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Rock Falls (rock + fall)

Distribution by Scientific Domains

Earth and Environmental Science	75%

Selected Abstracts

Quantifying periglacial erosion: insights on a glacial sediment budget, Matanuska Glacier, Alaska

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 15 2009
Colin R. O'Farrell
Abstract Glacial erosion rates are estimated to be among the highest in the world. Few studies have attempted, however, to quantify the flux of sediment from the periglacial landscape to a glacier. Here, erosion rates from the nonglacial landscape above the Matanuska Glacier, Alaska are presented and compare with an 8-yr record of proglacial suspended sediment yield. Non-glacial lowering rates range from 1·8 ± 0·5,mm,yr,1 to 8·5 ± 3·4,mm,yr,1 from estimates of rock fall and debris-flow fan volumes. An average erosion rate of 0·08 ± 0·04,mm,yr,1 from eight convex-up ridge crests was determined using in situ produced cosmogenic 10Be. Extrapolating these rates, based on landscape morphometry, to the Matanuska basin (58% ice-cover), it was found that nonglacial processes account for an annual sediment flux of 2·3 ± 1·0 × 106,t. Suspended sediment data for 8 years and an assumed bedload to estimate the annual sediment yield at the Matanuska terminus to be 2·9 ± 1·0 × 106,t, corresponding to an erosion rate of 1·8 ± 0·6,mm,yr,1: nonglacial sources therefore account for 80 ± 45% of the proglacial yield. A similar set of analyses were used for a small tributary sub-basin (32% ice-cover) to determine an erosion rate of 12·1 ± 6·9,mm,yr,1, based on proglacial sediment yield, with the nonglacial sediment flux equal to 10 ± 7% of the proglacial yield. It is suggested that erosion rates by nonglacial processes are similar to inferred subglacial rates, such that the ice-free regions of a glaciated landscape contribute significantly to the glacial sediment budget. The similar magnitude of nonglacial and glacial rates implies that partially glaciated landscapes will respond rapidly to changes in climate and base level through a rapid nonglacial response to glacially driven incision. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Slope dynamics of Lake Albano (Rome, Italy): insights from high resolution bathymetry

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2009
Francesca Bozzano
Abstract New detailed data about the morphology of the submerged slopes of Lake Albano (Rome, Italy) have been collected by a sonar multibeam survey financed by the Italian Department of Civil Protection. These data allow for investigation of the subaqueous slope dynamics of the lake, which partially fills a volcanic depression, and the elucidation of the relationships between subaqueous and subaerial slope processes. Subaerial, submerged and combined subaerial/submerged landslide-related morphologies were detected around the inner slopes of the lake. In the submerged slopes, several gravity-induced landforms were recognized: landslide scar areas, landslide accumulations, erosional chutes and channels, block fields, isolated blocks, scarps and slope breaks. An attempt to evaluate the state of activity of the submerged slopes was carried out by taking into consideration the relative freshness of some selected landforms. Interpretation of bathymetric data, as well as direct surveys of the subaerial slopes, was used to assess the morphometric features and interpret the type of movement of the landslides. We propose a comprehensive classification based on the landslide's size and type of movement. We recognized rock fall/topples, debris flows, rock slides and slump, complex rock slides/channelled flows and debris slide and slump. The volume of the main landslides ranged between 101 and 103 m3, while a few rock and debris slides have volumes ranging between 103 and 105 m3. Two large palaeo-landslides with volumes on the order of 106 m3 were identified in the southern and northern part of the lake, respectively. Velocities of the recognized landslides range from rapid to extremely rapid. Two main landslide hazard scenarios have been depicted from the results of the integrated analysis of both subaerial and submerged gravity-induced landforms. The most hazardous scenario involves extremely rapid large volume events (>106 m3) that could, if they interacted with water, induce catastrophic tsunamis. Copyright © 2009 John Wiley & Sons, Ltd. [source]

GEOCHEMICAL AND ENGINEERING GEOLOGICAL PROPERTIES OF THE VOLCANIC TUFFS USED IN THE ETRUSCAN TOMBS OF NORCHIA (NORTHERN LATIUM, ITALY) AND A STUDY OF THE FACTORS RESPONSIBLE FOR THEIR RAPID SURFACE AND STRUCTURAL DECAY

ARCHAEOMETRY, Issue 2 2010
P. CICCIOLI
The geochemical and engineering geological properties of the tuffs used in the rock-cut cliff tombs of the Etruscan necropolis of Norchia were investigated to evaluate their susceptibility to different weathering agents and confirm their origin. For the first time, materials were characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT,IR), thermogravimetric analyses (TGA, DGA and DTG), scanning electron microscopy (SEM,EDS) and energy-dispersive X-ray fluorescence (ED,XRF), and their different origins confirmed. Tests of material properties indicate that both tuffs are poorly durable, but one of them is less susceptible to weathering. Although tombs made with the more resistant material show limited surface weathering, they undergo severe structural damage because of stress release and plant root infiltration. This, combined with the microclimatic conditions established inside river canyons, can trigger rock falls, leading ultimately to the complete destruction of these tombs. [source]

Typology of Natural Hazards and Assessment of Associated Risks in the Mount Bambouto Caldera (Cameroon Line, West Cameroon)

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009
Ghislain T. ZANGMO
Abstract: Mount Bambouto is a polygenic stratovolcano of the Cameroon Volcanic Line, built between 21 Ma and 4.5 Ma. It is situated approximately 200 km NE of Mount Cameroon, between 09° 55, and 10°15, longitude east and, 05°25, and 05°50, latitude north. The volcano covers an area of 500 km2 and culminates at 2740 m at Mélétan dome and bears a collapsed caldera at the summit (13 × 8 km). Mount Bambouto is characterized by several natural hazards of different origins: meteorological, such as landslides and rock falls; anthropogenic, such as bushfires, tribal wars and deforestation; and volcanological, such as volcanic eruption. The thematic map shows that 55,60% of the caldera has high probability of occurrence of mass movement. The caldera has a high population density (3000 inhabitants), which increases the level of risk, evaluated at approximately $US3.8 million for patrimony, 3000 civilian deaths and destruction of biodiversity. [source]