THE GREAT SAND DUNES

By Amalia McCoyGEO 111

Spring 2012

The Great Sand dunes of Colorado are the tallest in North America.

Rising about 750 feet Covering roughly 30 square miles

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

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

SLIP FACE The steeper leeward face of a sand dune

Image taken from: http://www.geocaching.com/seek/cache_details.aspx?guid=c93e835c-617b-4c33-bc61-1e2b484e267a

•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.

STAR DUNES

• Formed by multidirectional winds

•Have 3 or 4 arms

•Large pyramid shape dunes

BARCHAN DUNES

• form in places where there is limited sand and a constant wind direction

•crescent-shaped dunes that concave downwind

•Face the prevailing wind

Image taken from: http://www.nps.gov/grsa/naturescience/images/star_dune_formation.jpg

Image taken from: http://www.indiana.edu/~geol116/Week11/dunes2.jpg

•become aligned together along a plane perpendicular to the wind

•Occur where the supply of sand is greater than that of where barchans are formed

•Face the prevailing wind

Image taken from: http://web.arc.losrios.edu/~borougt/DesertDiagrams.htm

SEIF DUNES

Image taken from: http://icons-ak.wunderground.com/data/wximagenew/e/Eaglz/196.jpg

Image taken from: http://giltphoto.com/images/Colorado/Great%20Sand%20Dunes%20National%20Park/GreatSandDunes35w.jpg

Image taken from: http://digital-desert.com/natural-formations/SDGfig4.gif

•Linear or longitudinal dune

•Represents an intermediate direction between 2 dominate wind directions, blowing from one direction part of the year and another direction the rest of the year

•Usually parallel

TRANSVERSE DUNES

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

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

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_monu

ment.html http://web.ncf.ca/jim/sand/overview/grainflowAnimation.gif http://www.geocaching.com/seek/cache_details.aspx?guid=c93e835c-617b-4c3

3-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%2

0Park/GreatSandDunes35w.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