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This study presents a new methodology to identify landslide and landslide-susceptible locations in Interior Alaska using only geomorphic properties from light detection and ranging (LiDAR) derivatives (i.e., slope, profile curvature, and roughness) and the normalized difference vegetation index (NDVI), focusing on the effect of different resolutions of LiDAR images. We developed a semi-automated object-oriented image classification approach in ArcGIS 10.5 and prepared a landslide inventory from visual observation of hillshade images. The multistage work flow included combining derivatives from 1-, 2.5-, and 5-m-resolution LiDAR, image segmentation, image classification using a support vector machine classifier, and image generalization to clean false positives. We assessed classification accuracy by generating confusion matrix tables. Analysis of the results indicated that LiDAR image scale played an important role in the classification, and the use of NDVI generated better results. Overall, the LiDAR 5-m-resolution image with NDVI generated the best results with a kappa value of 0.55 and an overall accuracy of 83 percent. The LiDAR 1-m-resolution image with NDVI generated the highest producer accuracy of 73 percent in identifying landslide locations. We produced a combined overlay map by summing the individual classified maps that was able to delineate landslide objects better than the individual maps. The combined classified map from 1-, 2.5-, and 5-m-resolution LiDAR with NDVI generated producer accuracies of 60, 80, and 86 percent and user accuracies of 39, 51, and 98 percent for landslide, landslide-susceptible, and stable locations, respectively, with an overall accuracy of 84 percent and a kappa value of 0.58. This semi-automated object-oriented image classification approach demonstrated potential as a viable tool with further refinement and/or in combination with additional data sources.

Within the Brooks Range of Alaska, several frozen debris lobes (FDLs) – or slow-moving landslides in permafrost – are approaching critical infrastructure. FDL-A, the largest and closest of these features, was 32.3 m from the toe of the Dalton Highway as of October 2016. Here we present the analysis of nearly three years of data from a MEMS-based in-place inclinometer installed within FDL-A. Analysis of the strain within the active layer indicates that it is closely tied to air temperature and water, suggesting that cooling and/or draining the FDL may be effective mitigation techniques. Within the lobe body, strain rates are comparable to those measured within rock glaciers. Using the cyclical pattern and phase lag identified within the strain data, and surface movement rates 1) derived from historic imagery analysis and InSAR data, and 2) measured using a differential GPS system, we developed and vetted a predictive function for surface movement of FDL-A. The predictive function indicates that FDL-A moves at an average rate of 4.9 m yr − 1 , reaching a maximum velocity of 7.9 m yr − 1 during the fall, and falling to 1.9 m yr − 1 in the early spring. We hypothesize that the seasonal movement pattern is due to the infiltration of snow melt, and the subsequent reduction of effective stress within the shear zone. Using the predictive function and the measured October 2016 distance, we predict that FDL-A will reach the current Dalton Highway embankment during early 2023.

Frozen debris lobes (FDLs) are large masses of soil, rock, incorporated organic material, and ice moving down permafrost-affected slopes in the south-central Brooks Range, Alaska. In this paper, we focus on FDL-A, which is an impending geohazard to the Dalton Highway, located just under 40 m away from the highway embankment. We present the results of multi-faceted research, including field-based studies, laboratory testing of soil samples, slope stability analysis, and a GIS analysis. Subsurface instrumentation indicates that major movement of FDL-A occurs in a shear zone 20.6 to 22.8 m below the ground surface, with temperature-dependent internal flow as a secondary movement mechanism. Surface measurements show an overall average rate of movement of 1.2 cm per day, which is an increase over historic rates. The slope stability analysis required a back analysis to determine soil strength parameters at failure, resulting in cohesion values between 43 to 53 kPa and friction angles between 10° and 16°. The modeling results indicated a high sensitivity to pore water pressure and cohesion. This is critical since the melting of massive ice and thawing of frozen soil will increase pore water pressure and lower shear strength, resulting in the acceleration of FDL-A towards the Dalton Highway. The GIS analysis also provided insight into the movement and instability of FDL-A, and provided groundwork for a GIS protocol to examine catchment and lobe features of all FDLs along the highway corridor.

Frozen debris lobes (FDLs) are elongated, lobate permafrost features that mostly move through shear in zones near their bases. We present a comprehensive overview of eight FDLs within the Dalton Highway corridor (southern Brooks Range, Alaska), including their catchment geology and rock strengths, lobe soil characteristics, surface movement measurements collected between 2012 and 2015, and analysis of historic and modern imagery from 1955 to 2014. Field mapping and rock strength data indicate that the metasedimentary and metavolcanic bedrock forming the majority of the lobe catchments has very low to medium strength and is heavily fractured, thus easily contributing to FDL formation. The eight investigated FDLs consist of platy rocks typical of their catchments, organic debris, and an ice-poor soil matrix; massive ice, however, is present within FDLs as infiltration ice, concentrated within cracks open to the surface. Exposure of infiltration ice in retrogressive thaw slumps (RTSs) and associated debris flows leads to increased movement and various stages of destabilization, resulting in morphological differences among the lobes. Analysis of historic imagery indicates that movement of the eight investigated FDLs has been asynchronous over the study period, and since 1955, there has been an overall increase in movement rates of the investigated FDLs. The formation of surface features, such as cracks, scarps, and RTSs, suggests that the increased movement rates correlate to general instability, and even at their current distances, FDLs are impacting infrastructure through increased sediment mobilization. FDL-A is the largest of the investigated FDLs. As of August 2015, FDL-A was 39.2 m from the toe of the Dalton Highway embankment. Based on its current distance and rate of movement, we predict that FDL-A will reach the Dalton Highway alignment by 2023.

Ice wedges are common features of the subsurface in permafrost regions. They develop by repeated frost cracking and ice vein growth over hundreds to thousands of years. Ice-wedge formation causes the archetypal polygonal patterns seen in tundra across the Arctic landscape. Here we use field and remote sensing observations to document polygon succession due to ice-wedge degradation and trough development in ten Arctic localities over sub-decadal timescales. Initial thaw drains polygon centres and forms disconnected troughs that hold isolated ponds. Continued ice-wedge melting leads to increased trough connectivity and an overall draining of the landscape. We find that melting at the tops of ice wedges over recent decades and subsequent decimetre-scale ground subsidence is a widespread Arctic phenomenon. Although permafrost temperatures have been increasing gradually, we find that ice-wedge degradation is occurring on sub-decadal timescales. Our hydrological model simulations show that advanced ice-wedge degradation can significantly alter the water balance of lowland tundra by reducing inundation and increasing runoff, in particular due to changes in snow distribution as troughs form. We predict that ice-wedge degradation and the hydrological changes associated with the resulting differential ground subsidence will expand and amplify in rapidly warming permafrost regions. The polygonal patterns in permafrost regions are caused by the formation of ice wedges. Observations of polygon evolution reveal that rapid ice-wedge melting has occurred across the Arctic since 1950, altering tundra hydrology.

We present the results of a reconnaissance investigation of unusual debris mass-movement features on permafrost slopes that pose a potential infrastructure hazard in the south-central Brooks Range, Alaska. For the purpose of this paper, we describe these features as frozen debris-lobes. We focus on the characterisation of frozen debris-lobes as indicators of various movement processes using ground-based surveys, remote sensing, field and laboratory measurements, and time-lapse observations of frozen debris-lobe systems along the Dalton Highway. Currently, some frozen debris-lobes exceed 100 m in width, 20 m in height and 1000 m in length. Our results indicate that frozen debris-lobes have responded to climate change by becoming increasingly active during the last decades, resulting in rapid downslope movement. Movement indicators observed in the field include toppling trees, slumps and scarps, detachment slides, striation marks on frozen sediment slabs, recently buried trees and other vegetation, mudflows, and large cracks in the lobe surface. The type and diversity of observed indicators suggest that the lobes likely consist of a frozen debris core, are subject to creep, and seasonally unfrozen surface sediment is transported in warm seasons by creep, slumping, viscous flow, blockfall and leaching of fines, and in cold seasons by creep and sliding of frozen sediment slabs. Ground-based measurements on one frozen debris-lobe over three years (2008–2010) revealed average movement rates of approximately 1 cm day−1, which is substantially larger than rates measured in historic aerial photography from the 1950s to 1980s. We discuss how climate change may further influence frozen debris-lobe dynamics, potentially accelerating their movement. We highlight the potential direct hazard that one of the studied frozen debris-lobes may pose in the coming years and decades to the nearby Trans Alaska Pipeline System and the Dalton Highway, the main artery for transportation between Interior Alaska and the North Slope.

Frozen debris lobes (FDLs) are slow-moving landslides along permafrost-affected slopes. Within the Dalton Highway corridor in the southern Brooks Range, Alaska, the authors have identified 43 FDLs, with 23 occurring less than one mile uphill of the Dalton Highway. FDL-A, which is the largest and closest FDL to the Dalton Highway, was just over 42 m away from the highway embankment when measured in August 2014. Since the completion of a preliminary subsurface investigation in 2012, they continue to collect subsurface temperature and inclinometer data, to measure surface movement rates, and to make field observations, which reveal the dynamic nature of FDLs. Significant rainfall during the summer of 2014 caused a deepening of the active layer on FDL-A and exposed massive “infiltration” ice in the head scarps of two retrogressive thaw slumps on its surface. The infiltration ice occurs in bands associated with transverse and longitudinal cracks, and the 2014 observations indicate that FDL-A may contain more massive ice than previously indicated. FDL-A moves mostly through basal shearing and through slow to moderate flow, which is highly dependent on temperature. The average rate of movement of FDL-A from 2013 to 2014 was 1.3 cm day−1. Comparing this value to the trend of historic rates indicates that the overall rate of movement of FDL-A continues to increase.

A permafrost-related geohazard is approaching the Dalton Highway near MP219. Analysis of historic remotely-sensed imagery indicated that this feature, termed a frozen debris lobe (FDL), was moving at an average rate of 0.4 in. per day between 1955 and 2008. More recent measurements indicate an increased rate of movement. As this frozen debris lobe (FDL- A) is less than 200 ft from the Dalton Highway, it is necessary to determine its current rate of movement, the nature of its movement, and its internal structure. We conducted field investigations in 2012 to determine the thickness and stratigraphy of FDL-A, and to install instruments to measure temperature, water pressure, and slope movement. Temperature measurements indicate that, although frozen, FDL-A is 2oF warmer than the surrounding permafrost. Results from the field work indicate that FDL-A is fairly homogeneous, consisting of silty sand with gravel, and is 86.5-ft thick where drilled, overlying white mica schist bedrock. It is moving mostly along a shear zone between 66 ft and 74 ft below the ground surface, at an average rate of 1.0 in. per day. As this rate was measured only during the fall season, however, it does not reflect any slowing of the lobe that may occur through the winter months. As these results are preliminary, future work will entail recording the positions of surface markers on FDL-A, conducting geophysical surveys of the feature, and modeling FDL-A to determine the geometry of the shear surface and residual strength in the shear zone, and to identify possible mitigation strategies.

[1] Nonsorted circles, ubiquitous to the Arctic Tundra region, are patterned ground features with circular semibarren areas surrounded by vegetation. These circles are formed and persist as an ecosystem due to complex soil-water-energy-ice-plant relationships and dynamics in the Arctic. In this paper, we present the first model that captures the dynamics of the physical and biological components of the nonsorted circle ecosystem in order to understand its formation and persistence, especially in a changing climatic environment. We have applied a coupled model describing (1) vegetation dynamics (ArcVeg) and (2) coupled heat and moisture transport with phase change (WIT) in the active layer of the soil where such circles are initiated and developed. We simulated the system behavior during the formation process starting with a random vegetation development. The vegetation provided heterogeneous insulation to the soil surface. During freezing, the noninsulated areas froze first, resulting in preferential ice accumulation in those areas. The ice prevented the vegetation from developing further in those areas and thus developed and stabilized the nonsorted circle pattern. The model produced a nonsorted circle pattern that was well compared to those observed in the field. The model also illustrated that the availability of water was critical for the sustenance and stability of the nonsorted circle. The effect of climatic variations on the freezing process on the other hand did not seem to affect the formation and sustenance of nonsorted circles.

Degrading permafrost below roadway embankments is a widespread problem in the north. Thermal modeling can help to determine thermally stable embankment configurations; however, this modeling typically does not include the effects of groundwater flow on the geosystem, which will cause permafrost degradation to occur faster than atmospheric warming alone. As part of a larger, ongoing research project, we present preliminary results of heat transfer modeling for an Alaska Highway test section near Beaver Creek, Yukon Territory, Canada. This experimental highway test section is located in an area characterized by muskeg vegetation underlain by ice-rich permafrost. While the overall project includes field work and laboratory measurements, this paper focuses on the results of exploratory modeling. A two- dimensional finite element program capable of mathematically coupling both heat and groundwater flow was used for modeling. Comparing model results produced using conductive heat flow only to model results using both heat and groundwater flow (heat advection) indicates that groundwater has a significant effect on the configuration of the thaw bulb and the temperature distribution within and below the roadway embankment. For example, using 50-year model results, including groundwater flow increases modeled thaw depths below the embankment by approximately 8 m, and can increase temperatures to an excess of +2.5°C at the bottom of the embankment. For wet terrain conditions, these preliminary modeling results indicate that it is essential to incorporate groundwater flow into thermal modeling, in order to understand better the complex interactions between roadway embankments and underlying permafrost.