Landslide Deposits Research Articles

An Experimental Study on the Hydromechanical Behaviours of the Evolution of Postearthquake Landslide Deposits

In this study, a series of experiments of the full-scale physical model was employed to investigate the hydromechanical behaviours of the postearthquake landslide evolution, in forms of rill erosion and shallow headward failure on the rill bank slopes under unsaturated conditions. Soil-water characteristic curves (SWCC) were established using the Brooks-Corey (BC) and van Genuchten (VG) models. The stability of the shallow failure was then analyzed via a one-dimensional and unsaturated stability analysis model of the infinite slope. This measurement revealed that the preferential flow and the matrix flow coexisted when infiltration occurred and the VG model performs better in fitting the SWCC than the BC model. Consistent feedback between stability calculations and experimental observations enables the analysis of mechanisms of rill erosion and slope failure of postseismic landslide under the impact of preferential flow. Furthermore, the seepage-induced internal erosion phenomenon was observed in the experiment. This work thus provides a new perspective on the triggering mechanisms of debris flow during the postseismic period.

Mechanism of a low-angle translational block slide: evidence from the September 2018 Naga landslide, Philippines

There is a general lack of understanding on the detailed processes and mechanism of low-angle translational block slides. The September 20, 2018 Naga landslide, with a volume of 27 M m3 and a runout distance of 1.34 km, provided new insights on the initiation, transport, and deposition mechanisms of this type of landslide. Drone photogrammetry, video footage, satellite images, slope stability analyses, and field evidence revealed that the landslide occurred as multiple block detachments along a series of tension cracks that formed and grew progressively prior to the main failure. Predominance of intact upright blocks traceable to the distal end of the deposit indicates dominant translational motion. Facies within the Naga landslide deposit revealed that at least three processes (slide, dry flow, and fall) occurred during the main movement. Post-slide processes immediately after emplacement included small avalanches and rockfalls related to the instability of the landslide deposit and the main scarp. Preliminary slope stability analyses showed that the slopes were marginally unstable (FoS 0.67–3.96) even in dry conditions. The low-angle profile of the slip surface (6°) favors stability, but low shear strength of the limestone bedrock and unsupported cut slopes may have contributed to the failure.

Enhanced landslide mobility by basal liquefaction: The 2014 State Route 530 (Oso), Washington, landslide

AbstractLandslide mobility can vastly amplify the consequences of slope failure. As a compelling example, the 22 March 2014 landslide near Oso, Washington (USA), was particularly devastating, traveling across a 1-km+-wide river valley, killing 43 people, destroying dozens of homes, and temporarily closing a well-traveled highway. To resolve causes for the landslide’s behavior and mobility, we conducted detailed postevent field investigations and material testing. Geologic and structure mapping revealed a progression of geomorphological structures ranging from debris-flow lobes at the distal end through hummock fields, laterally continuous landslide blocks, back-rotated blocks, and finally colluvial slides and falls at the landslide headscarp. Primary structures, as well as stratigraphic and vegetation patterns, in the landslide deposit indicated rapid extensional motion of the approximately 9 × 106 m3 source volume in a closely timed sequence of events. We identified hundreds of transient sand boils in the landslide runout zone, representing evidence of widespread elevated pore-water pressures with consequent shear-strength reduction at the base of the slide. During the event, underlying wet alluvium liquefied and allowed quasi-intact slide hummocks to extend and translate long distances across the flat valley. Most of the slide material itself did not liquefy. Using geotechnical testing and numerical modeling, we examined rapid undrained loading, shear and collapse of loose saturated alluvium, and strong ground shaking as potential liquefaction mechanisms. Our analyses show that some layers in the alluvium can liquefy when sheared, as could occur with rapid undrained loading. Simultaneous ground shaking could have contributed to pore-pressure generation as well. Two key elements, a large and rapid failure overriding wet liquefiable sediments, enabled the landslide’s high mobility. Basal liquefaction may enhance mobility of other landslides in similar settings.

Earthquake‐Induced Chains of Geologic Hazards: Patterns, Mechanisms, and Impacts

AbstractLarge earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate‐ and large‐magnitude earthquakes trigger landslides, ranging from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake‐induced landslides and their consequences: the magnitude M 7.6 Chi‐Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface.

Geomorphologic and Glacial Evolution of the Cachapoal and southern Maipo catchments in the Andean Principal Cordillera, Central Chile (34°-35º S)

We present here a reconstruction of the post late Miocene landscape evolution of the western slope of the Andean Cordillera Principal near 34°20’ S. We base our analysis on the available geological information, a morphological characterization of the landform assemblages in the Cachapoal and southern Maipo catchments, and the first 10Be exposure ages for moraines in this area. The Cachapoal drainage basin is characterized by a variety of morphological features, like an elevated low-relief surface, volcanoes and lava flows on valley slopes, U-shaped valley sections, roches moutonnées, and large glaciated areas. Different kinds of deposits have been included in the study, such as moraines, lacustrine and landslide deposits, and a well-developed system of fluvial terraces in the more distal part of the Cachapoal catchment. Landslides are mostly developed on rocks of the late Eocene-early Miocene Abanico Formation. and are less frequent in outcrops of the overlying, early to middle Miocene Farellones Formation. We estimate that the lowest end moraine in the Cachapoal catchment is located next to the locality Bocatoma Chacayes (~950 m altitude), though covered by a major landslide. No evidence exist for glacial deposits further down stream in this region. Lateral moraine ridges of the Cachapoal Glacier at Los Cerrillos yielded 10Be exposure ages of 20.3±2.9 and 21.9±5.3 ka that indicate they are associated with the Last Glacial Maximum (LGM). Holocene moraines exist next to all glacier tongues. Of particular interest in this region is the 12 km-long debris-covered Cachapoal Glacier, the longest valley glacier in the central Chilean Andes, and its distal and proximal moraine deposits. Two lateral moraines adjacent to the present-day Cachapoal Glacier yielded exposure average ages of 13.5±2.4 ka for the external ridge, indicating the Younger Dryas, and 3.8±0.8 ka for the internal ridge, an age that coincides with the 4.2 ka global climatic event that marks the beginning of the Meghalayan Age, at the end of the Holocene. The large size of this moraine on both sides of the ice tongue indicates the great development of the glacier at that time. Some of these ages coincide with ages obtained further north in the Maipo drainage basin, at the latitude of Santiago, and in the eastern flank of the cordillera, however, no pre-LGM deposits were found here, unlike the other mentioned regions. This difference together with the much lower altitude of the LGM moraine deposits in the study region suggests that the Cachapoal catchment is a transition zone to a more humid region further south, and indicates the great need for further reconnaissance and dating of glacial deposits in this Andean region. Our analysis of the geomorphological evolution is consistent with incision start for the Cachapoal Valley in latest Miocene. In this process, glacier incision was apparently not much effective until mid-Pleistocene time, when volcanism was active in the higher regions of the mountain range covering areas not yet incised, whereas in the western Principal Cordillera lavas flowed in deeply incised valleys. Pleistocene glaciers deepened and shaped the already incised valleys, which are presently mostly occupied by rivers.

Testing a failure surface prediction and deposit reconstruction method for a landslide cluster that occurred during Typhoon Talas (Japan)

Abstract. Reconstructions of failure surfaces (prior to potential landslides or after their release), landslide deposits, or other palaeotopographic features are important for hazard and erosion assessment. The volumes involved in landslide and failure surfaces constrain the propagation of a landslide, and knowledge of the past topography helps us to understand these hazards. Some methods exist to characterise landslide geometry, but these methods usually require monitoring information. This study tries to assess the validity of the sloping local base level (SLBL) method for this purpose. Two sets of airborne lidar digital elevation models (DEMs) of the Kii Peninsula (Japan) are used: the first one was acquired before Typhoon Talas, and the second one was acquired after. A total of 70 deep-seated landslides occurred during this event between 2 and 5 September 2011. This study shows that the SLBL method is efficient using either the slope deformations identifiable on the DEM before the release of the landslide or a reliable 2.5-D failure surface created by using both DEMs (the 2.5-D corresponds to a surface which has only one z value for each x–y coordinate; in other words, no true vertical topography or overhang can be represented perfectly). In addition, this method allows for the reconstruction of eroded deposits and buried valleys. Most of the volumes estimated are within ±35 % of the estimation made by Chigira et al. (2013), and the coefficients of expansion range from 10 % to 25 %. These results show considerable sensitivity to the parameters used for the reconstruction of the landslide volume estimations and demonstrate the need for an efficient and fast tool to reconstruct potential landslide geometries or histories.

Field investigation and numerical simulation of the seismic triggering mechanism of the Tahman landslide in eastern Pamir, Northwest China

Landslides are one of the most common geological hazards in many parts of the world, which have brought catastrophic consequences to mankind. Seismic shaking can be an important trigger factor generally resulting in large-scale landslides. For some paleolandslides triggered by earthquakes, despite the lack of historical records, certain paleoseismic parameters can be back-analyzed. In this paper, the discrete element method (DEM) was applied to back-analyze the peak ground acceleration (PGA) triggering the Tahman landslide, a paleolandslide located in eastern Pamir, northwest China. Firstly, detailed field geological and geomorphological investigation was conducted to reveal the natural and seismic characteristics of the landslide. Subsequently, discrete element modeling was carried out. Simulation results suggested that the Tahman rock slope was stable under natural conditions. Owing to arid climate and water shortage of the study area, the influence of water was ignored. Additionally, from the perspective of the occurrence time of the landslide and geomorphologic feature of the deposits, the landslide was not caused by glacier activity and freeze–thaw events, and thus, must have been triggered by an earthquake. A peak ground acceleration (PGA) of 0.55 g was found to be a critical value for triggering landslides, and a PGA of 0.76 g could best simulate the kinematic process of a landslide when the simulation results were calibrated against the current geomorphological features of the landslide deposits. It can be concluded from the present study that: (1) PGA amplification in the rock slope was related to the topography during earthquake excitation; (2) the effective duration of the seismic wave had a considerable impact on the back-analyzed PGA, which decreased with increasing effective duration; and (3) the long runout of the Tahman landslide was due to its large volume and the interaction of the slide mass with moraines.

Predicting debris-flow clusters under extreme rainstorms: a case study on Hong Kong Island

Debris flows can cause severe loss of human lives and damage to property, especially on densely populated hilly terrains. In the changing climate, the frequency of debris flows is on a rising trend. Therefore, it is important to forecast possible scenarios of debris flows under extreme weather conditions. Previous numerical studies often deal with one individual debris flow in one analysis. Yet a large number of debris flows can occur in a large storm. This paper presents a physically based model to predict likely debris flow clusters on Hong Kong Island with an area of approximately 80 km2 considering the influence of the changing climate. Firstly, a slope stability analysis is conducted, and unstable cells and landslide deposition areas are predicted. Then clusters of debris flows initiating from these landslides are simulated considering hillslope erosion. The models are validated with historical debris flows triggered by a rainstorm in 2008. Finally, debris flow clusters under three reference extreme rainstorms (i.e. 44%, 65% and 85% of the 24-h probable maximum precipitation, PMP) are predicted. With the increase of rainstorm magnitude, numerous debris flows can occur simultaneously and merge, posing much greater threat to society. The consequences of debris flows grow dramatically when the magnitude reaches a certain extent, i.e. 65% of the 24-h PMP.

From catastrophic collapse to multi-phase deposition: Flow transformation, seafloor interaction and triggered eruption following a volcanic-island landslide

The current understanding of tsunamis generated by volcanic-island landslides is reliant on numerical models benchmarked against reconstructions of past events. As the largest historical event with timed tsunami observations, the 1888 sector collapse of Ritter Island, Papua New Guinea provides an outstanding opportunity to better understand the linked process of landslide emplacement and tsunami generation. Here, we use a combination of geophysical imaging, bathymetric mapping, seafloor observations and sampling to demonstrate that the Ritter landslide deposits are spatially and stratigraphically heterogeneous, reflecting a complex evolution of mass-flow processes. The primary landslide mass was dominated by well-bedded scoriaceous deposits, which rapidly disintegrated to form an erosive volcaniclastic flow that incised the substrate over much of its pathway. The major proportion of this initial flow is inferred to have been deposited up to 80 km from Ritter. The initial flow was followed by secondary failure of seafloor sediment, over 40 km from Ritter. The most distal part of the 1888 deposit has parallel internal boundaries, suggesting that multiple discrete units were deposited by a series of mass-flow processes initiated by the primary collapse. The last of these flows was derived from a submarine eruption triggered by the collapse. This syn-collapse eruption deposit is compositionally distinct from pre- and post-collapse eruptive products, suggesting that the collapse immediately destabilised the underlying magma reservoir. Subsequent eruptions have been fed by a modified plumbing system, constructing a submarine volcanic cone within the collapse scar through at least six post-collapse eruptions. Our results show that the initial tsunami-generating landslide at Ritter generated a stratigraphically complex set of deposits with a total volume that is several times larger than the initial failure. Given the potential for such complexity, there is no simple relationship between the volume of the tsunamigenic phase of a volcanic-island landslide and the final deposit volume, and deposit area or run-out cannot be used to infer primary landslide magnitude. The tsunamigenic potential of prehistoric sector-collapse deposits cannot, therefore, be assessed simply from surface mapping, but requires internal geophysical imaging and direct sampling to reconstruct the event.

Tsunami Squares modeling of landslide generated impulsive waves and its application to the 1792 Unzen-Mayuyama mega-slide in Japan

The frequent occurrence of landslide tsunami has aroused great social concern, hence an efficient approach for modeling the phenomena is required urgently. Herein, we present and supplement a meshless numerical model named ‘Tsunami Squares’ (TS). TS simulates both the landslide and its generated wave using an updated numerical scheme that has enhanced computational efficiency. TS also provides an artful way of approximating linear dispersive wave propagation and non-linear wave inundation that makes it quite capable of simulating real-scale events. A well-designed test that compares TS output with an analytical formula for a tsunami propagation calculation provides firm validation of the approach. We then applied the ‘Tsunami Squares’ to simulate the 1792 Unzen-Mayuyama mega slide and generated tsunami. This event remains the largest volcanic disaster in the history of Japan. Landslide dynamics simulated by TS coincide with historical reports and the known geometry of landslide deposits. The model output of tsunami runup heights well match the observed values recorded by the locations of historical ‘Tsunami Stones’. This well documented and data-rich case further validates the ‘Tsunami Squares’ model and the excellent reproduction of the 1792 event provides new insights for better understanding of landslide tsunami hazards.

Seismic cycles, earthquakes, landslides and sediment fluxes: Linking tectonics to surface processes using a reduced-complexity model

In tectonically active mountain ranges, landslides triggered by earthquakes mobilise large volumes of sediment that affect river dynamics. This sediment delivery can cause downstream changes in river geometry and transport capacity that affect the river efficiency to export this sediment out of the epicentre area. The subsequent propagation of landslide deposits in the fluvial network has implications for the management of hazards downstream and for the long-term evolution of topography over multiple seismic cycles. A full understanding of the processes and time scales associated with the removal of landslide sediment by rivers following earthquakes however, is still lacking. Here, we propose a nested numerical approach to investigate the processes controlling the post-seismic sediment evacuation at the mountain range scale, informed by results from a reach scale model. First, we explore the river morphodynamic response to a landslide cascade at the reach-scale using a 2D modelling approach. The results are then used to describe empirically the evacuation of a landslide volume which avoids using a computationally extensive model in catchments which may have thousands of co-seismic landslides. Second, we propose a reduced-complexity model to quantify evacuation times of earthquake-triggered landslide clusters at the scale of a mountain range, examining the hypothetical case of a Mw 7.9 earthquake and its aftershocks occurring on the Alpine Fault, New Zealand. Our approach combines an empirical description of co-seismic landslide clusters with the sediment export processes involved during the post-seismic phase. Our results show that the inter-seismic capacity of the mountain range to evacuate co-seismic sediment is critical to assess the sediment budget of large earthquakes, over one to several seismic cycles. We show that sediment evacuation is controlled by two timescales, 1. the transfer time of material from hillslopes to channels and 2. the evacuation time of the landslide deposits once it has reached the fluvial network. In turn, post-seismic sediment evacuation can either be connectivity-limited, when sediment delivery along hillslopes is the main limiting process, or transport-limited, when the transport by rivers is the limiting process. Despite high values of runoff, we suggest that the Southern Alps of New Zealand are likely to be in connectivity-limited conditions, for connection velocities <10 m.yr−1. Connection velocities >2 m.yr−1 are sufficient to allow most of co-seismic sediments to be mobilised and potentially exported out of the range within less than one seismic cycle. Because of the poorly-constrained rate of sediment transfer along hillslopes, our results potentially raise the issue of co-seismic sediment accumulation within mountain ranges over several seismic cycles and of the imbalance between tectonic inputs and sediment export. We, therefore, call for renewed observational efforts to better describe and quantify the physical processes responsible for the redistribution and mobilization of sediment from landslide scars and deposits.

Molards as an indicator of permafrost degradation and landslide processes

Molards have been defined in the past as conical mounds of debris that can form part of a landslide's deposits. We present the first conclusive evidence that molards in permafrost terrains are cones of loose debris that result from thawing of frozen blocks of ice-rich sediments mobilised by a landslide, and hence propose a rigorous definition of this landform in permafrost environments. We show that molards can be used as an indicator of permafrost degradation, and that their morphometry and spatial distribution give valuable insights into landslide dynamics in permafrost environments. We demonstrate that molards are readily recognisable not only in the field, but also in remote sensing data; surveys of historic aerial imagery allow the recognition of relict molards, which can be used as an indicator of current and past permafrost conditions. The triggering of landslides as a result of permafrost degradation will arguably occur more often as global atmospheric temperatures increase, so molards should be added to our armoury for tracking climate change, as well as helping us to understand landslide-related hazards. Finally, we have also identified candidate molards on Mars, so molards can inform about landscape evolution on Earth and other planetary bodies.

Mineralogy of siliceous concretions, cretaceous of ionian zone, western Greece: Implication for diagenesis and porosity

Siliceous (chert) concretions are a prominent component of Cretaceous limestones in the Ionian zone of western Greece. This study investigates the diagenetic evolution of such cherts from two localities: largely undeformed strata on Kastos Island and highly faulted strata at Araxos. In both areas, lower Cretaceous limestones contain abundant small chert nodules, whereas in the upper Cretaceous nodules are larger but less abundant. Seventy seven powdered samples, from 67 representative field samples, were analyzed by X-ray Powder diffraction (XRPD). The analyzed samples came from both nodular and siliceous beds and showed that quartz is the dominant mineral, with rare to common residual calcite. The presence of moganite and opal-A minerals suggests that quartz recrystallized from original amorphous silica. A few samples from Araxos contain traces of halite and anhydrite. The variability in the calcite content and the presence/absence of halite and anhydrite in the different studied areas are related with the different tectonic activity in these areas, with more intense tectonic activity in NW Peloponnesus than in Kastos Island. Size of nodules is related to variation in primary porosity of the host rocks. Finally, the presence of dolomite was related with the pre-existing underlying dolomites of Early Cretaceous age in Ionian basin, whereas the presence of maghemite is due to the presence of iron minerals in water solutions. • Zoned chert nodules and beds in Cretaceous calcturbidites and landslide deposits. • Moganite and opal-A minerals recrystallized from original amorphous silica. • Size of chert concretions related to porosity of host limestones. • Dolomite in cherts only where underlying dolostone. • Halite and anhydrite in cherts due to Paleogene deformation of Triassic evaporites .

Evaluating emplacement temperature of a 1000-year sequence of mass flows using paleomagnetism of their deposits at Mt. Taranaki, New Zealand

Temperature can be an important characteristic used to distinguish primary pyroclastic density currents or block-and-ash flows from other collapses not primarily related to an eruption, and also governs the type and level of hazard presented by these mass flows. We examined several mass-flow deposits within the AD1000-1800 Maero Formation at Mt. Taranaki, New Zealand, for field characteristics of hot emplacement - such as the presence of charcoal, baking of soils, or gas-elutriation piping - and conducted a paleomagnetic study of their thermoremanent magnetization (TRM) to determine emplacement temperatures. Results show that the majority of the deposits result from block-and-ash flows emplaced over ~500°C. Some of these deposits were indistinguishable in the field from a re-worked or low-temperature emplaced lahar or landslide deposit, indicating that sedimentary features are not a clear determinant of high emplacement temperature. The high emplacement temperatures suggest that the time between dome emplacement and collapse during this period was usually brief (&lt;30 years), with some events consisting of rapid and repeated growth and collapse of lava domes, possibly within the same prolonged lava effusion episode.

Reactivation of a huge ancient landslide by surface water infiltration

An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finite-element method (FEM)-based models. The results show that the reactivation of old landslide deposit was triggered by the long-term leakage of diversion ditch before October 2012, and the reactivation was triggered again by the intense rainfall on 7–9 October 2012. The old cracks, which formed in the earlier reactivation of landslide, played a key role for the rainfall infiltration. They offered a preferential path for much more rainfall to infiltrate fast into deep soil, and caused wetting front to move down faster in landslide. The old slip zone with lower permeability was another important factor to cause the infiltrated water to accumulate and form a high pore water pressure above slip zone. Then the high pore water pressure decreased the shear strength of slip zone and triggered the reactivation of the old landslide deposit again.

Permeation grouting in Chelburn Valley

Upper Chelburn Impounding Reservoir is situated within Chelburn Valley, located approximately 2 km north of Littleborough in Rochdale, England. Upper Chelburn is formed by two embankments with the north embankment being the main embankment containing the draw-off and overflow facilities. The embankment is homogenous, founded on old landslide deposits, glacial clay material and weathered bedrock. The dam has a history of leakage issues, in particular the right-hand abutment, which has resulted in a number of remediation works. In 2013 United Utilities undertook an internal erosion assessment for the dam which identified an intolerable risk of failure by contact erosion between the embankment and the cohesionless soil foundation. In response, permeation grouting remedial works were completed in 2017, targeting this cohesionless soil foundation zone. While supervising the construction works a number of issues were encountered, including the requirement for high quantities of grout at numerous locations and the potential ineffectiveness of a historically grouted zone. In order to mitigate these issues, effective management of safety, health and environment, quality, programme, contractor management, cost and design was required by the supervisor (author) throughout the works. The supervisor applied a comprehensive understanding and interpretation of the ground model when looking at the required grout zone.

Deep Electrical Resistivity Tomography for the Hydrogeological Setting of Muro Lucano Mounts Aquifer (Basilicata, Southern Italy)

The proposed work concerns the application of a deep geoelectrical survey to a carbonate aquifer in order to define the best location for exploitation well drilling for increasing water supply. However, an optimal characterization of a groundwater resource is the necessary condition to reach the indicated aim. Therefore, the geoelectrical investigation was guided from the previous geological and hydrogeological characterization. Moreover, geophysical methods are good tools to improve the groundwater model when detailed information is necessary, such as the localization of a pumping well. The work summarizes the hydrogeological knowledge at the West of the Basilicata Region (Muro Lucano, Italy). The investigated area is characterized by the presence of a karst aquifer which is made up of a carbonate ridge (Castelgrande, Muro Lucano) that tectonically dips southward and is widely covered by Pliocene deposits (sands and conglomerates), by the Irpinian unit and Sicilide unit formations, and by debris slope and landslide deposits. The assessment of the complex hydrogeological framework of the area was detailed by the use of a new multichannel deep geoelectrical technique (DERT). In details, the proposed technique was able to successfully locate a less resistive zone connected to a more fractured limestone and then it was suitable for the localization of a groundwater exploitation well.

A Simplified, Object-Based Framework for Efficient Landslide Inventorying Using LIDAR Digital Elevation Model Derivatives

Landslide inventory maps are critical to understand the factors governing landslide occurrence and estimate hazards or sediment delivery to channels. Numerous semi-automated approaches for landslide inventory mapping have been proposed to improve the efficiency and objectivity of the process, but these methods have not been widely adopted by practitioners because of the use of input parameters without physical meaning, a lack of transparency in machine-learning based mapping techniques, and limitations in resulting products, which are not ordinarily designed or tested on a large-scale or in diverse geologic units. To this end, this work presents a new semi-automated method, called the Scarp Identification and Contour Connection Method (SICCM), which adapts to diverse geologic settings automatically or semi-automatically using interventions driven by simple inputs and interpretation from an expert mapper. The applicability of SICCM for use in landslide inventory mapping is demonstrated for three diverse study areas in western Oregon, USA by assessing the utility of the results as a landslide inventory, evaluating the sensitivity of the algorithm to changes in input parameters, and exploring how geology influences the resulting landslide inventory results. In these case studies, accuracies exceed 70%, with reliability and precision of nearly 80%. Conclusions of this work are that (1) SICCM efficiently produces meaningful landslide inventories for large areas as evidenced by mapping 216 km2 of landslide deposits with individual deposits ranging in size from 58 to 1.1 million m2; (2) results are predictable with changes to input parameters, resulting in an intuitive approach; (3) geology does not appear to significantly affect SICCM performance; and (4) the process involves simplifications compared with more complex alternatives from the literature.

Geomorphological effects of the 1840 Ahora Gorge catastrophe on Mount Ararat (Eastern Turkey)

Ahora Gorge is a 400 m deep canyon located along the North Eastern flank of Mt. Ararat (Turkey), a compound volcanic complex covered by an ice cap. In the past, several diarists and scientific authors reported a calamitous event on July 2, 1840, when a landslide triggered by a volcanic eruption and/or an earthquake obliterated several villages located at the foot of the volcano. The reasons and effects of this Ahora Gorge Catastrophe (AGC) event have been obscure and ambiguous. To reappraise the 1840 catastrophe and the geomorphic evolution of the Ahora Gorge, we used high-resolution satellite images, remote sensing thermal data supplemented by observations collected during two field surveys. According to our interpretation, an earthquake in 1840 triggered an abrupt volcanic eruption, which caused the consequent rapid melting of glacial ice and mountain snow. This event produced significant mud and ice flow along the Ahora Gorge that inundated the villages downslope. The flooding, which we interpret as a lahar, deposited a wide alluvial fan at the foot of the volcano. Today, an elongated landform present within the Ahora Gorge has alternately been interpreted as a landslide deposit. Our multi-data integrated analysis and ground-based observations demonstrate that this feature is an unmapped glacier. The shape of the landform coupled with ASTER thermal satellite data and ground-based observations reveal that a debris-covered glacier (DCG) formed soon after the catastrophic lahar. Our discovery of the Ahora Gorge Glacier in context of a reappraisal of the Ahora Gorge Catastrophe demonstrates the contribution of glaciers in shaping the landscape near ice-capped volcanoes. Moreover, our data underscore the importance of being more aware of the potential future geo-hazards posed by Mount Ararat, particularly where glaciers are still present along several valleys and seismically-induced lahar events might occur.

Olistostrome and its implications to geological disaster on coastal area with special reference to the Bantimala tectonic complex, Pangkep Regency South Sulawesi Province

Olistostrome is clastic sedimentary rock, its formation related to tectonic activity along the plate subduction edge on the front region of the accretion prism. Its formation is a submarine landslide with a mudflow sediment mass. The material components can be mixed from various continental and oceanic sources. As in the complex area of Bantimala tectonics, olistostrome shows typical properties of ugly sorting, floating rock blocks in the sandy matrix, tectonite textures, and constituent rocks generally in the form of metamorphic rocks of subduction and plate collision. The criterion shows the submarine sludge deposits formed in the subduction tectonic area of the marine trough environment where there is an increase in slope due to subduction accretion. This study aims to examine the characteristics of olistostrome as a landslide deposit in the subduction zone about the correlation of disaster in convergent tectonic areas in the present. In the area of Bantimala, the exposure of olistostrome rock is large enough with large dimensions with a mega-landslide. This can happen by earthquakes or critical slope in the past. This phenomenon can be a reference to disaster present-day in subduction areas, as in the island arc of Indonesia, which is a collision area of three plates very vulnerable to this disaster. A submarine landslide can cause disaster to infrastructure, telecommunication cable, gas hydrate dissolution, tsunami disaster and environmental destruction of marine benthos.