St. Anthony Dunes, Fremont County, Idaho

ST. ANTHONY DUNES, FREMONT COUNTY, IDAHO

 

The St. Anthony Sand Dunes

Eastern Idaho’s climate became warmer and drier. Lakes shrank, exposing fine sand. Persistent winds from the south-west blew the sand north-east across the lava plain visible in the lower left corner of the image. Dunes form only when sand encounters a soft surface or obstacle that prevents it from blowing away. The St. Anthony Dunes began to form when the sand reached the weathered mass of the Juniper Buttes, extinct volcanoes. Each individual dune forms a curve, with ends pointing north-east in the direction of the wind. This type of dune is a barchan dune, Arabic for ram’s horn. East of the volcanoes, the sand encountered another obstacle that kept it in place: more dunes. These older dunes, longitudinal dunes, are plant-covered sand dunes that formed in a previous, more arid climate, says Idaho State University geologist Paul Link. The longitudinal dunes formed on top of an old flood plain, from a branch of the Snake River, probably from sand blown from the river’s bank. The longitudinal dunes are long, dark stripes under the newer brilliant white dunes—layers of climate history visible at a glance. Jesse Allen and Robert Simmon - NASA Earth Observatory

 

 

GRAIN DISTRIBUTION CHARACTERISTICS (AGI CHART)

International Space Station 400mm Photograph Image credit:  Image Science and Analysis Laboratory, NASA Johnson Space Center

GRAIN SHAPE CHARACTERISTICS

(PREPARED BY GAMMA ZETA CHAPTER , SIGMA GAMMA EPSILON, KENT STATE UNIVERSITY - AGI CHART))

Roundness is the degree of smoothing due to abrasion of sedimentary particles. It is expressed as the ratio of the average radius of curvature of the edges or corners to the radius of curvature of the maximum inscribed sphere.

The sphericity of a particle is: the ratio of the surface area of a sphere (with the same volume as the given particle) to the surface area of the particle.

     
     

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