Causes of Bluff Failure

Bluff instability has been a problem for property owners for as long as people have been building homes overlooking the Great Lakes. The three main causes of bluff failure and erosion are:

Examples of Soil Layers

Roughly 13,000 years ago glacial activity created the unstable soil and sand layers visible today along much of the Lake Michigan shoreline. Bluffs that contain layers of soil with low permeability (clay and silt), alternating with layers of soil with high permeability (sand), result in perched water tables - water moving above the main water table or saturated zone. This happens because clay and silt make it difficult for water to travel down to the water table, instead, the water travels along the sand layer to the bluff face, causing erosion and failures. Properties where perched water tables are present are typically the most prone to slope instability and failure. The perched water adds weight to the bluff and decreases cohesion and normal stress between soil particles, resulting in bluff slides and failures where the sand layer slides. In addition, during the winter months, if the sand layers in the bluff cannot drain water freely due to clay and silt layers, then water storage and pore pressure builds in the sand layer, resulting in slope movement and failures, which accelerate during the spring thaw.