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Great Sand Dunes National Park Capstone
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  • 1. GEOMORPHOLOGY:THE GREAT SAND DUNES NATIONAL PARK GEO 111-500 THOMAS RUSSELL
  • 2. LANDFORMSGEOMORPHOLOGY LANDFORM PROPERTIES• “Geo” = “Earth” • Structure: Composition and orientation• “Morph” = “Change” • Process: Events that have produced• “Ology” = “Write about” the landform as it appears currently• Study of landform • Slope: Angular relationship between origin, properties, and changes over the landform face and the earth’s time. Including… surface • Structure, process, slope, drainag • Drainage: “…[M]ovement of water e (from rainfall or snowmelt), either over • Driven by internal or external the Earth’s surface or down into the processes soil and bedrock.” 1 7/26/2012 2
  • 3. GEOGRAPHIC LOCATION35 Miles Northeast of Alamosa, Colorado in the San Luis Valley. Park is located at37.73434, -105.640411 or 37 ̊ N 42’ 59.24” , 105 ̊ W 40’ 56.30”. Figure 1Winds blow sediment from the west side of the valley to the east side, where it accumulates asthe sand dunes at the base of the Sangre de Cristo Mountains. 7/26/2012 3
  • 4. THE GREAT SAND DUNES LANDFORM PROPERTIES• Structure: Sand in the dunes is derived primarily from the San Juan Mountains• Process: Large rocks in the mountains undergo erosion, and the resulting smaller sediment is carried by the Rio Grande River to the San Luis Valley floor and then by the wind across to the sand dunes• Slope: Due to the fine-grained nature of the sand, the dunes form with low angles of repose and broad parabolic summits • Angle of Repose: Concerning the formation of sedimentary hills; Angular threshold at which downward pull of gravity is offset by the static friction of the piled material. Disturbance of the balance will cause the material to slide downward.• Drainage: Runoff from the westerly Sangre de Cristo Mountains encapsulates the sand dunes with Sand Creek on the north and Medano Creek on the south; both streams wash away sediment as the dunes attempt to migrate across 7/26/2012 4
  • 5. GEOLOGIC STRUCTURE Figure 2 Figure 3• Watershed: Main source of water for the sand • Precipitation in the watershed to the east runs dunes—the Sangre de Cristo Mountains off in a series of streams around and under the• Dunefield: Approximately 30 square miles in dunefield area, this is where the tallest dunes are found • Water sinks under the dunes in a process• Sand Sheet: Accounting for nearly 90% of the known as infiltration. It continues flowing sand deposits in the National Park, the sand sheet outward under the sand sheet contains small dunes and vegetation 2 • Water can be found mere inches below the surface of even the highest the dunes and even• Sabkha: Found where the water table meets the closer to the surface in the sand sheet surface, creating marshlands. “The Sabkha forms…when the water evaporates away in late • Mineral deposits in the Sabkha can either be summer, [and] minerals similar to baking soda returned to the dunefield by winds or can be cement sand grains together into a hard, white flushed further down the valley by fluvial forces. crust” 3 7/26/2012 5
  • 6. BUILDING THE GREAT SAND DUNESMechanical weathering in the form of frost wedging beginsdisplacement of large rocks Rock can also be weakened through biological weathering from lichens as the organisms extract minerals from the rock Mass wasting on mountainsides in the form of mudflows, landslides, or rock falls can move large amounts of material Fluvial forces (e.g. rainfall, snowmelt, rivers) flush rocks down mountains and through valleys, further weathering the rocks Once eroded down the Rio Grande River to the valley floor, much of the finer sediment washes up on shore where it can be swept away by the prevailing southwesterly winds 7/26/2012 6
  • 7. MECHANICAL WEATHERING: FROST WEDGING • Occurring across the mountains surrounding the San Luis Valley, frost wedging begins breaking down large rocks • Lichen can also form on rocks and weaken their Figure 4 structural integrity by extracting minerals. This is called biological weathering • Once rocks are weathered down to a manageable size, mass wasting is the next erosive process 7/26/2012 7
  • 8. MASS WASTING & EROSION • Mudflows occasionally • Erosion occurs by fluvial forces and gravity until occur when a slope the fine sediment reaches the valley floor where it becomes so quickly is then taken by the wind oversaturated that the ground is unable to • Fluvial forces include absorb water. These can rainfall, snowmelt, streams, and rivers, all of which move large amounts of also further break down rocks sediment as well as large • Erosion eventually leads the sediment down to the rocks San Luis Valley floor where it can wash up on the shore, dry out, and be swept away in the wind. • Landslides are the least • Ultimately, the wind carries the sediment to the common but can occur if east edge of the valley and up to the base of the a given area not Sangre de Cristo Mountains. structurally sound is subjected to sudden stimuli • Rockfalls occur when Figure 6 rocks become dislodged and fall downslope; the resulting pile of rock is called talus. Rockfalls can be the result of frost wedging, repeated weathering from rainfall, or sudden stimuliFigure 5 7/26/2012 8
  • 9. SEDIMENT RECYCLING • Winds build up sand dunes from west to east while water washes them down from east to west • With Sand Creek to the north and Medano Creek to the south, the sand dunes are slowly eroded back into the San Luis Valley as they attempt to migrate across the streams • This is the process of sand recycling in the Great Sand Dunes National ParkFigure 7 7/26/2012 9
  • 10. BEYOND THE EXTERNAL PROCESSES• Due to the unfathomable nature of geologic time, the present geologic activity of the region seems to be controlled by external processes. However, it will ultimately be internal processes that control the sand dunes• “Over the last 25 million years, a gigantic rift has ben opening up at the southern end of the Rocky Mountains. It stretches over 160,000 square miles and is known as the Rio Grande Valley…as the rift opens, the mountains to each side crumble into the valley.” 4• Rifting is caused by a sinking and thinning of the earth’s crust by “…lava from a source deep in the mantle [that] periodically spreads across the surface. In the near geologic future, several million years or so, a youthful ocean basin may occupy this area.” 5 Figure 8 7/26/2012 10
  • 11. DEMISE OF THE SAND DUNES: RIO GRANDE RIFT Figure 9The San Luis Valley resides on the Rio Grande Rift and over the next several million years, as therift deepens and widens, the Sangre de Cristo and surrounding mountains will erode, and theGreat Sand Dunes will be lost to the wind 7/26/2012 11
  • 12. IN THE DISTANT GEOLOGIC FUTURE….Figure 10 Figure 11 • Millions of years in the • The sediments currently composing the Great future, North America could Sand Dunes will eventually find their way into the ocean, become compacted into the oceanic split along the Rio Grande Rift crust, and be subducted back into the mantle • The resulting in-land sea would • As the oceanic crust melts in the mantle, the be similar to the ancient sea sediments that once sat atop the Great Sand that existed some 70 million Dunes will be liquefied and eligible to be returned years ago to the surface in a volcanic eruption 7/26/2012 12
  • 13. TOURISM: A CHANCE TO LEARN AND SEE GEOGRAPHY IN ACTION • Daily Entrance Fee: $3.00 per adult, children are always free 6 • Annual Pass: $15.00 per adult, good for whole family free of charge • Visitor’s Center is full of educational plaques, diagrams, videos, books, and experiments Figure 13 Figure 12 7/26/2012 13
  • 14. BIBLIOGRAPHY1. Tom McKnight. McKnight’s Physical Geography (New Jersey: Pearson Prentice Hall, 2011), 367.2. Stephen Trimble. Great Sand Dunes National Monument: The Shape of the Wind. (Tucson: Western National Parks Association, 2000), 6.3. National Park Service. “Great Sand Dunes System.” http://www.nps.gov/grsa/naturescience/sand_system.htm. (Accessed July 18, 2012).4. “How the Earth was Made: The Rocky Mountains.” http://www.history.com/shows/how- the-earth-was-made/episodes#slide-9. (Accessed July 18, 2012).5. “A Tapestry of Time and Terrain: The Rio Grande Rift.” http://tapestry.usgs.gov/features/28riogrande.html. (Accessed July 18, 2012).6. National Park Service. “Fees & Reservations.” http://www.nps.gov/grsa/planyourvisit/feesandreservations.htm. (Accessed July 18, 2012). 7/26/2012 14
  • 15. BIBLIOGRAPHY (CONT.)Figure 1: Google Maps: San Luis Valley, Colorado. https://maps.google.com/maps?hl=en&q=great+sand+dunes&ie=UTF-8. Accessed July 18, 2012.Figure 2: Great Sand Dunes System. http://www.nps.gov/grsa/naturescience/sand_system.htm. Accessed July 18, 2012.Figure 3: Great Sand Dunes Cross-Section water flow. http://www.handsontheland.org/grsa/resources/curriculum/high/images/hydro_cycle.htm . Accessed July 18, 2012.Figure 4: Frost Wedging. http://itc.gsw.edu/faculty/bcarter/physgeol/weather/mechwth.htm. Accessed July 18, 2012.Figure 5: Weathering and Erosion & Groundwater. http://www.semi.sd36.bc.ca/mleziva/unit4/U04L01.htm. Accessed July 18, 2012.Figure 6: Weathering and Erosion & Groundwater. http://www.semi.sd36.bc.ca/mleziva/unit4/U04L01.htm. Accessed July 18, 2012.Figure 7: Great Sand Dunes and Pike’s Peak Colorado. http://jugalbandi.info/2007/08/great-sand-dunes-and-pikes-peak-colorado/. Accessed July 18, 2012.Figure 8: Rio Grande Rift FAQ. http://cires.colorado.edu/science/groups/sheehan/projects/riogrande/faq /. Accessed July 18, 2012.Figure 9: Rio Grande Aquifer System. http://pubs.usgs.gov/ha/ha730/ch_c/C-text4.html. Accessed July 18, 2012.Figure 10: How the Earth was Made: Rocky Mountains. http://www.history.com/shows/how-the-earth-was-made/episodes#slide-9. Accessed July 18, 2012.Figure 11: Types of Collisions. http://www.geosci.usyd.edu.au/users/prey/Teaching/Geol-3101/EReport03/GroupD/Report1/web%20pages/assignment_1.html. Accessed July 18, 2012.Figure 12: Great Sand Dunes, N.P. http://alpineadventures.blogspot.com/2010/07/great-sand-dunes-np.html. Accessed July 18, 2012.Figure 13: Medano Creek. http://usparks.about.com/od/parkphotographs/ig/greatsanddunes/grsa-medano_creek_dunes_her.htm. Accessed July 18, 2012. 7/26/2012 15