Surface roughness dating of long-runout landslides near Oso, Washington (USA), reveals persistent postglacial hillslope instability

Documenting spatial and temporal patterns of past landsliding is a challenging step in quantifying the effect of landslides on landscape evolution. While landslide inventories can map spatial distributions, lack of dateable material, landslide reactivations, or time, access, and cost constraints generally limit dating large numbers of landslides to analyze temporal patterns. Here we quantify the record of the Holocene history of deep‐seated landsliding along a 25 km stretch of the North Fork Stillaguamish River valley, Washington State, USA, including the 2014 Oso landslide, which killed 43 people. We estimate the ages of more than 200 deep‐seated landslides in glacial sediment by defining an empirical relationship between landslide deposit age from radiocarbon dating and landslide deposit surface roughness. We show that roughness systematically decreases with age as a function of topographic wavelength, consistent with models of disturbance‐driven soil transport. The age‐roughness model predicts a peak in landslide frequency at ~1000 calibrated (cal) years B.P., with very few landslide deposits older than 7000 cal years B.P. or younger than 100 cal years B.P., likely reflecting a combination of preservation bias and a complex history of changing climate, base level, and seismic shaking in the study area. Most recent landslides have occurred where channels actively interact with the toes of hillslopes composed of glacial sediments, suggesting that lateral channel migration is a primary control on the location of large deep‐seated landslides in the valley.

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“…Dates from Rowan, Headache Creek, and the Fluvial Terrace Buried by Rowan are From LaHusen et al . [].…”

Section: Absolute Agessupporting

confidence: 91%

“…from this study (Table ) and from LaHusen et al . []. Landslide polygons include examples of gullies and roads excluded from the roughness analysis.…”

Section: Landslide Mapping and Surface Roughness Analysismentioning

confidence: 99%

Holocene history of deep‐seated landsliding in the North Fork Stillaguamish River valley from surface roughness analysis, radiocarbon dating, and numerical landscape evolution modeling

et al. 2017

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“…Although promising results for regional landslide chronologies and relative-age determinations based on landslide degradation were obtained by Bell et al (2012) and LaHusen et al (2015), the method turned out to be more complicated when applied to our study area in northern Finland. While the degree of surface roughness degradation of landslide scars in Fennoscandian may indeed be time-dependent, it is also influenced by a range of other variables, including the thickness of superficial deposits, the original slope, the specific type of debris slide, and the degree of liquefaction of diamictic material at the time of mass movements.…”

Section: Geomorphological Degradation Of Debris Slides In Finlandmentioning

confidence: 96%

“…Without recent or historical landslides with known earthquake magnitudes, we cannot calibrate our surface roughness or backwall slope curves to the true ages of landslide degradation, as has been done by Bell et al (2012), LaHusen et al (2015), and Booth et al (2017). In Figure 6 we have, however, indicated the radiocarbon ages of the currently dated landslides on these individual curves.…”

Section: Surface Roughness Interpretationmentioning

confidence: 99%

“…While the degree of surface roughness degradation of landslide scars in Fennoscandian may indeed be time-dependent, it is also influenced by a range of other variables, including the thickness of superficial deposits, the original slope, the specific type of debris slide, and the degree of liquefaction of diamictic material at the time of mass movements. It is also evident that the modelled age-roughness curve of the Oso landslide (LaHusen et al, 2015) is not applicable in northern Finland, and based on the results from nine presently dated landslides, the amount of age information is insufficient to construct the age-roughness curve for northern Fennoscandia. It is also evident that the modelled age-roughness curve of the Oso landslide (LaHusen et al, 2015) is not applicable in northern Finland, and based on the results from nine presently dated landslides, the amount of age information is insufficient to construct the age-roughness curve for northern Fennoscandia.…”

Section: Geomorphological Degradation Of Debris Slides In Finlandmentioning

confidence: 99%

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Dating of paleolandslides in western Finnish Lapland

Ojala

Markovaara‐Koivisto

Middleton

et al. 2018

Earth Surf Processes Landf

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The dating of landslide‐buried organic materials potentially indicates non‐stationary seismicity in northern Finland attributable to the release of lithospheric stresses during and after retreat of the Scandinavian Ice Sheet. The landslide age data reveals three episodes of increased slope instability and formation of landslides, from 9000 to 11 000 cal BP, from 5000 to 6000 cal BP, and from 1000 to 3000 cal BP. While a seismogenic origin cannot be unequivocally established, we interpret that at least the early Holocene episode reflects increased seismic activity in northern Finland in association with late‐glacial and postglacial faulting. The foci of slope instabilities changes through time, implying that different segments of the postglacial fault systems were active at different times during the Holocene. We also show that the correlation of landslide ages with the surface roughness and backwall slope is complicated. The morphology of landslide scarps is significantly affected by thickness of glacial sediments, liquefaction during landslide formation, and accumulation of peat upon landslide scars and deposits, and thus, the time‐dependent erosional smoothing of the surfaces should be considered as descriptive and non‐qualitative. Copyright © 2018 John Wiley & Sons, Ltd.

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Hillslope response under variable microclimate

Regmi

McDonald

Rasmussen

2019

Earth Surf Processes Landf

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Solar radiation‐controlled microclimatic variation has been considered a major force on hillslope evolution via feedback among geomorphology, vegetation, soil and hydrology. In this study, we investigate the influence of solar radiation on hillslope dynamics on Santa Catalina Island, CA by comparing hillslope morphology and frequency–magnitude relationships of shallow landslides, rills and gullies on slopes receiving low annual solar radiation (LSR) and high annual solar radiation (HSR), which were found equivalent to north‐ and south‐facing slopes, respectively. LSR slopes on Santa Catalina Island were found more vegetated compared to HSR slopes. LiDAR elevation‐derived hillslope morphology showed LSR slopes steeper, rougher and more concave than HSR slopes. Similarly, frequency–magnitude plots showed larger relative frequency of high‐magnitude shallow landslides, rills and gullies on LSR slopes, and low‐magnitude shallow landslides, rills and gullies on HSR slopes. We argue that the morphology, mass movement and erosion characteristics of LSR and HSR slopes reflect the process–response of microclimate‐controlled variation in type and density of vegetation cover, soil physical properties – including moisture, texture, structure, infiltration and erodibility – and surface and subsurface hydrology. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.

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Surface roughness dating of long-runout landslides near Oso, Washington (USA), reveals persistent postglacial hillslope instability

Cited by 65 publications

References 24 publications

Holocene history of deep‐seated landsliding in the North Fork Stillaguamish River valley from surface roughness analysis, radiocarbon dating, and numerical landscape evolution modeling

Holocene history of deep‐seated landsliding in the North Fork Stillaguamish River valley from surface roughness analysis, radiocarbon dating, and numerical landscape evolution modeling

Dating of paleolandslides in western Finnish Lapland

Hillslope response under variable microclimate

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