Sergey Chernomorets

Monitoring of Bashkara Glacier lakes (Central Caucasus, Russia) and modelling of their potential outburst

Glacier lakes pose threat to downstream settlements and infrastructure. In recent decades the number and area of lakes have been growing at an accelerating rate due to worldwide glacier shrinkage. In the Russian Caucasus this process is understudied. We present results obtained during a 12-year (1999–2010) continuous field monitoring of the Bashkara proglacial lakes group, which we identified as the place with the highest GLOF risk in the region. Recession of the parent Bashkara Glacier was the main driver of the rapid expansion of the lower Lake Lapa. The upper Lake Bashkara has not been enlarging, but its water level has shown significant inter- and intra-annual fluctuations. The lake outburst probability has increased in recent years, and in 2008 we observed surface overflow over the moraine dam. Taking into account that in the late 1950s lake outbursts at this site led to large-scale glacial debris flows, we have simulated a potential outburst using River and FLO-2D software and carried out hazard zonation. An early warning system has been designed and established at Lake Bashkara, and measures to mitigate risk have been proposed. Rapid change of proglacial lakes requires regular monitoring in ‘hot spot’ areas where the GLOF hazard is high and is dynamically changing.

Glacial lake inventory and lake outburst potential in Uzbekistan

Climate change has been shown to increase the number of mountain lakes across various mountain ranges in the World. In Central Asia, and in particular on the territory of Uzbekistan, a detailed assessment of glacier lakes and their evolution over time is, however lacking. For this reason we created the first detailed inventory of mountain lakes of Uzbekistan based on recent (2002-2014) satellite observations using WorldView-2, SPOT5, and IKONOS imagery with a spatial resolution from 2 to 10m. This record was complemented with data from field studies of the last 50years. The previous data were mostly in the form of inventories of lakes, available in Soviet archives, and primarily included localized in-situ data. The inventory of mountain lakes presented here, by contrast, includes an overview of all lakes of the territory of Uzbekistan. Lakes were considered if they were located at altitudes above 1500m and if lakes had an area exceeding 100m2. As in other mountain regions of the World, the ongoing increase of air temperatures has led to an increase in lake number and area. Moreover, the frequency and overall number of lake outburst events have been on the rise as well. Therefore, we also present the first outburst assessment with an updated version of well-known approaches considering local climate features and event histories. As a result, out of the 242 lakes identified on the territory of Uzbekistan, 15% are considered prone to outburst, 10% of these lakes have been assigned low outburst potential and the remainder of the lakes have an average level of outburst potential. We conclude that the distribution of lakes by elevation shows a significant influence on lake area and hazard potential. No significant differences, by contrast, exist between the distribution of lake area, outburst potential, and lake location with respect to glaciers by regions.

Measuring Internal Velocity of Debris Flows by Temporally Correlated Shear Forces

Debris flow is a kind of geological hazard occurring in mountain areas. Its velocity is very important for debris flow dynamics research and designing debris flow control works. However, most of past researches focused on surface velocity and mean velocity of debris flow, while few researches involve its internal velocity because there is no available method for measuring the internal velocity for its destructive power. In this paper, a method of temporally correlated shear forces (TCSF) for measuring the internal velocity of debris flows is proposed. The principle of this method is to calculate the internal velocity of a debris flow using the distance between two detecting sections and the time difference between the two waveforms of shear forces measured at both sections. This measuring method has been tested in 14 lab-based flume experiments.

Geophysics in Glacial-hazard Initiation Zones, Russian Caucasus

Numerous glacier lakes have formed in recent decades due to worldwide glacier retreat induced by climate change. These lakes, dammed by glaciers and moraine ridges, are hazardous because of potential glacial lake outburst flows (GLOF). The GLOF probability is increasing in the Russian Central Caucasus, like at the Bashkara glacier which has been extensively studied, but detailed information about the ground is missing. A pilot geophysical campaign carried out during summer 2009 tested GPR and resistivity profiling at this site, using towed-systems to facilitate acquisition. The GPR measurements were successful with penetration depth down to 70 m on icy ground, though the acquisition was difficult due to rough ground terrain. The results show that GPR measurements would greatly improve the knowledge of the internal structure of that complex zone, thus helping for hazard assessments, but more field work is needed, including CMP measurements. The resistivity measurements were not that successful, the towed system requiring repeating each profile with increasing offset, the progression on the ground being heavy. Only the very first meters of the ground were retrieved, i.e, not really providing useful information. Results and experience gathered in 2009 are now analysed to plan another campaign summer 2011.

Modeling potential scenarios of the Tangjiashan Lake outburst and risk assessment in the downstream valley

This research is devoted to Tangjiashan Lake, a quake landslide-dammed lake, situated in Sichuan Province, China, which was formed by a landslide triggered by the Wenchuan Earthquake on 12 May 2008. A STREAM_2D two-dimensional hydrodynamic model of Russia was applied to simulate the process of two flood scenarios: 1, lake dam outbreak, and 2, dam overtopping. An artificial dam outbreak was made after the earthquake to lower the water level of the lake in 2008, which led to a great flood with a maximum water discharge of more than 6400 m3/s. The negative impact of the flood was reduced by a timely evacuation of the population. Flood hazards still remain in the event of new landslides into the lake and lake dam overtopping (Scenario 2), in which case a maximum water discharge at the dam crest would reach 5000 m3/s, placing the population of Shabacun and Shilingzi villages in the zone of flood impact.

Dendrogeomorphic reconstruction of lahar activity and triggers: Shiveluch volcano, Kamchatka Peninsula, Russia

Lahars are highly concentrated, water-saturated volcanic hyperconcentrated flows or debris flows containing pyroclastic material and are a characteristic mass movement process on volcanic slopes. On Kamchatka Peninsula (Russian Federation), lahars are widespread and may affect remote settlements. Historical records of past lahar occurrences are generally sparse and mostly limited to events which damaged infrastructure on the slopes or at the foot of volcanoes. In this study, we present a tree-ring-based reconstruction of spatiotemporal patterns of past lahar activity at Shiveluch volcano. Using increment cores and cross sections from 126 Larix cajanderi trees, we document 34 events covering the period AD 1729–2012. Analyses of the seasonality of damage in trees reveal that 95% of all lahars occurred between October and May and thus point to the predominant role of the sudden melt of the snow cover by volcanic material. These observations suggest that most lahars were likely syn-eruptive and that lahar activity is largely restricted to periods of volcanic activity. By contrast, rainfall events do not seem to play a significant role in lahar triggering.