Ground-penetrating radar stratigraphy and dynamics of megaflood gravel dunes

Abstract

Ground-penetrating radar was used to elucidate the stratigraphy of late Pleistocene gravel dunes in the Altai Mountains of southern Siberia that formed when a lake emptied as a result of ice-dam failure. Survey-lines across dunes had a resolution of decimetres, with depth penetration of 20 m. The reflections identify bounding surfaces and radar facies. Two classes of unconformities are identified: (1) an erosional unconformity at the base of the dunes; (2) steeply inclined unconformities that truncate underlying inclined reflections and are downlapped by overlying inclined reflections within the dunes. Unconformities define six radar facies (RF): RF 1, basal subhorizontal discordant reflections; RF 2, poorly defined discordant reflections; RF 3, planar inclined reflections; RF 4, sigmoidal inclined reflections; RF 5, trough fills; RF 6, lowangle inclined reflections. The basal unconformity represents the flood-cut surface, across which the dunes migrated. The inclined unconformities may be interpreted in two ways: (1) erosional surfaces induced by unsteady flow within one flood, or (2) erosional surfaces developed by a series of floods reactivating dunes left stranded by previous floods. The evidence favours the latter model, which is consistent with the occurrence of several dune-forming events within the basin. The broader implications of the study are considered with respect to investigations of megaflood bedforms worldwide.

Revisiting the dynamics of catastrophic late Pleistocene glacial-lake drainage, Altai Mountains, central Asia

“…13c). As for Aktru, having subcritical flow at Kuray is in accordance with the prior identification of these bedforms as dunes (Carling et al, 2016). Carling et al (2016) related between three and five reactivation surfaces within the Kuray dunes to either intermittency in sediment transport during a single event or due to several distinct flood events reactivating the dunes.…”

“…As for Aktru, having subcritical flow at Kuray is in accordance with the prior identification of these bedforms as dunes (Carling et al, 2016). Carling et al (2016) related between three and five reactivation surfaces within the Kuray dunes to either intermittency in sediment transport during a single event or due to several distinct flood events reactivating the dunes. Due to the short period of potential transport modelled by Bohorquez et al (2016, 1.3 hours), Carling et al (2016) concluded that several floods were probably responsible for the reactivation surfaces.…”

“…The large field of bedforms sculpted in the basins during the lake drainage ( Fig. 1a) include the most notable example of giant gravel dunes on Earth (Carling, 1996a(Carling, , 1999, the paleohydraulic significance of which has been recently revisited (Carling et al, 2016). Intricate two-dimensional currents in the Kuray Basin provoked the formation of the dunefields (Rudoy, 2002;Inishev et al, 2015;Bohorquez et al, 2016).…”

Sand dunes and valley fills from Preboreal glacial‐lake outburst floods in south‐eastern Norway – beyond the aeolian paradigm

“…The imprints of the floods are numerous including impressive morphological features such as mega-sized bedforms and thick coarsegrained deposits (e.g. Parde, 1942;Bretz et al, 1956;Malde, 1968;Baker, 1973;Carling, 1996Carling, , 2013Maizels, 1997;Carling et al, 2016;Winsemann et al, 2016). Unravelling the influence of such extreme events on present-day landscapes is not always easy due to their enormous scale.…”

Application of Ground-Penetrating Radar for Detecting Internal Anomalies in Tree Trunks with Irregular Contours

“…In recent years, ground penetrating radar (GPR), which allows for rapid and real-time measurements, has received great attention for nondestructive testing (NDT). This technique has been applied for pavement investigation [ 4 ], geological exploration [ 5 ], civil engineering [ 6 ], subsurface archaeological investigation [ 7 ] and thin-layer thickness estimation [ 8 ]. In the forestry field, GPR has provided an important method of root system architecture reconstruction [ 9 ], root diameter or biomass estimation [ 10 ], and moisture content [ 11 ].…”