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Processes of Sea Cliff and Platform Erosion
Published in Paul D. Komar, J. Robert Moore, CRC Handbook of Coastal Processes and Erosion, 1983
Coastal cliff recession is one of the significant geomorphic events occurring at the interface of the lithosphere, hydrosphere, and atmosphere. In an attempt to understand cliff recession processes, geologists, geomorphologists, and physical geographers have studied this phenomenon from purely scientific interest. Recently, due to increased use of the coast, considerable attention has been focused on the erosion of sea cliffs in connection with coastal zone management and engineering problems. From the viewpoints of not only pure but also applied sciences, the elucidation of erosional mechanisms is of basic importance. Such studies also give a promising clue for understanding the formative processes of shore platforms which are primarily created by the retreat of sea cliffs. Applications of cliff erosion research are possible to the problems of (1) development of continental shelves with erosional origin,139 and (2) formation of uplifted marine terraces, if wider spatial and longer temporal scales are considered.
Normandy cliff stability: Analysis and repair
Published in Vladimir Litvinenko, EUROCK2018: Geomechanics and Geodynamics of Rock Masses, 2018
The Channel is the part of the Atlantic Ocean that separates the island of Great Britain from northern France and joins the North Sea to the Atlantic. Duperret et al. (2004) reported nine different chalk units along the coastline of NW France (120 km from upper Normandy to Picardy). The chalk sea cliffs retreat along the Normandy coast of France over decadal time scales, is ranging from effectively stable to landward retreat between 0.1 to 0.5 m/yr with a mean value of 0.23 m/yr (Duperret et al. 2004). The retreat usually takes place by successive local collapse. Many authors (e.g. Emery & Kuhn 1982; Sunamura 1992) propose that marine parameters acting at the toe of rock cliffs are responsible for under cutting the cliff, which leads to rock failures. The coastal monitoring program at the Sandown Bay, UK, which is about 140 km north of Pointe du Hoc, gives a range of maximum wave height, Hmax, between 5 and 6 m during the storm season. Benumof and Griggs (1999) also state that waves are one of the leading forcing mechanisms of sea-cliff erosion, secondary only to the material properties of the rock itself. The typical geology of the Pointe du Hoc area consists of the following sequence. At the top is a layer of sediments, which have been deposited in the Bajocien—Bathonien period. Below is a limestone layer of “Calcaire de St Pierre du Mont” also called “Calcaires du Bessin”. This limestone layer is based on a marl layer of “Marnes de Port en Bessin”. This marl is apparent in the nearby small harbor of Port en Bessin under the form of slopes created by the erosion on both sides of a small river that reaches the sea at this location.
Landslide triggers and types
Published in Jan Rybář, Josef Stemberk, Peter Wagner, Landslides, 2018
Robert L. Schuster, Gerald F. Wieczorek
Coastal erosion combined with landslide activity is a problem faced by many of the world’s seacoasts and along the coastlines of several of the world’s largest lakes, such as the Great Lakes in the United States. The problem is generally one of “undermining” of the coastline by erosion due to wave and tidal action. This erosion often forms sea cliffs, and results in destabilization and landslide activity, ranging from rock falls to major rock slumps and slides.
Study on structural mechanical characteristics and safety warning of NATM tunnel in aquifer
Published in Marine Georesources & Geotechnology, 2022
Binke Chen, Zhiqiang Zhang, Yinjun Tan, Yiwei Liu
The geographical location of the Lujiazhi undersea tunnel is shown in Figure 1. The project starts from the east side of Lujiasi Island, connecting with the planned intersection of Wanlu and Xiner Roads, forming a T-shaped intersection with Xiner Road. After setting a subsea tunnel to pass through Shenjiamen Port, mountain tunnel is used to pierce the Pengshan mountain, finally connecting Haizhou Road in front of Banshengdong Petroleum Company. The whole line is equipped with a motor vehicle passage tunnel of length of 1920 m, including a 210 m open section, 785 m submarine shield section and 745 m mountain tunnel section (all of which are the length of left line tunnel). The overall layout scheme of the tunnel is as follows: shield section of submarine and mountain tunnels adopt separate layout schemes. The clear width and height of the single hole construction limit in the open-cut section on shore and mountain tunnel section are 9.75 and 5.0 m, respectively. The clear width and height of the single-hole building limit of the submarine shield section are 8.75 and 5.0 m, respectively. Lujiazhi mountain tunnel has a maximum depth of 100 m. It comprises a small range of shield tunnel segments, large range and local flat roads. The tunnel moves into the cave mouth for the ancient sea cliff and out of the cave mouth for artificial excavation slope. The weathered bedrock is exposed. The area also comprises valleys, mountain tunnel, and hilly vegetation. At the foot of the slope distribution, one can find farmlands and local construction waste.
Paleoseismology of the Akatore Fault, Otago, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2020
Briar I. Taylor-Silva, Mark W. Stirling, Nicola J. Litchfield, Jonathan D. Griffin, Ella J. van den Berg, Ningsheng Wang
To aid with the interpretation of the GPR profiles, mineralogical and grain size analyses were undertaken of sands exposed either side of the fault in the relict sea cliff to assess the total displacement on the fault post deposition of the sands (Figure 2B). The samples were air-dried, and some gentle crushing was required to separate agglutinated particles, prior to analysis. The samples were put through a −1 Φ to 4 Φ nest of dry sieves with 0.5 Φ intervals and shaken for 2 min in a RO-TAP Sieve Shaker. Grains <4 Φ were collected in the pan at the base of the sieve nest. Each sieve fraction was weighed and recorded. Samples were also examined under a reflection microscope. This preparation enabled the footwall and hanging wall sediments to be compared across the Akatore Fault according to grain size distribution and composition.
Late Holocene uplift of a coastal terrace near the Akatore Fault, southern New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Dave Craw, Elahe Parvizi, Stephen Read, Ceridwen I. Fraser, Jonathan M. Waters
The Holocene terrace is largely accessible on foot for the whole of the studied coast, and our field observations on the terrace were augmented by observations from aerial photography from Otago Regional Council and GoogleEarth. The Holocene terrace can be readily distinguished from the higher Late Pleistocene highstand terrace by the presence of loess on the latter terrace, and absence of loess on the former. In addition, beach sands on the Late Pleistocene highstand terrace are typically cemented with clay and iron oxyhydroxide, and form erosional cliffs, whereas beach sands on the Holocene terrace are loose and uncemented. The fossil sea cliff separates these terraces (Figure 2A).