Paper No. 81-7
Presentation Time: 9:35 AM
THE GEOGRAPHY AND PROGRESSION OF BLOWOUTS IN THE COASTAL DUNES ALONG THE EASTERN SHORE OF LAKE MICHIGAN SINCE 1938
Coastal dunes are prominent features of the Lake Michigan shoreline, especially along the Lower Peninsula of Michigan. These dunes, perhaps the largest freshwater coastal dunes in the world, comprise a unique aeolian system because they developed under different conditions than coastal dune systems elsewhere and without tectonic or tidal activity. Blowouts, erosional features which scour existing dunes, are notable landforms in many dune systems, including those along Lake Michigan. Blowouts are often key indicators of natural and anthropogenic disturbances. These disturbances, which can include changes in precipitation, temperature, or the introduction of a built environment, can destabilize existing dunes and cause blowout formation. The late-Holocene geomorphic evolution of Lake Michigan’s dunes has been the focus of past research; less work has been conducted on these systems in the modern period. The work we present here attempts to address portions of this gap in knowledge. Here, we examine the blowouts of Lake Michigan’s eastern shoreline and determine how they have evolved since the 1930s. We conducted a spatiotemporal analysis of ~200 blowouts by comparing repeat aerial images of the Lake Michigan coast beginning in 1938. Using an unsupervised classification known as iso-clustering, we mapped blowout morphologies from aerial images at three intervals – 1938, 1988, and 2018. We then compared the blowout geographies through a technique known as a spatial–temporal analysis of moving polygons (STAMP) model, which allowed us to analyze how each individual blowout changes in time and space. Preliminary results show that since 1938 most blowouts are “healing” – or being stabilized through an expansion of vegetation. Moreover, we have not identified any new blowouts that have formed since 1938 along the ~500km shoreline or on any of the Lake Michigan islands. This suggests that the blowouts we have mapped could be artifacts of the drought conditions of the 1930s or perhaps the result of the stormier conditions during the Little Ice Age (1300−1900 CE). Our preliminary findings comport with recent regional studies which showed an expansion of vegetation over the last ~100 years in Lake Michigan dunes, resulting in further stabilization of this sensitive landscape. Our findings also agree with studies in Europe that have shown a trend toward dune stabilization since the Little Ice Age.