RECONSTRUCTING LAND-SURFACE PROCESSES AT THE HEART OF THE “DUST BOWL” DROUGHT, HAMILTON AND KEARNEY COUNTIES, SOUTHWEST KANSAS, USA

The 1930s Dust Bowl was an epic drought reflecting both extreme climate variability and human-induced landscape degradation. The dust generated during this event was a regional health hazard, exacerbated warming and increased hemispheric dust loads. The High Plains is the largest source of mineral dust aerosols in North America. Thus, a better understanding of land surface processes during the 1930s drought will yield insight on land-atmosphere interactions for severe droughts in the past and the future.

This study classifies land-surface changes from the first generation of black and white aerial photography taken August 17 and 25, 1936 and March 22, 1939, covering an area of ~250,000 km². The analysis of georeferenced mosaics evaluated the relative vegetation cover with varying amounts of eolian activity to infer particle sources from reactivated eolian landforms and/or adjacent agricultural fields. We identified seven spectral reflectance classes for the images; each class has specific attributes related to eolian surface processes, agricultural practices, vegetation cover and/or soil erosion and reflects the variable land surface response to the 1930s drought in SW Kansas. Time-series analyses of aerial photographs from 1936 and 1939 shows an increase of bare sediments in uncultivated area, coincident with an apparent decrease in particle source-area in cultivated areas. Dense vegetation expanded slightly by 1939 in cultivated areas, suggesting that natural eolian processes contributed substantially to sediment availability during the Dust Bowl.

Selection of stratigraphic studies was guided by aerial photographic analyses to identify areas with maximum denudation and deposition of eolian sand during the 1930s. There was noticeable sand availability on the topographically highest, antecedent barchanoid-ridge forms and stratigraphic studies focused on these land surfaces. The 1930s eolian sand was 1 to 3 m thick and deposited mostly in a sand sheet environment. These deposits gave OSL ages of ca. 70 ± 5 ka and bury an inceptisol, developed in eolian sand that yielded the OSL age of 200 ± 10 yr ago. These and other stratigraphic studies indicate that reactivation of antecedent dune fields occur on centennial timescales, with possibly more pervasive reactivation ca. 400 to 1000 years ago.