Stereoscopic Aerial Photographs Research Articles

Geomorphological landslide inventory map of the Daunia Apennines, southern Italy

Abstract. Detailed and accurate geomorphological historical landslide inventory maps are an invaluable source of information for many research topics and applications. Their systematic preparation worldwide has been advised by many researchers as it may foster our knowledge on landslides, their spatial and temporal distribution, their potential interaction with the built environment, their contribution to landscape dynamics, and their response to climate change in the past. Due to the extreme variability of the morphological and radiometric elements that can reveal historical landslides, geomorphological historical landslide inventory maps are produced by expert interpretation, which makes it a time-consuming and expensive process, which often discourages wide-area mapping activities. In this paper we present a new geomorphological historical landslide inventory map for a 1460 km2 area in the Daunia Apennines, the north-western sector of the Apulia (Puglia) region, in southern Italy. The inventory contains 17 437 landslides classified according to relative age, type of movement, and estimated depth. Landslides were mapped according to rigorous and reproducible criteria applied by two teams of expert photo interpreters to two sets of stereoscopic aerial photographs taken in 1954/55 and 2003. The dataset consists of a digital archive publicly available at https://doi.org/10.1594/PANGAEA.942427 (Cardinali et al., 2022).

Geomorphological features of Favignana Island (SW Italy)

ABSTRACT We present a large scale (1:10,000) geomorphological map of Favignana Island, in which landforms were recognized and genetically categorized based on analysis of stereoscopic aerial photographs and freely available satellite images, complimented by a few validation tests performed in the field. The map was created following the guidelines of the Italian Geomorphological Working Group for landforms symbolic representation. This includes an immediate visual differentiationof the genetic character and the state of activity of landforms. Favignana, belonging to the Egadi Archipelago in the Tyrrhenian Sea (SW Italy), is a mid-sized (ca. 20 km2) mostly carbonatic island. The marine protected area surrounding the island represents the main attraction for tourists. Through this map, it was possible to highlight the richness and diversity, in terms of abundance and peculiarity of landforms, that characterizes the Island. This peculiarity makes of Favignana an excellent candidate for the exploitation of its geoheritage for touristic purposes.

The relation of spatio-temporal distribution of landslides to urban development (a case study from the Apulia region, Southern Italy)

ABSTRACT The paper describes the multitemporal landslide inventory map prepared for the urban areas of Motta Montecorvino and Volturino, two municipalities located in the Southern Apennines (Apulia Region, Italy). These territories show a high propensity to landslides of different types and magnitude, which periodically interfere with the anthropic structures and infrastructures. For the study area, the spatial and temporal distribution of landslides is detected for the period between 1954 and 2003, through the visual interpretation of multiple sets of black and white digital stereoscopic aerial photographs at different scales. The analysis reveals locally high frequency of landslide occurrence and built-up areas on existing landslides, either on the body or on the crown areas. In particular, we show that over the years new residential areas were developed despite the presence of large old mass movements.

Visual interpretation of stereoscopic NDVI satellite images to map rainfall-induced landslides

Landslide inventory maps are commonly prepared through the visual interpretation of stereoscopic aerial photographs and field checks. Stereoscopic satellite images can also be interpreted visually to recognize and map landslides. When interpreting stereoscopic imagery, shadows can conceal the photographic elements typical of landslides, hampering the recognition and mapping of the landslides. To mitigate the problem, we propose a method that exploits normalized difference vegetation index (NDVI) images and digital stereoscopy for the 3D visual recognition and mapping of landslides in shadowed areas. We tested the method in the 25 km2 Pogliaschina catchment, northern Italy, where intense rainfall caused abundant landslides on 25 October 2011. Using a PLANAR® StereoMirror™ digital stereoscope, we prepared an event landslide inventory map (E-LIM) through the visual interpretation of a pair of NDVI images obtained from a WorldView-2 stereoscopic multispectral bundle. We compared the event inventory with two independent E-LIMs for the same area and landslide event. The 3D vision of the NDVI stereoscopic image pair maximized the use of the radiometric (color and tone) and the terrain (elevation, slope, relief, and convexity) information captured by the stereoscopic multispectral images, allowing for the recognition of more landslides and more landslide areas than the other E-LIMs in the shadowed areas. Our results confirm that use of NDVI images facilitates the visual recognition and mapping of landslides in terrain affected by shadows. We expect that the proposed method can help trained interpreters to map landslides more accurately in areas affected by shadows.

Landslide inventory map of the upper Sinni River valley, Southern Italy

In this paper, we present a geomorphological landslide inventory map for an intermountain catchment in the southern Italian Apennines. The study area is seismically active, and it is characterized by high uplift rates produced by Quaternary tectonics. A total of 531 landslides of different types, relative age, and sizes, including some kilometer-scale relict landslides were mapped through the visual interpretation of 1:33,000-scale stereoscopic aerial photographs, and dedicated field surveys. Analysis of the inventory map revealed that recent landslides consist chiefly of reactivations of older landslides, and of the new landslides formed in pre-existing landslide deposits, triggered primarily by intense rainfall events, or prolonged rainfall periods. We expect that the inventory will be used for the evaluation of landslide susceptibility and hazard in the area, and to investigate the long-term geomorphological evolution of a portion of the southern Apennines.

Comparison of event landslide inventories: the Pogliaschina catchment test case, Italy

Abstract. Event landslide inventory maps document the extent of populations of landslides caused by a single natural trigger, such as an earthquake, an intense rainfall event, or a rapid snowmelt event. Event inventory maps are important for landslide susceptibility and hazard modelling, and prove useful to manage residual risk after a landslide-triggering event. Standards for the preparation of event landslide inventory maps are lacking. Traditional methods are based on the visual interpretation of stereoscopic aerial photography, aided by field surveys. New and emerging techniques exploit remotely sensed data and semi-automatic algorithms. We describe the production and comparison of two independent event inventories prepared for the Pogliaschina catchment, Liguria, Northwest Italy. The two inventories show landslides triggered by an intense rainfall event on 25 October 2011, and were prepared through the visual interpretation of digital aerial photographs taken 3 days and 33 days after the event, and by processing a very-high-resolution image taken by the WorldView-2 satellite 4 days after the event. We compare the two inventories qualitatively and quantitatively using established and new metrics, and we discuss reasons for the differences between the two landslide maps. We expect that the results of our work can help in deciding on the most appropriate method to prepare reliable event inventory maps, and outline the advantages and the limitations of the different approaches.

A method for the assessment of the influence of bedding on landslide abundance and types

Bedding planes are a known factor that controls the type, abundance and pattern of landslides. Where layered rocks crop out, the geometrical relationships between the attitude of the bedding and the geometry of the terrain is crucial to understand landslide phenomena. Obtaining information on bedding attitude for large areas through field surveys is time-consuming, and resource intensive, hampering the possibility of quantitative investigations on the control of bedding planes on landslides. We propose a GIS-based method to extract information on bedding planes from the analysis of information captured through the visual interpretation of stereoscopic aerial photographs and a digital representation of the terrain. We tested the method in the Collazone study area, Umbria, Central Italy, where we used spatially distributed information on beddings and terrain information obtained from a 10 × 10-m DEM to determine morpho-structural domains. We exploited the morpho-structural terrain zonation, in combination with landslide information for the same area, to investigate the role of beddings in controlling the distribution and abundance of landslides in the study area. We found that beddings condition the location and abundance of relict and deep-seated landslides, most abundant in cataclinal slopes, and do not condition significantly the shallow landslides. We expect the method to facilitate the production of maps of morpho-structural domains in layered geological environments. This will contribute to a better understanding of landslide phenomena and to foster the preparation of advanced landslide susceptibility and hazard models.

Assessment of extraction drainage pattern from topographic maps based on photogrammetry

The extraction of the water hydrographical pattern and watershed and subwatershed boundary is very important for many types of study. In Jordan the topographic map scale 1:25,000 produced at the Royal Jordanian Geographic Center is considered the most important source of contour lines and drainage pattern; therefore, it is imperative to estimate the accuracy of these types of data extracted from the previous topographic maps. In this project we aim to extract the hydrographical pattern of the Humrat Assahn basin in two methods: (1) an orthophoto based on aerial photographs using Socetset as photogrammetric software and (2) topographic maps at scale 1:25,000. A precise Digital Terrain Model (DTM) was built from stereoscopic aerial photographs using Socetset software. As we know, the quality of DTM is imperative to assure precise results and depends on the method of creation of this DTM besides other factors. A complete data base for the necessary information for achieving this objective was built. The obtained results were evaluated using GPS points and photo-interpretation. The results show that the drainage pattern extracted from DTM using photogrametric software was very accurate; meanwhile, the accuracy of the drainage pattern extracted from topographic maps has some flaws.

Data fusion using aerial photographs and satellite images for detailed landslide assessment

Hong Kong is one of the world's mountainous international cities, and landslides are a constant threat to human life and property. Monitoring landslides in Hong Kong is important and this is always done by field surveying. However, although conventional survey techniques provide accurate landslide information, they are limited to small areas and physical contact with the slope may be dangerous. Remote sensing techniques can provide an alternative for collecting information about landslide causes and occurrences, and they may assist in the prediction of future landslide occurrences. This article demonstrates the use of monoscopic and stereoscopic aerial photographs, along with satellite images from the IKONOS very high resolution (VHR) sensor for detailed landslide hazard assessment over Hong Kong. For monoscopic aerial photographs, a fusion technique for generating pseudo true colour images from false colour aerial photographs was demonstrated. The pseudo true colour image is useful for better visual analysis in the photogrammetric model. For monoscopic IKONOS image, a set of image fusion techniques was applied in order to improve landslide interpretation, and the results were examined visually and statistically. The Pan-sharpening method among all the image fusion techniques has been demonstrated to have superior performance for identifying both landslide trails and crowns. Stereoscopic viewing using a stereoscopic pair of aerial photographs and stereoscopic IKONOS images was employed for more detailed landslide investigation such as landscape positional relationships (e.g. streams and ridges). Digital elevation models (DEM) were generated from aerial photographs and IKONOS stereoscopic images, and they were compared with digital contour data with 2 m contour interval. The DEMs generated from digital photogrammetric model and IKONOS stereoscopic images are consistently more accurate than an existing DEM, and are sensitive to micro-scale terrain features. The Hong Kong Civil Engineering Department may use the derived monoscopic fused images, stereoscopic images, DEM and anaglyph as objective measures for a detailed landslide study within Hong Kong.

Landslides on Gault: geomorphological identification and qualitative risk assessment

Abstract A geomorphological assessment was undertaken to determine the risk of landslide damage to 38 km of the M25–M26 motorway underlain by the Gault Formation (a stiff clay to weak mudstone). Conventional methods for geomorphological mapping using stereoscopic aerial photography were found to be unhelpful, owing to the low topographic expression of landslips in the study area. In contrast, Light Detection and Ranging (LiDAR)-generated topographic contour maps proved invaluable, giving the landscape a pseudo-relief and allowing identification of the subtle landslide features. Relict (inactive) landslides were found to lack a definable backscarp and were mainly discernible by their indistinct toe lobes. Two types of active landslides were identified within the study area: slow creep failures barely distinguishable from relict slides, and rapid slides. A specific list of descriptors for landslides on Gault is presented based on the results of the geomorphological investigation. Four factors were found to be of particular importance in governing the potential for landsliding: the presence of relict slips; slopes of 7° or over; an abundant source of water; and close proximity to the top of the Gault where extremely high-plasticity Upper Gault crops out. The results of this investigation indicated that the section of motorway most affected by historical landsliding was also most at risk from future landslides. The similarity in morphology between active creep-type landslides and relict slides has implications for landslide management on Gault.

Impact of Vehicles as Obstacles in Vehicular Ad Hoc Networks

A thorough understanding of the communications channel between vehicles is essential for realistic modeling of Vehicular Ad Hoc Networks (VANETs) and the development of related technology and applications. The impact of vehicles as obstacles on vehicle-to-vehicle (V2V) communication has been largely neglected in VANET research, especially in simulations. Useful models accounting for vehicles as obstacles must satisfy a number of requirements, most notably accurate positioning, realistic mobility patterns, realistic propagation characteristics, and manageable complexity. We present a model that satisfies all of these requirements. Vehicles are modeled as physical obstacles affecting the V2V communication. The proposed model accounts for vehicles as three-dimensional obstacles and takes into account their impact on the LOS obstruction, received signal power, and the packet reception rate. We utilize two real world highway datasets collected via stereoscopic aerial photography to test our proposed model, and we confirm the importance of modeling the effects of obstructing vehicles through experimental measurements. Our results show considerable obstruction of LOS due to vehicles. By obstructing the LOS, vehicles induce significant attenuation and packet loss. The algorithm behind the proposed model allows for computationally efficient implementation in VANET simulators. It is also shown that by modeling the vehicles as obstacles, significant realism can be added to existing simulators with clear implications on the design of upper layer protocols.

Discussion of ‘Some limitations in the interpretation of vertical stereo photographic images for a landslide investigation’ by A.B. Hart, J.S. Griffiths & A.E. Mather, Quarterly Journal of Engineering Geology and Hydrogeology , 42, 21–30

Roly Edwards writes: Having been centrally involved in the early development of terrain evaluation for engineering practice there are two matters of fact, which are misreported in what is otherwise a useful contribution drawing attention to the value of the use of land surface evaluation techniques for land stability studies. First, in their resume and evaluation of the use of vertical stereoscopic aerial photography in the investigation of the nature and distribution of landslide features in the Rio Aguas catchment in Spain, the authors suggest that stereoscopic images in the non-visible part of the electromagnetic spectrum were unavailable until the launch of SPOT in 1986. I would remind them that false colour IR and multispectral stereoscopic aerial photography at 1:5000 and 1:10 000 scales was routinely available, at a cost, as long …

Introducing the remote sensing of hazardous terrain

With human population and associated environ-mental degradation continuing to increase, it isinevitable that more and more people will be livingin zones of hazardous terrain, and therefore the riskof disaster will increase. Add to this the growingevidence for global warming and the increasedseverityofgeohazardsrelatedtolargerandmorefre-quentstorms(i.e.stormsurges,coastalerosion,land-slides, fluvial flooding, erosion) and both thefrequency and severity of disasters is set to increase(e.g. Kesavan & Swaminathan 2006; Smolka 2006;van Aalst 2006).Remote sensing (measuring and mapping theEarth’s surface from aircraft or satellites) can helpus to rapidly assess, and therefore better manage,geohazards. Remote sensing and hazardous terrainmapping can play key roles in the managementand mitigation of natural disasters (e.g. Cutter2003; Zeil 2003), with applications grouped intothree main stages.(1) Pre-disaster. Maps showing the distri-bution of geohazards and their relative severitiescan be used by key decision makers in government,the insurance industry and the local population, tominimize the danger to people and infrastructure.For this stage, geomorphological mapping basedon stereoscopic aerial photography has beenwidely used for many years (e.g. Verstappen V Doornkamp et al. 1979;Mantovani et al. 1996). A new development ismapping based on spectral responses and digitalelevation models (DEMs), either regionally usingsatellite sensors (e.g. Liu et al. 2004; AndrewsDeller 2006; Theilen-Willige 2006), or in detailusing airborne hyperspectral sensors and laser alti-metry (e.g. Brown 2004; Deronde et al. 2004). Fur-thermore, early warnings of disasters caused byslope instability, seismic activity or volcanic erup-tion should be feasible within a few years, usingconstellations of radar satellites to detect grounddeformation (e.g. Kerle & Oppenheimer 2002;Bruno et al. 2005; Singhroy 2006).(2) Event crisis. With the onset of a disaster,medium-resolution (15–250 m pixel) satelliteimagery (e.g. Landsat or MODIS) is useful forassessing the regional extent and relative severitiesof the various impacts. With rapid-onset disasters,such as earthquakes, explosive volcanic eruptionsor landslides, aerial photography or very high resol-ution(0.5–2 mpixel)satelliteimagery(e.g.Ikonos,Quickbird) is needed to assist rapid search andrescue operations. A useful summary of remotesensing applications in the emergency response toa major disaster, the 2004 Sumatra earthquake andIndian Ocean tsunami, has been given by Kelmeliset al. (2006).(3) Post disaster. Geomorphological and geo-ecological mapping, based on the interpretation ofaerial photography or spectral and DEM data fromsatellites, can assist disaster recovery by highlight-ing locations with essential resources (e.g. water,wood fuel) and materials for reconstruction, suchas timber and sand–gravel or clay deposits. Earthresource maps of Banda Aceh, produced by theBritish Geological Survey in the 1970s, were veryuseful in the reconstruction of that region after the2004 earthquake and tsunami (M. Culshaw, pers.comm. 2005).The hazardous terrains examined in this publi-cation include landslides, flooding, contaminatedland, shrink–swell clays, subsidence, fault zonesand volcanic landforms (Table 1). Featured remotesensing systems include aerial photography,thermal scanning, hyperspectral sensors, laser alti-metry, radar interferometry and multispectral satel-lites, notably Landsat and ASTER. Relatedtechniques, such as the processing of DEMs anddata analysis using geographical informationsystems (GISs), are also discussed.The coverage starts with tectonic geohazards,then moves on to ground instability and flooding,before finishing with linear engineering projectsand disaster management. Kervyn et al. provide acomprehensive review of optical and radarapproaches to the satellite remote sensing of volca-nic terrain, with case studies from Hawaii and theRungwe rift valley of Tanzania. Next, the thermalproperties of Iceland’s Gri´msvo¨tn volcano areexamined by Stewart et al.developments in Newsatellite radar interferometry, which can detectmillimetre-scale ground deformation, are presentedby Reidmann & Haynes, who give examples fromTurkey’s 1999 Izmit earthquake and subsidence inRussia. Dowman & Balan provide a new approachfor correcting errors that occur when linkingtogether DEMs produced by the Shuttle Radar

Failure mechanisms and triggering factors in calcareous cliffs of the Subalpine Ranges (French Alps)

In order to enhance the detection of prospective rock falls in calcareous cliffs, 25 rock falls have been described in a more detailed way than for an inventory. They are representative of middle size rock falls (10 to 100,000 m 3) occurring in the French Subalpine Ranges, at an elevation between 200 m and 2000 m. Structural conditions of the rock masses, morphology of the initial cliff surface and the scar, possible failure mechanisms and processes have been studied. Typical failure configurations have been identified, based on the attitude of the failure surface, in relation to the bedding planes and the cliff surface. Irregular cliff morphology appears to be another important susceptibility factor. In most cases, the classical comparison of the average planes of the main joint sets with the average plane of the slope could not define the potentially unstable masses. Rather, those ones are due to joint planes that deviate from their mean set plane or to irregularities of the cliff surface. The proposed investigation method to detect prospective rock falls mainly consists in observing stereoscopic aerial photographs in order to look for critical configurations. Once a critical mass has been detected, its failure probability for a period of the order of one century must be evaluated (or its life expectancy). The main factor to consider for this purpose appears to be the proportion of rock bridges in the potential failure surface. The triggering factors of rock falls in our study area have been investigated, by analysing an inventory of 46 rock falls. Statistical tests have been carried out to study the relation between rock falls and daily rainfall, freeze–thaw cycles or earthquakes. A good correlation has been obtained with freeze–thaw cycles, a slight correlation with rainfall and no correlation with earthquakes. This suggests that ice jacking could the main physical process leading to failure by causing microcrack propagation.

Airborne laser scanning and usefulness for hydrological models

Abstract. Digital terrain models form the basis for distributed hydrologic models as well as for two-dimensional hydraulic river flood models. The technique used for generating high accuracy digital terrain models has shifted from stereoscopic aerial-photography to airborne laser scanning during the last years. Since the disastrous floods 2002 in Austria, large airborne laser-scanning flight campaigns have been carried out for several river basins. Additionally to the topographic information, laser scanner data offer also the possibility to estimate object heights (vegetation, buildings). Detailed land cover maps can be derived in conjunction with the complementary information provided by high-resolution colour-infrared orthophotos. As already shown in several studies, the potential of airborne laser scanning to provide data for hydrologic/hydraulic applications is high. These studies were mostly constraint to small test sites. To overcome this spatial limitation, the current paper summarises the experiences to process airborne laser scanner data for large mountainous regions, thereby demonstrating the applicability of this technique in real-world hydrological applications.

An improved method for determination of Holocene coastline changes around two ancient settlements in southern Anatolia: a geoarchaeological approach to historical land degradation studies

AbstractTwo well‐known ancient sites in southern Anatolia were selected to investigate and quantify the impact of historical land degradation on the Mediterranean coast of Turkey. These sites are the Luwian settlements of Kelenderis (modern Aydıncık) and nearby Nagidos (Bozyazı), both in Mersin Province and both occupied since around 4000 BP. Changes in local climatic conditions over this period have produced variations in the rates of fluvial transport of sediment/soil from the hinterland into the relevant deltaic regions, thus influencing rates of coastal progradation and aggradation. In addition, both eustatic and neotectonic movements have contributed to deltaic subsidence and/or hinterland uplift, with consequential impact on coastal evolution (positive or negative). The novel geoarchaeological methodology adopted in this study involves the creation of a graphical archive from detailed and standardised measurements taken from rectified mono‐ and stereoscopic aerial photographs. These archival data were then integrated with data from several types of historical map and field measurements in order to develop a geographical information system (GIS) database that could be interrogated, enabling graphical models of past coastal change to be constructed and calculations then made of the coastal configurations at successive historical periods.These calculations reveal that over the past 6000 years there has been only limited erosion/degradation in the karstic hinterland supplying the sediment to these two study sites (contrary to some previous statements concerning the high degradation risk of Mediterranean karst terrains). Furthermore, rates of progradation in each delta appear to have become diminished or even reversed in the past several decades as a result of both natural and anthropogenic factors. The precise contribution of neotectonic movements in this seismically active zone remains unquantified and is a topic requiring further interdisciplinary study. Copyright © 2003 John Wiley & Sons, Ltd.

Lithologic, structural, and geomorphic controls on ribbon forest patterns in a glaciated mountain environment

So-called “ribbon forests” have been attributed to snowdrift patterns and fire history without reference to geomorphology [Vegetatio 19 (1969) 192.]. This paper illustrates how site conditions of geomorphology and geology explain the origin of ribbon forests. In Glacier National Park, MT (USA), regional tectonic uplift associated with the Laramide Orogeny produced structural features that amplify lithologic differences. Pleistocene glaciation scoured deeply along the strike of bedding planes, highlighting this pattern and in some cases producing fine-scale parallel finger lakes between forested ribbon strips. Twelve ribbon forest sites on both sides of the Continental Divide were closely studied on stereoscopic aerial photographs, and several of these sites were examined in the field or from helicopter overflights. In all cases, geologic and geomorphic conditions explain the location and distribution of the ribbon forests. Change-detection of the distribution of trees versus nontree-covered surfaces in an area of ribbon forest on Flattop Mountain, a complex uplifted synclinal structure, was undertaken using panchromatic, low-altitude aerial photographs from 1966 to 1991. Areas changed from forest to meadow and from meadow to forest in roughly equal amounts in a generally random spatial pattern. No evidence was seen to suggest that the creation of one ribbon eventually created another downwind, as suggested by Billings. Aerial photograph interpretation, field examination and soils analyses of forest ribbons and adjacent unforested meadows clearly illustrated that trees occupy higher, parallel to subparallel, well-drained sites where the spatial pattern is in turn a distinct reflection of the spatial pattern of structure and stratigraphy. Meadows occupy topographically lower positions between ridges where erosion along bedding plane strike was concentrated. Topography sets conditions that allow tree growth in certain locations while precluding it in immediately adjacent areas. Ribbon forests there are thus a spatial manifestation of the interaction between structure, lithology, and topography.

Comparative assessment of analytical and digital photogrammetric methods in the construction of DEMs of geomorphological forms

AbstractTraditionally, landforms have been measured using a combination of field survey techniques and analogue and analytical photogrammetry. With advances in computing power digital photogrammetric solutions are now seen as offering an affordable and cost effective way of mapping topographic features. This paper looks at the relative merits of each of these photogrammetric techniques, in terms of the practical considerations involved in data extraction and accuracies that can be achieved for a case study. The site investigated is Maiden Castle, situated southwest of Dorchester in Dorset, UK. This paper examines the relative accuracies of both digital and analytical photogrammetric techniques in relation to ground control points recorded using a global positioning system (GPS). Colour stereoscopic aerial photographs were taken of Maiden Castle, Dorset, in November 1999 at a scale of approximately 1 : 4000. Stereo models were constructed using pre‐marked ground control points positioned using post‐processed differential GPS. Subsequent analysis involved the calculation of residual values produced by comparing the computer‐generated surface with a set of test points measured using differential GPS. This research demonstrates that the optimal digital system matched the performance of analytical photogrammetry for the collection of geomorphological data. Copyright © 2003 John Wiley & Sons, Ltd.

Glacier changes in southern Spitsbergen, Svalbard,1901–2000

AbstractHigh-resolution ground-penetrating radar surveys at 50 MHz on the polythermal glaciers Hornbreen, Hambergbreen and several surrounding glaciers in southern Spitsbergen, Svalbard, are presented and interpreted. Accurate positioning was obtained using differential global positioning system (DGPS). Digital elevation models (DEMs) of the bedrock and surface were constructed. Comparison of DGPS data and surface DEMs with data from the topographic mappings from 1936 oblique stereoscopic aerial photographs and from Mission Russe in 1899–1901 shows that the Hornbreen and Hambergbreen surfaces are about 60–100 m thinner today in the upper part than at the beginning of the 20th century. Hornbreen has retreated by 13.5 km from the central part of the front, and Hambergbreen by 16 km. All the fronts of the nearby east-coast glaciers in this area have retreated. The bedrock DEM shows that the Hornbreen and Hambergbreen beds lie at –25 to 25 m a.s.l. The combination of sub-sea-level fronts and increasing steepness of the glaciers suggests that the low-lying glaciated valley filled by Hornbreen and Hambergbreen may become a partially inundated ice-free isthmus within perhaps 100 years.

A geomorphological approach to the estimation of landslide hazards and risks in Umbria, Central Italy

Abstract. We present a geomorphological method to evaluate landslide hazard and risk. The method is based on the recognition of existing and past landslides, on the scrutiny of the local geological and morphological setting, and on the study of site-specific and historical information on past landslide events. For each study area a multi-temporal landslide inventory map has been prepared through the interpretation of various sets of stereoscopic aerial photographs taken over the period 1941–1999, field mapping carried out in the years 2000 and 2001, and the critical review of site-specific investigations completed to solve local instability problems. The multi-temporal landslide map portrays the distribution of the existing and past landslides and their observed changes over a period of about 60 years. Changes in the distribution and pattern of landslides allow one to infer the possible evolution of slopes, the most probable type of failures, and their expected frequency of occurrence and intensity. This information is used to evaluate landslide hazard, and to estimate the associated risk. The methodology is not straightforward and requires experienced geomorphologists, trained in the recognition and analysis of slope processes. Levels of landslide hazard and risk are expressed using an index that conveys, in a simple and compact format, information on the landslide frequency, the landslide intensity, and the likely damage caused by the expected failure. The methodology was tested in 79 towns, villages, and individual dwellings in the Umbria Region of central Italy.