Lost landslides: Rock-avalanche occurrence and fluvial censoring processes on South Island, New Zealand

Rock-avalanches (RAs) are a large (typically >10⁶ m3) and extremely rapid (30 - >100 m/s) type of landslide. RAs pose a significant hazard as they can runout over long distances and generate secondary hazards such as tsunami and unstable, cross-valley dams. Previous research on the distribution of rock-avalanche deposits (RADs) on the South Island, New Zealand has suggested that there are fewer deposits than would be expected for a seismically active, high-mountain region. This is due to their removal from the sedimentary record (censoring) by fluvial erosion, glacial entrainment, vegetation cover, sub-aqueous occlusion and deposit misidentification. Censoring of deposits skews magnitude-frequency relationships of RA occurrence and hinders hazard planning. This research examines processes acting to fluvially censor RADs on the South Island. 268 known, and 47 possible RADs were identified to provide the first RAD inventory for the entire South Island. The temporal distribution of RADs indicates censoring of the record over the Holocene. >500 year intervals exist between RA events from 12,000 to 2,000 years ago; a more complete record is shown for the last 1,000 to 100 years with intervals of >50 - <150 years. The last 100 years shows phases of co-seismic RAD generation, a period of RAD quiescence and a recent increase in aseismic RAD occurrence. The spatial distribution of RADs suggests that the West Coast, Fiordland and Nelson could have experienced fluvial censoring of deposits. The sediment routing characteristics of catchments in these regions, where the majority of rivers have direct pathways from RADs to the ocean, suggest that fluvially reworked RAD material could be stored within alluvial flats and braidplains. Agglomerate grains (microscopic grains which are diagnostic of RAs) were used to identify fluvially reworked RAD material. Grains were detected in dam-breach flood terraces up to 1km downstream of known RADs. Contemporary river sediment samples showed no agglomerate presence, this suggests that 1) agglomerates break down under extended fluvial transport, 2) they are not supplied to river systems outside of flood events, 3) agglomerates become diluted by other river sediment or 4) they become buried in discrete sedimentary layers. In order to investigate the redistribution of coarse RAD material within South Island rivers, a micro-scale flume model was developed. Using ultra-violet sand as a novel analogue for a RAD, the redistribution of material through an idealised South Island catchment could be examined. The model showed that RAD material is deposited in discrete aggradational layers in dam proximal locations. Downstream, the sedimentary signal is rapidly diluted by ordinary river sediment flux. The research shows that the RAD record for the South Island is incomplete and that fluvial censoring is prevalent within the West Coast, Nelson and Fiordland. The agglomerate tracing method can be used to identify the presence of RADs in fluvial systems proximal to RADs but the signal is undetectable after ~1km from the deposit. Both field sampling and flume modelling show that localised flood derived aggradational layers, close to deposit locations, will archive reworked RAD material. These results have important implications for understanding the magnitude and frequency of RADs within New Zealand and other similar high-mountain, tectonically active regions of the globe

Spatial variation of hydroclimate in north-eastern North America during the last millennium

Climatic expressions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) vary regionally, with reconstructions often depicting complex spatial patterns of temperature and precipitation change. The characterisation of these spatial patterns helps advance understanding of hydroclimate variability and associated responses of human and natural systems to climate change. Many regions, including north-eastern North America, still lack well-resolved records of past hydrological change. Here, we reconstruct hydroclimatic change over the past millennium using testate amoeba-inferred peatland water table depth reconstructions obtained from fifteen peatlands across Maine, Nova Scotia, Newfoundland and Québec. Spatial comparisons of reconstructed water table depths reveal complex hydroclimatic patterns that varied over the last millennium. The records suggest a spatially divergent pattern across the region during the Medieval Climate Anomaly and the Little Ice Age. Southern peatlands were wetter during the Medieval Climate Anomaly, whilst northern and more continental sites were drier. There is no evidence at the multi-decadal sampling resolution of this study to indicate that Medieval mega-droughts recorded in the west and continental interior of North America extended to these peatlands in the north-east of the continent. Reconstructed Little Ice Age hydroclimate change was spatially variable rather than displaying a clear directional shift or latitudinal trends, which may relate to local temporary permafrost aggradation in northern sites, and reconstructed characteristics of some dry periods during the Little Ice Age are comparable with those reconstructed during the Medieval Climate Anomaly. The spatial hydroclimatic trends identified here suggest that over the last millennium, peatland moisture balance in north-eastern North America has been influenced by changes in the Polar Jet Stream, storm activities and sea surface temperatures in the North Atlantic as well as internal peatland dynamics

Detection and forecasting of shallow landslides: lessons from a natural laboratory

Shallow-rapid landslides are a significant hillslope erosion mechanism and limited understanding of their initiation and development results in persistent risk to infrastructure. Here, we analyse the slope above the strategic A83 Rest and be Thankful road in the west of Scotland. An inventory of 70 landslides (2003-2020) shows three types of shallow landslide, debris flows, creep deformation and debris falls. Debris flows dominate and account for 5,350m3 (98 ) of shallow-landslide source volume across the site. We use novel time-lapse vector tracking to detect and quantify slope instabilities, whilst seismometers demonstrate the potential for live detection and location of debris flows. Using on-slope rainfall data, we show that shallow-landslides are typically triggered by abrupt changes in the rainfall trend, characterised by high-intensity, long duration rainstorms, sometimes part of larger seasonal rainfall changes. We derive empirical antecedent precipitation (>62mm) and intensity-duration (>10 hours) thresholds over which shallow-landslides occur. Analysis shows the new thresholds are more effective at raising hazard alerts than the current management plan.The low-cost sensors provide vital notification of increasing hazard, the initiation of movement, and final failure. This approach offers considerable advances to support operational decision-making for infrastructure threatened by complex slope hazards

Buber, educational technology, and the expansion of dialogic space

Buber’s distinction between the ‘I-It’ mode and the ‘I-Thou’ mode is seminal for dialogic education. While Buber introduces the idea of dialogic space, an idea which has proved useful for the analysis of dialogic education with technology, his account fails to engage adequately with the role of technology. This paper offers an introduction to the significance of the I-It/I-Thou duality of technology in relation to opening dialogic space. This is followed by a short schematic history of educational technology which reveals the role technology plays, not only in opening dialogic space, but also in expanding dialogic space. The expansion of dialogic space is an expansion of what it means to be ‘us’ as dialogic engagement facilitates the incorporation, into our shared sense of identity, of aspects of reality that are initially experienced as alien or ‘other’. Augmenting Buber with an alternative understanding of dialogic space enables us to see how dialogue mediated by technology, as well as dialogue with monologised fragments of technology (robots), can, through education, lead to an expansion of what it means to be human

Monitoring Icequakes in East Antarctica with the Raspberry Shake

Abstract We evaluate the performance of the low-cost seismic sensor Raspberry Shake (RS) to identify and monitor icequakes (which occur when glacial ice experiences brittle deformation) in extreme environments. In January 2020, three RS3D sensors were installed on a katabatic wind-scoured blue ice area (BIA) close to the Princess Elisabeth Antarctica research station in Dronning Maud Land, East Antarctica. The sensors were configured for Antarctic deployment and placed in insulated enclosures to protect them from harsh weather systems. The RS network (installed in a triangular array) performed well in the cold and with rapid air temperature change, as diurnal temperatures fluctuated from a high of 0.0°C to a minimum temperature of −15.0°C. Although battery connectivity issues in one unit limit full triangulation of seismic signals, and high background noise may mask some seismic signals, data from the RS2 unit reveals that 2936 icequakes were detected over a 10-day period. The temporal occurrence of these icequakes, combined with satellite-derived surface temperature measurements and automatic weather station data, suggest that diurnal fluctuations in solar radiation control ice surface temperature changes, driving thermal contraction of the ice. Seismic investigations like these can therefore provide information on the thermal state and ice fracture mechanics of ablation zones such as BIAs. Our work highlights the potential application of the RS (after minimal modification) in glaciated environments where equipment often needs to be portable, temporary and lightweight, and able to perform in extreme weather conditions.</jats:p

Low-Cost Automatic Slope Monitoring Using Vector Tracking Analyses on Live-Streamed Time-Lapse Imagery

Identifying precursor events that allow the timely forecasting of landslides, thereby enabling risk reduction, is inherently difficult. Here we present a novel, low cost, flow visualization technique using time-lapsed imagery (TLI) that allows real time analysis of slope movement. This approach is applied to the Rest and Be Thankful slope, Argyle, Scotland, where past debris flows have blocked the A83 or forced preemptive closure. TLI of the Rest and Be Thankful are taken from a fixed station, 28 mm lens, time lapse camera every 15 min. Imagery is filtered to counter the effects of misalignment from wind induced vibration of the camera, asymmetric lighting, and fog. Particle image velocimetry (PIV) algorithms are then run to produce slope movement velocity vectors. PIV generated vectors are automatically post-processed to separate vectors generated by slope movement from false positives generated by harsh environmental conditions. Results for images over a 20-day period indicated precursor slope movement initiated by a rainfall event, a period of quiescence for 10 days, followed by a large landslide failure during proceeding rainfall where over 3000 tons of sediment reached the road. Results suggest low cost, live streamed TLI and this novel PIV approach correctly detect and, importantly, report precursor slope movement, allowing early warning, effective management and landslide impact mitigation. Future applications of this technique will allow the development of an effective decision-making tool for asset management of the A83, reducing the risk to life of motorists. The technique can also be applied to other critical infrastructure sites, allowing hazard risk reduction.</jats:p

Spatial variation of hydroclimate in north-eastern North America during the last millennium

Climatic expressions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) vary regionally, with reconstructions often depicting complex spatial patterns of temperature and precipitation change. The characterisation of these spatial patterns helps advance understanding of hydroclimate variability and associated responses of human and natural systems to climate change. Many regions, including north-eastern North America, still lack well-resolved records of past hydrological change. Here, we reconstruct hydroclimatic change over the past millennium using testate amoeba-inferred peatland water table depth reconstructions obtained from fifteen peatlands across Maine, Nova Scotia, Newfoundland and Québec. Spatial comparisons of reconstructed water table depths reveal complex hydroclimatic patterns that varied over the last millennium. The records suggest a spatially divergent pattern across the region during the Medieval Climate Anomaly and the Little Ice Age. Southern peatlands were wetter during the Medieval Climate Anomaly, whilst northern and more continental sites were drier. There is no evidence at the multi-decadal sampling resolution of this study to indicate that Medieval mega-droughts recorded in the west and continental interior of North America extended to these peatlands in the north-east of the continent. Reconstructed Little Ice Age hydroclimate change was spatially variable rather than displaying a clear directional shift or latitudinal trends, which may relate to local temporary permafrost aggradation in northern sites, and reconstructed characteristics of some dry periods during the Little Ice Age are comparable with those reconstructed during the Medieval Climate Anomaly. The spatial hydroclimatic trends identified here suggest that over the last millennium, peatland moisture balance in north-eastern North America has been influenced by changes in the Polar Jet Stream, storm activities and sea surface temperatures in the North Atlantic as well as internal peatland dynamics