Shared Flashcard Set


5th exam
Undergraduate 1

Additional Geology Flashcards




Hurricane Tracks on US Coast
60+ hurricanes for East Coast and Atlantic side coast (right of Florida, SC, NC, etc)
Hurricane Top 5 Relative Risks

01) Miami

02) Mobile, Alabama

03) Galveston, TX

04) Florida Keys

05) New Orleans 

Financial/Property/Human Losses by hurricanes

- #’s in property damage increase in developed areas

- Area by Louisiana, TX area is center for oil platforms

- Decrease in deaths, Increase in dollar loss

- Hurricanes are predictable so can give plenty warning

- Population growth = increase in damage

Global warming/Society impact on Hurricanes

- Hurricane # may increased with the surface water warmth temperature, increase = strength increases

- Climate largest sensitivity 10% increase

- Smallest societal sensitivity 20% increase

- Global warming will have small effect on hurricanes and climate but will not be as great as the effect of development on shores. 

Variables that affect storm surge

- How low atmospheric pressure falls

- Wind speed (category 1-5)

- Wind direction (left or right side of eye)

- Spring v. neap tide (tidal range)

- Durations of fetch in Open Ocean

- Timing of landfall (relative to high/low tide)

- Coastal Topography (steep v. flat)

- Atmospheric pressure affects surge height: L pressure = High surge, H pressure = Low surge

- Storm surge worse on right side of hurricane as it approaches land, wind blows toward shore

Variables affecting Run-Up
- Run up based on wind pressure & surge & wave impact
Hurricane Season 2004

- 2004 Ivan Category 5

            Houses built to have open foundation on beach. Still able to salvage after storm.

Hurricane Season 2005

2005 Katrina

-Wind damage

-City was flooded a few days after storm

-Large part of New Orleans under sea level (ground is subsided –sinking)

-Failure of levees engineering caused failure: man made failure

-Multiple levee failures: was known to be possible allowing info structure to fail.

-Mississippi coast had a lot more damage than New Orleans but not as publicized because there were fewer deaths


Hurricane Season 2008

Ike 2008 Galveston, TX

-95 deaths

        -$30 bill damage

            -3rd worst in history

            -Storm surge > 17 ft

Causes of Ground Subsidence

           a) Dissolution of limestone (karsts topography)

            b) Permafrost (thermokarst)

            c) Shrinking/swelling of soils

            d) Mining or petroleum extraction

            e) Overdraft of ground water

            f) Compaction of sediment

            g) e & f most important to consider near shore

Groundwater pumping leads to subsidence

- Compaction occurs when ground water extracted from the subsurface

- Pressure exerted on a cube of rock/soil in the subsurface

- Each layer of rock exerts pressure on layers below

- Central Valley, CA

Subsidence: Total Normal stress
Total normal stress = total weight per unit
Subsidence: Magnitude of water Pressure

(unit weight of water) x ( height of water column)

- Pressure measured in lake or ocean is measure at the free water surface

- Pressure at base of water column = height of water column

- Pressure exerted by water below the ground depends on depth below water table (upper level of saturated zone)



Subsidence: Effective stress

pressure exerted by fluid in pore space helps support the weight of overlying layers of rock and soil

Subsidence: Effective Normal Stress

- exerted on saturated clay layer depends on weight of overlying sand layers minus pressure exerted by fluid in clay layer

- Extraction of ground water lowers the water table, which decreases fluid pressure at all depths below the water table – that increases value of effective normal stress

Subsidence near shoreline: Galveston, TX

consequences: entire subdivisions have permanent flooding by seawater b/c ground sinking. Closer packing process of voids & solids.  Only way to prevent this is to add layers on top. Net effect. A natural process except w/ water pumping from ground.

Compaction Consequences

- New Orleans: Engineering on Mississippi river cuts off natural sediment to build on top of the natural subsidence.

- The city has subsided below sea level and river.

-Discharge on Miss. R. is controlled, land has been lost since and can never be recovered and only to fix it is add artificially.

 - Hurricanes increase severity with decrease in land. Coastal loss rate: 34.9 mi2/yr, Basin loss rate: 33.5 mi2/yr, Subsidence rates increase since 1978

Compaction (Subsidence) - Construction phrase & Abandonment phase

a) Constructional phase: rapid buildup on sediment

b) Abandonment phase: layers compact surface subsides. 

Earth Climate

- Hydrologic Cycle: year ago sea levels was 100+ m less b/c there was so much water stored in ice caps

- Atmosphere Composition: Nitrogen, Oxygen, Argon, Neon, Helium, Krypton, green house gases.

- Earth Movements (winds): water motion, distribution of light, seasons (angle of the earth towards the sun). Rotation of earth. All factors continuously change

El Nino (Short term climate cycle)

(a.k.a southern oscillation)

            -Surface water circulation

            -Sea surface temperature

            -Atmospheric circulation temp.

            -Effect on precipitation

- 5-7 yrs, pacific water temperature higher = different weather, more wet and warmer, possible flooding

Milankovitch (orbital) forcing: Procession of equinoxes

cycle ~ 23,000 years. Rotation of the season when earth is closest to sun (perihelion)

- North hem. Closer to sun in winter but earth is just tilted away.

- Procession of equinoxes. Earth now closer to sun during Jan. in 11,500 yrs earth will be closer to sun during July.


Milankovitch (orbital) forcing: Obliquity of plan of ecliptic



cycle ~ 41,000 years. Change in angel of equatorial plane relative to orbital plane.


Milankovitch (orbital) forcing: Orbital Eccentricity

cycle ~ 100,000 years

Elliptical orbit – more seasonal contrast – warmer summer and cooler winter.

Circular orbit – less seasonal contrast – cooler summer and warmer winter

- Equatorial plane tilted at 23.5 degrees

- Sun not center of earth’s elliptical orbit

- Orbital forcing matters b/c: warmer winter = more precipitation (snow), colder winter = less precipitation, cooler summer = less snow melt, hotter summer = more

snow melt, Net effect: less yr round contrast: glaciers expand, more yr round contrast: glaciers retreat




Ancient Climate studies

- Historical records, tree rings & pollen, ice cores (oxygen isotopes, gas bubbles), micro fossils (oxygen isotopes).

- Climate trends aren’t completely controlled by humans but they do have some affect in addition to natural cycle.

- Climate change causes partitioning of oxygen isotopes w/in the hydrologic cycle

- Changes in oxygen isotope in marine microfossils reflect change with/in ocean-water reservoir.

Oxygen isotope analysis, sea floor sediment

 --> When temp high: more evaporation, more heavier isotope

 --> When temp low: less evaporation, less O18 (heavier isotopes) and more O16

Interglacial cycle 18,000 yrs, sea level wroldwide

- Last glacial max – 18,000 yrs

- Extensive (thick) continental ice sheets

- Sea level lowered by ~ 120-130 m

- Shorelines shifted to edge of continental shelf

- Melting of ice then led to rise of sea level

Trends for global temp. and sea level in past 150 yrs

-      Incoming solar radiation (sun spots)

-      Reflection + absorption + transmission of incoming solar radiation

-      Transmission + retention of heat radiated from Earth’s surface

-       Anthropogenic influences

-       Inputs > outputs = global warming

-       Sea level rise is linked in its timing to warming of global air temp.

-      No rational mechanism for sea level rise except for global warming

-       2005-2008: Very small cooling

-       2009: warmer-       Last 10 yrs: warmest in entire instrumented record

-       Magnitude of solar variability is ~0.1 degree C, much smaller than actual measure change in average global temp.

Greenhouse effect

- Atmosphere transmits short wave (UV) radiation (solar emission)

- Greenhouse gases CO2, CH4, absorb long wave (IR) radiation (Earth emission)

- Transmit shortwave radiation absorb long wave radiation

Carbon Cycle

- Ocean reservoirs, land reservoirs, atmosphere, fossil fuels

- Burning fossil fuels shifts carbon very quickly in global budget, from “permanent” storage in rocks into the atmosphere

- Issue: transferring carbon and burning it making it go into the atmosphere

Natural cycles of CO2 in atmosphere 250,000 yrs: Anthropogenic forcing

Anthropogenic forcing:

-Increases in release of CO2, CH4 since industrial revolution

-Increases correlate with other manmade pollutants

-Increases correlate with increases in temperature.

- Increases non linear, increase of ~40% in 200 years

-Carbon Dioxide and methane biggest issue

- Increases more extreme magnitude and quicker than natural cycles

-Climate responds to both natural and anthropogenic forcing

Continental and alpine glaciers to global warming

- Thickness of sea ice – little influence on sea level

- Retreats of Alaskan glaciers melt drains into the ocean

- Acceleration in the retreat of continental glaciers

- Global av. Temp from glacial length records increase

- Effect on sea level: continental ice stores 90% of Earth’s fresh water, Greenland

Continental and alpine glaciers to global warming: variables

sea level

- shelf exposure,

- riverine flux of phosphate

- oceanic concentration of phosphate

- intensity of biological pump

- atmospheric CO2

- global surface temp

- glacial ice volume

Mitigation of coast hazards: problems, strategies

- Problems: loss of beach sand, retreat of sea cliffs, harbor protection, flooding during storms, subsidence, SL rise

- Strategies: engineering, land-use management


Mitigation of coast hazards: Engineering - Beach nourishment

sand must be continuously replenished e.g. worked great in Miami Beach where beach development was so valuable that worth investment.


Mitigation of coast hazards: Engineering - stabilize/coastal dunes
dunes act as buffer
Mitigation of coast hazards: Engineering - Groins

Def: rigid structures perpendicular to shoreline

§  Adv. growth of beach protects upland areas. Local recreation benefit. Moderate initial cost. Low maintenance cost.

§  Disadv. Down-drift areas will probably experience rapid erosions. Cost. Extremely complicated engineering design problem.

§  Problem: transport of sand is parallel to shoreline


Mitigation of coast hazards: Engineering - Sea Walls

§  Adv. protects from waves. Low maintenance cost. Stabilizes backshore.

§  Disadv. Extremely high initial cost, may fail from scour underneath, difficult to repair, often cause erosion and loss of sand.


Mitigation of coast hazards: Engineering - Revetments

§  Adv. Inexpensive, easy construction, easily repaired, reduces wave run-up, absorbs wave energy

§  Disadv. Large blocks are difficult to obtain, require filter material to fill voids, may be extremely unattractive especial if concrete blocks, protects narrow barrier island seawalls continued with revetment also protect seacliff


Mitigation of coast hazards: Engineering - harbor protections

§  Jetties, attached breakwater, detached breakwater, jetties @ harbor entrance intercept long shore drift. Erosion accelerates on the down-drift side, building codes, relocation

Mitigation of coast hazards: Engineering - Relocation

§  Adv. permanent, adaptable to short reaches of shoreline, can be accomplished by individual owner, no maintenance

§  Disadv. Special skills & equipment, open area must be available for relocation, does not stop erosion


Mitigation of coast hazards: Land-use Management

- Recurrence interval v. flood run-up

- Areas of expected erosion/flooding

-E – lines, E- zones, Flood – lines, F – zones

- Flood insurance premiums tied to risk level

- High-risk zones set aside: open space, parks, and golf courses

Flood Recurrence interval

(RI) = (n+1)/m

   a) Pick max run-up for ea. Yr. on tidal gauge record

   b) Place all annual – max events on record in rank order

e.g. n = 59 yrs, m= 3rd highest flood, RI= once every 20 yrs

            - Calculate average rate = distance/time

            - E lines and E zones based on rates of shoreline retreat


5 scientific zone management

01) Coastal erosion is a natural process NOT natural hazard. Fixed built structures in coastal zone cause erosion

02) Any type of shoreline construction changes natural equilibrium of coastal zone

03) Engineering structure are meant to protect beach, but may change or harm (cannot destroy a beach)

04) stabilization of coastal zones through engineering protect property of relatively small # of people - paid by general public, and failed to protect aesthetic value of natural beach.

05) Once constructed, engineering produce a trend in development that is difficult if not impossible to reverse. Cost of protective structure may exceed value of beach property saved.

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