Fabio Vittorio De Blasio

Investigation of rock fragmentation during rockfalls and rock avalanches via 3-D discrete element analyses

This paper investigates the characteristics of dynamic rock fragmentation and its influence on the postfailure fragment trajectory. A series of numerical simulations by discrete element method (DEM) were performed for a simple rock block and slope geometry, where a particle agglomerate of prismatic shape is released along a sliding plane and subsequently collides onto a flat horizontal plane at a sharp kink point. The rock block is modeled as an assembly of bonded spherical particles with fragmentation arising from bond breakages. Bond strength and stiffness were calibrated against available experimental data. We analyzed how dynamic fragmentation occurs at impact, together with the generated fragment size distributions and consequently their runout for different slope topographies. It emerges that after impact, the vertical momentum of the granular system decreases sharply to nil, while the horizontal momentum increases suddenly and then decreases. The sudden boost of horizontal momentum can effectively facilitate the transport of fragments along the bottom floor. The rock fragmentation intensity is associated with the input energy and increases quickly with the slope angle. Gentle slopes normally lead to long spreading distance and large fragments, while steep slopes lead to high momentum boosts and impact forces, with efficient rock fragmentation and fine deposits. The fragment size decreases, while the fracture stress and fragment number both increase with the impact loading strain rate, supporting the experimental observations. The fragment size distributions can be well fitted by the Weibulls distribution function.

Modeling Potential Tsunami Generation by the BIG'95 Landslide

The BIG’95 landslide was emplaced 11,500 years ago and is one of the largest known submarine landslides in the Mediterranean Sea. The simulated landslide dynamics matches the observed run-out and deposited thickness. Water elevation simulated by using a dispersive tsunami model exceed 10 m close to the landslide area and at the nearest shorelines. Modeling further indicates that the tsunami probably had widespread consequences in the Mediterranean. Compared to previous studies, this new simulation provides larger waves. There is, however, still a need to better constrain the landslide dynamics in order to illuminate the uncertainties related to the tsunamigenic power of this, and other, submarine landslides.

The Surface of Mars

On Earth, the formation of mountain ranges as the consequence of geotectonic cycles, the deposition of sediments on continents and oceans, the eruption of volcanoes, and catastrophic phenomena such as earthquakes and landslides has continued incessantly. By accumulating new rocks and creating new morphologies, the geological forces have changed the layout of the preexisting ones. Meanwhile, erosion due to rivers, glaciers, thermal effects, wind, and also biological activity have quickly covered or deleted the traces of earlier geological structures in a never-ending cycle. As a result, the landscape on Earth is often geologically recent.But on Mars, both the superficial expression of new geological phenomena and the erosive phenomena have been much slower. The lack of plate movements and the absence of life, at least in terms of terrestrial characteristics, have aided in the conservation of traces of geological activity after extremely long periods. Just as a family picture shows people of several generations, images of Mars often display morphologies that are billions of years old, along with much more recent features.On the following pages, we will see many astonishing images of the Martian surface. We will investigate the nature of huge meteorite impact craters, appreciate what they can reveal about the properties of the Martian terrain, examine the highest volcanoes in the solar system, and be surprised by the volume and length travelled by landslides as large as the whole of France. We will see structures that, surprisingly, often appear very close to each other, and are much neater and tidier than those on Earth.

History and Physiography of Mars

Observing Mars from a spacecraft in polar orbit, the plains of the northern hemisphere would appear smooth and with few features except for the polar ice cap. As the spacecraft shifts to the south and the planet spins in front of our eyes, huge volcanoes would appear, well recognizable even at distances of thousands of kilometers. Approximately at the equator, we would observe the long canyons of Valles Marineris. Only continuing to the southern part of Mars would we notice a mountainous surface completely crammed with craters, reminding us a little of our Moon. This division of the planet into two morphologically different hemispheres has been defined, by some, as one of the most amazing discoveries in planetology. It still appears extremely enigmatic today.Before looking at the morphology of Mars in more detail, it is useful to know its main features. In the pages that follow, we shall start with the strange dichotomy of Mars, see the most extensive landscapes of the Red Planet, and then go into its history.We will assess the current knowledge on the planet’s interior, the mystery of the disappearance of the magnetic field, to which the destiny of life on the planet could be tied, and shed light on its main geographic features and history as deduced from the images.

Mars Through the Millennia

For the Egyptians it was “the red one,” for the Sumerians, the star of death Nergal. It was Ares to the Greeks and Mars to the Romans. For most, it represented the god of war. It must have been the red color of the planet, evoking blood or the eyes of a furious animal, that suggested a violent personality for Mars. In the Middle Ages, being born with Mars in one’s zodiac sign could make you violent and vicious. But it was thanks to Mars that Kepler came to understand the laws of planetary motion, paving the way for the theory of universal gravitation of Newton.On the following pages, we will consider the myths about Mars built by ancient cultures, but also their valuable observations; the first attempts to observe the surface of the planet with telescopes; how some remarkable discoveries were made, while other features induced early observers to ruminate about huge engineering feats built by aliens. We will see how our understanding of the Red Planet changed with the observations made in space, and familiarize ourselves with some of the characteristics of the planet.

Global Scale Analysis of Martian Landslide Mobility and Paleoenvironmental Clues

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 dataset based on the deposit area, a new volume-area relationship based on a representative dataset of 222 landslides is used. Plotting the H/L ratio between fall height H and runout L versus volume, landslide mobility is analyzed and compared with existing empirical relationships for Martian and terrestrial landslides. Analyzing the mobility in terms of normalized residuals, i.e., the relative deviation of the H/L ratio from the dataset best-fit line, mobility is found to depend on both the landslide location on Mars, and 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 explained by the peculiar flow mechanics. The fourth class includes landslides associated with isolated craters, those in the regions wetted by the putative Oceanus Borealis, and the ones at high latitudes. We suggest that the common factor behind all the hypermobile landslides of this fourth kind is the presence of ice. This is confirmed by our data showing that landslides increase in mobility with latitude. The latitudinal trend mirrors the distribution of ice as detected by radar, neutron probes, and the presence of glacial and layered ejecta morphologies. Because the overall landslide distribution supports the presence of ice-lubricated conditions, two ice lubrication models are presented showing how ice melting within or underneath the landslides could enhance mobility. By proper analysis in terms of apparent friction residuals, we find that the mobility of landslides in Valles Marineris with the largest landslide concentration is lower than average. We explain this circumstance partly from the smaller role of ice in equatorial Valles Marineris, and partly because the collapses from high slope relief imply high-speed impact with the floor valley confinement, loss of momentum, and decrease in mobility. Environmental consequences imply that the present subsurface ice distribution may have been persistent throughout the Amazonian period.