Staircase Falls Rockfall on December 26, 2003, and Geologic Hazards at Curry Village, Yosemite National Park, California

Wieczorek, Gerald F.; Snyder, James B.; Borchers, James W.; Reichenbach, Paola

doi:10.3133/ofr20071378

Cited by 2 publications

(3 citation statements)

References 9 publications

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“…To determine the fragmentation energy, we first need to estimate the fraction of the boulder mass transformed into the sandy‐powdery fraction (section 5.1). Data gathered by Wieczorek et al () show that the largest blocks were deposited on a steep and volumetrically significant talus, while the powdery fraction, whose volume we need to evaluate, was deposited beyond this talus. To calculate the fraction η v , we thus interpolated the isopach curves presented by Wieczorek () and Wieczorek et al () and found a volume of the sandy‐powdery fraction η v V b = 1,437m 3 corresponding to a value η v = 0.062.…”

Section: Case Studiesmentioning

confidence: 99%

“…Data (Viero et al, ; Wieczorek et al, ) show that during an EER, two populations of clasts are produced upon impact. Relatively large, centimeter‐sized blocks to boulders up to few meters in diameter are partly deposited in the talus immediately beneath and downslope of the impact point, and partly are ejected at high speed.…”

Section: Impact Study and Fragmentationmentioning

confidence: 99%

“…The particles resulting from the disintegration may hit trees and obstacles at very high speed, scouring them severely or penetrating deeply. Finally, the finest component of the fragments is capable of traveling as a turbulent suspension, hereafter referred to as dust cloud (Wieczorek et al, ). Because this dust cloud may blanket an area about 5–10 km 2 ahead of the rockfall with powder composed of rock fragments, it may cause a temporary darkness (Wieczorek et al, ) ranging from tens of minutes to several hours.…”

Section: Introductionmentioning

confidence: 99%

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Extremely Energetic Rockfalls

2018

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Extremely energetic rockfalls (EERs) are defined here as rockfalls for which a combination of both large volume and free fall height of hundreds of meters results in energy larger than about 80 GJ released in a short time. Examples include several events worldwide. In contrast to low energy rockfalls where block disintegration is limited, in EERs the impact after free fall causes immediate release of energy much like an explosion. The resulting air blast can snap trees hundreds of meters ahead of the fall area. Pulverized rock at high speed can abrade vegetation in a process of sandblasting, and particles suspended by the blast and the subsequent debris cloud may travel farther than the impact zone, blanketing vast areas. Using published accounts and new data, we introduce physically based models formulated on analogies with explosions and explosive fragmentation to describe EERs. Results indicate that a portion of the initial potential energy of the block is spent in rock disintegration at impact (typically 0.2%–18%), while other sources of energy loss (air drag, seismic, sound, and ground deformation) are negligible; consequently, more than 80% of the potential energy is converted to kinetic energy of the fragmented block (ballistic projection, shock wave, sand blast, and dust cloud). We also propose simple estimates for the flow of the dust cloud associated with an EER and its long settling time. The areal extent of the affected zone is estimated from the energy balance and an empirical power law relationship.

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Section: Case Studiesmentioning

confidence: 99%

Section: Impact Study and Fragmentationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Extremely Energetic Rockfalls

2018

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Rockfalls, fragmentation, and dust clouds: analysis of the 2017 Pousset event (Northern Italy)

Crosta,

Dattola,

Lanfranconi

et al. 2023

Landslides

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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 fragmentation energy is proportional to the generated area. The fragmentation energy was found to be about 0.4% of the initial potential energy. Most probable fragmentation points and block deposition areas were evaluated and positioned by means of the HyStone 3D rockfall simulator. Furthermore, we calculated the flow rate of the suspended powder generated by the fragmentation process and compared the results with observations available for the evolution of the phenomenon and the collected samples. The Pousset event, in its relatively simple dynamics, may be a good testing ground to address the current theories of rockfall and rock avalanche fragmentation and dust cloud behavior.

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Staircase Falls Rockfall on December 26, 2003, and Geologic Hazards at Curry Village, Yosemite National Park, California

Cited by 2 publications

References 9 publications

Extremely Energetic Rockfalls

Extremely Energetic Rockfalls

Rockfalls, fragmentation, and dust clouds: analysis of the 2017 Pousset event (Northern Italy)

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