geology lab 7 humid and arid landscapes
trellis drainage pattern
abundance of right angle intersection with strong structural control, usually found in strike valleys
landforms susceptible to wind deflation
alluvial fans, playas and pediments
where are angular landforms more common
arid lands where physical weathering gains relative importance
what is land like in dry environments
bare rock surfaces common because of absence of soil and vegetation mantle
types of eolian dune
blowout, migrating blowout, linear dunes, transverse ridges, barchanoid ridges, barchans, star dunes
parabolic dune
blowouts elongated through time with their sediment deposited on downwind side
blowout or deflation hollow
closed depression scooped out by prolonged deflation
desert pavement
coarse lag deposit of gravelly material remaining after deflation occurs
point bar deposit
deposition on inside on meander bend resulting in sand/gravel bar
floodplain
flattish area adjacent to channel of lateral cutting stream regularly flooded
intermittent streams
flow only seasonally
oxbow lake
formed from cutoffs
radial drainage pattern
formed when streams flow radially outward from central peak
drainage pattern
geometric pattern stream and its tributaries form
youthful arid climate
high relief, fault scarps, extensive alluvial fans, interior drainage, intermittent streams, angular topography, playa
braided channel patterns
high width to depth ratio because too much solid/coarse load carried by water
mature humid climate
high yet decreasing relief, broader valleys, no remnants, floodplain development, gentle valley sides, main streams by base level
youthful humid climate
increasing relief, v shaped valleys, steep stream gradients, lack of floodplains, remnants of initial uplifted surface, rapid downcutting
playa
intermittent lake bed
streams in arid regions
intermittent streams disappearing only few miles from sources
environmental factors promoting wind erosion in arid regions
lack of soil moisture, incomplete vegetation cover, periodic strong winds, availability of loose surficial deposits
old age humid climate
low relief, broad floodplains, gentle round interfluves, monadnocks, streams approaching base level with low gradients
old age arid climate
low relief, extensive pediments and bajadas, thickened playa deposits, scattered inselbergs
how does braided channel pattern get its appearance
mid channel bars protruding above water level during periods of normal stream flow
mature arid climate
moderate relief, steep mount front, parallel retreat, pediments, bajadas, rising base level, eolian dunes, angular topography
pluvial climates
more humid climates from past producing many features such as wave cut cliffs and beaches formed around pluvial lakes existing only during these wetter periods
dendritic drainage pattern
most common pattern which forms branch like pattern, smaller streams join larger ones at acute angle
meandering channel patterns
narrow single sinuous channel; high channel velocities at outside of bends create periodic erosion; low velocities at inside create deposition
wind, glaciers, waves, currents
other erosional agents
backswamps
oxbow lakes filled with silt, sand, clay, vegetation
interruptions to erosion cycle
periodic effects of climatic change, tectonic activity (folding and faulting), glaciation, changes in sea level and volcanism
wind deflation
process selectively removing finer grain from surface
the base level in humid climates
sea level because most rivers run to sea
what is land like in humid environments
soil and vegetation cover concealing bedrock outcrops
cutoff
stream meandering wildly and looping back on itself
rejuvenation
stream's energy is renewed and cycle of erosion not completed
where does increase in discharge happen
streams in humid regions as they are traced downwards
natural levee
successive deposits built by deposition of alluvium next to main stream channel
meander scroll
successive point bar deposits form series of arcuate deposits
why do rounded landforms dominate humid climates
the abundance of water and dominance of chemical over physical weathering
remaining 25% of continents on earth
the amount of earth arid and semi arid climates cover
75% of continents on earth
the amount of earth humid climates cover
streams
the dominant erosional agent in humid and arid climates
the base level in arid climates
the level of the playa because of interior drainage
base level
the lowest vertical limit to which streams can erode
the controls of climate contrasts
the way streams modify landscape and the importance of other agents in sculpting land
what kind of streams have distinctive channel pattern
those flowing across alluvial floodplain
stream terraces and entrenched meanders
two common landforms thought to reflect rejuvenation
discharge
volume of water flowage
lateral cutting
when streams approach local base level or erosion and decrease downcutting
alluvial fans
widespread stream deposits at base of many western mountains due to intermittent streams in arid regions
eolian features
wind produced and more obvious in arid lands, especially where eolian dunes are widespread
how does humid cycle of erosion begin
with low relief as an entire block of crustal material is uplifted
how does arid cycle of erosion begin
with maximum relief due to block faulting