Geomorphological evidence of active faulting in low seismicity regions - examples from the Valley of Lakes, southern Mongolia

<p>The tectonically active northern margin of the Gobi Altai in southern Mongolia is best known for the 1957 Mw 8.1 Bogd earthquake. Cumulative offsets along the Bogd fault indicate that the area was subject to repeated earthquakes in the past. North of the Bogd fault, the Valley of Lakes characterises a seismically quiescent zone between the Gobi Altai and the central Mongolian Hangay dome, with little to no instrumentally recorded earthquakes. However, Quaternary alluvial fans of rivers that drain toward the endorheic lakes in this basin are crosscut by multiple fault scarps with displacements up to 15 m. Additionally, river channel morphology is significantly altered by tectonic lineaments indicating that, despite the lack of recorded seismicity, this area may indeed have been seismically active in the recent past. By applying remote sensing techniques, UAV photogrammetry, and morphometric studies, we aim to understand i) the effect these faults had on the landscape evolution of the Valley of Lakes, ii) their relationship to deformation along the Bogd fault and iii) whether these faults accommodate a significant amount of strain related to the India-Eurasia collision.</p><p>The lack of available material for dating requires palaeoseismological studies to make use of morphotectonic observations as an alternative, relative dating method. At the Bogd fault, such studies were combined with sparsely available cosmogenic nuclide age data to determine that vertical slip rates vary between 0.1 and 1 mm/yr on individual faults and at the scale of the entire mountain front, respectively. In the Valley of Lakes, a total lack of age data complicates the extrapolation of slip rates, however scarp degradation indicates that slip rates are likely lower than at the Bogd fault. Fluvial terraces of the Tuyn Gol river are crosscut by at least three major fault scarps, which contribute to valley width variations of the river from ±3500 m to ±20 m at the current fan apex, and which are reflected in steepness index variations along minor drainages. Additionally, a large paleochannel suggests that major drainage reorganisation events took place in Quaternary times, either reflecting periods of high tectonic activity or as a result of significant climate variations. The transtensional nature of some faults in the Valley of Lakes is unique; however fault mechanisms in the area are generally in line with the active deformation in the Gobi Altai. Our results stress the earthquake potential of regions with low instrumental seismicity and demonstrate that deformation in the Gobi Altai may reach further north than previously expected.</p>

An Integrated Approach for Constraining Depositional Zones in a Tide-Influenced River: Insights from the Gorai River, Southwest Bangladesh

The tidal to fluvial transition (TFT) of estuaries and coastal rivers is one of the most complex environments on Earth with respect to the transportation and deposition of sediment, owing in large part to competing fluvial and marine processes. While there have been recent advances in the stratigraphic understanding of the TFT, it is still unclear whether these findings are site-specific or representative of mixed tidal-fluvial systems worldwide. Yet, research from this depositional domain holds profound societal and economic importance. For instance, understanding the underlying stratigraphic architecture of channel margins is critical for assessing geomorphic change for fluvio-deltaic settings, which are generally vulnerable to lateral channel migration and resultant erosion. Findings would also benefit paleo-geographic reconstructions of ancient tide-influenced successions and provide an analog for hydrocarbon reservoir models. In the Ganges-Brahmaputra Delta of Bangladesh, the Gorai River is one of two Ganges distributaries actively connected to the Bay of Bengal. With fluvial input from the Ganges and meso-scale (2–4 m range) tides at the coast, the Gorai exhibits a variety of hydrodynamic regimes across its 350-km reach, providing a unique opportunity to investigate along-channel depositional patterns across the TFT. This study integrates multiple datasets—core sedimentology, river channel bathymetry, and remote sensing—to provide a process-based framework for determining the relative position of sedimentary deposits within the tidal-fluvial continuum of the Gorai River. The results of this investigation reveal coincident, abrupt shifts in river channel morphology and sediment character, suggesting the occurrence of backwater-induced mass extraction of relatively coarse sediments (i.e., fine sand). Despite being situated in an energetic tidal environment, evidence of tidal cyclicity in cored sediments is relatively rare, and the bulk stratigraphy appears strongly overprinted by irregularly spaced cm- to dm-scale sediment packages, likely derived from monsoonal flood pulses. Such findings differ from previously-studied mixed tidal-fluvial systems and underscore the site-specific complexities associated with this depositional domain.

Landuse Types within Channel Corridor and River Channel Morphology of River Ona, Ibadan, Nigeria

The importance of river a corridor warrants a well thought out and balanced management approach because it helps in improving or maintaining water quality, protecting wetlands, etc. Hence, this study seeks to identify major landuse types within the River Ona Corridor; examine the impact of these landuse types within the River Ona corridor on its channel morphology and understand the risk being posed by these landuse types. The study is designed by selecting two reaches of six times the average width from each of the four major landuse types that exist along the river corridor. This study revealed that along the downstream section of Eleyele Dam of River Ona, natural forest stabilizes river channel banks, thereby presenting a narrow and shallow width and depth respectively but the widest of all is found at the agricultural zones.

THE BENEFITS OF RIVER INDICATORS TO ASSESS THE ECOLOGICAL STATUS OF IIUM CAMPUS

The concept of sustainable campus has emerged from the social, economic and environmental impacts due to anthropogenic activities around the world. One of the initiatives of sustainable campus is the application of ecological indicators. The indicators provide information about the current condition and early warning on the possible risks of environmental impacts to the campus environment. However, lack of understanding on the values of natural ecosystem in campusand the lack of proper planning has led to the depletion of natural ecosystem. The study seeks to examine river degradation in IIUM campus and to explore the benefits of river indicators towards achieving IIUM as an ecologically sustainable campus. Data were gathered using a qualitative approach involving three methods of data collection namely: (i) document analysis, (ii) semi-structured interview and (iii) site inventory. The finding reveals that the application of river channel morphology indicators is an important basis for physical planning in making a campus ecologically sustainable. Further analysis suggests that the suitable indicators to assess the condition of IIUM River are the river channel morphology indicators such as width, depth, channel pattern and slope ratio. The process of selecting the indicators are carried out based on six criteria of good indicators discussed in this study. The study concluded that the application of river channelmorphology indicators is a critical process in physical planning of a sustainable campus as it contributes in preventing the loss of natural ecosystem and it offers a credible basis for creating a conducive place for campus residents.

THE BENEFITS OF RIVER INDICATORS TO ASSESS THE ECOLOGICAL STATUS OF IIUM CAMPUS

The concept of sustainable campus has emerged from the social, economic and environmental impacts due to anthropogenic activities around the world. One of the initiatives of sustainable campus is the application of ecological indicators. The indicators provide information about the current condition and early warning on the possible risks of environmental impacts to the campus environment. However, lack of understanding on the values of natural ecosystem in campusand the lack of proper planning has led to the depletion of natural ecosystem. The study seeks to examine river degradation in IIUM campus and to explore the benefits of river indicators towards achieving IIUM as an ecologically sustainable campus. Data were gathered using a qualitative approach involving three methods of data collection namely: (i) document analysis, (ii) semi-structured interview and (iii) site inventory. The finding reveals that the application of river channel morphology indicators is an important basis for physical planning in making a campus ecologically sustainable. Further analysis suggests that the suitable indicators to assess the condition of IIUM River are the river channel morphology indicators such as width, depth, channel pattern and slope ratio. The process of selecting the indicators are carried out based on six criteria of good indicators discussed in this study. The study concluded that the application of river channelmorphology indicators is a critical process in physical planning of a sustainable campus as it contributes in preventing the loss of natural ecosystem and it offers a credible basis for creating a conducive place for campus residents.

Contribution of River Mouth Reach to Sediment Load of the Yangtze River

This paper examined the sediment gain and loss in the river mouth reach of the Yangtze River by considering sediment load from the local tributaries, erosion/accretion of the river course, impacts of sand mining, and water extraction. A quantitative estimation of the contribution of the river mouth reach to the sediment load of the Yangtze River was conducted before and after impoundment of the Three Gorges Dam (TGD) in 2003. The results showed that a net sediment load loss of 1.78 million ton/yr (Mt/yr) occurred from 1965 to 2002 in the study area. The contribution of this reach to the sediment discharge into the sea is not as high as what was expected before the TGD. With impoundment of the TGD, channel deposition (29.90 Mt/yr) and a net sediment loss of 30.89 Mt/yr occurred in the river mouth reach from 2003 to 2012. The river mouth reach has acted as a sink but not a source of sediment since impoundment of the TGD, which has exacerbated the decrease in sediment load. Technologies should be advanced to measure changes in river channel morphology, as well as in water and sediment discharges at the river mouth reach.