Eolian History of North America

The word "eolian" (or "aeolian" as spelled in many countries) comes from the Greek "Aeolus." Aeolus, in Greek mythology, was the god of the winds. "Eolian" thus refers to any process of sediment entrainment, transport and deposition by wind. Study of eolian processes and sediments is a part of the disciplines of geomorphology, sedimentology and paleoclimatology.

Eolian sediments fall into three broad categories: eolian sand, loess, and airborne dust:

Eolian sand is the coarsest particle size (>50 microns (µm)) and on the landscape forms dunes or relatively flat deposits called sand sheets. Large fields of active sand dunes are usually found in arid climates.

Figure 1a: Examples of active sand dunes from the USA and Egypt

Algodones dunes

(a) Algodones dunes, Colorado Desert, southern California, USA

Dunes in Sinai Desert

(b) Northern Sinai Desert, Egypt

(d) Great Sand Dunes National Park, Colorado, USA

Many semiarid climates have stabilized (vegetated) sand dunes that may have been active in a climate of the past and may become active again in the future.

Figure 1b: Examples of stabilized (non-active) sand dunes from Egypt, Canada, the USA, and the Bahamas

stabilized sand in northern Sinai Desert

(a) Northern Sinai Desert, Egypt

stabilized sand at Brandon Sand Hills

(b) Brandon Sand Hills, Manitoba, Canada

stabilized sand in Mojave Desert

Sand dunes in Bahamas

(d) Carbonate-cemented, oolitic eolianite ridge, East Street Cut, New Providence Island, Bahamas

stabilized sand at Nebraska Sand Hills

(e) Nebraska Sand Hills, USA

Loess is a geologic deposit composed dominantly of silt-sized (50-2 µm) particles, which are smaller than sand. Loess has the texture of flour or talcum powder. Loess usually forms thick blankets of material (some many tens of meters thick) over hundreds of square kilometers of landscape. It is the uppermost geologic deposit in the Midwest, Great Plains and northwestern United States, central and northern China, Europe, Argentina, and New Zealand. Loess, over time, forms very fertile soils which are important for agriculture. Ancient soils buried in loess deposits can tell us a great deal about past climates.

Figure 2: Examples of loess deposits from Alaska, Iowa, Nebraska (note buried soils, shown here as darker horizontal zones), and Arkansas

(a) Birch Hill, Alaska, USA	(b) Loveland, Iowa, USA
(c) Eustis, Nebraska, USA	(d) Crowley's Ridge, Arkansas, USA

Airborne dust is composed of particles that are very small, almost always less than 20 µm in diameter, and usually less than 2 µm. Airborne dust can travel thousands of kilometers and can even travel intercontinental distances. Dust from desert regions can be deposited in the oceans, into humid tropical or midlatitude ecosystems and soils, and on top of high-altitude mountain ranges.

Figure 3: Examples of dust storms from Alaska, the Canary Islands (see Fig. 4, also), and Israel

(a) Dust from the Delta River near Delta Junction, Alaska, 2004 (photo by E.A. Bettis)	(b) Dust from the Sahara on Lanzarote, Canary Islands, Spain, 2006 (photo by H.M. Roberts)
(c) Dust from the Sinai and Negev Deserts in southern Israel, 1981 (photo by D.R. Muhs)

Task 1, Eolian sand: to understand the processes responsible for sand dune activity in the U.S. and to assess the potential for reactivation of stabilized sand dunes in the U.S. under changing conditions of climate and land use

Task 2, Loess: to investigate records of natural climate variability recorded in loess deposits

Task 3, Airborne dust: to test hypotheses about the role of dust in climate change and to assess the importance of far-traveled, airborne dust in soil formation

Eolian History of North America

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