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Proactive disclosure Print version   | |  Sand Dune & Climate Change Studies in the Prairie Provinces Past Dune Activity
In addition to understanding the historical changes in land cover, it is important to understand the changes in dune activity that have occurred in pre-settlement and geologic times. It is also important to determine the causes of these changes. In this respect, drought appears to have played a major role in dune activity and land-cover change in the past. Pre-settlement Dune Activity in the Great Sand Hills Region Geologic investigations in the Great Sand Hills region have determined when stabilized sand dunes were last active (by determining the last time sand was exposed to sunlight). These studies have revealed that widespread sand dune activity began around AD 1800 and continued, at levels higher than observed at any time in the 20th century, for a period of about 80 years. Additional data from tree-ring records in the Cypress Hills and in the Rocky Mountain foothills indicate that the most likely cause of this widespread activity was below-average precipitation during much of the 1700s, culminating in drought in the 1790s. It further appears that dunes in this area have been stabilizing from this event throughout the 19th and 20th centuries. The most important conclusions from this study are that: i) droughts occurring in pre-settlement times (eg. 1790s) have been more severe than any in historic times; ii) these droughts have had significant impacts on the landscape, which may require many decades, if not centuries, to recover; and iii) the magnitude of the impact of drought also depends upon the climatic conditions preceding the event. Source: Past Dune Activity in the Brandon Sand Hills, Manitoba Geologic studies have been conducted in the Brandon Sand Hills of southwestern Manitoba to determine when dune activity and stability occurred in the geologic past. These studies investigated past soil development and determined the ages of soils buried in dune deposits. The ages revealed that the area had been subjected to recurrent intervals of dune activity and stability in the past 5000 years. Notable periods of soil development occurred around 500 to 600, 1000 to 1400, and 2000 to 2300 years ago, with major periods of dune activity occurring around 300, 800, 1800 and 3500 years ago. The episodes of dune activity may correspond to periods of regional drought, whereas the buried soils indicate periods of increased moisture availability and stabilization by vegetation. It is also significant to note that most of the Brandon Sand Hills are presently stabilized by forest vegetation cover. An exception is the Spirit Sand Hills area which is presently active, but is in the process of stabilizing. Dune activity in this area may be attributed to pre-settlement droughts that were more severe than those in post-settlement times. The rapid stabilization of these dunes may also be related, in part, to the spread of forest cover over the past few hundred years.
Source: Earlier Dune Activity With the exception of the Athabasca Sand Dunes, which is the largest region of active dunes in Canada, most of the sand dunes in the northern parts of the Prairie Provinces are stabilized by forest vegetation cover. At present, little is known about when these dunes were last active or what the environment was like during their activity. In the most northerly regions of the provinces, it is believed that the dunes were probably active during deglaciation, when strong off-ice winds blew in a northwesterly direction. Dunes in other parts of this region are oriented towards both the northwest and the southeast, suggesting that two different, and opposite, winds moved the dunes in this area. It is generally inferred that all of these dunes were active between 8000 and 11000 years ago, and that most stabilized soon after deglaciation when the strong winds abated and vegetation colonized the region. Detailed geologic studies are presently underway to determine the timing of past dune activity and provide a better understanding of the environment that prevailed when these dunes were moving.
Source: Prairie Drought and Surface Winds from Eolian Deposits Geological information from sand dunes helps determine the timing and impacts of past droughts on the southern prairies. In addition, because sand dunes are formed by wind-related processes, they also provide direct evidence of wind directions during their time of formation. By combining the age of dune activity with their orientations, data from sand dunes can be used to determine records of past climatological and circulation patterns. The figure above depicts the pattern of sand dune orientations in the Prairie Provinces. Most of the dunes show that surface winds were blowing from the northwest when these dunes were active, much as they do today. Presently, however, most of these dunes are stabilized by vegetation, and the wind is unable to move them. Additional geologic studies will determine when these dunes were active, and what the past climate conditions were at the time of their activity. In southern Saskatchewan and Alberta, dune orientations indicate that winds have blown from the northwest and the southwest at different times. Today, most of the active dunes in this area are oriented with the winds from the southwest, and it is these winds that bring most of the dry conditions responsible for droughts on the prairies. Further studies will help to determine how circulation patterns have changed over time in this drought-prone part of the Prairie Provinces.
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