Chapter 1 Introduction to the geology of Myanmar

Zaw, Khin; Swe, Win; Barber, Asa H.; Crow, M. J.; Nwe, Yin Yin

doi:10.1144/m48.1

Cited by 16 publications

(3 citation statements)

References 76 publications

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“…Both river basins are composed of a wide variety of sedimentary, igneous, and metamorphic rocks, ranging from Pre‐Cambrian to Cenozoic in age and transposed by a complex network of sutures and faults (e.g., Licht et al., 2013; Mitchell et al., 2012; Najman et al., 2020; Searle et al., 2007; Westerweel et al., 2019; Zaw et al., 2017; Zhang et al., 2018). The climate of both basins is dominated by the southwest Asian monsoon (and to a lesser degree the northeast monsoon), with most precipitation and discharge taking place in June through September (Zaw et al., 2017). Mean annual precipitation rates vary from <800 up to >4,000 mm/year within the Irrawaddy basin, depending on the location (e.g., Chen et al., 2017; Sein et al., 2018).…”

Section: Methodsmentioning

confidence: 99%

Integrating Suspended Sediment Flux in Large Alluvial River Channels: Application of a Synoptic Rouse‐Based Model to the Irrawaddy and Salween Rivers

et al. 2020

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A large portion of freshwater and sediment is exported to the ocean by a small number of major rivers. Many of these megarivers are subject to substantial anthropogenic pressures, which are having a major impact on water and sediment delivery to deltaic ecosystems. Due to hydrodynamic sorting, sediment grain size and composition vary strongly with depth and across the channel in large rivers, complicating flux quantification. To account for this, we modified a semi-empirical Rouse model, synoptically predicting sediment concentration, grain-size distribution, and organic carbon (%OC) concentration with depth and across the river channel. Using suspended sediment depth samples and flow velocity data, we applied this model to calculate sediment fluxes of the Irrawaddy (Ayeyarwady) and the Salween (Thanlwin), the last two free-flowing megarivers in Southeast Asia. Deriving sediment-discharge rating curves, we calculated an annual sediment flux of 326 þ91 −70 Mt/year for the Irrawaddy and 159 þ78 −51 Mt/year for the Salween, together exporting 46% as much sediment as the Ganges-Brahmaputra system. The mean flux-weighted sediment exported by the Irrawaddy is significantly coarser (D 84 ¼ 193 ± 13 μm) and OC-poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 μm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of 1:9 þ1:4 −0:9 Mt C/year, 53% as much as the Ganges-Brahmaputra. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment flux, given the increasing anthropogenic pressures on these river basins. Plain Language Summary The sediment (clay, silt, and sand) carried by rivers is a crucial but dwindling resource, sustaining agriculture in fertile deltas, while huge amounts of sand particularly are used to produce concrete, glass, and electronics. The amount of sediment that rivers carry globally is, however, not well known. It is especially difficult to measure in large rivers because most sand is carried near the channel bottom, tens of meters beneath the surface. In this study, we present an improved approach to measure the amount of sediment carried by large rivers. It combines sediment samples collected at various depths in the river with measurements of river flow via acoustic sensors. We apply this method to some of the world's largest riversthe Irrawaddy (Ayeyarwady) and the Salween (Thanlwin) in Myanmar, which have been understudied for decades. Our results show that they both currently discharge immense quantities of sediment to the ocean. However, this is likely to decrease drastically in the coming decades, given the projected industrialization and future damming of these two basins. The results presented in this study thus provide an important baseline against which to measure future changes in sediment discharge by these rivers.

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Section: Methodsmentioning

confidence: 99%

Integrating Suspended Sediment Flux in Large Alluvial River Channels: Application of a Synoptic Rouse‐Based Model to the Irrawaddy and Salween Rivers

et al. 2020

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“…Myanmar lies continuously as Indo Myanmar Ranges in Eastern Himalayan Syntaxis of a continental collision of the Indian and Eurasian plate extended southwards to the north from the Indonesian Arc System to the Eastern Himalayan orogenic belt (Khin et al 2017;Sloan et al 2017). Northern Myanmar consists of exposed Indian Plate with various slices of faults also overlain by the Naga hills.…”

Section: Geological Settingsmentioning

confidence: 99%

“…Northern Myanmar consists of exposed Indian Plate with various slices of faults also overlain by the Naga hills. Nevertheless, the active subduction of the Indian plate develops transcurrent faults, whereas the pre-collision margin of the Indian Eurasian plate can be evidenced by the most prominent Magok metamorphic belt (Searle et al 2007;Khin et al 2017;Sloan et al 2017), which mainly composed of the oldest rock units in Myanmar, and lies in the major tectonic structural belt. The Magok metamorphic belt (Fig.…”

Section: Geological Settingsmentioning

confidence: 99%

Topographical features of rainfall-triggered landslides in Mon State, Myanmar, August 2019: spatial distribution heterogeneity and uncommon large relative heights

Panday

Dong

2021

Landslides

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Continuous 5-day (August 4–9, 2019) torrential rainfall in the monsoon season triggered more than 90 landslides on northwest-southeast extended mountain range of Mon State, Myanmar. In this study, remote sensing images, DEM, and limited fieldworks were used to create the landslide inventory. The topography features of these landslides are analyzed via ArcGIS. The largest one occurred on 9 August 2019 and caused 75 deaths and 27 buildings were damaged. This landslide occurred on gentle topography (slope angle, 23°) with long run-out, in which the angle of reach was relatively low (10°). The volume was 111,878 m3 was mainly composed of weathered granite and red soil and the sliding depth was approximately 7.5 m. Topographic characteristics including the relative slope height, angle of reach, and slope angle of source area of 35 landslides with areas > 4000 m2 were analyzed. The spatial distribution characteristics and topographic features of the 35 landslides below are distinguished: (1) the concentration of most of landslides on southwest-facing slopes showing the heterogeneous spatial distribution of landslide; (2) an uncommon landslide distribution in which more than half of landslide originates from upper slope; (3) the range of the angle of the source area (17°–38°) compatible with the internal friction angle of soils in tropical regions (17°–33°); and (4) the tangent of the angle of reach is generally smaller than 0.5 (angle of reach < 27°) shows a relative high mobility and the relation between landslide mobility and the slope angle of the landslide source area is similar to the one of earthquake-triggered landslides, even though the triggering mechanism, landslide type, and landslide volume are dramatically different.

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