On September 2, 1806, the Swiss village of Goldau was destroyed in a landslide. After an estimated 40 million cubic meters of earth came down on the village and 457 people died, the first professional geologist studied the landside. For the first time, we attempted to understand what happened and how. With the study of this landside, some of the first theories about landslides were developed. Since that time, geologists have continued to research and understand landslides. How has the science changed recently?
Post Wildfire Landslides
All over the world, from the United States to Australia, we have seen an increase in the number and severity of wildfires. A study done by the American Geophysical Union signals shows that not only is an area with increased wildfires, like Southern California, at risk for future wildfires due to climate change, but an increased risk of landslides. The extreme weather of very dry followed by very wet makes for an unpleasant combination.
Shockingly, the study found that in Southern California landslides with the ability to damage 40 or more structures can now be expected to occur as often as a magnitude 6.7 earthquake – every 10 to 13 years. Small landslides are now expected to be an annual occurrence.
Findings seem to suggest that with climate change creating more unpredictable and intense weather patterns, Southern California could find itself in a deadly cycle of longer, hotter burning seasons followed by intense rain.
By combining historical data with computer simulations, the researchers were able to pinpoint not just where post-wildfire landslides are likely to occur, but also how big they might be and how often they will likely happen. The main goal of the study was to create landslide hazard maps similar to the ones created for earthquakes.
Duke University engineers have developed a new model for deep-seated landslides. A deep-seated landslide has the sliding surface mostly far below the maximum rooting depth of trees. These types of landslides occur due to geologic or hydrologic changes, such as the groundwater level going up or seismic shaking. They typically move slower than shallow-rapid landslides but have the potential to suddenly accelerate.
The researchers found that the key signal for catastrophic failure was an increase in the temperature of a thin layer of clay.
How does the temperature tell us about the potential for a landslide? The study started with the Vajont Dam disaster in northern Italy. This landslide started out slow – moving around an inch a day. Suddenly, the landslide accelerated, seemingly without warning.
At first scientists were stumped why the landside accelerated so quickly. Years later, we finally understand what happened. Water seeped into the thin clay layer previously mentioned which started the creeping landslide. Over time, friction caused this clay to heat up until the clay layer failed. In 2021 that initial model was improved and designed to model more than just the Vajont Dam failure.
Researchers speculate this information could be used to not only monitor creeping landslides, but also to create solutions to prevent a sudden failure. They imagine circulating a cold fluid through the thin clay layer or pumping the water out of the ground that is causing the creeping landslide.