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Special Issue 2006
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Special Issue 2006
PRESENTATION
Special Issue 2006
MODES OF FLOODING RESULTING FROM LANDSLIDE DAMS Landslide dams cause two types of floods: (1) upstream (backwater) flooding as the impoundment fills, and (2) downstream flooding resulting from failure of the dam. Although less common than upstream flooding, downstream flooding is usually more serious and may be catastrophic. The world’s worst landslide-dam disaster occurred when the 1786 Kangding-Louding earthquake in Sichuan Province, China, triggered a huge landslide that dammed the Dadu River (LI, 1989
Special Issue 2006
Building on the work of COSTA (1988), COSTA & SCHUSTER (1988, 1991), recent work has attempted to quantify aspects of the formation and failure of landslide dams (e.g., CASAGLI & ERMINI, 1999; ERMINI & CASAGLI, 2003; KORUP, 2004). Together with our growing knowledge of landslide magnitude and frequency distributions (e.g., HUNGR et alii, 1999; GUZZETTI et alii, 2003; DUSSAUGE et alii, 2003) at spatial and temporal scales, this work forms a promising basis for a first approximation to quantitative risk asses
Special Issue 2006
Landslide dam lakes are fairly frequent phenomena in mountainous regions, but are often unknown or not recorded because of their frequently temporary character, following their rapid destruction or filling with sediments, especially if the reservoir displays a limited volume. Indeed detailed data on the landslides are quite scarce in the case of rapid dam breaches. However the major phenomena have left significant traces in history following the destructive consequences induced by the dams breaches that are
Special Issue 2006
Studying the blockage of mountain rivers by bedrock landslides offers both fascinating and challenging prospects. It allows us to investigate not only some of the largest processes of mass movement on the Earth surface, but also the fluvial response to the emplacement of many millions of tons of rock and debris. The decay process of river-blocking debris links geomorphology to hazard and risk assessment, given the potential for catastrophic outburst floods and debris flows from rockslide-dammed lakes (SCHUS
Special Issue 2006
Landslide dams may form suddenly and unexpectedly, thereby posing hazards that must be rapidly assessed. In areas placed upstream, respect to the river dammed section, waters blocked by the dam may provoke floods spreading for kilometers, causing damages to human activities and interrupting communication lines. This can happen downstream as well, because of the risk of a sudden outburst of the landslide dam, especially when it is not possible to set up a control system for water drainage. As a result the da
Special Issue 2006
The Andean cordillera of Argentina is more than 3500 km long and 50 to 550 km wide and characterized by steep relief contrasts throughout. Except for a few valleys, most of this region is scarcely populated. Hence geologic mapping was mainly carried out on a scale (1:250000), which is often too small to map out various Quaternary units and therefore to highlight relations of landslide deposits with lakes or lake deposits. However, in the last years various studies have been carried out, concentrating on lar
Special Issue 2006
NATURAL DAMMING ON THE UPPER INDUS STREAMS Rivers of the transHimalayan Indus basin are subject to damming by glaciers and a variety of mass movements. Among the many catastrophic outburst floods, ice dam bursts dominate the historical record, but the two largest were from failure of landslide dams in 1841 and 1858 (HEWITT, 1982, 1998a). Far more numerous are impoundments by debris flows and snow avalanches, and along glacier margins (HUGHES & NASH, 1985; KREUTZMANN, 1994). However, they tend to be small, t
Special Issue 2006
This paper attempts to work out the stability conditions of 20 landslide dams in the Indian and Nepal Himalayas as well as two in China. All of them formed lakes upstream by damming the main river. The categories of study areas that they created differ in their shape, their volume and composition of the deposited landslide material, as well as in the size and life span of their former dammed lakes. This representative group of case studies affords the opportunity to obtain new results on this rare phenomeno
Special Issue 2006
Mountainous regions of Tadjikistan have been very active from the seismo-tectonic point of view during the last 1.0-1.5 millions years. Geological processes in the alpine, seismically active regions are characterised by their scale and high activity and very often their manifestations can be considerd as natural catastrophes. It is especially typical of the outburst floods and debris flows associated with the dams’ breaches. In Tadjikistan blocking of the deeply incised river valleys is a common phenomeno
Special Issue 2006
The historic and prehistoric rockslide dams in the Alps give a good indication about the possible evolution and the dam stability. The two extremes are either an early break of the dam, releasing all the water in a catastrophic flush-flood, or a total filling of the basin by sediments. Between these extremes exist many possibilities. The survival of a lake in most cases is only a temporary condition. Nevertheless ABELE (1974) counts 33 remaining lakes among the 285 rockslide sites he discusses. This means a
Special Issue 2006
Armenia lies in the central part of the Armenian Highland that has a high-energy relief, which, under the conditions of high seismicity, determines development of large-scale rockslides and landslides. Armenian historical chronicles record many cases of major earthquake-induced rockslides forming large retaining water bodies, and numerous smaller ones (Table 1). The use of GIS-format databases on historical chronicles, remote sensing, field study results and geotechnical investigation helps to obtain import
Special Issue 2006
Formation of the Karmadon blockage (Northern Ossetia-Alania, Russia) was caused by a rock-ice avalanche on September, 20, 2002. Taking into account that ice-composed features outside the permafrost zone are not a “long-living” in the geological sense, the Karmadon blockage should be considered as a unique natural phenomenon. Only indirect evidences can indicate existence of similar dams in the past due to their rapid destruction. It is necessary to note that according to the archive data, at least 6 sim
Special Issue 2006
The area in the midstream of the Mailuu-Suu River is the most landslide-prone and vulnerable of the entire Kyrgyzstan territory. More than 200 landslide sources distinct by genesis, age and development stages have been fixed at present in the outskirts of the Mailuu-Suu town within an area of 80 km2 only. The main reasons of mountain slopes instability in this area are the geologic conditions and geodynamic peculiarities of the region. Seismic, climatic and man-caused factors play a role of rather a trigger
Special Issue 2006
Mass movements are an important factor in shaping the Earth’s surface. They result in changes of the morphology and the surface cover as well as the near-surface underground. In dependence on the varying terrestric and atmospheric conditions a wide range of different mass movements has been observed, described and classified, e.g., (Cruden & Varnes, 1996). Under certain natural conditions most of them have the potential for forming landslide dams whereas their majority results from rotational and translat
Special Issue 2006
Detailed sedimentological data for rock-avalanche deposits are sparse in the current literature. A review yields the following common results based on both observation and direct measurement: i. highly fragmented but undisaggregated clasts (MCSAVENEY, in press); ii. preservation of original stratigraphy (STROM, 1999); iii. crude inverse grading (CRUDEN & HUNGR, 1986). Recent work has attempted to better quantify the sedimentology of rock-avalanche deposits using either a facies approach (SCHNEIDER et alii,
Special Issue 2006
The most common and widespread geomorphic effect of landslides is to block a drainage system forming a landslide dam. The stability of landslide dams is of the utmost importance; if the dam fails, it releases the impounded water to form a potentially destructive dambreak flood, and it also releases the debris of the dam and any accumulated reservoir sediment to the river downstream, causing severe aggradation and progressive channel instability. Landslide dam stability depends to a large extent on the mater
Special Issue 2006
The Scanno rockslide-avalanche dammed the Tasso river and caused the impoundment of the Scanno Lake which is one of the most famous example of naturally dammed lake in Central Apennines; it has an area of approximately 1 km2, a perimeter of about 5 km and a maximum depth of 33 m (RICCARDI, 1929). Far more significant is the presumed age of the lake. In fact, according to reports and documents by Roman historians the event could date back to 217 B.C. (NICOLETTI et alii, 1993). Further, radiocarbon dating of
Special Issue 2006
Construction of blast-fill dams is a promising, but risky technology. The traditional methods of both embankment and concrete dams construction, when the structure is erected slowly - dumper by dumper - allow to change, if necessary, either the material or technology or, even, the design. But the blast-fill dam, regardless of is it constructed by pin-point blast or by artificial rock avalanche (KORCHEVSKY, 2004) would be erected “in one gulp”. The most important parameters of the blast-fill dam that mus
Special Issue 2006
The presence of groundwater in a rock or soil slope mass can have several destabilizing effects, for example those related to freeze-thaw, weathering, seepage forces and/or erosion (either at the slope's toe or internally through piping). Although some of these processes may be treated in a slope stability analysis, they generally require the use of complex techniques that are applied in a highly conceptual fashion (EBERHARDT et alii, 2004). Instead, it is usually only the counterbalancing effect of pore pr
Special Issue 2006
Landslide dams (i.e., the natural blockage of river channels by hillslope-derived mass movements, COSTA & SCHUSTER, 1988) are natural phenomena with great relevance on geomorphological conditions and on the safety of people. Landslide dams can induce significant geomorphic hazards in the adjacent areas. Flooding by impounded water can create large lakes in the upstream areas, causing damages to human activities. Catastrophic outburst floods and/or debris flows can be triggered by a rapid dam failure with ex
Special Issue 2006
Some 50% of landslide dams fail within 10 days of emplacement (SCHUSTER & COSTA, 1986), producing dangerous flooding downstream. The risks deriving from such sudden, catastrophic scenarios could be substantially reduced, if it were possible to predict the geometry of a dam resulting from a given potential slope instability. Often, the location and volume of the landslide can be anticipated with reasonable accuracy. The remaining crucial question is how the unstable mass will deposit.
Special Issue 2006
The occurrence of sector collapse and debris avalanche at Mount St. Helens in 1980 brought to light the recognition of uniquely hummocky morphology of many analogous avalanches at volcanoes around the world (FRANCIS & WELLS, 1988; SIEBERT, 1984; SIEBERT et alii, 1987; UI & GLICKEN, 1986; VALLANCE et alii, 1995). Subsequent studies revealed the occurrence of edifice collapses at several of the better-known volcanoes of the world. Since a debris avalanche is a very rapid gravitational flow, its emplacement ge
Special Issue 2006
All floods result from the rapid release of water, stored either in the atmosphere or in terrestrial reservoirs (lakes, snow and ice), onto the landscape (O’CONNOR &WEBB, 1988). The magnitude of the flood therefore reflects the characteristic volume and release rates of the water source and the physiographic properties of the landscape that receives it, while the combination of geologic, climatic and physiographic factors make some areas of the Earth more floodprone than others. Large-scale terrestrial im
Special Issue 2006
WHAT BIG QUESTION? The impact of a landslide on society is determined by many factors but principally its location, speed, and size. Location is with reference to people and their infrastructure, and it is not a fundamental landslide property. In contrast, speed and size convey information relating to a landslides impact on its surroundings. They would be useful information to know in advance of a landslide’s occurrence. By “size” of a landslide, we mean any of the quantities of mass, volume, and area
Special Issue 2006
The catastrophic landslides can occur on slopes that may be considered as mechanical system at the unstable equilibrium state. The term “equilibrium” implies such state of a system, when two (and may be more) forces applied at rock massif balance each other. Such equilibrium could exist at certain values of elasticity and density of the geomechanical systems. For landslides these two main forces are the gravity force and the cohesive elastic or friction force between the landslide body and underlying ro
Special Issue 2006
Landslides and rockfalls can provoke river damming, valley impoundment, and as a result, floods and debris flows after dam’s breach (SCHUSTER, 1993). Such phenomena are common in mountainous regions and often occurred in Tadjikistan in the past and recent times. The well-known Sarez, Yashilkul, Zorkul Lakes in Pamirs, the Iskanderkul Lake and the cascade of Shing Lakes in the Southern Tien Shan exist till now. There are 1300 lakes with total area of 705 km2 in Tadjikistan. Most of them have the water surf
Special Issue 2006
Lake Sarez is the result of an earthquake triggered collapse which in 1911 threw about 2 km3 of rock in the Murgab Valley from its right flank. The dam that resulted from this event (called Usoy dam from the name of the buried village) has blocked the Murgab river and led to the formation of Lake Sarez (from the name of the drowned village) which now extends over a length of more than 60 km. Usoy dam is built by the local Sarez Sandstones, limestones and gipsum. The dammed water with a maximum depth of 500
Special Issue 2006
Elaboration of the technology of dams and embankments construction based on utilization of powerful explosions started in Russia in the 30’s of the XX Century. Advantages of this technology lie in use of rock material available just at the dam site, in the construction period decrease, in the possibility to construct large structures in the remote areas where no qualified workmen are available, and, finally in the project’s cost reduction.
Special Issue 2006
The Orogenic belt of the South-Eastern Kazakhstan is formed by the northern arches of the Tien-Shan, Dzhungaria, Saur-Tarbagatai, Altai divided by the intermountain areas. It is characterized by the intensive neotectonic movements and high seismic activity (6-9 degree of the MSK-64 scale and even more). They formed the modern relief and cause intensive endogenic and exogenic geodynamic processes. Endogenic phenomena, associated with seismic events, follow strong earthquakes and are expressed as linear and t
Special Issue 2006
Dams construction in mountainous regions by use of strong explosions is the promising technology that can be applied for the dams designed for various purposes, for water retaining in particular. Such projects have been realised successfully for the erection of the Nurek HPP cofferdam, the Medeo debris flow protection dam, the Baipasa HPP dam, the experimental Burlykia and Uch-Terek dams, of several dams in China. The constructed blast-fill dams are up to 90-m high. In favourable conditions (deep narrow val
Special Issue 2006
Peculiarities of the blast-fill dams erection technology predestine specific approaches to their safety assessment during the design and construction. First of all, in contrast to the hydraulic projects with “traditional” types of dam, those that include blast-fill dams, contemplate construction of the spillway and powerhouse in advance, before dam erection. Explosions used for such dam construction provide significant seismic effect on these structures and on the host rock massif. It can cause either t
Special Issue 2006
The new, untraditional way of dam erection by use of large explosions, that have been developed in the XX Century, required the extensive natural studies and modelling to validate possibility of the bulk of blasted rock utilisation as a structure which properties can be predicted beforehand. It is not surprising that this technology was utilised at a greatest extent in the USSR and China – countries with planned economy, which could perform expensive large-scale natural experiments funded by the state bud
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