1,721,022 research outputs found
Susceptibility to translational slide-type landslides: Applicability of the main scarp upper edge as a dependent variable representation by reduced chi-square analysis
Full text linkThe applicability of main scarp upper edge (MSUE) as dependent variable representation was performed in a translational slide susceptibility zonation of the Milia and Roglio basins, Italy. Two landslide inventories were built thanks to detailed geomorphological mapping and aerial photograph analysis. The landslides were used to create the models before 1975, while those after 1975 were employed to validate the predictive power of the model. Possible landslide-related factors were chosen from a geomorphological survey. The inventory landslide maps and the landslide-related factor maps were processed by conditional analysis, producing landslide susceptibility maps with five susceptibility classes. A comparison between the distribution of landslides after 1975 and those derived from models provided the predictive power of each model, which in turn was used to define the best predictive model. Reduced chi-square analysis allowed to define the efficiency of MSUE as dependent variable representation. MSUE can be applied as dependent variable representation to landslide susceptibility zonation with appreciable results. In the Roglio basin, slope angle, distance from streams, and from tectonic lineaments proved to be the main controlling factors of translational slides, whereas in the Milia basin, lithology and slope angle gave more satisfactory results as landslide-predisposing factors
High-resolution coherency functionals for improving the velocity analysis of ground-penetrating radar data
Full text linkWe aim at verifying whether the use of high-resolution coherency functionals could improve the signal-to-noise ratio (S/N) of Ground-Penetrating Radar data by introducing a variable and precisely picked velocity field in the migration process. After carrying out tests on synthetic data to schematically simulate the problem, assessing the types of functionals most suitable for GPR data analysis, we estimated a varying velocity field relative to a real dataset. This dataset was acquired in an archaeological area where an excavation after a GPR survey made it possible to define the position, type, and composition of the detected targets. Two functionals, the Complex Matched Coherency Measure and the Complex Matched Analysis, turned out to be effective in computing coherency maps characterized by high-resolution and strong noise rejection, where velocity picking can be done with high precision. By using the 2D velocity field thus obtained, migration algorithms performed better than in the case of constant or 1D velocity field, with satisfactory collapsing of the diffracted events and moving of the reflected energy in the correct position. The varying velocity field was estimated on different lines and used to migrate all the GPR profiles composing the survey covering the entire archaeological area. The time slices built with the migrated profiles resulted in a higher S/N than those obtained from non-migrated or migrated at constant velocity GPR profiles. The improvements are inherent to the resolution, continuity, and energy content of linear reflective areas. On the basis of our experience, we can state that the use of high-resolution coherency functionals leads to migrated GPR profiles with a high-grade of hyperbolas focusing. These profiles favor better imaging of the targets of interest, thereby allowing for a more reliable interpretation
AIGEO Working Group “Past distribution of the periglacial environment in the Italian mountain chains: reconstructions based on the study of relict forms”
No full textGlacier expansions in southwestern Macedonia (FYROM): implications for paleoclimatic and environmental reconstructions
Full text linkThe Former Yugoslavian Republic of Macedonia (FYROM, Macedonia) provides numerous remnants of glacial advances, particularly in its western part. Geomorphologic analyses of glacial valleys in southwestern Macedonia reveal several cirques, terminal moraines, and some lateral moraines. After detailed geomorphic mapping, the best-preserved terminal moraines were dated using samples from stable boulders at the moraine crests. At Mt Pelister an average 10Be age of 15.24 0.85 kyr (2215 m a.s.l, Oldest Dryas) is retrieved from three quartz-rich schists covering/ranging between 14.8 and 15.3 (0.8) kyr, and in the Galicica mountains an average 36Cl age of 11.97 0.57 kyr results from five limestone boulders yielding between 11.3 and 12.8 (1.2) kyr (2050 m, Younger Dryas) (Ribolini et al., 2017; Gromig et al., 2017).
The Oldest Dryas moraine at Mount Pelister marks the youngest glacial feature in this area, suggesting that the wide cirque was not or not significantly re-glaciated during the Younger Dryas and Little Ice Age (ruling out significant topoclimation snow accumulation). The temporal relationship between Older Dryas glacier advances in the Balkan region and recorded changes in the Atlantic thermohaline circulation during the Laurentide Ice Sheet massive ice discharge (H1 event), confirms the strong climatic link between the Mediterranean regions and the North Atlantic Ocean. The reconstructed equilibrium line altitude (ELA, 2250 m) at Mt Pelister is in good agreement with the height of the ELAs of Oldest Dryas glaciers in the Mediterranean mountains, demonstrating a comparable response to this cold event.
In contrast, the ELA during the Younger Dryas in the Galicica mountains (2130 m) is most likely not suitable for regional climate reconstructions due to topoclimatic driven snow input in the small enclosed cirque. Such additional windblown snow accumulation has been observed at other small cirques (Hughes, 2009; Kozamernik et al., 2017). The analyses of nearby lake sediments indicate that cold conditions promoted the formation of Oldest and Younger Dryas local cirque glaciers. However, studies of sediment records of the adjacent lakes Ohrid (Republic of Albania/FYROM) and Prespa do not indicate the presence of a proximal glaciation. An explanation might be a combination of (i) the small size of the cirque glacier, generating only small amounts of debris or meltwater, and (ii) the karstic bedrock, which hampers fluvial transport and traps sediment in its aquifer system.
Gromig, R., et al. (2017). Evidence for a Younger Dryas deglaciation in the Galicica Mountains (FYROM) from cosmogenic 36Cl. Quat. Int., in press, doi:10.1016/j.quaint.2017.07.013.
Hughes P.D. (2009). Twenty-first Century Glaciers and Climate in the Prokletije Mountains, Albania, Arct. Antarct. Alp. Res. 41, 455–459, doi:10.1657/1938-4246-41.4.455.
Kozamernik E., et al. (2017). Spatial and climatic characterization of three glacial stages in the Upper Krnica Valley SE European Alps. Quat. Int., in press, doi:10.1016/j.quaint.2017.05.047.
Ribolini, A., et al. (2017). An Oldest Dryas glacier expansion on Mount Pelister (Former Yugoslavian Republic of Macedonia) according to 10Be cosmogenic dating, J. Geol. Soc. Lond., in press, doi:10.1144/jgs2017-038
Early to late Holocene vegetation and fire dynamics at the treeline in the Maritime Alps
Full text linkWe used pollen, plant macrofossil, and charcoal records to investigate local long-term timberline shifts and changes in vegetation composition in relation to fire activity at the modern upper forest limit (ca. 2,000 m a.s.l.) in the Mont Bégo area, Maritime Alps of France and Italy. The area is an important place for Alpine archaeology because it has thousands rock-art carvings whose age cannot be directly assessed. Our new record confirms the occurrence of distinct land use phases (7,450–7,150, 6,200–4,900, and 4,250–3,700 cal bp), as suggested by earlier studies of rock art typology. Moreover, the vegetation reconstruction from macrofossils, with co-dominance of Pinus and Betula, suggests that early Holocene conditions were moister than in drier inner Alpine valleys, where Larix decidua played a more important role, both in the past as well as in modern timberline forests. After 8,000 cal bp, the timberline shifted upwards and mixed Abies alba and Pinus cembra stands established around the study site. These fire sensitive trees were finally replaced during the Bronze Age (around 4,000 cal bp) by L. decidua, which still dominates the subalpine woodlands in the area today. Our study supports the notion that while the range of A. alba has been reduced at the colder end of its natural distribution, that of L. decidua has been widened by land use changes and fire disturbances to create high alpine wood pastures
Geomorphology of the topmost part of the Bistra Mountain, Mavrovo Park, North Macedonia
No full textIdentification of the remnant traces of paleo-glaciers provides important proxies to understand the response of the environment to rapid climate changes. We present a 1:25,000 scale geomorphological map covering ∼12.5 km2 of the upper part of Mount Bistra (North Macedonia) on the basis of remote sensing analyses and geomorphological surveys. Particular attention is given to the description of glacial and periglacial landforms, to the reconstruction of single glacier shapes and to Equilibrium Line Altitude (ELA) value calculation. The results of the survey and the reconstructed ELAs indicate the occurrence of three glacial phases that led to the formation of frontal and lateral moraines. The age of these phases is tentatively attributed to the Late Pleistocene by comparing these ELAs with those of other Balkan mountains. This map is the first step of a wider project aimed at reconstructing the relation between climate change and geomorphic response in this area
Ground-penetrating radar prospections to image the inner structure of coastal dunes at sites characterized by erosion and accretion (Northern tuscany, Italy)
Full text linkIn this study we aimed to gain insights into dune formation and evolution from select coastal tracts of Northern Tuscany by inspecting their internal sedimentary architecture with Ground-Penetrating Radar (GPR) analysis. Erosion, equilibrium and accretion characterize the selected coastal tracts, and this analysis remarks on some GPR features consistently associated with specific coastal evolution states. A standard sequence of data processing made it possible to trace several radar surfaces and reflectors in the GPR profile, eventually interpreted in terms of depositional processes and erosive events. The stable or currently accreting coastal sectors show radar features compatible with a general beach progradation process, punctuated by berm formation in the general context of a positive sedimentary budget. Additionally, the radar facies distribution locally supports a mechanism of dune nucleation on an abandoned berm. Conversely, the GPR profile of the coastal sector today affected by erosion shows how a negative sedimentary budget inhibited coastal progradation and favored destructive events. These events interacted also with the active dunes, as demonstrated by the overlapping of wave run-up and aeolian radar facies. GPR prospections were effective at delineating the recent/ongoing coastal sedimentary budget by identifying radar features linked to construction/destruction phenomena in the backshore, and to dune nucleation/evolution
SH-wave seismic reflection at a landslide (Patigno, NW Italy) integrated with P-wave
Full text linkThe aim of this paper is to present the acquisition and processing up to the depth migrated section of an SH-wave reflection seismic profile. This experience is conducted on a deep-seated gravitational slope deformation located in the Northern Apennines in Italy. The SH-wave depth-migrated image in the investigated area provides a detailed description of the small reactivation slip surfaces delineating minor landslides at shallow depths, which are responsible for the major damages observed. These results are integrated with a recently acquired P-wave seismic reflection profile investigating the same slope and delineating the highly deformed layer at depth, liable for the deep-seated gravitational slope deformation. The combined use of P-waves and SH-waves allows to gain a deeper knowledge of the landslide internal setting that is necessary to mitigate the risk associated with the mass movement
- …
