THE PICTURES AND DIAGRAMS IN THIS PRESENTATION DO NOT BELONG TO ME. This information and presentation is being used for educational purposes only.

1. Great Sand Dunes National
Monument

2. • Located between the San Juan and Sangre de Cristo
Mountains in Southwestern Colorado’s San Luis
Valley
• Over 12,000 to 130,000
years old (exact time they formed is unknown)
• Approximately 42,000 acres
• Composed of black magnetite, pink feldspar, red and
tan sandstone, green epidote, white quartz, and
many other minerals.

3. Medano Creek
Fluvial Process
• Seasonal stream that runs through the national
monument
• Created from mountain run off and seasonal rain,
this determines the volume of flow.
• Moisture from the creek keeps dunes stabilized so
they don’t move
• “Conveyor belt for sand”- flow carries sand
downstream and when the creek dries up the wind
blows the sand back to the dunes

4. Different flows of Medano Creek
Drying up Light Flow
Heavy Flow

5. Wind (aeolian) Transportation
Arid Land
• Dunes are created by a combination of wind patterns.
Northeast wind blows strongly across the valley, weaker
winds blow southwest through a gap in the mountains
• Particles are moved by saltation and traction or in other
words bounced and rolled
• The surface layer moves slowly downward as a result of
saltation, this is called creep
• When the sand is deposited (known as aeolian
deposition) it creates a sand dune

6. Aeolian Transportation Diagram

7. Different Types of Dunes
Barchan
Star Dune
Seifs Transverse Dunes

8. Where all the Sand Came From
Glacial Modification of Terrain
• During the Pleistocene Epoch the San Luis Mountains were covered
in glaciers
• Relatively warm summers during this time and the melting glacier
seasonally flooded the valley
• Glacial plucking occurred as the glaciers moved down the mountain
which is when the glacier picks up rocks and sand
• Meltwater carried tons of sand that the glaciers had scoured from
the mountains and deposited it in an alluvial fan
• Winter winds carried the sand across the valley
• The Sangre de Cristo Mountains blocked the wind and the sand
piled up forming the dunes.

9. Glacier of a Mountain Glacial Plucking Alluvial Fan
Caused from Meltwater
Sand Dunes are Formed Wind Blowing and
Moving Sand