Reconstruction of Pleistocene ice-dammed lake outburst floods in the Altai Mountains, Siberia

Abstract

In the Siberian Altai Mountains, where the sources of the River Ob are located, ice-dammed lake outburst fl oods, so-called jökulhlaups, occurred in Pleistocene times. Valley glaciers extended within the upper Chuja River catchment and dammed the river upstream of the village of Aktash, which generated ice-dammed lakes in the intramountainous Kuray and Chuja Basins. Indicated by shorelines and ice-rafted boulder deposits, the maximum lake level reached an altitude of 2100 m above sea level, which reveals a maximum lake volume of 607 km 3 . The failure of the ice dam caused outburst fl oods, which left traces by giant bars, fl uvial gravel dunes, and boulder deposits. Run-up sediments deposited in front of local obstructions along the valley slopes indicate a maximum depth of fl ow of 400 m above the valley bottom. Like the giant bars, they consist of characteristic relatively fi ne suspension gravels. Occasionally, secondary lakes are formed in tributary valleys that were blocked by giant bar deposits. The alternation of lacustrine deposits and suspension gravels in the tributary Injushka valley near Inja village give evidence for at least three large outburst fl oods. Age estimations by a variety of dating methods, such as luminescence methods, exposure dating, and accelerator mass spectrometry radiocarbon applied on different fl ood features and lake sediments, indicate that the outburst fl oods occurred between 40 ka and 13 ka. This estimation should be taken as preliminary, as problems occurred with the different dating techniques, resulting in partly contradictory results. This study focuses on the paleohydraulic reconstruction of the fl ood rather than describing fl ood-related features in detail. Seven different approaches are applied to estimate the discharge of the fl oods. Several new methods are developed within the study, partly based on previous approaches carefully considering the hydraulic background. Data for paleohydraulic estimations are obtained during repeated fi eld trips by observations, surveys, and sedimentological investigations in Chuja and Katun valleys. Peak discharge is estimated by the elevation of the surfaces of the giant bars indicating the depth of fl ow and additionally by the run-up sediments, which reveal information about the velocity head of the fl ood fl ow along the valleys. A value of 10 × 10 6 m 3 /s is estimated for peak discharge, which is considerably less than previous estimations derived. Dimensions of gravel dunes and obstacle marks obtain information of fl ow conditions during the decreasing fl ood. The application of regression formulae between drained lake volume and peak discharge, an established method to estimate discharges of jökulhlaups, and estimation of fl ow velocity considering fl ow *herget @giub.uni-bonn.de on May 27, 2015 specialpapers.gsapubs.org Downloaded from 2 J. Herget competence indicated by transported boulders yield problems as the magnitude of the outburst fl oods and the size of the boulders are beyond the level of experience.Based on the...

Streamlined islands and the English Channel megaflood hypothesis

“…In the Altai Mountains of Siberia, for example, floods 546 produced extensive deposits (Rudoy and Baker, 1993), including streamlined bars, but large erosional 547 streamlined forms are largely absent (Burr et al, 2009). This has been interpreted as due to the 548 channelization of floodwaters down previously incised river valleys (Herget, 2005) Our English Channel observations of streamlined islands also make interesting comparisons to those 557 described from Germany (Meinsen et al, 2011). This latter island population is found within 10 km of the 558 spill-point, and spread over a 50 km wide zone and surrounded by a network of channels.…”

Coupled flood and sediment transport modelling with adaptive mesh refinement

“…The glacier dam-break flood in the Altai Mountains was one of the largest floods on the Earth [34]. The background of this megaflood was presented before [34][35][36].…”

“…The background of this megaflood was presented before [34][35][36]. This megaflood was modelled by Carling et al [36] using integrated 1D and 2D hydraulic models over a presumed fixed bed.…”

Pleistocene glaciations of the SE Altai, Russia, based on geomorphological data and absolute dating of glacial deposits in Chagan reference section

“…Based on terrestrial cosmogenic nuclide dates of moraines in the Chagan-Uzun valley, Gribenski et al (2016) suggested the Last Glacial Maximum in the SE Altai to be occurred about 17-19 ka. Associated with the glacial degradation final draining of ice-dammed lakes in the Chuya and Kurai intermountain depressions (Butvilovsky, 1993;Rudoy, 1995;Carling et al, 2002 andHerget, 2005) took place about 15.8 ± 1.8 ka, as it is evidenced by terrestrial cosmogenic nuclide dating (Reuther et al, 2006). The development of the Sartan ice-sheet glaciation within the framing ridges of the Chuya basin about 14 ka BP (Rudoy, 2005) does not confirmed by radiocarbon age of paleopeat in the Chikhachev range (Agatova et al, 2016).…”

“…In contrast to Tuva, the effusive and tephra layers are absent in the sections of the Russian Altai. Repeated developing giant ice-dammed lakes in the region (Butvilovsky, 1993;Carling et al, 2002;Rudoy, 2005 andHerget, 2005) complicate utilizing terrestrial cosmogenic nuclide dating of ancient moraines within intermountain depressions. Besides the difficulties of applying the numerical dating techniques, in glacial sediments of Altai reference sections there is a lack of finds of macro-and microfauna (ostracods), and species composition does not allow establishing the glacial sequences.…”