1. THE GREAT SAND DUNES
By Amalia McCoy
GEO 111
Spring 2012

2.  The Great Sand dunes of Colorado are the tallest in
North America.
 Rising about 750 feet
 Covering roughly 30 square miles

3. EARTH’S NATURAL PROCESS
 Formed by sand and soil deposits of the Rio Grande
and other streams and smaller rivers which flow into
the Rio Grande
 Western winds picked up the sand and soil deposits
from the River’s flood plain
 The wind loses power right before crossing the
Sangre de Cristo Range
 The sand was deposited on the eastern edge of the
valley
 The wind changes the formation and shapes of the
dunes daily

4. AEOLIAN DEPOSITION
Definition: Sand and dust moved by the wind
are eventually deposited when the wind dies
down.
Image taken from: http://web.ncf.ca/jim/sand/overview/grainflowAnimation.gif

5. SLIP FACE
 The steeper leeward face of a sand dune
•Wind erodes the windward
side of the dune which force
the grains of sand up and over
the crest to be deposited on
the other side
•Maintains an angle of 32
degrees- 34 degrees.
Image taken from: http://www.geocaching.com/seek/cache_details.aspx?guid=c93e835c-617b-
4c33-bc61-1e2b484e267a

6. STAR DUNES BARCHAN DUNES
• Formed by multidirectional winds • form in places where there is
limited sand and a constant wind
•Have 3 or 4 arms direction
•Large pyramid shape dunes •crescent-shaped dunes that
concave downwind
•Face the prevailing wind
Image taken from:
http://www.nps.gov/grsa/naturescience/images/star_dune_form Image taken from: http://www.indiana.edu/~geol116/Week11/dunes2.jpg
ation.jpg

7. TRANSVERSE DUNES SEIF DUNES
•become aligned together along a plane •Linear or longitudinal dune
perpendicular to the wind
•Represents an intermediate direction
•Occur where the supply of sand is greater between 2 dominate wind directions, blowing
than that of where barchans are formed from one direction part of the year and
another direction the rest of the year
•Face the prevailing wind
•Usually parallel
Image taken from: http://icons-
ak.wunderground.com/data/wximagenew/e/Eaglz/196.jpg
Image taken from:
http://giltphoto.com/images/Colorado/Great%20Sand%20Dune
s%20National%20Park/GreatSandDunes35w.jpg
Image taken from: Image taken from: http://digital-desert.com/natural-formations/SDGfig4.gif
http://web.arc.losrios.edu/~borougt/DesertDiagrams.htm

8. FLUVIAL PROCESS
•The Medano Creek that flows next to the Sand
dunes, is an Intermittent Stream
•Intermittent stream- is known as a seasonal stream
where water flows for ONLY part of the year.
•When the water level is low the stream has braided
channels
•Braided channels- consisting of multiple interwoven
and interconnected channels that are separated by
low bars or islands of sand, gravel and other lose
debris.
•During the winter and wet seasons the stream fills up
•The stream carries and deposits sand
•Deposition- whatever is picked up must be set down

9. DEFLATION AND ABRASION
 Deflation- the overall shifting of lose debris
either through air or along the ground
 Abrasion- wind forces the particles of sand
against the mountains with such force that a
sand blasting effect takes place and erodes the
surface of other rocks and the Sangre de Cristo
Mountains.
 The landscape is constantly changing

10. BIBLIOGRAPHY
 http://en.wikipedia.org/wiki/Great_Sand_Dunes_National_Park_and_Preserve
 http://www.indiana.edu/~geol116/Week11/wk11.htm
 http://mycolorado.org/sand_dunes.html
 http://www.americansouthwest.net/colorado/great_sand_dunes/national_monument.html
 http://web.ncf.ca/jim/sand/overview/grainflowAnimation.gif
 http://www.geocaching.com/seek/cache_details.aspx?guid=c93e835c-617b-4c33-bc61-
1e2b484e267a
 http://www.nps.gov/grsa/naturescience/images/star_dune_formation.jpg
 http://www.indiana.edu/~geol116/Week11/dunes2.jpg
 http://giltphoto.com/images/Colorado/Great%20Sand%20Dunes%20National%20Park/Gre
atSandDunes35w.jpg
 http://web.arc.losrios.edu/~borougt/DesertDiagrams.htm
 http://icons-ak.wunderground.com/data/wximagenew/e/Eaglz/196.jpg
 http://digital-desert.com/natural-formations/SDGfig4.gif