In the United States, we may often think of landslides as primarily a West Coast problem, mostly affecting the mountainous terrain of California, Oregon, and Washington. A technical session at the upcoming GSA 2023 Southeast and Northeast Division meeting in Reston, VA, USA, will highlight the major impacts of landslides on the US East Coast and what is being done to save lives and deal with damage.
Landslides are expected to be a growing concern as climate change results in more extreme precipitation events that can destabilize slopes and trigger these events. Research presented at the session will include investigations of landslide hazards in Puerto Rico, Vermont, Pennsylvania, Michigan, Tennessee, West Virginia, and southern and central Appalachia.
Puerto Rico
After Hurricane Maria in 2017, researchers documented 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 the monitoring and forecasting of landslides on the island, and to fill that gap he started a program of research and outreach: Dynamics of the Impact of Storm-induced Landslides on Environment and Society in Puerto Rico (SLIDES-PR). Partnering with the USGS, SLIDES-PR developed a landslide sensitivity map for the island and installed 14 real-time monitoring stations on landslide-prone slopes.
“These landslides are relatively shallow and small, but they’re very widespread. It doesn’t matter if it’s a small landslide if it reaches your house,” says Hughes.
Monitoring stations measure soil moisture, pore pressure and groundwater level, collect data every five minutes and send 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 Naguapo that soil moisture had crossed the threshold of an impending slope collapse, prompting an evacuation before a debris flow could bury the house.
In addition to monitoring and forecasting, the SLIDES-PR program has developed guides for residents to understand landslide warning signs, what human activities can promote them, and ways to prepare and adapt after they occur. At the conference, Anishka Ruiz-Perea will share science and risk communication work done by SLIDES-PR, and Chiara Conilera Cott will present the development of prediction thresholds using data from monitoring stations.
Vermont
In 2019, a hillside in Vermont’s Mount Mansfield State Forest failed and triggered a 12.5-acre landslide the size of 80 Olympic-sized swimming pools. The material formed a dam at Cotton Brook, which eventually carried the sediment flow into the nearby Waterbury Reservoir.
Smuggler’s Notch, one of the state’s most popular tourist destinations, is a 1,000-foot mountain chasm that has seen major rockslides over several decades, sometimes dropping boulders the size of school buses onto the road below.
“We are convinced, just like many others, that as climate change intensifies, we will produce more landslides and more sediment systems,” explains Jonathan Kim of the Vermont Geological Survey, who will present several approaches to assessing, monitoring, and mitigating landslide risks in the region. Vermont.
The Vermont Geological Survey is collaborating with the University of Vermont (Burlington) and the University of Norwich (Northfield, Vermont) to create comprehensive tools for monitoring and understanding landslide hazards in the state. These investigations led FEMA to purchase a parcel of land containing a large landslide that posed a threat of more slopeslides in 1999. Rain and flooding during Hurricane Irene in 2011 left slopes unstable across the state , prompting the development of landslide protocols at the state level and the formation of a landslide database to which landslide experts and residents can contribute.
Pennsylvania
The greater Pittsburgh area experienced record rainfall in February and April of 2018 causing more than 200 landslides. Built on sedimentary rock rich in clay and with steep terrain due to river erosion, southwestern Pennsylvania is one of the most landslide-prone regions in the country. Landslides are small and usually non-fatal, affecting housing, roads, streams, and other infrastructure. As a result of landslides in 2018, one of the natural gas pipelines collapsed, and the explosion destroyed a house and several other buildings.
“It’s very clear that this was an anomaly. We had an extremely anomalous amount of rain in February when Pittsburgh usually snows and the ground freezes. The ground wasn’t frozen, and almost all of the rain fell. As rain. We had shallow soil slides as well as deep slides.” 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 scope of damage from the landslides was extensive, a request for FEMA support was denied because the many months of mounting landslides did not count as a single event. When considered as separate events, they did not meet the damage threshold required to be declared a federal disaster. Delano says the record-breaking year raised awareness statewide of the need to prepare for landslides. Landslide clean-up in 2018 is still ongoing.
