Bluff erosion along the east shore of Lake Michigan: Synergy between water levels and lithology
Abstract
Along the east coast of Lake Michigan, shallow to intermediate depth landslides are influenced by lake water levels, bluff ground water saturation, and lithology. The bluffs are composed of unconsolidated glacial tills interbedded with / overlain by glaciodeltaic sand and lacustrine silt and clay. These bluffs are experiencing toe erosion due to lake level rise, surface erosion, creeping, and slumping due to water runoff and seepage. Lake Michigan water levels rose after 2013 following a below average period (~1999-2013), peaking at record levels in 2019-2020 before falling slightly in 2021. This rise accelerated bluff toe erosion, and longshore currents rapidly removed the sediment and redistributed it along the coast. Recent bluff failures have brought media attention due to real estate and roadway losses. Many property owners have chosen to armor the shoreline to prevent further erosion. This study is focused on 3 sites: (1). a 1.9 km stretch along Lakeshore Dr. in St. Joseph (SJo), MI; (2). a 2 km stretch of subdivisions centered on Miami Park (MP), MI; and {3). a 1 km stretch of natural vegetated area north of a water reservoir near Ludington (LU), MI. All sites have active groundwater seepage at clay layer contacts on the bluff faces. Nadir and obliques photos obtained in July 2019 and 2021 using Unmanned Aerial Systems (UAS) have shown that all sites experienced erosion, landslides, and bluff top retreat. SJo site has dense vegetation on the bluff face but recent failures have removed vegetation and sediment along the face slope. MP area experienced significant bluff retreat, despite toe armoring with large boulders along several sections. At a Nature Preserve (MP), the bluff top retreated as much as 5-10m, with loss of vegetation on the bluff face and multiple landslides. LU area had several landslides resulting in both vegetation and land surface loss. From 2019 to2021, the LU area experienced 177,000 ± 2300 m3 of erosion, which indicates a rate of erosion three times the erosion rate calculated for 2012-2019 (190,000 ± 14,000 m3). More than 5m of glaciodeltaic sand were lost during 2019-2021 around a water seep above lacustrine clay with marginal accumulation at the bluff toe, whereas during 2012-2019 toe erosion removed >10m underneath that location, with ~5m loss normal to the face.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMEP22A..02B