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...Muskegon, Michigan. From October through April each year, sand transport and dune surface changes were measured with erosion pins and sand traps. During the same time periods, surface conditions and microclimate were measured at the study area. During the summer months, dune conditions were observed and photographed at irregular intervals. Measurements and observations focused on the active foredune and established foredune ridge located between the lake and the large parabolic dunes common to Lake Michigan's east coast. Results show distinctly seasonal pattern to Lake Michigan coastal dune change. Aeolian processes are most effective during the late fall and winter when winds are strong and vegetation cover is at a minimum. Other variables that influence sand transport patterns are wind direction, surface moisture, ground-freezing, snow, ice and beach width. Despite considerable constraints, foredune growth was measured at 1.9-5 [m.sup.3] [m.sup.-1] yea[r.sup.-1], with yearly deposition at some foredune locations exceeding 30 cm. All wind-blown sand from the beach was captured by the foredune, but local redistribution of sand by wind occurs in active blowouts on the established foredune ridge. The measured dune activity takes place in the context of low lake levels; rates and types of coastal dune activity are expected to change with rising lake levels.
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INTRODUCTION
Lake Michigan coastal dunes are some of the most dynamic landforms in Michigan, undergoing significant changes over relatively short periods of time. The coastal dunes grow, change shape, and are destroyed as local winds move sand from one location to another. Processes of sediment entrainment, transport and deposition by wind are affected by surface moisture, vegetation, snow, ice, ground-freezing, and lake level fluctuations--variables that are typical of the moist, temperate dunes of the Great Lakes region.
As an important Michigan resource, the coastal dunes are valued for ecological, recreational, economic, and aesthetic reasons. Ongoing management and conservation activities require an accurate understanding of dune properties and behavior. However, little information is available on contemporary Lake Michigan coastal dune processes. The research summary below shows that a current momentum towards understanding coastal dune history has not been matched by studies on contemporary activity. The objective of this paper is to describe contemporary processes and change on Lake Michigan coastal dunes using the example of activity in P.J. Hoffmaster State Park near Muskegon, Michigan.
RESEARCH CONTEXT
The last decade has been an exciting time for those piecing together the history of coastal dunes along Lake Michigan's east coast. As some researchers have been constructing a Holocene record of lake levels based on cores from beach-ridges around the Great Lakes (Thompson and Baedke 1995, 1997; Baedke and Thompson 2000), other researchers have been identifying the sequence of coastal dune development using buried soils as indicators of dune stability followed by dune activity (Arbogast and Loope 1999; Loope and Arbogast 2000; Van Oort et al. 2001; Arbogast et al. 2002). The picture that has emerged refutes previously held assumptions that the large coastal dunes were products of rapid dune growth during the Nipissing high lake stage (approximately 5,500 years ago) followed by thousands of years in which the dunes remained essentially unchanged (for example, Dorr and Eschman 1970). Instead, Loope and Arbogast (2000) discovered that dunes on the northeast coast of Lake Michigan formed within the last 1,500 years and experienced numerous periods of activity that correspond to lake high stands recurring at ~150-year intervals. From Manistee, Michigan, south to Indiana Dunes National Lakeshore, buried soils point to an initial period of dune building corresponding to the Nipissing high stage or later at some locations (Arbogast and Loope 1999; Van Oort et al. 2001; Arbogast et al. 2002). The buried soils records indicate a long period of dune growth, probably lasting several thousand years, punctuated by brief periods of stability. Dune activity was followed by a period of stability, perhaps lasting as long as 1,500 years, before the current period of dune activity lasting 300-500 years (Van Oort et al. 2001; Arbogast et al. 2002). Studies are underway to add more dates and locations to the story of Lake Michigan coastal dune history.
In contrast to the research momentum generated by new information about coastal dune history, knowledge about contemporary Lake Michigan dune processes relies on classic studies with only a few recent quantitative measurements. Lake Michigan dunes are internationally known for the pioneering work by Cowles (1899) on ecological succession and Olson (1958a, b, and c) on the foredunes along the south shore of Lake Michigan. Olson examined relationships between wind-velocity profiles and sediment movement over dunes (Olsen 1958a), vegetation and dune formation (Olson 1958b), and changing lake levels and dune distribution and form (Olson 1958c). He concluded that active beach-margin dune ridges on the south shore of Lake Michigan maintain average deposition rates of 30 cm per year. Working in Indiana Dunes National Lakeshore thirty years after Olson, Olyphant and Bennett (1994) used wind data and a computer simulation to calculate that 3.8-7.3 [m.sup.3] [m.sup.-1] of sand are transported inland from the beach annually. Olyphant and Bennett (1994) note their calculated sand flux value is high compared to historical rates of 0.8 [m.sup.3] [m.sup.-1] [yr.sup.-1] between 3.2 and 0.5 ka, calculated from beach-ridge dune topography. On the Indiana dunes, wind and sand transport patterns are temporally and spatially variable because antecedent soil moisture, rainfall, snow cover and ground freezing affect transport rates (Bennett and Olyphant 1998). The topography of large blowouts affects wind flow patterns and resulting sand transport rates (Fraser et al. 1998), and different coastal dune subenvironments--such as a foredune compared to a parabolic dune--may have sand transport rates with orders of magnitude differences (Bennett and Olyphant 1998).
Research north of the Indiana border has not focused on small-scale processes. Lichter (1995) showed that beach-ridge dunes on the northeast shore of Lake Michigan record lake level fluctuations related to changes in late Holocene climate. Lichter's work focused on the timing of sequential dune development rather than rates of sand transport. In Ludington State Park, Brown and Arbogast (1999) explored digital photogrammetry as a method of monitoring coastal dune change. From sequential air photographs, they were able to discern directions of movement, identify areas of surface deposition or erosion, and estimate volumes of transport over a period of 22 years and at the scale of individual dunes. At smaller spatial and temporal scales, quantitative data on coastal dune activity on the east shore of Lake Michigan are not available.
Contemporary coastal dune studies have taken place at many locations besides Lake Michigan, including studies in the Great Lakes region (e.g., Davidson-Arnott and Law 1990; Law 1990), on the east and west coasts of North America (e.g., Gares 1990; Psuty 1990; Wiedemann and Pickart 1996; Giles and McCann 1997), and locations outside North America (e.g., Hesp 1984; Illenberger and Rust 1988; Sarre 1989; Carter and Wilson 1990; Arens and Wiersma 1994). A small number of the studies report annual volume changes to foredunes, with results ranging from 3 to 50 [m.sup.3] [m.sup.-1] [yr.sup.-1] (Illenberger and Rust 1988; Sarre 1989; Carter and Wilson 1990; Arens and Wiersma 1994). Actual sand transport rates compared to potential (calculated) rates may vary widely because vegetation, changing surface conditions, wind patterns, and variable sediment supply areas affect sand transport (Hesp 2002). As a result, a robust conceptual framework for understanding coastal dunes does not exist (Bauer and Sherman 1999), and studies on coastal dune evolution and variables governing coastal dune change are needed.
THE STUDY AREA
Study Location
P.J. Hoffmaster State Park is south of Muskegon, MI, on the east shore of Lake Michigan (Figure 1). The park has approximately 4 kilometers of Lake Michigan shoreline consisting of sandy beaches and coastal dunes. Coastal dunes range in size from relatively small, but dynamic, foredunes to large parabolic dunes which extend up to 0.5 km inland. East (inland) of the active dunes along the shoreline, the Hoffmaster dunes are stable and forested. Topographic maps...
NOTE: All illustrations and photos
have been removed from this article.
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