Geomorphic effects of recurrent outburst superfloods in the Yigong River on the southeastern margin of Tibet

Landslide dam outburst floods have a significant impact on landform evolution in high mountainous areas. Historic landslide dams on the Yigong River, southeastern Tibet, generated two outburst superfloods > 105 m3/s in 1902 and 2000 AD. One of the slackwater deposits, which was newly found immediately downstream of the historic dams, has been dated to 7 ka BP. The one-dimensional backwater stepwise method gives an estimate of 225,000 m3/s for the peak flow related to the paleo-stage indicator of 7 ka BP. The recurrence of at least three large landslide dam impoundments and super-outburst floods at the exit of Yigong Lake during the Holocene greatly changed the morphology of the Yigong River. More than 0.26 billion m3 of sediment has been aggraded in the dammed lake while the landslide sediment doubles the channel slope behind the dam. Repeated landslide damming may be a persistent source of outburst floods and impede the upstream migration of river knickpoints in the southeastern margin of Tibet.

Historical reconstruction and evolution of the large landslide of Inza (Navarra, Spain)

In the winter of 1714–1715, a large rotational landslide originated on the northern slope of the Sierra de Aralar (Navarra, Spain), generating an earthflow that slowly descended through the valley for a kilometer and a half destroying the village of Inza. An interdisciplinary research recreated the historical process of the event and the geomorphological characterization of this large landslide. The geological analysis and hydrogeological characteristics of the site also identified the determining factors of this historical event. From the analysis that triggered the landslide and how the climate affected events can now be demonstrated from historical records of excess rainfall and the initial start of the process. From the recreated pre-failure topography, the stability of the original slope was studied using a 3D numerical model to identify the factors, causes and mechanism that controlled the development of the landslide.

Change in Abundance and Activity of Microbocenoses in the Area of Influence of a Large Landslide at the Bureya Reservoir

The results of field and experimental microbiological studies of water, soil, and rock samples in the influence zone of large landslide are presented. The landslide occurred in December 2018 and blocked the Bureya Reservoir from coast to coast. An artificial channel was created to restore the hydrological regime with the use of TNT (trinitrotoluene) and RDX (hexogen). A comparative analysis of the abundance of cultivated heterotrophic bacteria around the landslide body and in the artificial channel is carried out. The activity of microbial communities in relation to easily available (peptone, lactate, and starch) and difficult-to-mineralize humic compounds is also determined. With the use of spectrometry and gas chromatography, it is shown that an increase in the diversity of aromatic compounds in water is accompanied by an increase in the abundance of heterotrophic bacteria. A number of toxic substances, including methanol and methylated benzene derivatives, are found among the dominant components in the water. Its concentrations increased after the water drained through the landslide body and after imploding works. Many of the volatile organic compounds may have been products of microbial metabolism when water interacts with rocks. A hypothesis on the role of methanotrophic and methylotrophic bacteria in the genesis of methanol and toluene is discussed.

Prediction of total landslide volume in watershed scale under rainfall events using a probability model

This study established a probability model based on the landslide spatial and size probabilities to predict the possible volume and locations of landslides in watershed scale under rainfall events. First, we assessed the landslide spatial probability using a random forest landslide susceptibility model including intrinsic causative factors and extrinsic rainfall factors. Second, we calculated the landslide volume probability using the Pearson type V distribution. Lastly, these probabilities were joined to predict possible landslide volume and locations in the study area, the Taipei Water Source Domain, under rainfall events. The possible total landslide volume in the watershed changed from 1.7 million cubic meter under the event with 2-year recurrence interval to 18.2 million cubic meter under the event with 20-year recurrence interval. Approximately 62% of the total landslide volume triggered by the rainfall events was concentrated in 20% of the slope units. As the recurrence interval of the events increased, the slope units with large landslide volume tended to concentrate in the midstream of Nanshi River subwatershed. The results indicated the probability model posited can be used not only to predict total landslide volume in watershed scale, but also to determine the possible locations of the slope units with large landslide volume.