Late 18th century drought-induced sand dune activity, Great Sand Hills, Saskatchewan

Geomorphic evidence and optical ages from seven locations indicate that wid espread dune activity occurred within the last 200 years in the Great Sand Hills region of southwestern Saskatchewan. Optical ages (n = 36) define an interval of dune activity bracketed by the earliest age of back ridges in t he Seward sand hills (185 +/- 8 years) and the average age of stabilized du ne heads (about 105 years). During this interval, parabolic dunes were acti ve in all areas studied. These ages indicate that the most recent interval of activity was initiated about AD 1800, and continued at a level higher th an present for approximately 80 years. The most likely cause of dune activa tion was lower-than-average precipitation (relative to 1960-1991 values) th rough the 1700s, culminating in drought in the late 1700s, as evidenced in dendroclimatic records from the Cypress Hills and from the Rocky Mountain f oothills. Dunes affected by such climatically induced regional activity req uire many decades to restabilize. Historical observations show that dunes i n this area have been restabilizing throughout the 20th century. For the so uthern Canadian Prairies, a region with serious concerns about the implicat ions of global warming, this study highlights the sensitivity of sand dunes to drought and cumulative moisture stress.