Exam 2 Geology 355 UL

Extrusive igneous rocks

Cool at or near the surface. has extensive columnar jointing or fracturing. subsurface voids, Cooling and contraction of rocks= fracture (one part of rock pulls away from adjacent) 

1. Decreases in overburden pressure=fracture 

2. Joints can develop in response to tensile stress (pull apart) 

composition of magma

the amount of silica (sio2) within the magma.

felsic is high silica and mafic is low silica.

four types of magma

1. Felsic: 

   1. high Silica 

   2. Feldspar and quartz 

   3. Non ferromagnesian silicates 

   4. Continental crust 

2. Intermediate  

   1. intermediate silica 

   2. Contain > 25% ferromagnesian materials 

3. Mafic:  

   1. Silica poor (45%-52%  

   2. Ferromagnesian silicates and Ca rich feldspar 

   3. Oceanic crust and volcanic islands are mafic 

4. Ultra mafic  

   1. <45% silica 

   2. Rare (highly unlikely to be continental) 

   3. Entirely ferromagnesian silicates 

magma viscosity

1. Low viscosity; flow easily (high mobility) 

2. High velocity: flow slowly (low mobility) 

3. Silica content influences magma viscosity µ by trapping gas in its complex bonds, single chain is way easier to move than a pile of chains

why does crystal size vary in cooled lava

rate of cooling (slow is larger crystals), depth of intrusion (if its deeper it takes way longer), and groundwater circulation

intrusive igneous rock

cooling takes place slowly beneath earths surface. less usceptible to weathering. good foundation rocks for structures. GRANITE

How magma intrudes into other rocks

Dike- tabular, discordant pluton

Sill- tabular, concordance ok it on

Laccolith- lens or mushroom shaped pluton

Pluton- deep seated infusion of igneous rock

Batholith- largest pluton

how does magma form

heat transfer melting where magma rises up into crust and melts the crust

pressure or decomposition melting caused by crust pulling away at an area and magma chamber is exposed to less pressure and causes an upwelling

volatiles (flux melting) water trapped along or in subducting plate gets hot and pressurized and released into sthensophere (causes volcanic arc)

textures of igneous rocks

fine grain: aphanitic

coarse grained: phaneritic

glassy texture: rapid cooling

porphyritic texture: 2 stages of cooling, large crystals in small crystal matrix

types of igneous rocks

rhyolite, granite, andesite, diorite, obsidian, pumice. pyroclastic rocks

types of pyroclastic rocks

tuff: ash sized fragments consolidated into volcanic ash. soft weak rock, hazard during construction

breccia: particles.

betonite: chemically altered tuff thru weathering, when its wet it expands and becomes unstable

Detrital sedimentary Rocks

Sediment is transported as solid particles. grains stuck togetehr by cement (clastic texture CEMENTING)

shale, sandstone, conglomerated, breccia

sedimentary process

1. Weathering

2. Erosion

3. Transportation

4. Depositon: sediment settles out of water 

5. Diagenesis and lithification:  

   1. Lithification:  

      1. Compaction: overburden pressure 

      2. Cementation: mineral rich fluid cement grains together (calcite, silica, iron oxide) 

   2. Diagenesis: chemical, physical and biological change after sediments are deposited 

      1. Effect 

         1. Grains are squeezed together 

         2. Reduction in porosity 

         3. Cementation 

chemical sedimentary rock

Sedimentary rock that forms when minerals precipitate from a solution or settle from a suspension (nonclastic)

limestone: can be organic from shells and stuff or inorganic rom calcium carbonate in water causing mineral deposition

chert: quartz or silica replaces calcite in limestone. can be petrified wood, agate, and evaporite

Environmental hazards caused by detrital sedimentary rocks

Mostly weak rocks that can cause environmental hazards in construction, the rocks have fine lamination which easily splits

Environmental hazards caused by chemical sedimentary rocks

Can be strong enough to support construction but they are susceptible to chemical weathering. They can cause sink holes or solution pits on the surface or cavern systems beneath it.

cementing material can be weak, if its calcite it causes same issues as limestone and degrades when exposed to acids, clay washes away, silica is way stronger as cement

Why do some metamorphic rocks cause environmental hazards

Foliation planes are planes of potential weakness, therefore foliated metamorphic rocks can result in an environmental hazard. It can cause things like: landslides, drainage issues, water leakage of dams

metamorphic rocks and their uses

slate; roofing materials, chalkboards

schist: soft rock and poor foundational material

gneiss: hard rock suitable for most engineering purposes

agents of metamophism

heat: recrystallization of minerals (magma and geothermal gradients)

pressure and stress: dense new minerals form

hydrothermal fluids: fluids react with rocks and changes rocks chemical compositions

intensity of metamorphism

intensity of metamorphism is the degree of metamorhpic change

metamorphic grade depends on texture. 

low grade mm rocks: low temps

high grade mm rocks: high temps

importance of subduction zones to metamorphic rocks

we find linear belts of metamorphic rocks parallel to trench.

continent- continent collisons cause major moutains

exhumation of metamorphic rocks

mountain building processes returns high grade metamorhic rocks back to the surface

metamorphic rock classifcation

foliated metamorphic rocks: planar arrangement of mineral grains, have alternating compositional layers of mafic and felsic rocks.

• slate is example, shale or clay has low temp pressure metamorphism.

• phyllite is slate at high temp with mica flakes. schist is coarse grained mica flakes.

• gneiss is compositional banding

non foliated metamorphic rocks: minimal deformation and foliation occur during metamorphism. no compression or shear

• hornfels

• marble: metamorphism of limestone and calcite crystal

• quartzite: quartz rich sandstone

shapes and types of volcanos

sheild: form from low viscosity basaltic flows (low silica), lava flows long distance. broad gentle domes

cinder cone volcano: high silica content, high viscosity. makes it taller bc lava cools fast. deep crater at summit with piles of tephra

stratovolcanos/composite volcanos: cone shaped, large and steeper near summit. layers of lava, tephra, and debris. way bigger than cinder

supervolcanos: ejecta volume over 1,000km³. yellowstone

types of eruptions

1. Effusive eruptions 

   1. Lava pours out of a summit vent 

   2. Flows great distances 

   3. Later solidified 

   4. Not explosive its gentle 

2. Explosive eruptions: 

   1. Gas pressure builds up and suddenly escapes 

   2. Explosion 

   3. Volcanic ash from eruption is dangerous and transported everywhere 

composition of lava

felsic lava: more silica bonds with lots of gases held between bonds. explosive eruptions

mafic lavas: gases easily escape, less silica, mild eruptions

explosivity and viscosity is determined by what factors

silica content: high silica= high viscosity, low silica low viscosity

temperature: high temperature less viscious

volatiles: how easily gases escape

volcanic activity classifications

Active volcanoes likely to erupt. ▪ erupting, erupted recently and Dormant volcanoes thousands years, but Not erupted for hundreds to have potential to erupt.

▪ Extinct volcanoes Active in the past, will never erupt in the future.

volcanic materials

extrusive materials ( form from lava on surface)

extruded materials (form from lava that flies into air and freezes)

volcanic gas

avalanche of hot ash

extrusive material types

pahoehoe lava: warm and pasty surfaces, smooth and glassy

Aa Aa lava: rough and blocky

columnar joints: final stage of cooling, lava flows, contracts and fractures

lava tubes: surface solidifies but inside the lava moves thru a tunnel like passageway

pillow lavas: rapid cooling of basalitc flow under water 

pyroclastic debris size

ash > 2mm

lapilli 2-64mm

bomb >64mm

volcanic gas

carbondioxide

sulfur dioxide

hydrogen sulfide

water

avalanche of hot ash

1. Pyroclastic flow: fast moving gaseous cloud of hot ashes and other debris. Moving around 200km/hr. Mt st helens 

2. Lahar: volcanic mudflow. Mixture of debris and water that moves down stream valleys and slopes. Forms a concrete over everything when dried 

volcanic hazards

lava flows: lava can destroy towns and cities, enough time for evacuations

pyroclastic flows: roiling ash and gas, high velocity and very hot

lahars: ash mixed with water, concrete once dried

ash and lapilli fall: can cause roof collapses, damage airplanes

sideways blast: landslide occurs and chamber tilted sideways (mt st helens- lateral blast tore off orth side of volcano. It can affect way more of an area due to the force coming out of it. Destroyed over 600km^2 of forest and killed 61 people)

earthquakes: moving magma causes slope failure. landslides, tsunamis

volcanic gases: poisonous co2, h2s. killed whole thing of sheep and cattle

how can volcanos affect climate

ash and aerosols high in atmosphere block sunlight

1. Ex: krakatau indonesia in 1883, mount st helens in 1980, mt st helens 

2. The year 1815 was the year without a summer due to the eruption of mt tambora in indonesia (stratovolcano)

clues for short term prediction of volcanic eruption

earthquake activity, changes in heat flow, changes in shape of magma chamber, increase in gas emission ands steam.

can measure this via satellite radar measurments of ground movement.

evacuate area from short term prediction, divert lava flow from towns, spraying cold seawater on lava flow

how to prepare for volcanic hazards

recurrence interval maps based off major volcanic events. probability of an event occuring based on avg time that passes bwtn major events of same magnitude

caldera and craters

steep walled depressions at summit, produced by collapse of volcano after eruption

caldera >1km 

crater <1km 

What type of volcanic rocks are produced by Mid-Oceanic ridge volcanism

Basalt and gabbro (extrusive igneous rocks)

earthquake magnitude

The size of an earthquake

deformation

changes in form &/or size of rock body

Displacement: change in location

Rotation: (change in orientation)

Distortion ( change in shape)

types of deformation

1. Brittle deformation: atomic bonds break and stay broken, permanent crack. More earthquakes 

2. Ductile deformation: bonds break but new bonds form quickly. Atoms rearrange. Grains change shape without permanent crack 

fault

major deformation causes earthquakes in brittle part of lithosphere

types of stress on rock

Compressional : shortens rock

Tensional :pulls apart rock

Shear: slides one rock past another

types of displacement

1. Fault creep: slow, gradual displacement 

2. Slip: by producing small eqs 

3. Rupture: store elastic energy for 100s of years before rupturing in major EQ's 

   1. Displacements occur along segments: 100-200 km long

major causes of earthquakes

1. Sudden formation of new fault 

2. Slip on existing fault 

3. Sudden change in arrangment of atoms in the minerals of rocks 

4. Movement of magma in volcano 

5. Explosion of volcano 

6. Giant landslide 

7. Meteorite impact 

human induced earthquakes

1. Nuclear explosions (bomb testss) 

2. Water reservoir-induced seismicity (fracture and faulting activated by increased load of water and water pressur 

3. Fracking: fracturing of formations in bedrock by pressurized liquid (used to extraction of oila nd natural gas) 

4. Deep waste disposal: injection of liquid waste in deep disposal well (3.6km) 

   1. Colroado dumps using deep waste disposal wells 

   2. Correlation between injection rates and frequency of earthquakes 

basic earthquake facts

1. Epicenter: directly over focus on ground above it 

2. Hypocenter: focus of an earthquake below surface 

3. ForeshocK: small eqs before major eqs dur to small cracks in vicinity of future major rupture zone (days or years) 
   aftershock: adjustments after major eqs 

types of seismic waves

surface waves: travel along outer part of earth, greatest destruction, greatest amplitude of ground motion. love wave, rayleigh wave (back and forth or rolling waves)

body waves: 2 types of it

• p wave: compression and dilation transmit elastic energy to next part. Primary wave. Side to side namely. Push pull wave. Solids, liquids and gas 

• s wave: response to incoming wave is up and down. Only thru solid. Shake motion at right angles, slower velocty than p waves. Amplitude is greater than p waves 

Mercalli intensity scale

based on perception of the extent of shaking and damage

Richter Magnitude scale

based on estimates amount of energy released. logarithmic in measurment. need a difference in arrival time of p and s wave and amplitude of largest wave to calculate intensity

locating an epicenter

1. Arrival delay times between s and p waves to seismic stations- delay time and s-p time interval proportional 

2. Distances of eq epicenter from at least 3 stations. From each stations by matching the delay times to standard p and s travel time curves (travel time graph) 

   1. Draw a circle around each station, point of intersection is the epicenter. Data from 3 stations can pinpoint epicenter

eq patterns

Shallow focus Deep : focus EQs along Mid oceanic ridge system  focus eq: occur in circum Pacific belt

where do majority of eqs happen at plate boundaries

divergent plate boundaries: normal faults and strike slip

transform fault plate: strike slip motion, shallow focus eq

suduction eq: convergent plate boundary

• shallow: subducting and overriding plate, large thrust fault

• intermediate: cool slab, mineral transformation

• deep: downgoing slab. shear between slab and surrounding asthenosphere and pull of deeper part of slab on shallow part

rifting: stretching crust creates normal faults

collision: thrust faults (compression)

intraplate: shallow focus eq, far field forces, interior of plae to break weak zones

reverse fault

a type of fault where the hanging wall slides upward; caused by compression in the crust.

strike-slip fault

a type of fault where rocks on either side move past each other sideways with little up or down motion

normal fault

A type of fault where the hanging wall slides downward; caused by tension in the crust

earthquake hazard depends on what

1. Magnitude of eqs 

2. Distance from epicenter 

3. Type of rock material 

between bedrock and sand, which would amplify the ground motion more

sand

ground shaking: 

accompanied with surface rupture and displacement 

s and p waves, love waves, rayleigh waves

p waves

first to arrive, rapid up and down mvement

s waves

back and forth motion, way stronger than p waves

love waves

Love waves (surface waves). First to follow, ground moves horizontally . ground writhes like snake

rayleigh waves

last to arrive. land surfaces acts like ripples in pond. last longer than other waves

extensive damage

fault scrap

san andreas fault

surface rupture (linear steep slope) produced by earthquake

liquefaction of ground

sediment flows under pressure 

EQ shaking results in Type compaction of saturated sediments Materials lose their strength and flow

can disrupt ground foundations

earthquake fire

shaking and surface displacements cn break electrical power and gas lines 

how can earthquakes cause landslides and ground failure

eq shaking often triggers landslide and can be extemely destructive, affects mainly hilly and mountainous areas 

tsunamis

caused by sudden verticle displacement of ocean water during an eq

in open ocean height is <1km, in shalllow waters is >30km

can also be caused by undersea landslides and volcanic eruptions

where is most at risk for tsunamis

coasts near major subduction zones

regional changes in groundwater level bc of earthquakes

Ground shaking can cause compaction of water saturated sediments and force water out 

how can earthquakes cause disease

eq can raise dust containing fungi spores that cause fever and wind can spread dust and disease or can break sewer and water lines which causes water pollution by disease causing organisms 

earthquake prediction clues

No short range!

clues:

1. Foreshocks 

2. Preseismic deformation of land surfaces 1-2 m uplift 

3. Water level changes in wells 

4. Gas emissions release of radion and helium 

5. Resullt from water influx when rocks fracture or expands 

6. Changes in electrical conductivity 

7. Anomalous animal behavior 

long range eq forecasts

1. Probability of eq occuring along a particular segment of fault 

2. Probabilistic approach assume eq are cyclical 

   1. determine of seismic zones via historical data

   2. identification of seismic gaps (places that havent slipped recently)

   3. determine eq cycles along fault segments

earthquake prep

1. Understand what happens during n earthquake 

2. Map active fault lines and areas likely to liquefy from shaking 

3. Develop construction code to prevent building failures (anchor bolts and cables, cross beams, rollers and spring) 

4. Regulate land use to control development 

5. Train the community in eq preparedness 

viscosity

resistance to flow (If something is highly viscous it will flow slowly)

mafic magma

low silica content, low viscosity

felsic magma

high silica content, high viscosity

Mafic lava

Low μ & Si content = form lava flow; move long distance

felsic lava

High μ & Si content = form a mound like lava dome

Shield volcano

a wide, gently sloping mountain made of layers of lava and formed by quiet eruptions. Form from low viscosity basaltic lava flows

cinder cone volcano

Cone-- shaped, symmetrical deep craters at their summit Form from piles of tephra

stratovolcano

Cone-- shaped , Large, steeper near the summit Consist of layers of lava, tephra and debris

a magnitude 9 earthquake releases how much more energy than a magnitude 7

1024 (About 1000x more)

Lahar hazards

Lahar can cover an area completely and cement it when dried

what type of river channel is characterized by multiple channels and gravel bars

braided

recurrence interval

the average length of time between floods of a given size along a particular stream

Why is flood hazard mapping considered an important step in floodplain management?

Flood hazard maps show which areas are likely to flood, how deep the water could be, and how frequently floods may occur.

Factor of Safety (FS)

ratio of resisting forces to driving forces. Analyzes how stable a slope is

What information are used in preparing landslide hazard maps?

Identify areas with Example high potential for landslides. Ex: Former landslides & sites of potential mass movement.

- Scarps

- open fissures

- tilted objects

- hummocky surface (tilted)

- sudden change in vegetation

What is the principal goal of beach nourishment

dumping new sand onto eroding beaches to restore them. to mitigate beach erosion by restoring and widening beaches

what adverse effects do groin and jetties have on coastal erosion

Groins and jetties cause increased erosion on the downdrift side by interrupting the natural flow of sand along the coast. They trap sand on the updrift side, causing a buildup, while starving the downdrift side of new sediment replenishment. This can worsen erosion in adjacent areas and lead to a buildup of sand on one side of the structure and erosion on the other.

Fluvial processes

Processes relating to erosion, transport and deposition by a river. driving force of flooding and flood hazards. processes include sediment erosion, transportation, and deposition

stream force

ability of a stream to erode, transport, and deposit sediment depends on the force balance between driving and resisting forces 

1. Driving force: shear stress exerted by flowing water, this force entrains and transports sediments 

2. Resisting force: shear strength (resistance) of the bed and bank forming materias, slows erosion 

3. In the case of fluid it’s a case of gravity as well, driving force is provided by flowing river itself 

stream power: 

rate of potential energy loss per unit channel length

stream discharge

volume of water flowing past a point on a stream per unit time

stream gauging station 

measures cross sectional area, depth, and avg velocity of stream

stream flow types

laminar: slow flow, no mixing of streamlines, thin layer of water above channel bed

turbulent flow: fast flow, velocity continuously fluctuates and casues eddies that mix the flow and increase the flow resistance

Coastal Processes

Waves, wind, currents, and their interactions and effects on the coastal environment

Sediment Erosion

particles being picked up in suspension