Fabio Vittorio De Blasio - Academia.edu (original) (raw)

Papers by Fabio Vittorio De Blasio

Submarine Mass Movements and Their …

Submarine mass wasting in the form of glacial mudflows, river-laden debris flows, rock avalanches... more Submarine mass wasting in the form of glacial mudflows, river-laden debris flows, rock avalanches, sandy debris flows, outrunner blocks, or turbidity currents, reveal an extraordinary mobility, demonstrated by the very long runout distance between the source area and the final deposit, even on very gentle gradients. Laboratory experiments reveal that the dynamical behaviour of artificial debris flows depends dramatically on the claysand ratio in the experimental slurry. Artificial debris flows with high clay content, which are possibly a realistic replica of mudflows in glaciallyinfluenced areas, tend to form a thin water layer underneath the head which acts as a natural lubricant. In contrast, lubrication cannot be easily invoked for sand-rich gravity flows. Experiments show that sandy debris flows lack cohesion, and that sand settles quickly during the rapid disaggregating phase. In the present work we review the field data, experimental results gained with debris flows of various compositions, and the status of theoretical studies and numerical simulations of submarine debris flows. When dealing with debris flows that remain compact, such as clay-rich debris flows and outrunner blocks, both experiments and simulations indicate the importance of water lubrication for mobility. On the other hand, sandy debris flows are far more complicated owing to the increased importance of water penetration, disintegration, and turbulence, and these difficulties are reflected in greater intricacy of experiments and computer simulations. Thus, the problem of whether sandy debris flows may be highly mobile in the natural setting still remains elusive.

CRC Press eBooks, Jun 6, 2016

Geological Society, London, Special Publications, 2018

Abstract Radiocarbon isotopic ages and sedimentological data are presented for material recovered... more Abstract Radiocarbon isotopic ages and sedimentological data are presented for material recovered from three adjacent translational submarine landslides (YS1, YS2 and YS3) identified on the upper-continental slope offshore Yamba, New South Wales, Australia. The age data indicate that these three co-located upper-slope slides probably occurred independently of each other and not in a single, widespread regional-scale failure event. Numerical estimates of the likely runout distances for slide blocks corresponding to the entire landslide scar volumes range between 10 and 27 km, and represent a ‘runout zone’ in which landslide blocks or debris might reasonably be expected to be located. There is no morphological evidence for large blocks or debris fields derived from two of the Yamba landslide scars within their identified runout zones (YS1 and YS2), suggesting these two failures involved complete disintegration of large slide blocks after failure or the removal of sediment from the landslide sites as grainflows or turbidites. In contrast, the third runout zone (YS3) presents good evidence of at least 12 slide blocks between 100 and 200 m in diameter, suggesting that they were shed as relatively small individual blocks or they were generated due to the dismemberment of a larger slab.

&lt;p&gt;The dynamics of rock fragmentation during the collapse of a rock avalanc... more &lt;p&gt;The dynamics of rock fragmentation during the collapse of a rock avalanche, a rockfall, or an extremely energetic rockfall, is insufficiently known (De Blasio et al., 2018). Fragmentation especially at the base of a rock avalanche may affect on the one hand the dynamics of the rock avalanche and the geometry of the final deposit. On the other hand, fragmentation in the upper layers produces a dust of rock particles which: i) impacts energetically with the surrounding areas, and in a later stage, ii) propagates as a dust cloud. Although such dynamics are commonly observed, they are still inadequately addressed.&lt;/p&gt;&lt;p&gt;Recently, a rock avalanche in the Italian Alps occurred in November 2017, giving us the possibility to investigate these phenomena in better detail. In particular, we analysed a &amp;#160;8,000 m&lt;sup&gt;3&lt;/sup&gt; collapse of serpentinites and metabasics (Grivola-Urtier metaophiolitic Unit) from the Pousset peak (Aosta Valley Region in Western Italian Alps). The peak collapsed from an average height of 2800 m a.s.l. to the foot of the slope 800 m below, where it completely disintegrated. The impact on the ground produced a rock dust cloud which subsequently flowed downstream over the successive few minutes. &amp;#160;The site was visited immediately after the event, and it was possible to investigate the fresh deposit of rock dust before alteration by climate or weathering. This collapse thus represents an interesting case study for trying to determine the energy threshold required for fragmentation and dust cloud formation, the redistribution of the kinetic energy after impact and the amount related to cloud generation within the energy balance.&lt;/p&gt;&lt;p&gt;After identifying &lt;em&gt;in situ&lt;/em&gt; the main characteristics of the collapse, we then concentrated our efforts on a more quantitative understanding of the event via numerical calculations. We reproduced the blocks trajectories and computed the impact points where a strong energy dissipation occurred by using the 3D rockfall simulator code HY-STONE (Crosta &amp; Agliardi 2004; Frattini et al. 2012). In these points, the block fragmentation has been taken place and the formation of dust occurred. Through laboratory analysis of dust samples collected from the few centimetres thick deposits on trees and paths, we determined the particle size frequency curves for each location. The fragmentation energy was then estimated by integrating the spectrum of the grains assuming that the fragmentation energy is proportional to the area just created.&lt;/p&gt;&lt;p&gt;Once obtained the fragmentation energy, we estimated the maximum speed and runout of the dust cloud and the settling time using a simple model for suspension flows. From the analysis of the results obtained in the three described procedures, the fragmentation energy was found to be a relatively small fraction of the initial energy of the landslide, and the calculated flow rate of the suspended powder was found to be compatible with the one observed, even though flowage parameters for the cloud still need to be understood from first principles. In conclusion this case study, even if volumetrically small (or perhaps because of it), may add interesting information on the ongoing debate about rock fragmentation in catastrophic events.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Earth Surface Processes and Landforms, Jun 23, 2015

Debris-flows are widespread natural phenomena characterized by high mobility (high velocity and l... more Debris-flows are widespread natural phenomena characterized by high mobility (high velocity and long runout distance) and impact forces, which frequently cause human casualties and significant damage to infrastructure. To better understand the dynamics of such events, analyzing in particular the effect induced by the valley geometry on flow velocity, runout and mobilized volumes, in this work we reconstruct a real debris-flow event through numerical modeling. Specifically, we used a modified version of the BING model, a fluid-dynamic depth-integrated numerical model for debris flows, which has been properly modified to account for width changes along the valley. The studied event, which occurred in Scaletta Zanclea (Messina, northeastern Sicily, Italy) on October 1, 2009, is exceptionally well constrained by field and topographic information. In this respect the flow velocity, estimated from two specific locations on the basis of field evidence, the distribution of erosional and depositional areas along the Racinazzo valley, based on the comparison of pre-and post-event digital elevation models (DEMs), and the runout distance were used as constraints to calibrate the model. Furthermore, we report a detailed description of the main event characteristics based on hydrological records and witness reports. The numerical modeling results are consistent with witness reports and the severe damage recorded in the Scaletta Marina village, and highlight the effect of the valley geometry on both the debris flow velocity and the erosion/deposition processes. The effect of changing valley width has been also quantified, resulting in accelerations of the debris in correspondence of the valley narrowing and stagnations at the plateaus.

EGU General Assembly Conference Abstracts, Apr 1, 2018

Landslides, Jun 5, 2019

Sedimentary structures within rock avalanche deposits have gained increasing attention in recent ... more Sedimentary structures within rock avalanche deposits have gained increasing attention in recent years, since they may provide useful information about the dynamics of such energetic events. This work then is aimed at better defining the physical processes arising during the propagation, paying particular attention to the kinetic sieving mechanism, and strengthening the assumption (widely diffused in the literature) that such a process does not occur for similar events. Specifically, after the examination of two rock avalanche deposits in Central Italy, where cuts through the fragmented deposits are accessible and illustrative of the sediment texture, a series of laboratory flume tests have been performed in order to investigate in detail the flowing process. A simplified physical model for granular agitation has been then introduced to explain how and why kinetic sieving may occur at the laboratory scale and, in the case of natural granular flows of reduced size, also at the field scale.

Landslides

The process and dynamics of rock fragmentation during the collapse of rockfalls and rock avalanch... more The process and dynamics of rock fragmentation during the collapse of rockfalls and rock avalanches is a poorly developed topic. The most severe fragmentation often leads to the formation of a rock dust that rises to form a cloud suspended in the air. The understanding of fragmentation processes is hampered by the environmental disturbances that alter the dust cloud deposit shortly after deposition. Here, we study the fragmentation of the October 2017 Pousset rockfall, detached from a NNE facing steep bedrock wall in the permafrost zone, that involved 8,300m3 of metamorphic rock and fell about 800 m. The collapse generated large boulders which rolled downslope and a thick and large dust cloud. The source and deposit were investigated, and dust cloud material was sampled at different locations to reconstruct an exponential thickness distribution and perform grain size characterization. The fragmentation energy was estimated by integrating the spectrum of the grains assuming that the ...

Earth and Space Science, 2018

Landslides have been observed in different terrestrial environments and also on planets, satellit... more Landslides have been observed in different terrestrial environments and also on planets, satellites, and asteroids. Long runout landslides are strongly dependent on the initial mass position, material and slope path properties, topographic relief, and presence of volatiles. Therefore, landslides represent a means for the description of rock properties and environment of deposition prevailing at the time of occurrence and may assist in understanding the geological and climatological history of the planetary surfaces. Concerning Mars, previous studies have concentrated on Valles Marineris, where among the largest and longest landslides have been observed. Using different imagery, we present and analyze an original database of 3,118 Martian landslides of deposit area greater than 0.1 km2 throughout the planet between 60°N and 60°S, resulting in a data set far richer than previously done. After a distinction is made between different typologies of landslides, their position and the stat...

Journal of Geophysical Research: Planets, 2018

The mobility of landslides on Mars is studied based on a database of 3,118 events. To establish t... more The mobility of landslides on Mars is studied based on a database of 3,118 events. To establish the volume of the landslides for the whole data set based on the deposit area, a new volume‐area relationship based on a representative data set of 222 landslides is used. By plotting the H/L ratio between fall height H and runout L versus volume, the landslide mobility is analyzed and compared with existing empirical relationships for Martian and terrestrial landslides. By analyzing the mobility in terms of normalized residuals, that is, the relative deviation of the H/L ratio from the data set best‐fit line, mobility is found to depend on both the landslide location on Mars and the landslide typology. This allows us to identify four different types of high‐mobility (hypermobile) landslides. Three classes of high‐mobility landslides are associated respectively to meteoroid impact, the Olympus Mons aureoles, and landslides with Toreva‐block failure style, and their mobility can be explain...

Landslides, 2016

An erodible substrate and a sharp slope break affect the dynamics and deposition of long runout l... more An erodible substrate and a sharp slope break affect the dynamics and deposition of long runout landslides. We study the flow evolution of a granular mass (1.5–5.1 l of sand or gravel) released on a bilinear chute, i.e., an incline (between 35 and 66°) followed by a horizontal sector, either sand-free or covered (1–2-cm-thick sand layer). Monitoring the time evolution of the falling mass profiled at 120 Hz, the impact dynamics, erosion of the basal layer, and modes of deposition are studied. The frontal deposition is followed by a backward propagating shock wave at low slope angles (<45°), or by a forward prograding flow at greater angles. Experiments with colored sand layers show a complex sequence of dilation, folding and thrusting within both the collapsing sand flow and the substrate. Experimental results are compared with real rock avalanche data and nearly vertical collapses. The observed increase of the drop height divided by the runout (H/L or Heim’s ratio) with both chute slope angle and thickness of the erodible substrate is explained as an effect of vertical momentum loss at the slope break. Data suggest a complex evolution, different from that of a thin flow basal shear flow. To provide an approximate explanation of the dynamics, three analytical models are proposed. Erosion of a 1-cm-thick substrate is equivalent to 8–12 % increase of the apparent friction coefficient. We simulate the deposition and emplacement over an erodible layer with a FEM arbitrary Lagrangian Eulerian code, and find a remarkable similarity with the time evolution observed in the experiments. 2D models evidence the internal deformation with time; 3D models simulate deposition.

IOP Conference Series: Earth and Environmental Science, 2015

Landslides often collapse in areas covered by alluvial deposits forming an erodible layer. This e... more Landslides often collapse in areas covered by alluvial deposits forming an erodible layer. This erodible substrate may deform plastically under the intense shear stress of the landslide mass. In other cases, the collapse occurs onto a water basin or tidal flat, creating impulse water waves whilst the landslide may be lubricated by a water layer underneath. In either cases the presence of a medium underneath the landslide will change its dynamics introducing complex processes. While frictional, dry masses and taluses generally hamper the landslide motion. In this work, we present some experiments mimicking the collapse of a landslide onto shallow erodible or water layers. The landslide is simulated with a granular material (sand or gravel) flowing on an incline (35-66°) followed by a horizontal sector covered with a granular bed 1 to 2 cm thick or with a 0.5-1 cm of water. Monitoring evolution in time allows us to describe in detail the process of fluidization of the material at impact, the generation of impact waves, and the erosion process. Concerning impact on a sand layer, the apparent friction coefficient (H/L) is found to increase with the chute slope angle and with the thickness of the erodible layer, and to decrease with the volume. At low slope angles, the material accumulates backwards in a shock wave mode, while at larger slope angles (>45°) it accumulates by prograding forward. A granular avalanche falling from the slope is partially reflected at the sharp slope break where erosion occurs and then propagates initially as a wave partially eroding the superficial material. Folding and thrusting occur within the dense shear flow and the erodible layer. Experiments with a water layer show that the dynamics depends much on the permeability of the granular avalanche. FEM numerical simulations replicate and allow to describe and understand both the spreading and the erosion, and internal deformation recorded in the erodible layer. Experimental findings are compared with real rock avalanches, flowslides and snow avalanches characteristics and morphological features. A medium with low permeability may be lubricated by the presence of water, resulting in a front acceleration and a final double-ringed deposit. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

ABSTRACT HiRISE images show the presence of boulders at the bottom of one pit of Arsia Mons, like... more ABSTRACT HiRISE images show the presence of boulders at the bottom of one pit of Arsia Mons, likely fallen from the flanks similar to rock falls on Earth.