Sentinel-1 and RADARSAT Constellation Mission InSAR Assessment of Slope Movements in the Southern Interior of British Columbia, Canada

Landslides are the most common natural hazard in British Columbia. The province has recorded the largest number of historical landslide fatalities in Canada, and damage to infrastructure comes at a great cost. In order to understand the potential impacts of landslides, radar remote sensing has become a cost-effective method for detecting downslope movements. This study investigates downslope movements in the Southern Interior of British Columbia, Canada, with Sentinel-1 and RADARSAT Constellation Mission (RCM) interferometric synthetic aperture radar (InSAR) data. The 2-dimensional time-series analysis with Sentinel-1 ascending and descending InSAR pairs from October 2017 to June 2021 observed distinct earthflow movements of up to ~15 cm/year in the east–west direction. The Grinder Creek, Red Mountain, Yalakom River, and Retaskit Creek earthflows previously documented are still active, with east–west movements of ~30 cm over the past four years. New RCM data acquired from June 2020 to September 2020 with a 4-day revisit capability were compared to 12-day Sentinel-1 InSAR pairs. The 4-day RCM InSAR pairs at higher spatial resolution showed better performance by detecting relatively small-sized slope movements within a few hundred meters, which were not clearly observed by Sentinel-1. The temporal variabilities observed from the RCM InSAR showed great potential for observing detailed slope movements within a narrower time window.

Integration of Satellite InSAR with a Wireless Network of Geotechnical Sensors for Slope Monitoring in Urban Areas: The Pariana Landslide Case (Massa, Italy)

Slow to extremely slow landslides in urban areas may cause severe damage to buildings and infrastructure that can lead to the evacuation of local populations in case of slope accelerations. Monitoring the spatial and temporal evolution of this type of natural hazard represents a major concern for the public authorities in charge of risk management. Pariana, a village with 400 residents located in the Apuan Alps (Massa, Tuscany, Italy), is an example of urban settlement where the population has long been forced to live with considerable slope instability. In the last 30 years, due to the slope movements associated with a slow-moving landslide that has affected a significant portion of the built-up area, several buildings have been damaged, including a school and the provincial road crossing the unstable area, leading to the need for an installation of a slope monitoring system with early warning capabilities, in parallel with the implementation of mitigation works. In this paper, we show how satellite multi-temporal interferometric synthetic aperture radar (MT-InSAR) data can be effectively used when coupled with a wireless sensor network made of several bar extensometers and a borehole inclinometer. In fact, thanks to their wide area coverage and opportunistic nature, satellite InSAR data allow one to clearly identify the spatial distribution of surface movements and their long-term temporal evolution. On the other hand, geotechnical sensors installed on specific elements at risk (e.g., private buildings, retaining walls, etc.), and collected through Wi-Fi dataloggers, provide near real-time data that can be used to identify sudden accelerations in slope movements, subsequently triggering alarms. The integration of those two-monitoring systems has been tested and assessed in Pariana. Results show how a hybrid slope monitoring program based on the two different technologies can be used to effectively monitor slow-moving landslides and to identify sudden accelerations and activate a response plan.

Analysis of Susceptibility to Slope Movements in the Environment of Road Infrastructures. Models for Obtaining Predictive Mapping Applied to Roads in the Provinces of Malaga and Granada (Spain)

This study addresses the peculiarities of the generation of slope movements in the context of road infrastructures and provide a predictive mapping of susceptibility to movements on slopes adjacent to road infrastructures (rockfalls). An inventory of slopes movements was mapped. From the development of the inventory of constant cases of mobilization that is used as a dependent variable, two statistical models can be obtained and compared for the same study area. One of them is based on the concept of frequency, whilst the other one is based on the application of a logistic regression. The results reveal the preponderant importance of lithology as a predictive variable, followed, at a considerable distance, by the slope gradient. Likewise, the importance of an unnatural and characteristic variable area of study, such as the presence of artificial cuts, is indicated as a causative factor. The results show a high degree of coincidence between the tendency of susceptibility predicted by the model, and the effective presence of empirical mobilization signs on the slopes, with Area Under Curve (AUC) values for Receiver Operating Characteristics (ROC) around 0.8.

The effects of the storm Gloria in Catalonia: The value of quick-response geological inventories as a tool for risk management

<p>The storm Gloria was an exceptional episode of east storm occurred in the north and east of Spain from Sunday 19<sup>th</sup> to Thursday 23<sup>rd</sup> of January 2020. The impact was especially strong in the Mediterranean coast, causing the overflow of some rivers, abundant slope movements, cuts in the road and rail network, isolation of populations, and huge damage on the coastline.  It was classified as historical, not only because of the multiplicity of phenomena (wind, rain, snow, and waves) that happened simultaneously, but also because of the extension, affecting the entire Catalan territory. In order to have an overview of the effects of the storm in Catalonia, the Institut Cartogràfic i Geològic of Catalonia has carried out a quick response report (González et. Al., 2020), which has consisted of an inventory of the geomorphological impact and its consequences. The work carried out includes the production of post-event orthoimages of the coastal strip and some fluvial courses, a post-event field survey during the days immediately after, and a compilation of the information published in the media between 01/20/2020 and 02/18/2020. Also, a data collection campaign through online forms sent by email has been carried out, which provides more information of the sea gale effects, and validates and complete the preliminary inventory of slope movements. Thus, an inventory of slope movements has been obtained with a total of 352 documented landslides throughout the Catalan territory. In addition, a geomorphological mapping with the changes associated to river dynamics has been carried out, in two of the most affected sectors in NE Catalonia: the lower section of the Tordera river and the lower section of Ter river. This 1: 5 000 scale cartography, identify geomorphological elements from fluvial dynamics (active fluvial channels during the flood, active flood plain, erosion scarps of river banks, flow direction lines) and from coastal dynamics (washoverfans, coastal erosion and new creation stream-mouth bars). Finally, based on the analysis of the data collected, an estimate has been made of the impact that the storm Gloria has had on the territory, and how it has affected the different municipalities, in terms of damages and economic losses. The results of this quick response report allow (i) to have a geomorphological record of the storm extent in the short term, (ii) to provide basic information for the management and recovery of river areas, and (iii) to propose new strategies for geological risk management, among others.</p>

Denudation, global change and the Anthropocene

<p>Changes occurred in denudation/sedimentation processes (understood here as the transfer of solid materials from one place of the earth’s surface to another, by different agents) in the latter part of the Holocene, mainly the last couple of centuries, are examined, trying to estimate rates and assess the role of human and natural agents. Three issues are addressed here, on the basis of some case studies: slope movements and their contribution to denudation and relief evolution; “technological denudation” due to human activities; general evolution of sediment accumulation (consequence of denudation).</p><p>Analyses of materials transfer by, and frequency of, slope movements in N Spain have shown the importance of human influence already in Neolithic times, and more so after the Industrial Revolution. Significant increases have been observed since the middle of last century and slope movements seem to be in some cases the main factor of relief evolution.</p><p>Human activities related to urban-industrial development, infrastructure and mining activities represent an important “human geomorphic footprint” (expressed as volume of materials displaced or area occupied by new “anthropogeoforms”; yearly total or per capita). If the materials thus moved were evenly distributed over all emerged lands they could be presently equivalent to a >1 mm a<sup>-1</sup> (“technological”) denudation. As this is the consequence of growing population, technological and economic development, it will probably intensify with time.</p><p>Sedimentation rates directly determined (Pb-210, Cs-137) in a number of estuaries, lakes and reservoirs show in general a clear increase since early 20<sup>th</sup> century, particularly after its middle. Compilation and analysis of sedimentation rates in a variety of sedimentation environments in different regions of the world, since late 19<sup>th</sup> century, also show, with almost no exception, a similar trend. Comparison with rainfall evolution does not explain the changes observed. However, indicators of the intensity of human activity, especially GDP (Gross Domestic Product; total, not per capita; strongly related to our capacity to transform land), show a good similarity with sedimentation rates trends. This indicator also shows a close correlation with geomorphic disasters frequency (another manifestation of the general intensification of geomorphic processes).</p><p>On the basis of the information gathered and results presented, some tentative conclusions are proposed. It appears that presently humans are, by far, the main denudation agent. Direct and indirect transfer of rock, soil and sediment by human activities could be one order of magnitude greater than by natural agents. The rates of some geomorphic processes seem to have experienced a significant acceleration (about tenfold?) in less than a century, due to land surface transformation rather than to climate change. This “great geomorphic acceleration” represents a part of the “Great Acceleration” occurred after mid-twentieth century. Global geomorphic change (independent of climate change) should thus be considered as one of the characteristics of the Anthropocene, for which the end of World War II would indeed be an appropriate starting date.</p>