Unit 5 (Ch. 15) EOLIAN SYSTEM Study Guide
(Revised 2/13
UNIT 5 HOMEWORK
WEB HIT HOMEWORK - part 1: ONE WRITTEN PARAGRAPH from any selected unit web hit site
VIDEO WEB HIT HOMEWORK – part 2: ONE WRITTEN PARAGRAPH from any selected unit video
site
For any Unit Web Hits and Unit Web Videos, go to the “DMC HOME” website; in Search box –type “Geology”,
select “Vernon Kramer”, scroll down to GEOL 1303, select “Syllabus”, select “Web Hit Links”, later then the select
“Video Web Hits”, click on icon of interest for web sites
OR: go to DMC Home website, select “Degrees, Certificates, Courses”, scroll down to Natural Sciences and select
“Geology”, select “Faculty Listings”, select “Walter Vernon Kramer”, find “Geol 1303”, select “Syllabus”, and there
you can find the” web hit links” click on icon of interest for web sites and then to “Web video hits”, click on icon of
interest for video site
[IF NONE OF THE WEB SITES COME UP, YOUR COMPUTER PROBABLY NEEDS TO BE REBOOTED (RESTARTED)
A good App is “intellicast” for weather and radar of approaching storms; “wet or dry” app for
droughts
Hydrologic Subsystem
Aeolus: Greek god of the winds whose name is used for this geologic system
Eolian system: a geologic system that involves the wind
- Wind behaves as a gaseous fluid; therefore wind is a part of the hydrologic system.
- Video of a 2012 tornado at a Dallas truck stop
Effectiveness of Eolian System
- The eolian system (wind driven system) is the least effective agent for erosion.
- Large and powerful dust storms are problems in many areas of the world.
- The eolian system is a very effective agent for the transportation of small-sized sediments (dust and
sand) and for the deposition of these sediments.
- People are affected by low visibilities, breathing problems, and hazardous driving from sandstorms.
- Video of a dust storm (2012) in Gilbert, AZ
Eolian Transport
- Winds can carry dust, mold spores and bacteria from one continent to another, which can impact
people with allergies. Example: sandstones from Africa that reach the Americas. These same dust
storms have been responsible for deaths of some coral reefs in the Caribbean.
- Wind can transport (erode) large quantities of sand and dust, in areas of:
1. deserts & semi-deserts,
2. beaches & shorelines,
3. construction sites,
4. in areas that had removal of vegetation by overgrazing, over-plowing, & burning;
5. in areas experiencing long periods of drought.
The US Dust Bowl and Black Blizzards
Dust Bowl (Page 148-149): The 1930’s recorded the worse drought in US history that was marked by
massive dust storms in the central US.
- These historical events of massive dust storms in the Central US and Texas have been referenced as
“black blizzards”. These dust storms were responsible for 850,000,000 tons of topsoil in prime
agricultural areas being blown away in 1935.
- Enforced conservation techniques such as planting wind breaks, preventing over grazing and rough
plowing have so far prevented other “dust bowls”.
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- 1930’s video of a black blizzard
- Unfortunately, localized dust storms and sandstorms still continue in the US and their numbers are
starting to increase.
Historical Texas Droughts
- At the end of this unit is a Texas State Historical Association report that shows that devastating
droughts occurred in Texas, as far back as 1720. Was this the result of man-made global warming????
The worst “modern” Texas drought lasted from 1949-1956!
US Droughts Today
- Droughts are normal, recurring events of abnormally low precipitation that affects life.
- Today, there are almost always areas of drought in Texas, and in the Southwestern US. (Google in
“drought index” for a website that shows the most current drought locations.)
Nothing in the world is more dangerous than sincere ignorance and conscientious stupidity - MLK
World Deserts
- Every continent has deserts, but the world’s largest desert continent is Antarctica (no rainfall).
Atacama Desert of Chile represents the driest desert in the world, with reportedly areas of “no known
rains” in 400 years.
Sunshine all the time makes a desert – Arab Proverb
Deserts and US Deserts
Desert: areas that generally receive less than 10 inches of rain a year
-There are four major deserts in the US:
1) Chihuahuan Desert (is also found in West Texas)
2) Mojave Desert mostly in California
3) Sonoran Desert mostly in Arizona
4) Great Basin Desert mostly in Nevada, Utah and Oregon
- Different map makers produce different boundaries for the US deserts
- (3-D presentation)
- The Chihuahuan Desert is less than 8,000 years old, forming late after the last Ice Age. Common
plants include prickly pear cactus, ocotillo, yucca and lechugilla
- Joshua trees and cholla (jumping) cactus are common in the Sonoran and Mojave deserts
- The saguaro cactus is indicative of the Sonoran Desert and must be over 80 years old to have their
famous arms.
Deserts and Rainfall
- Deserts are commonly found adjacent to oceans and man-made lakes.
- The Western half of Texas averages less than 24 inches of rain annually
- Far West Texas averages less than 8 inches of rain per year. Far East Texas averages almost five feet
of rain per year (which is how many inches??.
- Corpus Christi normally averages 34 inches rainfall per year which is almost ____ feet..
- Freer TX, to the west of Corpus Christi has a desert like environment
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Rain Shadow
- Western US rain shadow is an event that occurs because almost all moisture is removed from the
clouds by tall mountains, thus mostly dry air reaches the interior. It is this remaining dry air (a rain
shadow) that creates the US deserts.
- There are two major Earth features that are responsible for the western North America rain shadow:
1) an atmospheric Pacific High Pressure zone and 2) the high mountain ridges found along the
Pacific coast.
Effectiveness of Wind Erosion
- Wind has much less mass and force than does moving water. Thus wind is a less efficient agent of
erosion and deposition than moving water because water has more mass than air.
- But wind transport and deposition is still an important geological agent.
- Concept Test
For wind erosion and transport to be effective there must be:
1) Wind: a constant and generally unobstructed wind velocity for a period of time.
2) Dry soil: wet soil must be deeper than the surface and few plants - vegetation tends to hold
sediment in place.
3) Sand and silt: a movable supply of sand or silt supply.
4) The cohesion between grains must be broken for there to be loose particles available.
- Most rocks are too heavy; there must be particles small enough so that most winds can move them.
Two Agents of Wind Erosion (Sediment Removal)
1. Abrasion is the least effective agent for wind erosion. With abrasion impacting sand grains knock
off tiny fragments of rocks
Ventifact is a pebble or cobble shaped and polished as a result of “sand blasting” abrasion.
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2. Deflation is the most effective agents for wind erosion. Deflation is caused by the lifting and
removal of loose sand and dust particles from the Earth’s surface (i.e. – blowing all the smaller and
lighter particles away).
- Lag gravel is a residual accumulation of coarse fragments (rocks and gravel) that remains on the
surface after finer material has been removed by wind. This coarse material remains because the
winds cannot remove it.
-Lag gravel or desert pavement or desert varnish is the result of wind erosion, as compared to sand
dunes which are the products of wind deposition.
- Lag gravels are also found on Mars
Deflation (Wind Eroding Sand and Dust)
Deflation is produced by three methods:
A) Suspension: Silt and clay particles (dust) that can be lifted more than a mile high into the
atmosphere and carried very long distances
B) Saltation: “jumping grains” a grain is lifted into the air and falls back down, colliding with
another grain, which is lifted back into the air
C) Creep: grains too large to be lifted but can roll or slide along the surface
- Wind-produced rock “creep” can produce strange-looking trails on dry lake beds.
Saltation drawing
Hoodoos
- These are hard rock masses resting on top of soft sedimentary rock. The piece of harder, less -eroded
stone that protects the column of soft sedimentary rock or soil from rain erosion
- These features can be very picturesque
Hoodoos
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Haboob
- Suspension produces the highly visible “dust storms” of clay, silt and fine sand particles.
- A special type of dust storm, the haboob is a short term dust storm produced by thunderstorm
downbursts. Within a narrow band, haboobs can create a “mud storm”.
Wind Blown Sediments Can Be Deposited as:
1. Sand sheets are thin, flat deposits of coarse-grain sand that move as a thin sheet over large areas.
These sand sheets move slowly because of the relatively larger and heavier grain size particles.
2. Ripples (miniature dunes): a small “sand wave” produced on the surface by the drag of wind
(water) moving over the sand
- Example: The White Sand National Monument of New Mexico has unique desert sands because
these sands are composed of grains of pure gypsum.
- Formation of ripples:
1) ripples are formed perpendicular to the wind direction
2) ripples occur at regularly spaced intervals;
3) the sand particles arrive to their ripple sites by saltation
- There are also a series of White Sand Dunes (gypsum) near the Texas Guadalupe National Park
To different minds, the same world is a hell and a heaven – Ralph Waldo Emerson
3. Dunes: a) hills or ridges of sand deposited by wind
b) dunes usually have an asymmetrical shapes
c) dunes usually show shallow upwind slopes (10-12 degrees)
d) dunes usually show steep downwind slopes (33-34 degrees)
Draw a dune (later cross bedding)
Dune Migration
1) Sand is blown up windward face
2) Crest becomes unstable and the sand avalanches down the slip face; thus sand dunes migrate
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- CROSS BEDDING: angular deposition of sediments on a slip face (can be found in deposits of sand
from both wind and water currents). Lake deposits have thin, parallel layers
4. Loess: (to be reviewed later in this study guide)
Conditions Needed to Create Different Types of Sand Dunes
- Dune shapes will be determined by:
1. Size and quantity of sand
2. Surface below the sand
3. Prevailing wind directions
There are 5 types of major dune shapes:
1. Barchan dune shape:
a) Isolated, crescent shaped dunes with “horns” pointing down wind;
b) Dunes developed in areas of limited sand and “one-direction” winds
2. Traverse dune shape:
a) Numerous, aligned barchan dunes;
b) Greater availability of sand;
c) One prevailing wind direction
3. Parabolic dune shape: because of surface vegetation, these dunes create shapes with edges that point
in opposite direction than a barchan dune.
a) Crescent shaped dune with long trailing arms upwind;
b) Common in coastal areas with strong unidirectional winds,
c) Areas of abundant sand, and vegetation;
d) Vegetation helps anchor arms
4. Linear or longitudinal dune shape:
a) Forms evenly spaced ridges;
b) Strong bi-directional winds;
c) Found in areas of limited, available sand
5. Star Dune shape:
a) Isolated sand hills with pyramidal form;
b) Found in areas with no single prevailing wind direction
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Five Types of dunes (one sketch will be selected for the exam for name identification)
The answer is blowing in the wind – Bob Dylan
Other Specialized Dunes
- There are “specialized” dunes, which are very common in South and West Texas.
Coppice dune: small sand mounds that accumulate around vegetation or anything that can slow down
wind transport of sand
Draw a coppice dune
Padre Island and Oso Bay Dunes
Fore-Island Dune Ridge: high, fairly continuous grass-covered ridge adjacent to the beach which are
really coppice dunes
Blowout Dune Complex: a depression in a sand field created by destroyed vegetation
- Beyond a blowout can be found a complex of barchan, transverse and parabolic dune types
Clay dunes: 1) Small dunes composed of clay, which form downwind of local tidal flats; 2) Found
along west shore of Oso Bay, mostly covered by vegetation.
- The barrier islands (i.e. Padre Island) contain all types of dunes!
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Monahans Sand Hills State Park, found in West Texas has sand dunes up to 70 feet tall and an oasis
between some of the dunes.
Loess: unconsolidated, wind-deposited silt and dust that forms soil.
- Large areas of the world’s agriculture are found in the areas of loess deposition.
- The central US wheat belt has large deposits of loess that was largely derived from erosion by ice-age
glaciers.
Dust devils: Localized heating and associated convection can develop into small scale vortices.
- These vortices are created from “rapidly rising bubbles” of hot air and greatly resemble “tornadoes”.
- Dust devils have no formational relationship to rainstorm-associated tornadoes.
Mars have dunes and dust devils. Just like Earth; Mars has large collections of various types of dunes
including barchan dunes.
- Dust storms sometimes cover the entire Martian planet.
People who say it cannot be done should not interrupt those who are doing it – Anonymous
Stabilized Sand Dunes and Others
- Most sand dunes areas of the western US are stabilized by grass and shrubs
- Southwest Colorado is the site of 750 feet tall sand dunes
- Large sand dunes can eventually cover up entire towns
-In Namibia (South Africa) are large star dunes more than 1,500 feet tall
Singing Sands
- Deserts with very large dunes can produce “booming or singing” sounds by the sands sliding down or
avalanching down the sides of large dunes.
Wind Power Generation in America
- Coal generates about 49% of the US electricity production
- Other renewable energy sources (2.4%) includes wind power
- One of the earliest “wind farms” is at Tehachapi, CA
- Texas is the largest producer of wind-generated electricity, with the largest county being Taylor
County.
- The Corpus Christi area is rapidly becoming a large wind generator area. Taft has a large wind farm.
- Constant winds for power generation are a problem: the US average time of year that wind can
produce electricity is only 20% - 25% (rarely 40%)
- The times of the year with the least winds are the middle of the summer and the middle of the winter.
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- The US subsidies for wind electricity is about $23.34 MWH and would be non-competitive without
taxpayer payments; average US household added expense for wind turbines is about $600/year
- It takes about 190 wind turbines to equal the output of one small coal-fired generating plant!
-Wind turbines do interfere with radar images, a problem for airports
Dark areas are areas of more constant winds for turning the wind turbine blades
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DROUGHTS. Droughts have been recorded as a problem in Texas since Spaniards explored the area.
Álvar Núñez Cabeza de Vaca found a population of soil tillers near the site of present-day Presidio,
where it had not rained for two years. Regarding the white man as a god, they begged him to tell the
sky to rain. In 1720 a summer dry spell in Coahuila killed 3,500 of the 4,000 horses that the Marqués
de Aguayo, governor of Texas, was prepared to bring to Texas. A drought in Central Texas dried up
the San Gabriel River in 1756, forcing the abandonment of a settlement of missionaries and Indians.
Stephen F. Austin's first colonists also were hurt by drought. In 1822 their initial food crop of corn died
from lack of moisture. Each decade since then has been marked by at least one period of severe
drought. Associated with dry times are grasshopper plagues, brush and grass fires, sand and dust
storms, crop failures and depression, livestock deaths, disease resulting from insufficient and impure
drinking water, and migrations of citizens from parched territory.
Information concerning pioneer-day droughts is sketchy because of the absence of official statistics;
but data on some droughts, especially those during the nineteenth century, can be compiled from
individual complaints recorded in newspapers, diaries, and memoirs. In 1883 Texas opened its western
school lands, drawing thousands of immigrant farmers to the area. One of the worst droughts in Texas
history occurred in 1884–86, causing most of the farmers to fail and to return to the East.
In later years official detailed recordkeeping makes possible a better understanding of the
geographical distribution of droughts. Drought occurs when an area receives, in a given year, less than
75 percent of its average rainfall. The number of drought years in each of ten geographical areas of
Texas in the 100 years between 1892 and 1992 was as follows: Trans-Pecos, sixteen years; lower Rio
Grande valley, seventeen; Edwards Plateau, seventeen; South Central, fifteen; Southern, fifteen; North
Central, twelve; Upper Coast, thirteen; East Texasqv, ten; High Plains, ten; and Low Rolling Plains,
eight.
There has been at least one serious drought in some part of the state every decade of the twentieth
century. The most catastrophic one affected every part of the state in the first two thirds of the 1950s. It
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began in the late spring of 1949 in the lower valley, affected the western portions of the state by fall,
and covered nearly all Texas by the summer of 1951. By the end of 1952 the water shortage was
critical; Lake Dallas for instance held only 11 percent of its capacity. Spring rains in 1953 gave some
brief respite to Northeast Texas. In the Trans-Pecos, however, only eight inches of rain fell the entire
year of 1953, and the drought grew worse from 1954 to 1956. Streams only trickled or dried up
completely. The drought ended abruptly in the spring of 1956 throughout Texas with slow soaking
rains.
There were several less severe and shorter droughts in the 1970s. Most were ended by rain from
tropical storms. A massive heat wave in 1980 started a severe drought that blistered most of Texas
during the early 1980s. This gradually worsened until it reached extreme proportions in the Pecos
River valley during 1983. Even mesquite trees withered. It was ended in the western half of the state
by the residue of a north Pacific cyclone, which moved across Mexico. The drought shifted eastward in
1984, inflicting hardship on central and southern Texas; some towns ran out of water and others
enforced rationing.
On occasion, attempts to make rain artificially have been instituted by both private individuals and
public organizations, but these have met with little success. Constant improvement in moisture
conservation and utilization, however, has aided Texans in their struggle with drought.
BIBLIOGRAPHY:
Roy Sylvan Dunn, "Drought in West Texas, 1890–1894," West Texas Historical Association
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