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Earth slope stability and landslides
Published in Hsai-Yang Fang, John L. Daniels, Introductory Geotechnical Engineering, 2017
Hsai-Yang Fang, John L. Daniels
Debris flow is a general term which covers not only mud but mud–rock mixtures as well. It occurs in general at a high altitude. There are three basic factors causing debris flow: (a) steep slopes at high altitude, (b) sufficient water resources surrounding the site, and (c) relatively loose rock pieces and soil. For evaluating a debris flow, climatic and geological conditions as well as surface vegetation and tree root type and distribution are particularly relevant. A volcanic mudflow is a special type of mudflow. This type of mudflow is characterized predominantly by fine-grained tephra. Tephra is a collective term for material that has been ejected from volcano, irrespective of size, shape, or composition.
Tephrochronology in Aotearoa New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Jenni L. Hopkins, David J. Lowe, Joanna L. Horrocks
The term ‘tephra’ (from the Greek word τέφρα meaning ‘ash’ or ‘ashes’) includes all the explosively-erupted, unconsolidated, fragmental (pyroclastic) products of a volcanic eruption. ‘Cryptotephras’ are sparse, ash-sized glass-shard and/or crystal concentrations preserved in sediments (including ice) or soils but insufficiently numerous to be visible as a layer to the naked eye (Lowe 2011). ‘Tephrochronology’ (sensu stricto) is a correlational and dating method that uses characterised tephra or cryptotephra deposits as isochronous (time-parallel) beds to link or synchronise geological, palaeoenvironmental, or archaeological sequences or events, and to transfer and apply relative or numerical ages to them using the tephra/cryptotephra compositional ‘fingerprints’ in combination with stratigraphic superpositioning. ‘Tephrochronology’ (sensu lato) is also used as a portmanteau term for all aspects of tephra or cryptotephra studies, and their application including volcanology (Lowe 2008, 2011), which is the usage adopted for the title of this paper.
Middle–Upper Pleistocene tephras in the Papua New Guinea highlands
Published in Australian Journal of Earth Sciences, 2023
Tephra is an important product of volcanic eruptions. The word ‘tephra’ originates from the Greek word τεϕρα meaning ‘ashes’. The plural is either tephra or tephras—the former (as a singular collective noun) is more technically correct, but the latter avoids ambiguity and is in common usage (Alloway et al., 2007). As originally proposed (Thorarinsson, 1944), the term allows a distinction between tephra-fall deposits and tephra-flow deposits (see also Neuendorf et al., 2011). Here, ‘tephra’ is used for airfall volcanic ejecta, and tephra-flow materials are referred to as pyroclastic density current deposits (see Brown & Andrews, 2015).