Humid and Arid Landscapes Ch. 7

what are some of the many factors that may complicate landscape evolution? what is it referred to by geologists?

"Interruptions to the Cycle" Among these are the periodic effects of climatic change, tectonic activity (folding and faulting), glaciation, changes in the sea level and volcanism.

what environmental factors promote wind erosion in arid regions?

-lack of soil moisture to bind loose grains together -incomplete vegetation cover -periodic strong winds generated by temperature extremes -and availability of loose surficial deposits

what landforms are more common in arid lands, and why?

Angular landforms, where physical weathering gains relative importance

What is a natural levee?

Deposition of coarser alluvium next to the main channel of a stream may build successive deposits there forming a natural levee.

what is a point bar deposit?

Deposition on the inside of the meander bend results in the development of a sand or gravel bar

how do high and low channel velocities effect meander channels?

High channel velocities at the outside of meander bends create periodic erosion there, while Low velocities at the inside of the meander bend initiate deposition

what deposit is referred to as desert pavement?

In many places, a coarse lag deposit of gravelly material remains after deflation occurs.

what is gradually filled with silt, sand, clay and vegetation to become a backswamp?

Oxbow lakes

what were the previous, more humid climates called? and when did they exist?

Pluvial climates, produce many features such as the wave-cut cliffs and beach that formed around the huge pluvial lakes that existed ONLY during these wetter periods.

what is a meander scroll?

Successive point bar deposits form a series of arcuate deposits

what is a drainage pattern?

The geometric pattern that a stream and its tributaries form

Cycle of Erosion in an Arid climate

YOUTH: -high relief -steep mountain fronts (fault scarps) -extensive alluvial fans -interior drainage (into playa) -intermittent streams -angular topography -intermittent lakes (playa), often saline MATURITY: -moderate relief -steep mountain fronts, parallel retreat -occurrence of pediments -bajadas (voslescing alluvial fans) -thickened playa deposits (rising base level) -scattered blowouts, dunes (eolian) -angular topography OLD AGE: -low relief -extensive pediments -extensive bajadas -thickened playa deposits -scattered inselbergs (small erosional remnants)

Cycle of Erosion in Humid climates

YOUTH: -increasing relief -V-shaped valleys -steep stream gradients, especially tributaries -general lack of floodplain development -extensive remnants of initial uplifted surface -rapid downcutting of trunk (main) streams MATURITY: -high relied, but decreasing - broader valleys of main streams -no remnants of initial uplifted surface -floodplain development of main streams -valley sides become gentler -main streams approach base level OLD AGE: -low relied -broad floodplains, even in tributary valleys -gentle, rounded interfluves -small erosional hills may remain (monadnocks) -all streams approaching base level and have low gradients

What are braided stream patterns?

a high width-to-depth ratio, apparently the result of having to carry too much solid load and or a very coarse load.

what is wind deflation? what is especially susceptible to it?

a process that selectively removes finer grains from the surface. Alluvial fans, playas and pediments are especially susceptible to wind deflation.

what is a cutoff? what is formed from it?

a stream meanders so wildly that it loops back on itself and creates a cutoff, and an oxbow lake is formed

What are Trellis patterns?

are characterized by an abundance of right-angle intersections and they exhibit strong structural control

what are Radical drainage patterns and how are they formed?

are formed when a series of streams flow radically outward from a central peak, such as a volcanic mountain

where are Trellis patterns usually found?

areas in which there are linear weaknesses called strike valleys, separated by hogback ridges.

how does the wind deposition occur?

as the wind loses transporting energy. Any obstruction to wind flow can induce deposition.

what are the two most common channel patterns that stream flowing across an alluvial floodplain tend to have?

braided and meandering

what happens when streams approach their local base level of erosion?

downcutting slows down or ceases, and the stream begins to cut laterally.

Why is it that the cycle of erosion might not be completed?

due to rejuvenation, which means that a stream's energy is renewed. In such instances, downcutting is again initiated,

in what kind of environment are eolian features more obvious?

eolian features (wind-produced) are not exclusive to arid lands, but are certainly more obvious, especially in those regions where eolian dunes are widespread

Finer silts and clays are generally transported......

greater distances, then deposited as sheets of loess. The finest clays can be transported global distances, ultimately to be incorporated in ocean basin deposits or in soils on the continents.

comparison between humid environments and dry environments.

in humid environments, much of the land has a soil and vegetation cover which conceals bedrock outcrops. In dry environments, bare rock surfaces are much more common because of the general absence of a complete soil and vegetation mantle.

what is a meandering channel?

meandering channels are characterized by a single, sinuous channel that is relatively narrow compared to its depth.

what happens during a normal stream flow of a braided stream pattern?

mid-channel bars protrude above water level, breaking the channel into many separate mini-channels, thus giving it the braided appearance.

what is the base level in a humid landscape?

most rivers run to the sea, so sea level, is base level-- the lowest vertical limit to which streams can erode

what landforms tend to dominate in humid climates, and why?

rounded landforms, bause of the abundance of water and dominance of chemical over physical weathering.

what happens when a prolonged deflation scoops out a closed depression or blowout, what does it become?

some blowouts become elongated through time and the sediment derived from them is deposited on the downwind side of the blowout as a Parabolic dune.

What are the two most commonly referred to landforms that are thought to reflect rejuvenations?

stream terraces and entrenched meanders

comparison of streams in humid and arid landscapes.

streams in humid regions experience an increase in discharge (volume of water flowage) as they are traced downvalley, arid regions are the opposite, many streams rend to disappear only a few miles from their source, and most are intermittent (flow only seasonally) As a consequence, there are often widespread stream deposits (alluvial fans) at the base of many western mountains.

what is the base level for arid landscapes?

streams terminate in an intermittent lake bed (a playa)--thus the level of the playa represents base level

what is deposited first when wind deposition is occurring?

the coarser sand I deposited first in the form of either flattish sand sheets or more conspicuous eolian dunes

what is the most common drainage configuration?

the dendritic pattern, which forms a branch-like pattern in which most of the smaller streams join larger ones at an acute angle. Dendritic patterns reflect a lack of structural control.

what results from lateral cutting?

the development of a flattish area adjacent to the main stream channel that periodically becomes inundated by floodwaters during high flow periods--the floodplain