. The further away from the source the clast is, the smoother and smaller it will get. (breccia, conglomerate, sandstone, siltstone, shale, mudstone)

Difference between Slate and Schist.

Slate: has crystals that are too small to see without magnification.

Schist: has crystals that are visible to the the naked eye.

Metamorphic Index Minerals

Indicate the temperature and pressure in the rock when metamorphism occurred. (used to define metamorphic facies)

Naming Metamorphic Rocks

-Contact metamorphic rocks (country rock-rocks magma moved into)
-Hydrothermal metamorphic rocks (water is abundant and close to heat source)
-Regional metamorphic rocks (deep burial during mtn building events, presence of foliation)

Foliation

Orientation of platy or elongate minerals that crystalize during metamorphism.

Everything about Blueschist/Glaucophane

Indicates High pressure, and low temperature. Mimics conditions at subduction zones. Glaucophane: Blue mineral that is found in Blueschist.

Normal Fault

Footwall moves up relative to the hanging wall. Forms as a result of TENSION. Extend and Thin the Earth's Crust. (dip-slip fault)

Reverse Fault

Footwall moves down relative to the hanging wall. Forms as a result of COMPRESSION. Shorten and Thicken the Earth's Crust. (dip-slip fault)

Strike-Slip Faults

Form as a consequence of horizontal shear stress in Earth's crust. (train tracks example, left lateral and right lateral)

Releasing Bends

Form at right bends or steps along right lateral faults, because fault geometry causes localized TENSION and EXTENSION.

Restraining Bends

Form at left bends or steps along right lateral strike-slip faults, because fault geometry causes localized COMPRESSION and SHORTENING.

Transform Faults

Plate Boundaries within continental crust where two plates move past each other. Zones of overlapping and curvilinear faults.

The Transverse Ranges of California - why they exist. See notes regarding transform faults

Restraining bend in San Andreas fault... oblique convergence between Pacific and NA plate accomodated by ductile shear.

Brittle and Elastic Strain

Brittle: Change in shape or position accommodated along fractures.
Elastic: strains are instantly and totally recovered. (As the rocks snap back to their pre-elastic strain shape, earthquake waves are generated.)

Earthquakes and substrate: reasons why it is safer to build on fully lithified rock than on unconsolidated sediment.

When surface waves pass through unconsolidated sediment, resonance occurs because they oscillate at a similar period as the waves.
When surface waves pass through lithified rock, dampening occurs, because they oscillate at different periods.
Lithified rock is more stable.

Liquefaction

transformation of a solid material that temporarily behaves like a fluid. Triggered by seismic shaking, resultant increase in pore fluid pressure.

Family of earthquake waves (2)

Body Waves: Travel through the earth in all directions from the focus. Faster than surface waves.
Surface Waves: Travel along the earth's surface.

Types of earthquake waves (4)

Body Waves
P waves: Motion is analogous to how a slinky moves. They travel fastest.
S waves: Motion is analogous to a cracked whip or wave in a rope. Cannot pass through liquid.

Suface Waves (Greatest Threat to Humans)
Love/Long Waves: Can be visualized as a shearing motion perpendicular to the direction that they travel. Faster than Rayleigh waves.
Rayleigh Waves: Give rocking sensation in an earthquake. Similar to water waves, cause both vertical and horizontal movement.

What family/type of earthquake waves cause the most damage to human structures?

Surface Waves: Rayleigh Waves

The destructive character of Tsunami.

1) They travel at great speeds: 518 mph
2) Long Period: Water does not recede rapidly as wind waves do.
3) Long Wavelength: Huge amount of water traveling at tremendous velocity.

What triggers tsunami?

Fault rupture on the sea floor

Stream Power

w\=pgQs
Expended on transporting sediment. Excess power is spent on lowering the channel bed by stream incision.

Graded Stream

Stream that is adjusted to its base level. Neither lowers nor raises it bed. Shows how lazy streams are. When undisturbed by humans, streams will do as little work as possible.

Bedrock Stream

Stream that flows mostly over fully lithified bedrock. Flows over a thin veneer of alluvium that is largely mobilized during a large streamflow event.

Alluvial Streams

Streams that flow over unconsolidated sediment consisting of sediment that is transported by the stream called alluvium (recently deposited sediment)

Floodplain

adjacent to a stream channel having low topographic relief which is commonly (every 1-10 years) underwater during flood discharges. Dimensions are determined by the magnitude of the largest floods flowing through a given river system.

Stream Terrace

Stream terraces represent former postions of stream beds. Unlike floodplains, stream terraces are NOT UNDERWATER during 100 year floods.
STAGE 1:
Critical Power \> Available Power. Aggradation occurs: Stream cannot transport all of the sediment delivered to it, and the channel is filled with sediment.
STAGE 2:
Available Power \> Critical Power. It will cut through the channel-filled deposit and the abandoned channel becomes the terrace surface.

Shear Traction (stream channel)

T\=pgds
T: Shear Traction
p: Density of water
g: Gravity
d: Depth of flow
s: Slope (more significant factor than depth of flow)

100 Year Flood and Formula for recurrence interval.

R \= (n+1)/m
R: flood recurrence interval
n: number of years of record
m: rank of flood

There is a 1-in-100 chance, or a 1% probability, each year that a flood of this size will occur.

Mississippi flood of 1993

Central U.S. received 400% more rain than usual. Parts of nine states were underwater. 79 day flooding. 40,000 sq km of floodplain was submerged causing $12 billion in damage.

Dissolved Load

The products of chemical weathering that are in solution or in colloidal suspension.

Suspended Load

Relatively fine grained particles that are carried in suspension.

Bed Load

Sediment that is transported along the bottom of the channel by rolling, bouncing, or sliding. This is the key to determining when a stream will incise its bed.

Available Stream Power

W\=pgQs
W: Available stream power
p: Density of water
g: gravity
Q: Stream Discharge \=
Flow: [depth][width][velocity]
s: slope of water

(base level fall will increase Q, and stream power)

Critical Stream Power

The stream power needed to transport the sediment delivered to a stream.

Soil Creep

Caused by expansion and contraction of soil as result of heating and cooling, freezing and thawing, wetting or drying. When the soil expands, it does so perpendicular to the surface of the slope, and when it contracts, it does so under a dominantly gravitational component.

Signature of rapid episodic mass movement:

Hummocky Topography

Flows

Consist of unconsolidated or incoherent rock and soil debris that is sufficiently mobilized to have properties of a viscous fluid. in flows, sediment entrains water; in streams, water entrains sediment.

Debris Flow

Typically move rapidly (10-25m/s) and follow preexisting drainage.

Earthflows

Are usually slow and are large in areal extent. Do not follow preexisting drainage. Deep seated-affect significant thickness of hill slope.

Why debris flows are so destructive (according to shear traction equation)

T\=pgds
T\=Shear Traction
p\=density of flow
g\=gravity
d\=depth of flow
s\=slope
(Density is much larger than water, which explain why they are so destructive)

Events constituting a debris flow:

1) Soil or unconsolidated rock debris on a hill slope is destabilized and moves rapidly (10-25m/s) downslope.
2) The flow entrains more sediment, water, and vegetation (if present) as it moves downslope.
3) Valley bottoms or human structures are commonly buried as the debris flow stops, which occurs when slope gradients are too low to sustain motion.

Rock/Sediment type that facilitates the formation of SLUMPS.

Sumps are rotational slides, having curved failure surfaces. Typically occur in THICK, HOMOGENEOUS, COHESIVE SEDIMENTS. Ex: mud-rich part of franciscan complex

Triggering Mechanisms for slope failures.

1)Slope steepening: River Incision/Human Modification
2)Seismic Shaking:
a)Acceleration: Sets particles into motion, causing the yield strength of the material to lower, and the slope to fail.
b)liquefaction: All interparticle friction is lost, and the material looses all shear strength.
3)Dip slopes: layered rocks parallel to hill slope are unstable and likely to fail by rapid episodic mass movements
4)Water Saturation: Water is added making sediment heavier. Positive pore pressure.

Role of water in sediment transport debris flows versus the role of water in sediment transport streams

in flows, sediment entrains water. In streams, water entrains sediment.

Coastlines are dynamic settings where changes occur relatively quickly because....

Coastlines all over the world are still adjusting to the relatively rapid sea level rise that occurred at the end of the last glacial period.

Longshore Drift

Causes a littoral cell of sediment to form adjacent and parallel to the coast.

Littoral Cell

A corridor of sediment transport along the coast.

Factors necessary for Sand Spits/Bay Mouth Bars to form on tectonically active coastlines

Form in areas where there is a large input of sand at the coast and in areas where there is a relatively broad, shallow continental shelf.

Tectonically Active Areas:
Sand Spits form where there is a HUGE sediment supply from streams, and local faulting creates an embayment.

Recipe for Marine Terraces

1) Wave action at the coast carves a shore platform during an interglacial/sea level high stand.
2) Beach rocks and boulders are the cutting tools that carve the shore platform.
3) Sea Level falls during a glacial/sea level low stand.
4) Uplift of the high stand shore platform takes place during the low stand.
5) If the Shore Platform is raised above the sea level of the next high stand, then it is preserved as a marine terrace.

Shore Platforms

A smooth erosional surface that develop in the surf zone adjacent to coast lines.

Three important criteria for Landslide maps

Prior failure, rock/soil strength, slope steepness

Landslide inventories - portray locations of prior failure
landslide susceptibility map - likelihood of future slides
landslide hazard maps - unstable condition from current presence

Topple and its triggering mechanism

Forward rotation out of slope of a mass of soil/rock around a point below its center of gravity.

Trig mech: sometimes gravity, water, ice, vibration, undercutting, differential weathering, excavation, stream erosion.

Rotational slide and its triggering mechanism

Surface of rupture is curved upward (spoon shaped) and movement is more or less rotational about an axis parallel to contour of slope.

Trig Mech: Intense/sustained rainfall, drops in river level after floods, rise in level of streams, lakes, rivers causing erosion at base. Also can be earthquake induced.

Translational Landslide and its triggering mechanism

Mass moves out or down and outward along relatively planar surface with little rotational movement or backward tilting.

trig mech: primarily intense rainfall, rise in ground water within the slide. Also can be earthquake induced.

Lateral Spread and its triggering mechanism

Occur on very gentle slopes. Soil ground extends and fractures, pulling away slowly from stable ground and moving over weaker layer.

Trig mech: liquefaction, overloading of ground above, saturation of weaker layer underneath, plastic deformation of unstable material at depth.

Debris flow and its triggering mechanism

Rapid mass movement in which loose soil, rock and organic matter combine with water to form a slurry flowing downslope.

trig mech: intense surface-water flow (heavy precipitation), steep slope saturation consisting of silt or sand-sized material.

Subduction Zones

Are convergent plate boundaries that form where an oceanic plate collides with a continental plate or another oceanic plate. (Oceanic plate is more dense, so it usually gets subducted)

The Downgoing Slab

Oceanic lithosphere that is sinking into the mantle. Oceanic lithosphere can be subducted because once it is cooled it is more dense than the asthenosphere and probably the mantle.

The Trench

Forms where the down going slab is bent downwards as it is overridden by the upper plate of the subduction zone. The deepest parts of the ocean are subduction trenches.
(Offshore Faults)

Accretionary Prism

A prism-shaped mélange of sediment that is scraped off the down going slab. Mélange consists of a very ductile matrix of pervasively sheared mud. Large blocks of oceanic-crust rock are suspended in the mud matrix.
(Central and northern Coast Ranges)

Forearc Basin

A low lying area between the volcanic arc and the accretionary prism. Many sediments eroded from the volcanic arc are deposited in the forearc basin.
(Great Valley, San Joaquin/Sacramento Valleys)

Volcanic Arc

Chain of volcanoes that exists because water driven from down going slab causes melting of the asthenosphere/mantle above the subducting plate.
(Sierra Nevadas)

The Franciscan Complex

Underlies much of SLO county. It is an ancient accretionary wedge consisting largely of mélange. (mélange means mixture in french)

Granitoids of Sierra Nevada's

Volcanic arc. Mostly rhyolitic volcanic rocks and granitoids.

Great Valley Sequence

a forearc basin. Approximately 12 km thick sequence of sedimentary rock.

History and Evolution of mountain ranges in the Coast Ranges of central CA/SLO County

Strain partitioning and oblique convergence formed the CC ranges in SLO.

Prior 31 Ma: subduction zone off of California coast.

31 Ma: transform plate boundary separates NA/Pacific plate

31 Ma until 8-5 Ma: TRANSTENSION (pulling away while moving past each other) across NA/Pacific plate boundary is caused by shape of plate boundary relative to plate motions.

8 to 5 Ma: NA/Pacific plate boundary jumps eastward. Stress changes from transtension to TRANSPRESSION (moving past but slightly into each other), causing uplift of the coast ranges. This is ongoing.

Future location of the boundary between the North American plate and the Pacific plate

The Sierran Microplate. Large earthquakes in Mojave Desert and seismicity along eastern side of Sierra Nevadas indicate that the boundary will be east of its present location in a few to 10s of millions of years.

Microcontinent Sierran Microplate

Microcontinent between san andreas fault and sierra nevadas, moving independently of pacific and NA plates.