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The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the California Gold Rush. Types of placer deposits include alluvium, eluvium, beach placers, aeolian placers and paleo-placers. [2]
Wind erosion of soil at the foot of Chimborazo, Ecuador Rock carved by drifting sand below Fortification Rock in Arizona (Photo by Timothy H. O'Sullivan, USGS, 1871). Aeolian processes, also spelled eolian, [1] pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets).
Cross-bedding in lithified aeolian sand dunes preserved as sandstone in Zion National Park, Utah. A lithified (consolidated) sand dune is a type of sandstone that is formed when a marine or aeolian sand dune becomes compacted and hardened. Once in this form, water passing through the rock can carry and deposit minerals, which can alter the ...
Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.
In sand and rock, they are rarely preserved except in arid regions. [10] Outside of arid regions, moving water - which is heavier and more erosive than wind - erases aeolian landforms. [11] Large basins are complex and there is often one or more non-aeolian process at work, including tectonics, glacial and alluvial forces. There are several ...
Layers of sand and snow deposited by wind on a beach of Lake Michigan. Niveo-aeolian or cryo-aeolian deposition is the process by which fine-grained sediments are transported by wind and deposited on or mixed with snow or ice. The wind sweeps the snow and sand grains into aeolian landforms such as ripples, and further sorts the snow and ice ...
The Kelso Dunes are composed of five stacked sets of dunes, each set corresponding to a period of climate change over the last 25,000 years. During dry climate episodes, a decrease in stabilizing vegetation exposed surface sand to wind erosion, which ultimately brought the sand to the dunes (most of the eastern part of the Kelso dunes was formed when nearby Soda Lake and Silver Lake dried into ...
The sequence is interpreted as a 1.8 billion year old shallow marine to coastal sequence which includes dunal deposits (aeolian), beach sands, offshore sand deposits and deeper water pelitic sediments.