A University of Maine professor is exploring the possible link between catastrophic landslides in Westbrook that happened centuries ago and a recent incident in Argyle that displaced a family.
On June 4, 2024, the backyard of the Argyle home where Aaron and Elaine St. Louis lived suddenly slid into the Penobscot River. Since then, the river has slowly eaten away at the unstable land behind their house, threatening to take the structure with it.
Aaron Gallant, a geotechnical engineer and associate professor of civil and environmental engineering at UMaine, suspects a type of silty mud that has been present in landslides across Maine for centuries could be involved in this recent Argyle landslide.
The Penobscot Emergency Management Agency called Gallant to help evaluate the Argyle property in August.
Gallant and a graduate student have since begun evaluating the soil around the Argyle home, used drones to look at the area and installed sensors around the home’s foundation to track how much the structure moves. Their research, however, is far from complete.
The type of sediment, known as Presumpscot Formation, is found in coastal and riverfront areas, including Westbrook and Brunswick, across Maine. It contains soft, silty mud with a high water content, which Gallant said can act like “a house of cards” in terms of its stability. It’s also sometimes known as “blue clay” for its blue-gray color.
“It’s stable to some extent,” Gallant said. “But, it has a low resistance. It can be strong as long as you’re not disturbing it.”
The St. Louis’ home was also built along a point in the river known as a cut bank, where the river bends and erosion is more likely to occur, Gallant said. This is because the river can eat away at the land as it hits the bend and continues flowing.
Aside from soil instability, Gallant said things like periods of heavy rainfall can increase the likelihood of landslides.
If Presumpscot Formation is to blame for the Argyle landslide, it wouldn’t be the first time the clay has played a role in redesigning riverbanks and damaging homes. The material was involved in the largest documented landslide in Maine history, which displaced some 20 acres of land in Westbrook along the Presumpscot River in 1868, according to a 2014 study published by the Maine Geological Survey.
“These things are catastrophic — they’re rare, but when they happen, they’re no joke, and they happen quickly,” Gallant said. “We’re trying to figure out the root causes and whether there are similarities between what we’re seeing in Argyle and this event in Westbrook.”
Though state maps tell Gallant this type of soil lies beneath the Argyle home and in much of the surrounding area, his next step is determining whether the land “slipped” on the material, causing the landslide.
While the Argyle landslide was catastrophic to one family and their property, Gallant is also exploring whether the land around the home — including the nearby state road — contains the same material, putting it at risk of further damage, such as future landslides.
“[Presumpscot Formation] is all over Maine,” Gallant said. “It’s the material that causes all our issues. We’re trying to figure out why landslides occur in the places they occur and whether there are ways to mitigate the issue.”
