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112 Cards in this Set
- Front
- Back
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How many barrier islands on the Georgia coast?
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12
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Which GA barrier island experiences the highest erosional rates?
Why? |
St. Catherine's Island;
- greatest distance from discharge rivers - 2.7 meter spring tide - savannah river dredging -2.9 mm/yr sea level rise |
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Deserts cover ~ __% of land surfaces
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25%
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What controls deserts?
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plate tectonics
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Unique deserts are characterized by...
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- extreme dryness (hot or cold)
- specialized ecosystems - low human populations - unique geological processes |
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What prevents formation of permanent surface water in deserts?
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The land being so arid that all water evaporates
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Criteria for deserts?
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- less than 15% of surface covered in vegetation
- annual rainfall less than 10 inches (25 cm) |
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Where do hot deserts occur?
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- Low latitudes
- low elevations - far from oceans |
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Where do cold deserts occur?
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- high latitudes
- high elevations - near cold ocean currents |
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What are the five types of deserts?
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1) subtropical
2) rain shadow 3) coastal 4) continental interior 5) polar |
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what kind of deserts are The Mohave, Chihuahan and the Sonoran deserts?
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Typical hot deserts
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Which desert is the only "cold" desert in the U.S. ?
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The Great Basin Desert
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Which deserts are considered Earth's largest?
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Subtropical
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How do subtropical deserts form?
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patterns of atmospheric convection;
solar energy evaporates H2O, which rises as hot, moist air. Rising air cools and expands, dropping abundant rain on equatorial rainforests. This air, stripped of moisture, flows North and South. |
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Where are the Subtropics located?
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20º to 30º N to S
- cool, sinking air wicks water from the surface, air heats up and landscape dries out |
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Which African deserts exist N of the equator (above the rainforest)?
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Sahara and Arabian
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Which African deserts exist S of the equator (below the rainforest)?
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Namib and Kalahari
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How do Rainshadow Deserts form?
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Moist ocean winds are driven up over mountains;
- windward air is forced to rise, expand and cool. Moisture condenses, rains fall, creating rainforest. Leeward air, stripped of moisture, sink toward the surface. Sinking air absorbs moisture from the land, creating arid, dry regions. |
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What kind of deserts are the North American deserts?
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Rainshadow
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How do coastal deserts form?
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Cool air over cold ocean water holds little moisture, and absorbs moisture when interacting with the land.
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Example of a coastal desert?
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Atacama in Peru (driest place on Earth)
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How do interior deserts form?
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Air loses moisture as it crosses continents, land far from ocean is very dry.
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Example of an interior desert?
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The Gobi Desert in Mongolia
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Where do polar deserts form?
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Above 66º N and S latitudes, where there is little air moisture.
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How do polar deserts form?
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Air circulation carries dry air to polar regions where it is so cold, the air can't hold moisture.
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What type of weather dominates deserts?
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Physical weathering
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Desert soils are...
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thin with poorly defined horizons
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Desert varnish
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Dark surface coating of iron and manganese oxides. Forms (very slowly) due to bacterial activity, dust and water.
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Alluvial fans
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conical accumulations of sediment. form where water exiting a canyon spreads out and drops sediment.
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How do alluvial fans grow?
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grow outward from sources over time;
sediments are coarse near sources sediments are finer away from source |
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Bajadas
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Alluvial fans that have coalesced along a mountain front
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What kinds of sediment load does wind carry?
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Surface load - coarser, sand - sized particles
Suspended load - fine - grained, silt - sized "dust" |
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Sand seas
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Vast areas of sand dunes
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Dunes
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Windblown accumulations of sand, normally accumulates around an obstacle.
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How to dunes grow over time?
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They begin to move downwind;
sand saltates up windward side and tumbles down slip face. |
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Dunes generate enormous _____ ____
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cross beds
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What are ergs? Where are they found?
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Gigantic oceans of sand; Arabian peninsula and Namibia.
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Weatherin
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the disintegration, or break down of rock material
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Mechanical weathering
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no change in chemical composition, just disintegration into smaller pieces.
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What processes increase total surface area exposed to weathering?
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1) pressure release
2) water: freeze/thaw cycles 3) crystallization of salt in rocks 4) thermal expansion/contraction |
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Chemical Weathering
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breakdown as a result of chemical reactions; transformation/decomposition of one mineral into another
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Mineral breakdown
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Carbonate dissolves, primary minerals ---> secondary minerals (mostly clays)
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What is the main agent in chemical weather?
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H2O
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Dissolution: ionic and organic compounds that dissolve in water
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- silica, K, Na, Mg, Ca, Cl, CO3, SO4
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H2O + CO2 --->
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Carbonic Acid
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H2O + S --->
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sulfuric acid
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Which ion is effective at breaking down minerals?
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H+
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Goldrich Stability Series
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minerals that form last in Bowen's Reaction series (form closest to Earth's surface) are the last to weather
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Biological weathering
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- roots break rocks
- roots produce acids that dissolve rocks - tree throw - burrowing animals |
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Four classes of sedimentary rocks:
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1) Clastic
2) Biochemical 3) Organic 4) Chemical |
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Clastic Rocks
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Loose rock fragments (clasts) cemented together
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Biochemical Rocks
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cemented shells of organisms
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Organic Rocks
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carbon - rich remains of once living organisms
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Chemical Rocks
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minerals that crystallize directly from water
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What provides that raw materials for all sedimentary rocks?
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Physical and chemical weathering
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Clastic sedimentary rocks are created by...
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Weathering
Erosion Transportation Deposition Lithification |
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Weathering
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generation of a detritus rock via disintegration
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Erosion
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removal of sediment remains from parent rock
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Transportation
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dispersal by gravity, wind, water and ice
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Deposition
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settling out of the transporting fluid
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Lithification
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transformation into solid rock
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Compaction
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Burial adds pressure to rock;
squeezes out air and H2O and compresses sediment grains |
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Cementation
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Minerals grow in pore spaces;
often quart or calcite precipitate from ground water glues sediments together |
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How are clastic rocks classified?
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Based on texture and composition;
- clast size - clast composition - angularity/sphericity - sorting - character of cement |
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Sphericity
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degree to which a clast nears a sphere
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Fresh detritus is normally...
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Angular/nonspherical
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Grain roundness and sphericity increases with....
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transport
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Biochemical Rocks
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sediments are derived from the shells of living organisms
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Examples of biochemical rocks
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Limestone - calcite and aragonite (CaCO3)
Chert - Silica (SiO2) |
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Example of Organic Sedimentary Rocks
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Coal
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Coal
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altered remains of fossil vegetation;
- black, combustible sedimentary rocks - 50 - 90% Carbon |
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Cross Beds
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created by ripple and dune migration
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How do cross beds form?
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sediment moves up the gentle side of a ripple or dune.
sediment piles up, then slips down the steep face. slip face continuously moves downcurrent. added sediment forms sloping cross beds. |
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What are the two ways of dating geological materials?
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Relative Dating and Numerical Dating
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Relative Ages
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- based upon order of information
- qualitative method - older vs younger relationships |
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Numerical Ages
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- quantitative method
- assigns actual number of years since an event |
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Jame's Hutton's principle of uniformatarianism
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- "the present is the key to the past"
1) the processes seen today are the same as those in the past 2) geologic change is slow, requires long periods of time 3) therefore, there must have been a long time before humans |
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Principle of original horizontality
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Sediments settle out of a fluid by gravity, causing sediments to accumulate horizontally. Sediment accumulation is not favored on a slope, hence tilted sedimentary rocks must be deformed.
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Principle of Superposition
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In an undeformed sequence of layered rocks:
- each bed is older than the one above it and younger than the one below - younger strata on top, older on bottom |
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Principle of Lateral Continuity
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- Strata of form lateral extensive horizontal sheets.
- subsequent erosion dissects once - continuous layers. - Flat - lying rock layers are unlikely to have been disturbed. |
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Principle of Cross - Cutting Relations
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- Younger features truncate older features
ex. faults, dikes, etc MUST be younger than the material that is faulted, intruded or eroded. a volcano can't intrude rocks that aren't there. |
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Principle of Inclusions
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Inclusions = rock fragment within another
- inclusions are ALWAYS older than the enclosing material - weathering rubble must have come from older - fragments (xenoliths) are older than igneous intrusions |
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Principle of Faunal Succession (AKA fossil succession)
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- fossils are often preserved in sedimentary rocks
- fossils are time markers, useful for relative dating - fossils speak of past depositional environments - specific fossils are only found within a limited time range |
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Fossil Range
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the first - last appearance of fossil.
each fossil has a unique range. Range over lap narrows time. |
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Index Fossils
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Diagnostic of a particular geologic type
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Three types of unconformity
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1) angular unconformity
2) nonconformity 3) disconformity |
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Angular unconformity
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Represents a huge gap in time;
horizontal marine sediments deformed by orogenesis, mountains eroded completely away, renewed marine invasion, new sediments deposited. |
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Nonconformity
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igneous/metamorphic rocks capped by sedimentary rocks;
igneous or metamorphic rocks exposed by erosion & sediments deposited on eroded surface. |
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Disconformity
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parallel strata bounding nondeposition; hard to recognize.
due to an interruption in sedimentation: pause in deposition sea level falls, then rises erosion |
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stratigraphic column
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described the sequence of strata.
formations can be traced over long distances; contacts define boundaries between formations or bed. several formations may be combined as a group. |
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Lithographic correlation is based on ____ ____ and is ________
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rock type; regional
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Fossil correlation is based on....
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fossils within rocks and is applicable to much broader areas
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Eons
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largest subdivision of time (hundreds to thousands of Ma)
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Eras
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subdivision of an eon (65 to hundreds of Ma)
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Periods
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subdivisions of an era (2 - 70 Ma)
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Epochs
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subdivision of a period (0.011 - 22 Ma)
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"recent life"
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cenozoic
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"middle life"
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mesozoic
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"ancient life"
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paleozoic
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Radioactive decay
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decay of an isotopes proceeds at a known rate and act as internal clocks
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Isotopes
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elements with varying numbers of neutrons
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Radioactive Isotopes
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decay spontaneously as known rates along a decay chain
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Geochronology
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numerical age study of rocks
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Half - life
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the time it takes for half the unstable nuclei in an isotope to decay
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Parent Isotope
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the isotope that undergoes decay
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Daughter Isotope
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the product of the decay of the parent isotope
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after 1 half - life....
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half the parent remains
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after 2 half - lives...
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1/4 the parent remains
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after 3 half - lives...
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1/8 the parent remains
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Numerical age possible w/o isotopes
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growth rings and rhythmic layers
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growth rings
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annual layers from trees or shells
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rhythmic layersing
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annual layers in sediments or ice
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