Southwest Geographic Science Team

:: Sand Dune Morphology

Dune Field Evolution

A study of available aerial and satellite imagery combined with climate data affords us a unique view over time of the evolution of a sand-dune field and the landscape around it.

dunefield_extent

As the dunes move, they change the landscape, removing plants and mobilizing more sand

For the Grand Falls Dune Field, located approximately 30 miles east of Flagstaff, Az on the Navajo Nation adjacent to the Little Colorado river, 60 years of imagery records provide 7 snapshots in time of the change in size and location as the dune field begins it movement from the edge of the river northeastward.

Geo-rectified and layered into a Geographical Information System (GIS) this image data set provides the opportunity to study not just the advance of the dune field over time, but also the amount of landscape converted from stable and vegetated to vulnerable and barren between the dates of each image.

Through analysis of over 50 years of  wind, temperature, precipitation data from weather stations nearby, we can build insight into the influence of climate and drought into the mobility of the sand dune field and its effects on the surrounding landscape. Understanding the relative influences and potential time lag effects of these parameters is critical for knowing how the fluctuations in climate patterns, both short and long-term change the landscape.

In the plots below we can see correlations in time between an unusually wet period in the 1980s with an unusually calm period and a drop in dune field migration rate and growth. We also find an inverse effect in the 2000′s where the region has experience sustained drought, high wind activity, and accordingly rapid movement and expansion of the dune field.

Annual Precipitaton from 1960-2012 plotted as a normalized departure from the mean.

Annual Precipitaton from 1960-2012 plotted as a normalized departure from the mean.

Annual Wind Power from 1960-2012 plotted as a normalized departure from the mean.12ma_DP_ndm

Monthly Wind Power from 1960-2012 plotted as a normalized departure from the mean.

Dune field growth from 1953 to 2010 in sq. meters.

Dune field growth from 1953 to 2010 in sq. meters.

Preliminary analysis of these data sets reveals potential correlations between wet and dry periods and low and high wind activity. These correlated conditions: wet-calm and dry-windy, directly influence the vulnerability of landscapes to being shaped by the wind. Wet-calm years promote vegetation growth which can help stabilize the land surface and protect it from blowing, while dry-windy conditions tend to eliminate  stabilizing vegetation established and prevent new growth due to lack of moisture and higher winds.

Just how long  and to what degree the effects of either type of climatic phase influences the landscape is an important and open question which we are trying to understand. The implications of these effects are important because of the societal impacts that the changing landscape in the southwest has. Landscapes mobilized by wind move sand but also blow dust, both of which have significant economic and health impacts for the region. Mobile landscapes have poor nutrients, making agriculture, the primary livelihood in the region, difficult to sustain. Additionally, it has been recently shown that dust storm depositions on the colorado mountains, often originating from this region, dramatically change the timing and severity of spring snow melt influencing the availability of water resources for the entire southwest for the rest of the year.


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