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Soils, rocks, and groundwater
Published in Rodrigo Salgado, The Engineering of Foundations, Slopes and Retaining Structures, 2022
Basalt and other extrusive rocks tend to exist at the surface and immediately flow across large areas. This gives origin to what is referred to as basalt flows. The magma cools very fast, contracting in a way that generates predominantly vertical fractures, leading to relatively thin (of the order of 5–20 cm) columns of rock. The joint pattern is accordingly called columnar jointing.
Mechanical characteristics of class-I columnar jointed basalt of Baihetan hydropower station
Published in Jean-Pierre Tournier, Tony Bennett, Johanne Bibeau, Sustainable and Safe Dams Around the World, 2019
L.Q. Li, J.R. Xu, Y.L. Jiang, H.M. Zhou, Y.H. Zhang
Columnar joint often forms in lava flows, sills, dikes, ignimbrites (ashflow tuffs), and shallow intrusions of all compositions. Besides in many igneous rock types, such as basalt (Bulkeley, 1963; Milazzo, Keszthelyi & Jaeger, et al., 2009), rhyolite, andesite, dacite (DeGraff & Aydin, 1987), columnar joints are found in many other rock types, such as sandstone (Young, 2008) and coal, and in man-made materials, such as smelter slag, glass, chemically laced vitrified ice (Melton & Schulson, 1998), and certain types of drying starches (Müller, 1998; Goehring & Morris, 2005). Columnar jointing is a spontaneous fracture of rock or other materials into regular prismatic columns.
Igneous activity and landforms
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Basaltic lavas are of low viscosity, having no free silica, and may flow in a very fluid manner at extrusion temperatures of 1000°C–1100°C and velocities in excess of 30 m/s. As a consequence, individual flows may be very extensive (up to 100 km or more in length) but comparatively thin (normally a few metres, but occasionally very much thicker). The steplike eroded edges of thick sections of superimposed flows led to basaltic rocks being originally termed ‘trap’ (German: trappen – ‘steps’). The surface of such flows presents a twisted or rolled crust (pahoehoe), resulting from the continual movement of the lava beneath the cooled surface skin. This internal movement may cause partial drainage of the interior of flows to produce lava caves and tubes, as well as the deformation of the surface into pressure ridges of up to 20 m high. Submarine eruptions of basaltic lava (mostly spillite – i.e. basalt with excessive sodium) produces a ‘pillow’ structure of sacklike ellipsoids due to the rapid surface cooling and continued movement of small individual parts of the flow. The slower terrestrial cooling of basaltic lava commonly results in the production of vertical columnar jointing, with the joints set at angles of approximately 60° and separating four-to eight-sided columns 1–20 m thick, as in the Giant’s Causeway, Northern Ireland, and the Devil’s Postpile in the Sierra Nevada.
Investigation of an unusual landslide at Sai Kung Sai Wan Road, Sai Kung, Hong Kong
Published in HKIE Transactions, 2018
Dominic O K Lo, Rachel H C Law, Roland C T Wai, Axel K L Ng, Steven J Williamson, Jason K S Lee, Y M Cheng
The landslide is located on a southeast-facing hillside with a broad topographic depression. The summit is at an elevation of about 300 mPD and the Sai Kung Sai Wan Road is at an elevation of about 150 mPD. The source area is about 100 m (250 mPD) above the Sai Kung Sai Wan Road. The hillside adjacent to the source area is generally densely vegetated with tall shrubs and mature trees, and is inclined at an angle of about 35° to 45°. Locally, rock outcrops in linear bands traverse across the hillside and this is typically characterised by an increase in local slope angle and decrease in vegetation (Figure 2). Solid geology comprises fine ash vitric tuff of the High Island Formation with characteristic hexagonal columnar jointing [1], which is usually formed as a result of contraction in volcanic rocks during the cooling process. Several drainage lines are located within the hillside which drain down to the northern part of the High Island Reservoir. The landslide intersects one perennial drainage line just below the source area and another ephemeral drainage line is located along the west flank of the source area. A culvert underneath the Sai Kung Sai Wan Road discharges surface water from the hillside catchment into the confined perennial drainage line downstream (Figure 2).
Rocky relationships: the petroglyphs of the Murujuga (Burrup Peninsula and Dampier Archipelago) in Western Australia
Published in Australian Journal of Earth Sciences, 2019
E. R. Ramanaidou, L. C. Fonteneau
The rocky landscape of loose boulders is characteristic of the area (Figure 3) and Donaldson (2011) attributes it to the results of the columnar jointing formed during the cooling of the magma. The differential weathering between the solid rock and the cooling fractures have generated irregular pillars and loose boulders that seem ‘dumped’ in the landscape. Donaldson (2011) also records that the weathered layer developed on the fine-grained granophyres is favoured for engravings compared with that developed on the coarser-grained gabbro, which contains fewer petroglyphs (Figures 3 and 4). It is interesting to note that the hardened Quaternary sediments such as limestone and red sediment (Semeniuk, 1996) appear to be devoid of petroglyphs.