Figure 10.32: This crescent shaped dune forms from constant winds moving sand over hard
ground. ( 35 )
Loess
In many parts of the world, the finest grains of windblown silt and clay are deposited layer on
layer, covering whole regions with these tiny particles (Figure10.33). Geologists call these
depositsloess,which comes from the German word ‘loose.’ These deposits form downwind
of areas of glacial outwash or desert areas. There are extensive loess deposits in China where
deserts are the original source for these fine grained, windborne particles. One unusual
characteristic of loess deposits is their ability to form nearly vertical cliffs, without grains
sliding or slumping down the face. In China, people once built homes directly into these
deposits because they are easy to dig into and they keep their shape. Loess deposits are also
the source of wind transported materials that make very fertile soils in many regions of the
world.
Much of the fine grained mud that covers the deepest parts of the ocean floor comes from
silts and clays brought there by winds from the land. These tiny particles are easily carried
long distances by wind. Once they are deposited on the water surface, they settle ever so
slowly to the deep ocean floor, forming brown, greenish or reddish clays. Another source
of windborne particles is volcanic activity. Explosive volcanoes eject volcanic ash and dust
high into the air, sometimes reaching the stratosphere. Once these fine grained particles
are airborne, they can travel hundreds or thousands of kilometers. Regions closest to the
volcano are the areas with thickest deposits, but volcanic ash has even completely circled
the Earth in extremely violent eruptions like Krakatau in 1883. Windborne volcanic ash can
produce spectacularly beautiful sunsets, as well as decreasing worldwide temperatures, as
ash and dust block out incoming sun’s rays.