In the US, we may often think of landslides as primarily a West Coast problem, mostly plaguing the mountainous terrain of California, Oregon and Washington. A technical session at the upcoming 2023 GSA Southeast & Northeast Sectors Joint Meeting in Reston, Virginia, USA, will highlight the significant impacts of landslides on the US East Coast and what is being done to save lives and manage damage.
Landslides are expected to be a growing concern as climate change causes more extreme rainfall events that can destabilize slopes and trigger these events. Research presented at the session will include surveys of landslide hazards in Puerto Rico, Vermont, Pennsylvania, Michigan, Tennessee, West Virginia, and southern and central Appalachia.
After Hurricane Maria in 2017, researchers recorded more than 70,000 landslides on the island of Puerto Rico. Geologist Stephen Hughes at the University of Puerto Rico Mayagüez saw a gap in monitoring and predicting landslides on the island, and to fill that gap he launched a research and outreach project: Dynamics of Storm-Induced Landslide Impacts on Environment and Society in Puerto Rico (SLIDES-PR). Through collaboration with the US Geological Survey, SLIDES-PR developed a landslide susceptibility map for the island and installed 14 real-time monitoring stations on landslide slopes.
“These are shallow, relatively small landslides, but extremely widespread. It doesn’t matter if it’s a small landslide if it goes through your house,” Hughes says.
Monitoring stations measure soil moisture, pore pressure and groundwater levels, collecting data every five minutes and sending it back to the university every hour. The surveillance network has already saved lives. During Hurricane Fiona in 2022, Hughes was able to use real-time monitoring to warn the town of Naguabo that soil moisture had crossed the threshold for imminent slope failure, triggering an evacuation before a debris flow buried a house.
In addition to monitoring and forecasting, the SLIDES-PR program has developed guides for residents to understand the warning signs of landslides, what human activities can promote them, and ways to prepare and respond in the aftermath. At the conference, Anishka Ruiz-Perea will share the science and risk communication work done by SLIDES-PR and Kiara Cunillera-Cote will present the development of prediction limits using the data from the monitoring stations.
In 2019, a mountain slope in Vermont’s Mansfield State Forest failed and caused a 12.5-acre landslide with a volume equivalent to 80 Olympic-sized swimming pools. The material formed a dam in Cotton Brook, which eventually diverted the sediment influx into nearby Waterbury Reservoir.
Smuggler’s Notch, one of the most popular tourist destinations in the state, is a 1,000-foot-high mountain that has seen large rock slides for several decades, sometimes dropping boulders the size of school buses onto the road below.
“We are convinced, as are many others, that as climate change becomes more extreme, we will create more landslides and more sediment systems,” explains Jonathan Kim of the Vermont Geological Survey, who will present the many approaches being taken to assess , monitoring and mitigating landslide hazards in Vermont.
The Vermont Geological Survey is working with the University of Vermont (Burlington) and Norwich University (Northfield, Vermont) to create comprehensive tools to monitor and understand landslide risk in the state. These investigations led to a Federal Emergency Management Agency (FEMA) acquisition of a parcel containing a large landslide that threatened additional slope failures in 1999. Rainfall and flooding during Hurricane Irene in 2011 led to slope instability statewide, prompting the development of statewide landslide protocols and the creation of a statewide landslide database to which landslide experts and residents can contribute.
The greater Pittsburgh area experienced record rainfall in February-April 2018 that triggered more than 200 landslides. Built on clay-rich sedimentary rocks and with steep topography from the collapse of river erosion, southwestern Pennsylvania is one of the most landslide-prone regions in the country. Landslides are small and usually not fatal, affecting homes, roads, streams and other infrastructure. As a result of the 2018 landslides, a natural gas pipeline ruptured and the resulting explosion destroyed a house and several other buildings.
“It’s very clear that this was a climatically anomalous occasion. We had an extremely anomalous amount of rain in February when Pittsburgh would normally get snow and the ground would be frozen. The ground was not frozen and almost all of the precipitation fell. We had shallow landslides as and landslides in deeper locations that require greater changes in hydraulic conditions,” explains Helen Delano of the Pennsylvania Geological Survey, who will present on the record landslide year at the conference.
While the range of landslide damage was extensive, an application for FEMA support was denied because the several months of increased landslides were not considered an isolated event. When considered as separate events, they did not meet the damage threshold required to declare a federal disaster. Delano says the record year has raised statewide awareness of the need to prepare for landslides. Cleanup from the 2018 landslides remains ongoing.