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Geological Structures
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Small areas where sedimentary rocks are horizontal or nearly so are often preserved as hills capped by a resistant layer; e.g. many are seen along the western margin of the Cotswolds in England. On a larger scale, a flat-topped tableland of mesa (Fig. 3.11) has a capping of hard rock from which steep slopes fall away on all sides, as in the Blue Mountains of New South Wales and in Grand Canyon, Arizona. The capping may be a hard sedimentary layer or igneous rock such as a lava flow. Table Mountain, near Cape Town, is a mesa. The distance measured on the ground, between beds of horizontal strata will depend upon their thickness and the slope of the ground (Fig. 3.12).
Middle East & North Africa
Published in Ian Sims, Alan Poole, Alkali-Aggregate Reaction in Concrete: A World Review, 2017
Ted Kay, Alan B Poole, Ian Sims
Tunisia, Algeria and Morocco, when taken together, are composed of four main geographical regions which generally run east-west: A narrow discontinuous coastal strip, which generally runs along the southern shore of the Mediterranean and also extends north-south lying along the eastern side of Tunisia (the Sahel) and along the Atlantic coast of Morocco. In Tunisia and Algeria the coastal strip is known as the Tell. It consists of hills and fertile valleys and contains the main cities and most of the countries’ arable land.A high plateau or tableland marked by rolling hills and some steep cliffs and flat plains interspersed with large shallow basins. These basins collect water during the wet season, but dry out in the dry season sometimes forming salt flats known as chotts.A region occupied by a series of mountain chains the most dominant of which, the Atlas Mountains, occupies a band stretching diagonally across the region from the south-west to the north-east starting in southern Morocco and ending in the Northern Tell and High Tell in Tunisia. Within Algeria, the Saharan Atlas is formed of three chains: Jibal Amor in the south-west, Jibal Awlad Nail in the centre and the Monts du Zab in the north-east. There are three parallel chains in Morocco: the Moyen Atlas in the north, the Haut Atlas in the centre and the Anti-Atlas to the south.The Sahara desert, a desolate flatland of gravel plains and some areas of large sand dunes with dispersed oases. The region consists of a Precambrian basin unconformably overlain by thick Palaeozoic sediment deposits (Askri et al., undated).
Evaluation of loess-filled slope failure triggered by groundwater rise using a flume test
Published in Geomatics, Natural Hazards and Risk, 2022
Yi Zhu, Jianqi Zhuang, Yong Zhao
The north-south strike of the Dongzhiyuan loess tableland, located in the eastern part of the Gansu Province, is the ‘biggest loess plateau’. The loess of the Dongzhiyuan tableland is almost 300 m deep. The upper layer is primarily composed of Malan loess, about 20–40 m thick, deposited in the late Pleistocene period (Q3). The geomorphology of the Dongzhiyuan tableland belongs to the typical loess plateau tableland-gully, with a relatively flat surface and gullies that crisscross around the landscape. Since 2000, the headward erosion of gullies around the Dongzhiyuan tableland has intensified because of population growth and increased human activities. The gully and soil erosion in the Dongzhiyuan tableland is becoming increasingly serious and extends towards the center of the highland, causing the highland to be fragmented (Figure 1). Geohazards, such as landslides and collapses, occur frequently. Since the Tang Dynasty, the eroded area of the tableland has reached more than 599.6 km2, with an average annual loss of about 0.46 km2. According to investigations, the original Dongzhiyuan tableland was divided into 11 pieces in the last 1300 years, with the largest at 946.25 km2 and the smallest at 0.39 km2 (Shi 1987; Chen et al. 2009).
Statistical assessment of groundwater quality using hydrochemical parameters for drinking water of rural areas in Nashik district, Maharashtra, India
Published in Water Science, 2022
C.A. Patil, P.M. Nalawade, B. L. Gadakh, N.V. Khangar
The area of the Nashik district is underlain by the elementary lava flows of top Cretaceous to lower the Eocene epoch. The shallow alluvial formation of recent age also occurs as a narrow stretch along the banks of the Godavari, Mosam, and Girna River flowing in Nashik. Basaltic lava flows occupy about 85% of the area of the district. These flows are normally horizontally disposed over a wide stretch and give rise to tableland type of topography also known a plateau. These flows occur in layered sequences and are represented by a massive unit at the bottom and a vesicular unit at the top of the flow. These flows are separated from each other by a marker bed known as ‘bole bed.’ The groundwater in Deccan Trap Basalt occurs mostly in the upper weathered and fractured parts down to 20–25 m depth. At places, potential zones are encountered at deeper levels in the form of fractures and inter-flow zones. The top weathered and fractured parts form subterranean aquifer and groundwater occurs under water table (unconfined) conditions. At more limitless levels, the groundwater occurs under semi-confined to confined conditions.
Landslide-controlled soil erosion rate in the largest tableland on the Loess Plateau, China
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Pinglang Kou, Qiang Xu, Ali P. Yunus, Jie Liu, Yali Xu, Cuilin Wang, Huajin Li, Yong Wei, Xiujun Dong
The Dongzhiyuan tableland covers an area of 2,840 km2 in the southern Loess Plateau, China (Figure 1), and is the largest tableland on the Loess Plateau. It is called the largest “granary” in eastern Gansu Province, China. The coordinate position of the Dongzhiyuan tableland is N: 34°50′ to 37°19′, E: 106°14′ to 108°42′. The north-to-south length is approximately 89 km, and the east-to-west mean width is approximately 46 km. Thick loess formed under monsoon conditions during the Pleistocene (Derbyshire et al. 1995), and the loess thickness on the Dongzhiyuan tableland is 100-300m. The climate in the studied zone belongs to a temperate continental monsoon environment with an annual rainfall of 510 mm-550 mm (Figure 2e, 2f). The annual runoff and annual sediment output are estimated to be 637.8 million m3 and 16.83 million tons, respectively. The period from July to September is relatively wet, accounting for 60% of the annual runoff. Surface runoff in the summer accounts for 55% of the annual runoff. The Malian River flows in the eastern portion of the Dongzhiyuan plateau; the length of the river is 374.8 km. The Pu River flows on the western border, and the length of this river is 204 km. The average annual discharges of the Malian and Pu Rivers are 449 and 252 million m3 (Li and Sheng 2011), respectively.