Investigation and numerical simulation of the 22 February 2018 landslide-triggered long-traveling debris flow at Pasir Panjang Village, Brebes Regency of Central Java, Indonesia
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Debris flow
Breccia
Infiltration (HVAC)
Debris flows with different magnitudes can have a large impact on debris fan characteristics such as height or slope. Moreover, knowledge about the impact of random sequences of debris flows of different magnitudes on debris fan properties is sparse in the literature and can be improved using numerical simulations of debris fan formation. Therefore, in this paper we present the results of numerical simulations wherein we investigated the impact of a random sequence of debris flows on torrential fan formation, where the total volume of transported debris was kept constant, but different rheological properties were used. Overall, 62 debris flow events with different magnitudes from 100 m3 to 20,000 m3 were selected, and the total volume was approximately 225,000 m3. The sequence of these debris flows was randomly generated, and selected debris fan characteristics after the 62 events were compared. For modeling purposes, we applied the Rapid Mass Movement Simulations (RAMMS) software and its debris flow module (RAMMS-DF). The modeling was carried out using (a) real fan topography from an alpine environment (i.e., an actual debris fan in north-west (NW) Slovenia formed by the Suhelj torrent) and (b) an artificial surface with a constant slope. Several RAMMS model parameters were tested. The simulation results confirm that the random sequence of debris flow events has only some minor effects on the fan formation (e.g., slope, maximum height), even when changing debris flow rheological properties in a wide range. After the 62 events, independent of the selected sequence of debris flows, the final fan characteristics were not significantly different from each other. Mann–Whitney (MW) tests and t-tests were used for this purpose, and the selected significance level was 0.05. Moreover, this conclusion applies for artificial and real terrain and for a wide range of tested RAMMS model rheological parameters. Further testing of the RAMMS-DF model in real situations is proposed in order to better understand its applicability and limitations under real conditions for debris flow hazard assessment or the planning of mitigation measures.
Debris flow
Sequence (biology)
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Breccia
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Debris flow
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Debris flow
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Debris flow
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Hyperconcentrated flow
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Mudflow
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Abstract The widespread shower-bedded deposits of Rotoehu Ash consist of multiple airfall pyroclastic units (tephras) which underlie, are interbedded within and mantle the less widespread rhyolitic pyroclastic flow deposits of the Rotoiti Breccia Formation (late Pleistocene). No significant time intervals are recorded within the Rotoehu Ash, showing that the thick pyroclastic flow breccia deposits enclosed by the Rotoehu Ash units were also erupted in a short time interval. Recognition of the multiple nature of Rotoehu Ash has proved necessary in correlation of breccia deposits in the Rotorua area.
Breccia
Pyroclastic fall
Volcanic ash
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