Flashcards in Unit 5: 18, 19, 20 Deck (54)
What is cross bedding?
when sedimentary rock layers become folded and bent
How is cross bedding formed?
Describe an erg desert
sea of sand -- large area covered with loose sand generally arranged in some sort of dune formation by the wind
Describe a reg desert
stony deserts -- desert is covered in a layer of stones, which can sometimes be very thin. the finer material being removed, the surface pebbles often fit closely together, sealing whatever material is below from further erosion
Describe a hamada desert
barren bedrock -- exposed bedrock, but sometimes is composed of sedimentary material that has been cemented together by salts evaporated from groundwater.
Know the origin of loess
winds remove loess from glacial outwash plains
deflation of desert regions
What is loess's economic importance to farmers?
Loess deposits provide fertile possibilities for agriculture, for they serve as parent material for some of the world's most productive soils, especially for growing grain
What are some characteristics of barchan sand dunes?
individual dune migrates across a nonsandy surface, although they may be found in groups. crescent shaped, with the horns facing downwind. form where strong winds blow consistently from one direction
What are some characteristics of transverse sand dunes?
also crescent shaped, but less uniformly than barchans. occur where the supply of sand is much greater than that found in locations that have barchans; normally the entire landscape leading to the transverse-dune formation is sand covered. if the sand supply decreases, they are likely to break up into barchans
What are some characteristics of longitudinal sand dunes?
meager supply of sand
strong prevailing winds
parallel to wind direction
What are some characteristics of blow-out sand dunes?
coastal blowouts have strong persistent onshore winds
large supply of sand from beaches
Know how wind can change the character of deserts through the process of deflation.
shifting of loose particles
Be able to describe arid western landscapes
Be able to describe humid eastern landscapes
What is the particulate matter theory for ice ages
meteor impact in the Vredefort Dome, the oldest and largest clearly visible meteorite impact structure in the world -- south africa
What is the CO2 fluxuations theory for ice ages
earth experiences warming period
plants spread poleward and total biomass greatly increases
greater absorption of CO2 due to greater amounts of photosynthesis occuring
lower temps bring on an ice age and much biomass reduction
reduced biomass allows for CO2 restoration to the atmosphere
What is the warming earth theory for ice ages
polar regions are far colder than necessary for snow to occur
if temps rise in the polar regions greater snowfall should occur
greater snowfall causes glaciers to spread outward from the polar regions
extensive glaciation lowers polar temps and reduces snowfall
glaciers now recede
What is the eccentricity of orbit theory for ice ages
angle of the tilt also varies with a 41000 year cycle
shape of the orbit varies over time - aphelion and perihelion
produces a complex series of cyclical changes in the seasonal patterns of intensity of solar radiation
How do you determine if depositional material has been deposited by a river (stratified)
stratified - material is sorted by larger materials at bottom
How do you determine if depositional material has been deposited by a glacier (unstratified)
unsatisfied - all mixed together sizes
how does a glacier form
snowflakes compressed under pressure until density is 90% of water
What causes a glacier to move?
gravity pulls it at a certain point, sometimes a lubricating layer of water on the bottom allows the entire mass to slide
What is a mountain glaciation
limited to high elevations
results from surplus snow in high elevations
not necessarily dependent upon an ice age
more pronounced during ice ages
What is a continetal glaciation
large geographical coverage
usually associated with major climatic change
has profound affect on landscape
occured during pleistocene
What are eskers and how are they formed
These landforms are composed largely of glaciofluvial gravel and are thought to
have originate when streams flowing through tunnels in the interior of the ice sheet became choked off during a time in which the ice was neither flowing nor advancing.
What are drumlins and how are they formed
a low elongated hill, they are much smaller than moraines but composed of
similarly unsorted till. The long axis of the drumlin is aligned parallel with the direction of ice
movement. The end of the drumlin facing the direction from which the ice came is blunt and
slightly steeper than the opposite end.
What are kettle lakes and how are they formed
form when large blocks of ice left by a retreating glacier become surrounded
or even covered by glacial drifts; after the ice block melts, the morainal surface collapses,
leaving an irregular depression.
What are kames and how are they formed
small, steep mounds or conical hills of stratified drift are found sporadically in
areas of ice-sheet deposition. Associated with melt water deposition in stagnant ice. They are
mounds of poorly sorted sand and gravel that probably formed within glacial fissures or between
the glacier and the land surface. Many seem to have been built as steep fans or deltas against the
edge of the ice that later collapsed partially when the ice melted.
What are terminal moraines and how are they formed
a ridge of till that marks the outermost limit of glacial advance.