By Elliot Witscher, 2023 Science Communication Intern

Land movement is a fact of life anywhere with hilly terrain, whether it’s the foothills of southern California or the Yukon highways. Geoscientists are working to develop new understandings of landslides and ways to mitigate the impact that they have on human lives and infrastructure. 

While landslides can and do occur anywhere with hills and valleys, factors such as weather patterns can greatly impact how often landslides occur and how big they are when they do happen. And with a changing climate, extreme weather events have become more common. 

Several extreme weather events occurred in the first few months of 2023, when multiple atmospheric rivers dumped many inches of rain across California over the course of a few weeks. In a state that has experienced drought for much of the past decade, this sudden influx of water was more than soils normally receive, and hillslopes became destabilized, leading to an increase in landslides. 

Paul Burgess is a geologist at the California Geologic Survey (CGS) who works to identify and map landslides and other geologic hazards in the state, and has worked to produce an online database (and corresponding interactive map) of reported California landslides. Burgess says that the benefits of the database are twofold: it is both an educational and communication tool about the risks and prevalence of landslides and a data set for research and further planning to reduce risk across the state. 

The database and interactive map were created in 2019 and were used extensively in early 2023, as landslides happened suddenly across the state during and following the repeated atmospheric rivers. Burgess describes the rain, landslides, and resulting response as a “busy, busy, busy start to the year.” The landslide mapping efforts expanded quickly, as they were a key part of providing information to the California Office of Emergency Services. The “landside triage team,” as they came to be nicknamed, was responsible for sifting through reports of landslides and collecting as much information as possible about each one, so that responders and decision makers had the most accurate picture possible of the situation at hand. 

When the last atmospheric river of the season ended in March, the focus shifted from the immediate response toward the future and broader potential of the database and map. Burgess says that by showing that landslides occur across California, he and his collaborators hope to make people aware of the “active hazard” that landslides pose across the state. He says that this coming winter will be another El Niño winter in California, which means “more rain for this part of the world and with more rain, there’s going to be more landslides.” 

But it’s not only major rainstorms that can cause landslides. Land movement hazards exist across all different climates, from the coast of southern California all the way to the perpetually frozen landscape of the Yukon in Northern Canada. 

Heather Clarke is a Master of Science candidate at Simon Fraser University and works with Yukon Geological Survey. Her research is focused on permafrost-driven land movement, specifically along the Dempster Highway, which serves as a transportation corridor to remote communities near the Arctic Ocean. In 2017, a wildfire burned along a stretch of the highway, which has led to several permafrost related landslides in the region, disrupting the highway. 

Clarke defines permafrost as “ground that has been at or below 0 °C for two or more consecutive years,” regardless of if ice is present or not. With a changing climate, summers are warmer and winters do not get as cold, leading to degradation or loss of permafrost. 

There are two main types of permafrost-driven land movement: active-layer detachments and retrogressive thaw flows. As Clarke explains, active-layer detachments occur when the top layer of soil, which thaws annually, separates from the still-frozen permafrost layer and starts to slide across it.

Retrogressive thaw flows, on the other hand, are what Clarke describes as “this kind of interesting landslide” that occurs following an active layer detachment, where the previously covered permafrost is exposed to the elements and begins to thaw. As permafrost thaws, it slumps (moves downhill slightly), exposing the frozen material slightly upslope, and the process repeated. While active-layer detachments happen quickly (like a landslide), retrogressive flow occurs slowly over several years. 

Building in the far north poses several challenges, mostly associated with permafrost. Disturbing the ground, via heavy equipment used to build highways or pipelines, damages the permafrost and can result in melting. When the permafrost melts, it can result in the sinking of buildings and highways, as well as potentially adding water to the system, often causing an initially straight and flat highway to become unexpectedly bumpy and bendy. Having grown up in the Yukon, Clarke says “it can be frustrating to watch something being built knowing that it’s going to cause issues later on.”

And when the construction is vital infrastructure such as roads connecting remote regions, landslides and land movement can cause serious issues for people’s day-to-day lives, as well as their wellbeing and livelihoods. 

There are many solutions that have been developed to minimize the impact of building on permafrost, as well as to mitigate the risk of retrogressive flows occurring. Overall, Clarke says, “it’s cheesy to say this, but a lot of it comes down to making sure people respect the permafrost a little bit more and how it can really change things.”

Whether caused by melting permafrost or an atmospheric river, landslides have the same result: damaging infrastructure and disrupting lives and livelihoods. As the global climate continues to change, extreme weather events like the atmospheric rivers California experienced in winter 2023 will continue to increase, as will melting and degradation of the permafrost. Having geoscientists working to prevent, plan for, mitigate, and respond to landslides and other geologic hazards will only become more important in our changing world. 

References

Petley, D., 2023, A remarkable number of landslides in California: https://blogs.agu.org/landslideblog/2023/01/16/california-1/ (accessed 30 January 2024).

National Oceanic and Atmospheric Administration (NOAA), 2023, What are atmospheric rivers? https://www.noaa.gov/stories/what-are-atmospheric-rivers (accessed 30 January 2024). 

Acknowledgements

The GSA Science Communication Internship was a program offered at GSA Connects in Pittsburgh, Penn., designed for student attendees interested in science communication as a possible alternative career path.  Interns were paired with GSA’s Science Communication Fellow in order to gain experience in making science clear and exciting, under the tutelage of a professional writer.  Students were assigned to conduct interviews with presenters at the meeting and to compile summaries capturing the significance of the presenters’ work for a non-technical audience.  Media assignments and mentoring were useful learning experiences and exposure opportunities for students seeking to expand their knowledge into geoscientific reporting.