Georgina L. Bennett

Bio: Georgina L. Bennett is an academic researcher from University of Exeter. The author has contributed to research in topics: Landslide & Sediment. The author has an hindex of 11, co-authored 29 publications receiving 597 citations. Previous affiliations of Georgina L. Bennett include United States Forest Service & University of Oregon.

Erosional power in the Swiss Alps: characterization of slope failure in the Illgraben

Abstract: Landslides and rockfalls are key geomorphic processes in mountain basins. Their quantification and characterization are critical for understanding the processes of slope failure and their contributions to erosion and landscape evolution. We used digital photogrammetry to produce a multi-temporal record of erosion (1963–2005) of a rock slope at the head of the Illgraben, a very active catchment prone to debris flows in Switzerland. Slope failures affect 70% of the study slope and erode the slope at an average rate of 0.39 ± 0.03 m yr¯¹. The analysis of individual slope failures yielded an inventory of ~2500 failures ranging over 6 orders of magnitude in volume, despite the small slope area and short study period. The slope failures form a characteristic magnitude–frequency distribution with a rollover and a power-law tail between ~200 m³ and 1.6 × 106 m³ with an exponent of 1.65. Slope failure volume scales with area as a power law with an exponent of 1.1. Both values are low for studies of bedrock landslides and rockfall and result from the highly fractured and weathered state of the quartzitic bedrock. Our data suggest that the magnitude–frequency distribution is the result of two separate slope failure processes. Type (1) failures are frequent, small slides and slumps within the weathered layer of highly fractured rock and loose sediment, and make up the rollover. Type (2) failures are less frequent and larger rockslides and rockfalls within the internal bedded and fractured slope along pre-determined potential failure surfaces, and make up the power-law tail. Rockslides and rockfalls of high magnitude and relatively low frequency make up 99% of the total failure volume and are thus responsible for the high erosion rate. They are also significant in the context of landscape evolution as they occur on slopes above 45° and limit the relief of the slope. Copyright © 2012 John Wiley & Sons, Ltd.

Landslides, threshold slopes, and the survival of relict terrain in the wake of the Mendocino Triple Junction

Abstract: Establishing landscape response to uplift is critical for interpreting sediment fluxes, hazard potential, and topographic evolution. We assess how landslides shape terrain in response to a wave of uplift traversing the northern California Coast Ranges (United States) in the wake of the Mendocino Triple Junction. We extracted knickpoints, landslide erosion rates, and topographic metrics across the region modified by Mendocino Triple Junction migration. Landslide erosion rates mapped from aerial imagery are consistent with modeled uplift and exhumation, while hillslope gradient is invariant across the region, suggesting that landslides accommodate uplift, as predicted by the threshold slope model. Landslides are concentrated along steepened channel reaches downstream of knickpoints generated by base-level fall at channel outlets, and limit slope angles and relief. We find evidence that landslide-derived coarse sediment delivery may suppress catchment-wide channel incision and landscape denudation over the time required for the uplift wave to traverse the region. We conclude that a landslide cover effect may provide a mechanism for the survival of relict terrain and orogenic relief in the northern Californian Coast Ranges and elsewhere over millennial time scales.

Widespread initiation, reactivation, and acceleration of landslides in the northern California Coast Ranges due to extreme rainfall

Abstract: Episodically to continuously active slow‐moving landslides are driven by precipitation. Climate change, which is altering both the frequency and magnitude of precipitation worldwide, is therefore predicted to have a major impact on landslides. Here we examine the behavior of hundreds of slow‐moving landslides in northern California in response to large changes in annual precipitation that occurred between 2016 and 2018. We quantify the landslide displacement using repeat‐pass radar interferometry and pixel offset tracking techniques on a novel data set from the airborne NASA/JPL Uninhabited Aerial Vehicle Synthetic Aperture Radar. We found that 312 landslides were moving due to extreme rainfall during 2017, compared to 119 during 2016, which was the final year of a historic multiyear drought. However, with a return to below to average rainfall in 2018, only 146 landslides remained in motion. The increased number of landslides during 2017 was primarily accommodated by landslides that were smaller than the landslides that remained active between 2016 and 2018. Furthermore, by examining a subset of 51 landslides, we found that 49 had increased velocities during 2017 when compared to 2016. Our results show that slow‐moving landslides are sensitive to large changes in annual precipitation, particularly the smaller and thinner landslides that likely experience larger basal pore‐water pressure changes. Based on climate model predictions for the next century in California, which include increases in average annual precipitation and increases in the frequency of dry‐to‐wet extremes, we hypothesize that there will be an overall increase in landslide activity.

A probabilistic sediment cascade model of sediment transfer in the Illgraben

Abstract: We present a probabilistic sediment cascade model to simulate sediment transfer in a mountain basin (Illgraben, Switzerland) where sediment is produced by hillslope landslides and rockfalls and exported out of the basin by debris flows and floods The model conceptualizes the fluvial system as a spatially lumped cascade of connected reservoirs representing hillslope and channel storages where sediment goes through cycles of storage and remobilization by surface runoff The model includes all relevant hydrological processes that lead to runoff formation in an Alpine basin, such as precipitation, snow accumulation, snowmelt, evapotranspiration, and soil water storage Although the processes of sediment transfer and debris flow generation are described in a simplified manner, the model produces complex sediment discharge behavior which is driven by the availability of sediment and antecedent wetness conditions (system memory) as well as the triggering potential (climatic forcing) The observed probability distribution of debris flow volumes and their seasonality in 2000–2009 are reproduced The stochasticity of hillslope sediment input is important for reproducing realistic sediment storage variability, although many details of the hillslope landslide triggering procedures are filtered out by the sediment transfer system The model allows us to explicitly quantify the division into transport and supply-limited sediment discharge events We show that debris flows may be generated for a wide range of rainfall intensities because of variable antecedent basin wetness and snowmelt contribution to runoff, which helps to understand the limitations of methods based on a single rainfall threshold for debris flow initiation in Alpine basins

Glacier retreat and landform production on an overdeepened glacier foreland: the debris-charged glacial landsystem at Kvíárjökull, Iceland

Abstract: Glacier recession and landform development in a debris-charged glacial landsystem characterized by an overdeepening is quantified using digital photogrammetry, digital elevation model (DEM) construction and mapping of the Icelandic glacier Kviarjokull for the period 1945–2003. Melting of ice-cores is recorded by surface lowering rates of 0·8 m yr–1 (1945–1964), 0·3 m yr–1 (1964–1980), 0·015 m yr–1 (1980–1998) and 0·044 m yr–1 (1998–2003). The distribution/preservation of pushed and stacked ice-cored moraine complexes are determined by the location of the long-term glacial drainage network in combination with retreat from the overdeepening, into which glacifluvial sediment is being directed and where debris-rich ice masses are being reworked and replaced by esker networks produced in englacial meltwater pathways that bypassed the overdeepening and connected to outwash fans prograding over the snout. Recent accelerated retreat of Kviarjokull, potentially due to increased mass balance sensitivity, has made the snout highly unstable, especially now that the overdeepening is being uncovered and the snout flooded by an expanding pro-glacial, and partially supraglacial, lake. This case study indicates that thick sequences of debris-charged basal ice/controlled moraine have a very low preservation potential but ice-cored moraine complexes can develop into hummocky moraine belts in de-glaciated terrains because they are related to the process of incremental stagnation, which at Kviarjokull has involved periodic switches from transport-dominant to ablation-dominant conditions. Glacier recession is therefore recorded temporally and spatially by two suites of landforms relating to two phases of landform production which are likely typical for glaciers occupying overdeepenings: an early phase of active, temperate recession recorded by push moraines and lateral moraines and unconfined pro-glacial meltwater drainage; and a later phase of incremental stagnation and pitted outwash head development initiated by the increasing topographic constraints of the latero-frontal moraine arc and the increasing importance of the overdeepening as a depo-centre. Copyright © 2012 John Wiley & Sons, Ltd.

Global fatal landslide occurrence from 2004 to 2016

Abstract: . Landslides are a ubiquitous hazard in terrestrial environments with slopes, incurring human fatalities in urban settlements, along transport corridors and at sites of rural industry. Assessment of landslide risk requires high-quality landslide databases. Recently, global landslide databases have shown the extent to which landslides impact on society and identified areas most at risk. Previous global analysis has focused on rainfall-triggered landslides over short ∼ 5-year observation periods. This paper presents spatiotemporal analysis of a global dataset of fatal non-seismic landslides, covering the period from January 2004 to December 2016. The data show that in total 55 997 people were killed in 4862 distinct landslide events. The spatial distribution of landslides is heterogeneous, with Asia representing the dominant geographical area. There are high levels of interannual variation in the occurrence of landslides. Although more active years coincide with recognised patterns of regional rainfall driven by climate anomalies, climate modes (such as El Nino–Southern Oscillation) cannot yet be related to landsliding, requiring a landslide dataset of 30 + years. Our analysis demonstrates that landslide occurrence triggered by human activity is increasing, in particular in relation to construction, illegal mining and hill cutting. This supports notions that human disturbance may be more detrimental to future landslide incidence than climate.

Topographic site effects and the location of earthquake induced landslides

Abstract: In the epicentral areas of major recent earthquakes, landslide density scales with peak ground acceleration. Topographic site effects on seismic waves are known to cause important gradients in ground acceleration in individual mountain ridges. Using landslide maps from the epicentral areas of earthquakes near Northridge, California, Chi-Chi, Taiwan, and the Finisterre Mountains of Papua New Guinea, we have investigated the control of these site effects over the location of earthquake induced slope failure. In our examples, earthquake-triggered landslides clustered near ridge crests, where the susceptibility to landsliding was greatest. This pattern is strongest in the Northridge epicentral area, and secondary landslide clusters were found in colluvial slope toes in western Taiwan and above inner gorges in the Finisterre Mountains. In contrast, rainfall-triggered landslides in the western Southern Alps of New Zealand were evenly distributed over all slope segments, and the landslide susceptibility was lowest near ridge crests. Observed patterns of earthquake induced landsliding are consistent in a diverse geological substrate. They correlate with the distribution of very steep slopes in the epicentral areas, but we demonstrate that topographic site effects can also be a strong control. Using the impedance operator method, we have modeled the propagation of seismic waves in a generic ridge-and-valley topography with and without inner gorge. This topography has little effect on incoming P waves, but a strong effect on S waves, giving rise to a significant amplification of peak ground accelerations at or near ridge crests, and at convex knickpoints within ridge flanks. The preferential orientation of landslides away from earthquake epicenters in the Finisterre Mountains and central west Taiwan is likely caused by asymmetric amplification of oblique incoming seismic waves across mountain ridges, and indicates that topographic site effects have dominated over topographic controls on landslide location in these areas. Although orientation of landslides in the Northridge area does not conform with this interpretation, our results suggest that knowledge of topographic site effects and the attenuation of seismic waves can be an important tool in the prediction of spatial patterns of earthquake induced landsliding.

Global-scale evaluation of 22 precipitation datasets using gauge observations and hydrological modeling

Abstract: Abstract. We undertook a comprehensive evaluation of 22 gridded (quasi-)global (sub-)daily precipitation (P) datasets for the period 2000–2016. Thirteen non-gauge-corrected P datasets were evaluated using daily P gauge observations from 76 086 gauges worldwide. Another nine gauge-corrected datasets were evaluated using hydrological modeling, by calibrating the HBV conceptual model against streamflow records for each of 9053 small to medium-sized (