Vadose Zone Thickness Limits Pore‐Fluid Pressure Rise in a Large, Slow‐Moving Earthflow

Abstract

Introduction and BackgroundLandslides vary in size, speed, and destructiveness over several orders of magnitude, ranging from rapid, catastrophic hillslope failures that can wipe out roads and towns instantaneously to slow, persistent mass movements that last over decades or even centuries. The fatalities and property damage that can result from rapid landslides are well known (Fleming & Taylor, 1980;Froude & Petley, 2018). And while the consequences of slow, persistent landslides may not be readily obvious, they nevertheless have a suite of documented impacts ranging from progressive infrastructure damage (

Landslide Sensitivity and Response to Precipitation Changes in Wet and Dry Climates

“…Both shear-induced contraction and longitudinal compression of landslide material can cause pore-water pressures to increase sharply (e.g., Iverson, 2005;Iverson et al, 2015), as can weakening mechanisms, such as slip localization (e.g., Viesca & Rice, 2012). Although many mechanical-hydrological interactions contribute to the behavior of landslides, our results agree with Finnegan et al (2021) and Murphy et al (2022), which suggest that the volume of material that can accommodate water input exerts a primary control on the landslide sensitivity and response to precipitation.…”

“…and landslide behavioral patterns throughout California. While we currently cannot reliably predict landslide motion due to complex nonlinear relationships between precipitation, pore-water pressure, and velocity (e.g., Carey et al, 2019;Malet et al, 2002;Murphy et al, 2022), we may be able to predict relative changes in landslide velocity in response to relative changes in precipitation. Therefore, it is necessary to continue to document landslide behaviors during "normal" years that may serve as baselines for comparison and prediction of future landslide behaviors.…”

“…Prior work has shown that active slow-moving landslides typically have high groundwater levels year round and become effectively saturated during the wet season (Finnegan et al, 2021;Iverson & Major, 1987;Malet et al, 2002;Schulz et al, 2009Schulz et al, , 2018. The ability to maintain high groundwater levels may be a consequence of rock type-controlled critical zone (i.e., ground surface to unweathered bedrock) structure (Murphy et al, 2022). Hahm et al (2019) showed that landslides in a wet region of northern California (mean annual rainfall ∼1800 mm/yr) in the Franciscan mélange, the predominant bedrock of landslides in our inventory, have a critical zone characterized by a thin (<3 m) seasonally unsaturated zone with low hydraulic conductivity that becomes effectively saturated after ∼100-200 mm of seasonal rainfall.…”

“…Prior work has shown that active slow‐moving landslides typically have high groundwater levels year round and become effectively saturated during the wet season (Finnegan et al., 2021; Iverson & Major, 1987; Malet et al., 2002; Schulz et al., 2009, 2018). The ability to maintain high groundwater levels may be a consequence of rock type‐controlled critical zone (i.e., ground surface to unweathered bedrock) structure (Murphy et al., 2022). Hahm et al.…”

“…and their motion is closely linked to local groundwater conditions (Corominas et al, 2005;Iverson & Major, 1987;Murphy et al, 2022). Furthermore, the hydrologic controls on slow-moving landslides, via pore pressure changes, are akin to the hydrologic controls on faults (Bhattacharya & Viesca, 2019;Cappa et al, 2019), glaciers (Minchew & Meyer, 2020;Moon et al, 2014), and rock glaciers (Cicoira et al, 2019;Kenner et al, 2017), and therefore investigating these landslides allows us to better understand each system.…”