East Coast, US, Landslide Impacts from Puerto Rico to Vermont and Between – Zoo House News
- March 16, 2023
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In the US, we may often think that landslides are primarily a West Coast problem, primarily plaguing the mountainous terrain of California, Oregon, and Washington. A technical session at the upcoming GSA 2023 Joint Southeastern & Northeastern Section Meeting in Reston, Virginia, USA will highlight the major impact of landslides on the US East Coast and what is being done to save lives and manage the damage.
Landslides are projected to be a growing problem as climate change leads to more extreme precipitation events that can destabilize slopes and trigger these events. Research presented in the session includes landslide risk surveys in Puerto Rico, Vermont, Pennsylvania, Michigan, Tennessee, West Virginia, and the southern and central Appalachian Mountains.
After Hurricane Maria in 2017, researchers documented more than 70,000 landslides on the island of Puerto Rico. University of Puerto Rico Mayagüez geologist Stephen Hughes saw a gap in landslide monitoring and forecasting on the island and launched a research and outreach program to fill the gap: Storm-induced Landslide Impact Dynamics on Environment and Society in Puerto Rico (slide PR). Through a partnership with the US Geological Survey, SLIDES-PR has developed a landslide susceptibility map for the island and installed 14 real-time monitoring stations on landslide-prone slopes.
“These are shallow, relatively small landslides, but they’re extremely common. It doesn’t matter that it’s a small landslide if it comes through your house,” says Hughes.
The measuring 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 alert the city of Naguabo through real-time monitoring that soil moisture had exceeded the threshold for an imminent slope failure, prompting an evacuation before a debris flow buried a home.
In addition to monitoring and forecasting, the SLIDES PR program has developed guides for local residents to understand the warning signs of landslides, what human activities they may encourage, and how to prepare for and deal with them once they occur. At the conference, Anishka Ruiz-Perea will present the science and risk communication work done by SLIDES-PR and Kiara Cunillera-Cote will present the development of prognostic thresholds using data from monitoring stations.
In 2019, a slope in Vermont’s Mt. Mansfield State Forest failed, causing a 12.5-acre landslide with a volume equivalent to 80 Olympic-size swimming pools. The material formed a dam at Cotton Brook that eventually carried sediment inflow to nearby Waterbury Reservoir.
One of the state’s most popular tourist spots, Smuggler’s Notch is a 1,000-foot mountain gap that has seen large rock falls over several decades, sometimes hurling boulders the size of school buses onto the road below.
“We, like many others, are convinced that as climate change increases, we will create more landslides and more sediment systems,” explains Jonathan Kim of the Vermont Geological Survey, who will present the many approaches to assessing, monitoring and mitigating landslide risk in Vermont.
The Vermont Geological Survey has worked with the University of Vermont (Burlington) and Norwich University (Northfield, Vermont) to develop comprehensive tools to monitor and understand the risk of landslides in the state. These investigations led to the Federal Emergency Management Agency (FEMA) buying up a property with a large landslide that threatened further hanging failures in 1999. Rainfall and flooding during Hurricane Irene in 2011 caused slope instability across the state, prompting the development of statewide landslide logs and the creation of a statewide landslide database for landslide experts and local residents to contribute to.
From February to April 2018, the greater Pittsburgh area experienced record rainfall that triggered more than 200 landslides. Built on clayey sedimentary rocks and with steep topography caused by river erosion, southwestern Pennsylvania is one of the more landslide-prone regions in the country. The landslides are small and usually non-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 is very clear that this was a climatically abnormal circumstance. We had a tremendously abnormal amount of rain in February when Pittsburgh normally snowed and the ground was frozen. The ground was not frozen and almost all of the precipitation fell as rain. We’ve had both shallow landslides and deeper landslides that require major changes in hydraulic conditions,” explains Helen Delano of the Pennsylvania Geological Survey, who will report on the record year for landslides at the conference.
Although the extent of damage caused by the landslides was extensive, a request for assistance from FEMA was denied because the landslides, which lasted several months, were not considered a single event. Considered as separate events, they did not reach the damage threshold required to declare a federal disaster. According to Delano, the record year raised awareness at the state level of the need to prepare for landslides. The cleanup after the 2018 landslides is ongoing.