ChapterPDF Available

Rock Avalanche (Sturzstrom)

January 2013

January 2013

DOI:10.1007/978-1-4020-4399-4_301

In book: Encyclopedia of Natural Hazards (pp.875-875)

Authors:

Reginald L. Hermanns

Norwegian University of Science and Technology

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Content uploaded by Reginald L. Hermanns

Content may be subject to copyright.

Risk

Risk Assessment

Sociology of Disasters

Uncertainty

Warning Systems

ROCK AVALANCHE (STURZSTROM)

Reginald L. Hermanns

Geological Survey of Norway, Trondheim, Norway

Synonyms

Rock avalanche; Rock-fall avalanche; Rock-fall generated

debris stream; Sturzstrom

Definition

Rock avalanche (sturzstrom) were defined by Hsü (1975)

based on Heim’s(1932) description of phenomena

described with the German terms “Bergsturz,”

“Trümmerstrom,”“Sturzstrom”as a stream of very rapidly

moving debris derived from the disintegration of a fallen

rock mass of very large size; the speed of a rock avalanche

often exceeds 100 km/h, and its volume is commonly

greater than 1 10

Discussion

Rock avalanches are among the most hazardous land-

slides phenomena due to the speed, size, and run-out dis-

tance. Rock avalanches have destroyed entire villages

and killed thousands. The run-out distance of a rock ava-

lanche often exceeds several kilometers and the mobility

becomes visible by the run up on opposite valley slopes,

which is related to the volume of the initial rock failure

(Scheidegger, 1973) and the morphology of the flow path

(Nicoletti and Sorriso Valvo, 1991) but can also be

influenced by the entrainment of saturated soil material

or ice along the flow path (Hungr and Evans, 2004).

Systematic regional analyses of the temporal spatial

distribution of rock avalanches have shown that rock ava-

lanches do not distribute randomly but occur along litho-

logically, structurally preconditioned mountain fronts

during climatic phases of higher run off or following

deglaciation (e.g., Hermanns et al., 2006a, Blikra et al.,

2006). Due to post failure slope deformation, rock ava-

lanches often occur repeatedly at the same location with

short recurrence intervals while neighboring slopes remain

stable (Hermanns et al., 2006b). In addition, in tectonically

active mountain regions, rock avalanches are often trig-

gered by earthquakes and cause the formation of landslide

dams adding to the Disasters (e.g., Petley et al., 2007).

Rock avalanche Hazard assessment involves character-

izing potentially unstable slopes followed by Slope Stabil-

ity analyses of the slope and run-out modeling of the rock

avalanche. Due to the enormous energy released during

the event, rock avalanches cannot be mitigated, and

unstable rock slopes, which might form rock avalanches,

can rarely be prevented from failure (e.g., artificial

draining of slope). If a potential failure is imminent, com-

plete Evacuation of the potentially affected run-out area is

the only Disaster Risk Management measure.

Bibliography

Blikra, L. H., Longva, O., Braathen, A., Anda, E., Dehls, J. F., and

Stalsberg, K., 2006. Rock slope failures in Norwegian fjord

areas: examples, spatial distribution and temporal pattern. In

Evans, S. G., Scaraascia Mugnozza, G., Strom, A., and

Hermanns, R. L. (eds.), Landslides from Massive Rock Slope

Failures. Dodrecht: Springer, pp. 475–496.

Dunning, S. A., Mitchell, W. A., Rosser, N. J., and Petley, D. N.,

2007. The Hattian rock avalanche associated landslides triggered

by the Kashmir earthquake of 8 October 2005. Engineering

Geology,93, 130–144.

Heim, A., 1932. Bergsturz und Menschenleben. Zurich: Fretz &

Wasmuth Verlag.

Hermanns, R. L., Niedermann, S., Villanueva Garcia, A., and

Schellenberger, A., 2006a. Rock avalanching in the NW Argen-

tine Andes as a result of complex interactions of lithologic,

stuructural and topographic boundary conditions, climate change

and active tectonics. In Evans, S. G., Scaraascia Mugnozza, G.,

Strom, A., and Hermanns, R. L. (eds.), Landslides from Massive

Rock Slope Failures. Dodrecht: Springer, pp. 497–520.

Hermanns, R. L., Blikra, L. H., Naumann, M., Nilsen, B., Panthi,

K. K., Stromeyer, D., and Longva, O., 2006b. Examples of

multiple rock-slope collapses from Köfels (Ötz valley, Austria)

and western Norway. Engineering Geology,83,94–108.

Hsü, K. J., 1975. Catastrophic Debris Streams (Sturzstroms)

generated by rockfalls. Geological Society of America Bulletin,

86, 129–140.

Hungr, O., and Evans, S. G., 2004. Entrainment of debris in rock

avalanches: An analysis of long run-out mechanism. Geological

Society of America Bulletin,116 , 1240–1252.

Nicoletti, P. G., and Sorriso-Valvo, M., 1991. Geomorphic controls

of the shape and mobility of rock avalanches. Geological Society

of America Bulletin,103, 1365–1373.

Scheidegger, A. E., 1973. On the prediction of reach and velocity of

catastrophic landslides. Rock Mechanics,5, 231–236.

Cross-references

Disaster

Disaster Risk Management

Earthquake

Evacuation

Hazard

Landslide

Landslide Dam

Recurrence Interval

Slope Stability

ROCKFALL

Fausto Guzzetti

CNR –IRPI, Perugia, Italy

Synonyms

Rock fall

ROCKFALL 875

Triggers of present-day rockfalls in the zone of sporadic permafrost in non-glaciated mountain region: the case study of Turnia Kurczaba (the Tatra Mts., Poland)

Article

Full-text available

Mar 2024

In recent decades there has been growing evidence of the impact of ongoing climate warming on the frequency of rockfalls. However, these are not adequately documented, especially in non-glaciated, high mountain regions of middle latitude. This study comprehensively documents the Turnia Kurczaba rockfall, one of the most significant rockfalls recorded in recent decades in the Tatra Mountains. The precise projections of the volumes and distribution of rock losses and deposits, the determination of the trajectories, modes and speeds of movement of rock material, as well as information on the geological, morphological, and meteorological conditions behind the Turnia Kurczaba rockfall form a unique dataset. The data documents a spectacular episode in the contemporary development of a complex slope system in the Tatras in an all-encompassing way and can be used to validate and calibrate existing models and improve numerical simulations of other rockfalls, both for hazard and risk assessment and slope evolution studies. Moreover, in the context of archival data, they demonstrate that in the Tatra sporadic permafrost zone, only relatively small rockfalls have been recorded in recent decades. Their cause was not the degradation of permafrost but freeze-thaw processes with the co-participation of rainwater and meltwater. The largest of these occur within densely fractured cataclysites, mylonites, and fault breccias. The impact of rockfalls on the morphodynamics of talus slopes is uneven in the storied arranged rock-talus slope systems. Even colluviums belonging to the same slope system can differ in their development rate and regime, and different thermal and wetness drivers can control their evolution.

Insights on Multistage Rock Avalanche Behavior From Runout Modeling Constrained by Seismic Inversions

Article

Full-text available

Oct 2022

Inversion of low‐frequency regional seismic records to solve for a time series of bulk forces exerted on the earth by a landslide (a force‐time function) is increasingly being used to infer volumes and dynamics of large, highly energetic landslides, such as rock avalanches and flowslides, and to provide calibration information on event dynamics and volumes for numerical landslide runout models. Much of the work to date using landslide runout modeling constrained by seismic data has focused on using single‐phase models with frictional or velocity‐weakening rheologies. Awareness of multistage landslide initiations is increasing, with discrete failures separated in time contributing to the final impact of an event. Our work utilizes a method for incorporating seismic data as a calibration constraint for landslide runout models, considering variable rheologies and different initiation conditions. This study presents a systematic examination of multiple rheologies and initiation conditions, and shows how these factors affect the force‐time function derived from the landslide runout model. Our work confirms that, while rheology and fragmenting or initially coherent initiations affect the force‐time function, multiple collapses separated by tens of seconds have the greatest impact on the shape and amplitude. We apply this method to the analysis of three real rock avalanches to better constrain plausible initiation conditions and rheology parameters using both seismic and field data. This study provides insights on how assumptions about the initiation dynamics of the source zone and the runout model definition can aid in the interpretation of seismic inversions for multistage rock avalanches.

Rock Avalanche-Generated Sediment Mass Flows: Definitions and Hazard

Article

Full-text available

Sep 2020

Rock avalanches can trigger destructive associated hazards following the initial collapse and fragmentation of a rock slope failure. One of these associated hazards occurs when the material derived from the initial collapse of the source zone impacts and mobilizes a mass flow composed of sediment from along the travel path. These mass flows can be grouped into radial impact areas that occur on relatively flat, open terrain (typically a floodplain), and more linear impact areas that occur in channelized terrain. Rock avalanche-generated sediment mass flows are an important consideration because they can significantly increase the area impacted by an event, thereby increasing the hazard area, especially in valley bottoms where there are likely more elements at risk. Existing runout prediction methods do not consistently account for the increase in the impact area from rock avalanche-generated sediment mass flows. Thus, there is a need for a simple data-supported method for estimating the extent of mass flow impacts resulting from an initial rock avalanche event with sediments along the potential travel path. This paper presents data from 32 rock avalanches and 23 rock avalanche-generated sediment mass flows from around the world, described using a consistent set of quantitative and qualitative attributes. A wide range of mass flow impacts were observed, with the sediment mass flow impact area or runout length exceeding the impact of the coarse, rocky debris in some cases. The area and length impacted by the coarse, rocky debris is estimated using multiple linear regressions considering the event volume and topographic features. The sediment mass flow dataset is used as input to develop an exponential distribution of the area or runout length of the sediment mass flow over that of the coarse, rocky debris. A decision tree framework is presented for estimating the extent of potential rock avalanches and potential rock avalanche-generated sediment mass flows for hazard and risk analysis, which is demonstrated by comparing the stochastic empirical predictions to those from numerical runout modeling.

An analogue Toma Hill formation model for the Tyrolian Fernpass rockslide

Article

Full-text available

Jun 2019

The Fernpass rockslide occurred about 4100 years ago and is one of the largest rock slope failures in the Alps, the run-out area being characterized by a hummocky surface with Toma Hills that were formed after the rockslide event. These hills, characterized by a cone-like shape with a flattened top, are typical for many rockslides, and the name “Toma” is derived from local dialects in Switzerland and Tyrol, Austria. So far, five hypotheses have been proposed for the formation of Toma Hills, the two relating to glacial activity being outdated meanwhile. These hypotheses cannot explain all features observed on site. Therefore, to investigate one of these hypotheses, a qualitative laboratory-scale analogue groundwater flow model with the size 1.5 × 1 × 0.8 m was used to investigate the contribution of internal erosion by suffosion to forming Toma Hills. From the model, hydrogeological calculations of Darcy velocity and hydraulic conductivity were determined to help understand the present study. The average hydraulic gradient of the experiments was close to that in reality. Hydraulic conductivities in the five experiments were comparable to the calculated field hydraulic conductivity (Bialas and Seelheim equations). A limnokrene like one south-west of Biberwier developed in all experiments. Development of lateral and transversal cracks, water-filled lateral depressions of the material in the model and discharge of finer material implicated that internal erosion is a substantial contribution to the Toma Hill formation. Based on the experimental results, we deduce that Toma Hill formation took between 140 and 580 years.

Evolution of a hillslope by rock avalanches: insights from analog models

Article

Jun 2019

Rock avalanches are among the most hazardous processes on hillslopes because of high velocity, great dimensions, and long run-out distance. For this reason, understanding the dynamics and factors of rock avalanches and their role in hillslope evolution is crucial. Studies evidenced that occurrence and evolution of these phenomena are influenced by lithological, structural, and climatic factors. Statistical analysis on natural cases demonstrated correlations between slope geometry and rock avalanche volume. Most of the studies referred to experimental tests which represent powerful tools to understand these landslides. Many models focused on the mechanism leading to high velocity and long run-out, but few studies discuss the role of rock avalanches in the evolution of a bedrock hillslope. The influence of slope geometry and physical properties of the substratum on the dynamics of rock avalanches is poorly constrained. We present results from analog models of a hillslope evolving by base level lowering. We tested several slope widths and two analog materials. The experimental apparatus allowed for checking the mass of mobilized material at each step and for taking a 3D scan of the whole surface. Our results, coupled with a statistical analysis, indicated that hillslope evolution is influenced by the material internal friction and by the friction with box walls (i.e., valley walls) when the slope is narrow. Widening the slope, the influence of lateral friction disappears, confirming observations in other models and nature. These results represent a new contribution to understand the dynamics of rock avalanches on bedrock hillslopes.

Rock avalanching in the NW argentine andes as a result of complex interactions of lithologic, structural and topographic boundary conditions, climate change and active tectonics

Article

Full-text available

Jan 2006

In NW Argentina rock avalanching occurs in two geomorphic settings: A) narrow valleys draining large basins and B) mountain fronts bordered by wide piedmont areas. In the narrow valley environment, the deposits are relatively young. Landslide events concentrate during humid climate periods, and they occur with recurrence intervals of a few ka. In contrast, the deposits in piedmont settings are significantly older, while rock avalanches occur with recurrence intervals of several tens ka, and do not show any direct relation with climate change. Common to the regional distribution in both settings is the influence of lithology, structural control, as well as tectonic activity. Rock avalanches have occurred only in granites, low-grade metamorphic rocks and coarse clastic sedimentary rocks. These lithologies are competent enough to form steep slopes and provide planar structures that dip towards the valley. Because all rock-avalanches originated in the hanging wall of reverse faults with important Neogene displacement causing mountain-front oversteepening, it is inferred that most collapses were tectonically conditioned and/or triggered. However, only at a few sites detailed sedimentologic studies of related sediments show unequivocally that strong seismic activity triggered landsliding. Geological evidence and comparison with empirical data suggest that these earthquakes have been either crustal and of magnitude > M 7 or very shallow and of a magnitude > M 5.5.

Hungr, O. & Evans, S. Entrainment of debris in rock avalanches: An analysis of a long run-out mechanism. Geol. Soc. Am. Bull. 116, 1240-1252

Article

Sep 2004

Many rock avalanches entrain and liquefy saturated soil from their paths. Evidence for this includes mud displaced from the margins of rock avalanche deposits, substrate material smeared along the base of deposits, extrusion of liquefied soil upward through the deposits, and increases of volume. A hypothesis first suggested in 1881 and since reinforced by several authors suggests that entrainment of substrate material increases mobility. Although the process has been discussed in the literature for more than 100 years, few detailed and quantitative descriptions exist. The main purpose of this paper is to describe two recent cases from British Columbia, Canada, where rockslides entrained substrate on a very large scale, influencing the character of the events. Estimated volume balance curves, based on detailed field mapping, are provided for both cases. Dynamic analyses are carried out using a numerical model and using the same set of rheological parameters. The mechanism of material entrainment and displacement is discussed. The data suggest that rapid rock failures entraining very large quantities of saturated substrate material represent a special type of landslide, transitional between rock avalanche and debris avalanche. Many rock avalanches can thus be seen as end members of a continuum of phenomena involving rock failure followed by interaction with saturated substrate.

Catastrophic Debris Streams (Sturzstroms) Generated by Rockfalls

Article

Jan 1975

KENNETH J. HSÜ

Large rockfalls commonly generate fast-moving streams of debris that have been called "sturzstroms." The geometry of sturzstrom deposits is similar to that of mudflows, lava flows, and glaciers. Sturzstroms can move along a flat course for unexpectedly large distances and may surge upward by the power of their momentum. A currently popular hypothesis to account for their excessive distance of transport suggests that sturzstroms slide on air cushions. Contrary to that hypothesis, evidence is herein presented to support Heim's contention that sturzstroms indeed flow. The flow of a sturzstrom can be compared to flow of a mass of concentrated cohesionless grains in a fluid medium. Frictional resistance to such grain flow is, according to Bagnold, less than that for sliding of rigid bodies because of the buoyancy of an interstitial fluid which serves to reduce the effective normal pressure of the entrained grains. The presence of sturzstrom deposits on the Moon indicates that the interstitial fluid is not necessarily a compressed gas or a wet mud. The dispersion of fine debris and pulverized rock dust among the colliding blocks may have provided an uplifting stress during the motion of some terrestrial and lunar sturzstroms. Scale models to provide kinematic simulation of sturzstroms may have practical application. Preliminary results suggest that a bentonite suspension of a certain consistency is a suitable material for scale models and that the flow of thixotropic liquids is kinematically similar to sturzstroms. The parameter "excessive travel distance" is introduced to replace the expression "equivalent coefficient of friction" as a measure of mobility of sturzstroms. There is, on the whole, a positive semilog correlation of the excessive travel distance to the size of the fallen mass. Exceptions to the rule include on the one extreme the unusual mobile Huascaran rockfall which gave rise to a sturzstrom with a dense interstitial mud and, on the other extreme, the least mobile Vaiont rockslide which remained a sliding block and failed altogether to generate a sturzstrom.

On the Prediction of the Reach and Velocity of Catastrophic Landslides

Article

Jan 1973

Adrian E. Scheidegger

On the Prediction of the Reach and Velocity of Catastrophic LandslidesAn analysis of the data of rapid, catastrophic landslides shows that a correlation exists between the logarithm of the volume V of such landslides and the logarithm of the coefficient of frictionf which governs their course. This correlation is 10logf = - 0.15666 10logV + 0.62419{}_{10}\log f = - 0.15666 {}_{10}\log V + 0.62419 where the volume is in m3. The coefficient of correlation is 0.82. This correlation can be used to predict the reach and the velocity of an imminent landslide, if the volume can be estimated beforehand.ber die Vorhersage von Reichweite und Verlauf katastrophaler BergstrzeEine Analyse der Beobachtungen von schnellen, katastrophalen Bergstrzen zeigt, da eine Korrelation zwischen dem Logarithmus des Volumens V und dem Logarithmus des Reibungskoeffizientenf, der ihren Verlauf bestimmt, existiert. Diese Korrelation hat die Form 10logf = - 0,15666 10logV + 0,62419{}_{10}\log f = - 0,15666 {}_{10}\log V + 0,62419 wo das Volumen im m3 gemessen wurde. Der Korrelationskoeffizient betrgt 0,82. Diese Korrelation kann dazu verwendet werden, um die Reichweite und den Verlauf eines erwarteten Bergsturzes vorauszusagen, wenn dessen mutmaliches Volumen abgeschtzt werden kann.Sur la prdiction de la porte et du cours d'boulements catastrophiquesLes observations des boulements rapides et catastrophiques qui sont rapportes dans la littrature sont analyses. Il est dmontr qu'une corrlation existe entre le logarithme du volume V de ces boulements et le logarithme du coefficient de la friction qui gouverne leur cours. Elle est 10logf = - 0,15666 10logV + 0,62419{}_{10}\log f = - 0,15666 {}_{10}\log V + 0,62419 o le volume est mesur en m3. Le coefficient de la corrlation est 0,82. Cette corrlation peut tre utilise pour prdire l'extension et la vlocit d'un boulement imminent si son volume est estimable en avance.

The Hattian Bala rock avalanche and associated landslides triggered by the Kashmir Earthquake of 8 October 2005

Article

Aug 2007
ENG GEOL

The Kashmir Earthquake of the 8 October killed an estimated 87 350 people, 25 500 through co-seismic landslides. The largest landslide associated with the earthquake was the 68 × 106 m3 Hattian Bala rock avalanche that destroyed a village and killed around 1000 people. The deposit blocks the valley to a depth of 130 m impounding a lake that reached the dam-crest in April 2007. An outburst flood now threatens a major settlement 3 km downstream. A series of space images reveals landslide clusters in the rock avalanche source area prior to the earthquake. The images also reveal a large slow-moving landslide with its toe in the lake, failure of this landslide may induce dam failure through overtopping and scour. Eighty five landslides in the Hattian Bala catchment predate the shaking of 8 October 2005, a further 73 are co-seismic with the main shock, and 21 postdate it in the period up to October 2006. Landslide magnitude–frequency distribution plots derived from satellite images allow an assessment of the contribution of seismically triggered events as compared to background rates of activity.

Rock Slope Failures in Norwegian Fjord Areas: Examples, Spatial Distribution and Temporal Pattern

Book

Jan 2006

Rock avalanches and related tsunamis represent one of the most serious natural hazards in Norway, and during the last 100 years more than 170 people have lost their lives in western Norway. Large-scale rock-slope failures range from sliding of relatively intact masses of rock, to fully disintegrated rock avalanches. A wide variety of features mirror rock avalanches plunging into valleys or fjords. Bouldery fans, lobes and ridges characterize the proximal parts, while thin debris-flow deposits often occur far beyond this zone. Major deformations of valley-fill and fjord sediments are commonly related to the impact of large volumes of rock. The spatial and temporal pattern of rockavalanche events in Norway demonstrates that such events are common and occur within certain regions, and are important data for evaluating background hazard levels. The mechanisms for occurrence and triggering of rock-slope failures are still uncertain, but seismic ground shaking and creep processes are probably important although, in some areas, effects of glacial unloading during the deglaciation phase cannot be excluded. The geographic concentrations of events indicate that relatively large earthquakes may have played a role as triggering mechanisms. This hypothesis is strengthened by the identification of postglacial faults in two of the rock-failure zones.

Geomorphic controls of the shape and mobility of rock avalanches

Article

Oct 1991

A graphical and statistical treatment of data taken from a sample of 40 rock avalanches selected mainly from the literature enables us to distinguish three ways in which the local morphology controls the shape and motion of such landslides. The three different situations are characterized as follows: 1) channeling of the debris mass, 2) unobstructed spreading of the debris mass, and 3) right-angle or almost right-angle impact against an opposite slope. Mobility of rock avalanches decreases going from situation 1 to situation 3. -from Authors

Examples of multiple rock-slope collapses from Kofels (Otz valley, Austria) and westem Norway

Article

Feb 2006
ENG GEOL

This paper describes the effects of large massive rock-slope failures on subsequent slope stability. Three examples of large rock-slope failures from the Austrian Alps and Norway demonstrate that failure increases the probability of further collapses. At Kofels, Austria, a Holocene rock-slope failure several km3 in size filled the Otz valley. The morphology of the deposits indicates that at least one subsequent failure occurred along the head scarp of the first failure, most likely a slide of similar size. Debris of the second landslide slid over the older deposits, forming the famous Kofels frictionite. At least three rock-slope failures, all of them in excess of 106 m3, occurred from the same mountainside within the last 6000-8000 years at Tafjord in western Norway. The most recent of these failures in 1934, triggered a destructive tsunami. Five large failures with volumes >= 50,000m3 occurred at Ramnefjell, Norway within 50 years; two of them caused considerable damage and a large number of death due to the formation of destructive tsunamis. Two-dimensional finite element models of rock-slope stability before and after the Kofels and Tafjord landslides show that massive rock-slope failures produce: (a) irregular slopes, parts of which are as steep or steeper than the slope before failure and which represent new zones of instability; and (b) zones of weakness related to slow slope deformation and related cracking.

Bergsturz und Menschenleben

Jan 1932

A Heim

Heim, A., 1932. Bergsturz und Menschenleben. Zurich: Fretz & Wasmuth Verlag.

Rock Avalanche (Sturzstrom)

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