Foredune Erosion Along the Southern Shores of Lake Michigan During
2018-2021 High Lake Levels
Abstract
From January 18, 2013 (175.16 m a.s.l.) to September 8, 2020 (177.82 m
a.s.l.), Lake Michigan experienced its fastest and highest rise (2.67 m)
since 1860 when instrumental measurements began. Extensive foredunes
that developed since the last high lake levels in 1997 began eroding at
fast rates. This study focuses on coastal morphodynamics along the 800 m
coast within central Indiana Dunes State Park on Lake Michigan’s
southern shores from January 2018 to January 2021. Throughout 2018, the
easternmost foredunes exhibited the most erosion, totaling 4.25 m of
linear loss. The central foredunes lost 2.16 m, and the westernmost
foredunes lost only 1.79 m in width. An estimated 18.3 cubic meters of
sand per 1 meter of coast was eroded from the foredunes and transferred
to the backshore and foreshore. The lake levels were 6 - 42 cm higher in
2019 than in 2018 and amount of foredune erosion in 2019 was
significantly higher than in 2018. The easternmost foredunes recorded a
9.5 m shortening, the central foredunes lost 1.84 m, and the westernmost
foredunes lost only 0.6 m in width. A total of 27.51
m3 of sand per linear meter of coast was removed from
the foredunes and transferred to the dry or submerged part of the beach.
Lack of shelf ice along the shore, still rising lake levels, and
convective storms triggering meteotsunamis changed the foredune erosion
pattern in 2020. Erosion became most vigorous in the downdrift central
and western study areas. From January through September 2021 Lake
Michigan levels were 19 cm higher than in 2019. The total volume of
eroded foredune sand (64.42 m3/m) in 2020 was more
than double that of 2019 and almost quadruple that of 2018. Along the
200 m of coast in the central study area, the foredunes were completely
eroded, losing 13.2 m in width. The foredunes in the western study area
suffered extensive (11.2 m) erosion and were reduced to a total width of
6.8 m. Significant (7.8 m) erosion in the eastern study area reduced the
foredunes to 8.85 m in width. After foredune erosion events, the beach
rapidly recovered and maintained its width as the shoreline migrated
landward.