20,000 Kilometers Over Death Valley: The GPS View of the Sliding Rocks

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20,000 Kilometers Over Death Valley The GPS View
of the Sliding Rocks

• Paula Messina
• Geology Department
• San José State University

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Racetrack Playa Physical Setting

• 1131 meters
• 4 km. (north-south) 2 km. (east-west)
• Surface sand, silt, clay desiccation polygons

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February, 2001 Seven Inches of Snow
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Ponding Water September, 1997
Grandstand
Ditch
Racetrack Road
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Sliding Rocks
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Why Do Rocks Slide?

• Ice rafting?

• Wind alone?

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What is the Complete Network?

• Does non-parallelism among trails imply wind
  alone?
• How can all the trails be mapped?

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Does a Rocks Character Contribute to its
Activity?

• Do rounder rocks inscribe more-sinuous trails?
• Do larger (more massive) rocks produce shorter
  trails?

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Global Positioning System to the Rescue

• Full operational capability April 1995

• 24 satellites
• 20,000 km. (12,000 mile) orbits
• 24 hour global coverage
• Sub-meter accuracy

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How Does GPS Work?
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Mapping Mission

• July 16 - 23, 1996
• 162 rocks/trails
• Two field mappers
• Human digitizers walked over 100 km.

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Cartographic Entities
Points
Lines
Areas
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• In-field Data Download
• Post-processed differential correction
• Export to ArcView GIS Shape File format
• Export to MS Excel for Quantitative Analyses

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Final Map

• Predominant motion SW-NE (slightly uphill)
• Trail length ? f (rock size)
• Trail straightness ? f (rock shape)
• Parallelism is
• the exception not
• the rule.

Inferred Wind Rose
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Plots Showed No Statistically-Significant
Correlations
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What Factors Control A Rocks Ultimate Distance
Traveled?

• Trail length appeared spatially controlled
• (see following slides)

Image and trail map for Diane, the rock that
inscribed the longest trail
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What Factors Affect Trail Straightness?
Start?End Distance

• Straightness

Total Trail Length
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What Factors Control A Rocks Ultimate Path?

• Trail straightness appeared spatially controlled

Crooked trails
Straight trails
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What Factors Control A Rocks Ultimate Path?

• GIS-Generated Aspect Map

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Intervisibility Ray Tracing

• Cross-section
• Map View

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Intervisibility Maps for Representative Rocks
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Trail Character Correlates to Surrounding Terrain
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The Racetrack A Mosaic of Microclimates

• Wind tunnels
• Turbulence

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The Final Word How Can Rocks Converge?
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More Information on the Sliding Rocks

• Paula Messinas Racetrack Web Site
• Smithsonian magazine July, 1999
• California Geology January, 2001
• Savage Planet Episode IV Extremes

Discovery Channel Onlines Dancing Rocks Web Site