Geomorphological tools for mapping natural hazards

This special issue presents contributions about the methodologies and tools for representing and mapping geomorphological hazards, with a focus upon hazard and risk classification and tools for land planning, risk reduction and mitigation.

Geomorphological mapping can be described as a group of techniques employed to systematically record the morphology of the ground, landforms, landscape-forming processes and materials that constitute the surface of the Earth (Griffiths et al., 2011; Lee, 2001). In this sense, it represents the result of the synthesis between the different ways and methods used to represent landforms, both in natural and urban landscapes. The challenges that arise from socio-economic modifications of the landscape (e.g. abandonment of rural areas, inadequate exploitation of potentially hazardous zones) and climate change (e.g. increasing extreme weather events) demand that this cartography should quantitatively represent landforms and their associated processes, in order to elevate geomorphological maps into effective tools for land management and risk reduction.

Cartographic approaches, which are now used for the assessment of geomorphological hazards, involve methodologies for input creation (e.g. maps of predisposing/triggering factors and inventories of past geomorphological processes or instabilities; i.e.: Lazzari et al., 2018; Lupiano et al., 2019) and cartographic and/or WebGIS outputs (e.g. resolution, mapping units, classification criteria, methods of validation; i.e. Cama et al., 2016; Wilde et al., 2018). In addition, methodological standards and guidelines (i.e.: Gonçalves et al., 2015; Griffiths & Abraham, 2008) must also be defined through geomorphological cartography for complete coverage, the automatic and semi-automatic classification of terrain using remotely-sensed data and physically-based or statistical modelling in order to assess hazard and risk.

The use of geomorphological mapping in the academic community, but also in applied fieldwork, has shown significant potential (Smith et al., 2011) and reached a maturity such that it is systematically employed for the production of geomorphological maps that allow the representation of hazards and so contribute to an evaluation of related risks.

This special issue contributes to its ongoing development through the presentation of a range of perspectives, as well as related tools and methods used to acquire geomorphological data.

1. Special issue topics

Bosino et al. (2020) present a geomorphological map of the upper Mkhomazi River basin, located in the foothills of the Drakensberg mountains in KwaZulu-Natal Province, South Africa. The authors focus on erosional landforms to understand their spatial distribution and relationship to the colluvial deposits. The map makes evident the runoff processes preferentially incising into the poorly consolidated, highly erodible sediments causing severe hazards, such as gully erosion, that is responsible for widespread land degradation and desertification.

A dynamic and comprehensive information tool and multiscalar cartographic model, characterized by a ‘full coverage’ representation of landforms, is the topic in the paper by Bufalini et al. (2021). The authors, working on the median sector of the Chienti river basin (Marche Region, Central Italy), look at modernizing traditional geomorphological mapping within the context of hazard assessment when planning urban development.

Rockfalls on Mount Pellegrino, an isolated peak in the urban area of Palermo (western Sicily, Italy), is the topic of the paper by Cappadonia et al. (2020). Rockfalls cause extensive damage and subsequent social and economic impact; the map by these authors focuses on rockfall runout based on geological, geomorphological, and geomechanical analyses, exploiting information related to landslide inventories obtained using both analytical and empirical methods.

Carabella et al. (2020) present detailed geomorphological mapping and analysis of the superficial hydrographic network of Feltrino Stream and Lanciano area (Abruzzo, Italy). These are fundamental tools to assess geo-hydrologically critical areas such as urban areas and small catchments, where landslides and floods are common hazards caused by intense rainfall. The study aims to define the distribution of landslide–flood historical/recent events and related critical areas for the development of an urban early warning system.

Cignetti et al. (2020) also deal with rockfalls, proposing a procedure that involves rockfall occurrence databases to compute a susceptibility map using an Analytical Hierarchic Process. The example is focused on the road network of the Aosta Valley Region (northwestern Italy), with the results of the model highlighting the importance of morphometric factors on the investigated hazards.

Acquiring geomorphological data using unmanned aerial vehicles (UAVs) is the topic of the paper by De Beni et al. (2020). The authors present a map resulting from ten UAV surveys made during and after the 30 May–6 June 2019 eruption of Etna volcano (Sicily), projecting the data in a time context back to 1999. The process is shown to be a powerful tool for natural hazard identification, allowing the monitoring of the morpho-structural evolution of fissures, capturing lava flow propagation and the accumulation of pyroclastic deposits.

Faccini et al. (2020) outline Deep-Seated Gravitational Slope Deformations (DSGSDs) in the Ligurian Alps (Italy) identified through the integration of geological-geomorphological mapping, structural data, photo interpretation, and GIS-based analyses. The map describes one major complex-sagging-type DSGSD that is not present in national land planning and/or management databases but that is the origin of large-scale landslides which have affected villages in the area. This study once again highlights the importance of ground truth observations as the basis for further investigations.

Farabollini et al. (2020) present a geomorphological map of the Pescara del Tronto area (Sibillini Mts, Italy) focusing on a geomorphological analysis performed in a zone strongly affected by the 2016–2017 seismic sequence of the Central Apennines. Integrated geological-geomorphological field mapping and geomorphological profile drawing, supported by air-photo interpretation and GIS analysis are used, focused on the description of a geomorphological approach for representing and mapping the evidence of several debris flows and landslides recognized within the framework of seismic microzonation (SM) activities.

In the paper by Giacomelli et al. (2021), the ‘geo-historical’ map is described as a synthesis of historical and geomorphological data for landslides and landslide occurrence in the Ceno Torrent valley (Northern Apennines, Italy). The authors recognize the importance of the historical perspective in the study of landslides and present a tool for landslide hazard assessment at local and regional scales. The importance of the analysis of archive material from the perspective of the human geographer is also shown to be relevant in order to develop a useful tool to better describe landslide dynamics and related hazards.

In the paper by Huff et al. (2021), submarine geomorphologic maps are used to provide geologic context and spatial information on landforms and related geo-hazards for risk management. The authors produce a workflow for applying planetary geologic mapping methods to submarine data. They create an onshore-offshore geomorphologic map of the Christiana-Santorini-Kolumbo Volcanic Group (Greece) that can be used as a tool for hazard assessments at Santorini, a tourist location at high risk of volcanically- and seismically-induced hazards.

Mandarino et al. (2021a) present geomorphological features of the Bisagno Stream catchment, a torrent in the Northern Apennines (Italy), internationally known for its recurring high-magnitude floods and geo-hydrological hazards associated with an at-risk man-made environment. Geomorphological mapping allowed the authors to combine urban development with the geo-hydrological hazards associated with landslides and floods. Relevant information for land-use planning and land management, with a particular focus upon geo-hydrological hazard mitigation, is provided.

The topics of river management and land use planning are also covered by Mandarino et al. (2021b). The authors present the geomorphological features of the lower Orba River (NW Italy) and its adjacent floodplain following the geomorphic response to the 21–22 October 2019 extreme flood. The knowledge of flood-induced ground effects and flood-water dynamics is underlined as a crucial issue for hydro-geomorphic hazard assessment and mapping. In addition to a specific legend developed for flood-related and anthropogenic elements, mapping in a typical lowland agricultural landscape with regulated rivers is proposed.

Martinello et al. (2020) deal with landslide susceptibility modelling, focusing on the selection of mapping units; this is an important topic both in terms of geomorphological adequacy and the suitability of the models and final maps. The authors perform a test to integrate pixels and slope units applying Multivariate Adaptive Regression Splines modelling to the Imera Settentrionale river basin (northern Sicily, Italy) to assess landslide susceptibility based on a 12 predictors and a 1608 cases database.

UAVs allow repeat surveys of an area and this can be crucial – for example – when monitoring flood-vulnerable rivers, as a result of the rapid alteration of morphological properties of in-channel landforms. Özcan and Özcan (2020) apply this methodology to study of the Bogacay plain, located southwest of the city of Antalya, Turkey. High-resolution topography of the study region was acquired over two consecutive years and, after processing, detailed high-resolution maps of the river channels were produced.

The map by Raso et al. (2020) shows the outcomes of a geomorphological investigation carried out within the Cinque Terre National Park (Liguria, Italy), an important example of a human-modified landscape. The authors give special attention to the mapping of man-made landforms, such as terraced slopes, which are extremely vulnerable to gravity-driven processes and running water as a result of extensive farmland abandonment. The output map is a fundamental tool for future hazard assessment and land management.

Sulli et al. (2021) present geomorphological hazard mapping of the San Vito Peninsula offshore (Sicilian margin of Tyrrhenian Sea). In this paper a morpho-bathymetric model is produced by means of multibeam survey and scattered high resolution seismic profiles, highlighting some potential sites where geomorphological features can generate submarine hazards, represented by unstable sediment packages in canyon heads with regressive erosion and coastal landslides.

Viganò et al. (2021) present comprehensive geomorphological and structural mapping of the largest landslides in the central-eastern Southern Alps (NE Italy). Landslide occurrence is discussed underlining the use of geomorphological mapping in relation to structural geological features. The analysis of predisposing and triggering factors poses the question of present and future landslide hazards for densely inhabited Alpine valleys.

2. Conclusions

Geomorphological mapping is an effective and efficient methodology and tool for understanding the topography of territories, along with their related natural and man-made hazards. The effort of governments should therefore be towards the production of geomorphological maps of high scientific value, capable of use as effective tools to manage the environment. Many examples of geomorphological maps – such as flood and landslide events, earthquakes and tsunamis – have been proposed in recent years that explore the knowledge of a territory and how a lack of knowledge can be the cause of increased infrastructure damage and casualties. Within academic research there is an interest in geomorphological mapping as a tool to address the issues indicated in the previous paragraphs and demonstrated by the papers presented in this special issue. Within this context it is critical that geomorphological mapping is more widely employed, exploiting new systems to acquire data, promoting better use of territories and so contribute to the sustainable development goals (SDGs, 2015) of Agenda 2030, such as climate action and life on the land. In short, the focused and informed use of a territory can promote the well-being of its people both in developed and developing countries.