Weathering, Erosion, and Sedimentation

What is sand? Sand is a small sediment created over time by the weathering and erosion of rocks. It can be made of igneous, metamorphic, sedimentary, or mixed sediment.

Weathering The breaking down of rocks, soils, and minerals by environmental factors such as water, wind, glaciers, the freeze/thaw cycle, and acid rain. Which one of these factors do you think is chemical weathering? Which of these factors do you think are physical weathering?

Erosion The removal of soil, sediment, and rock fragments from the landscape.

Classification of Sand Sand grains are classified by the degree of rounding and sorting.

Rounding Sand Grains tend to become rounded the longer they are transported.

Well Rounded Poorly Rounded

Sorting As streams transport sediments, large particles fall out and are deposited first. This is called sorting.

Well Sorted Poorly Sorted

Sorting The more sorted the sediment, the farther it is from the source.

DUNE  (KELSO DUNES CALIFORNIA) Key to identification is the fine grained nature of the sand and the high degree of sorting.

PINK SAND DUNES STATE PARK UTAH PINK SAND DUNES STATE PARK UTAH.  Note the high degree of sorting, rounding and fine grained nature of this sample.

ALGODONNES DUNES CALIFORNIA ALGODONNES DUNES CALIFORNIA.  This dune (near the Colorado River) is fairly well sorted and sub rounded.  It is also fairly fine grained.

CANCUN MEXICO. This beach sand is composed of shell fragments CANCUN MEXICO.  This beach sand is composed of shell fragments.  In the high energy beach environment the shells are quickly broken and eroded.  The shells in this sample are even polished by agitation in the surf zone.  Notice also that this sand is only moderately sorted.

NAPOOPOO BEACH, HAWAII.   This beach sand shows the influence of the lava flows that make up the Hawaiian Islands.  The beach sand is dominated by olivine grains and basalt fragments.  The abundance of shell fragments clearly indicates its beach environment.

CHOLLA BAY, ROCKY POINT MEXICO Shell fragments are an important part of this sample.  This is a poorly sorted beach sand primarily because of the abundance of shell fragments.  There is also an abundance of quartz in the sample.  The source of the quartz is a nearby granite intrusion called Pelican Point.

TOPAZ WASH, TOPAZ MOUNTAIN UTAH This poorly sorted and angular sand is dominated by rhyolite sand grains.  The clear grains are topaz - not quartz.  The topaz has a well developed cleavage that distinguishes it from quartz.

SAN PEDRO RIVER, ARIZONA This is a classic example of a river (or fluvial) sand.  It is very poorly sorted and angular.  Quartz is the dominant mineral in the sample but there are grains of feldspar present.

RUBY RESERVOIR, MONTANA Sorry, no rubies, just garnets.  This sediment was taken from a small stream that empties into Ruby Reservoir.  It is very angular and poorly sorted.  The colorful, gemmy grains represent various hues of garnets.

DUNE  (KELSO DUNES CALIFORNIA) Key to identification is the fine grained nature of the sand and the high degree of sorting.