China
Africa
Explore chapters and articles related to this topic
Geotechnical analysis of large volcanic landslides. The La Orotava events on Tenerife, Canary Islands
Published in Jan Rybář, Josef Stemberk, Peter Wagner, Landslides, 2018
M. Hürlimann, A. Ledesma, J. Martí
Moreover, the field surveys have revealed that widespread residual soils (also called paleosols) might have been potential slip surfaces for large landslides. Such residual soils are common deposits on the island and represent the only material composing the volcano slopes with planar surfaces, weak properties and wide extensions.
Sensitive pyroclastic-derived halloysitic soils in northern New Zealand: Interplay of microstructure, minerals, and geomechanics
Published in Tatiana Rotonda, Manuela Cecconi, Francesco Silvestri, Paolo Tommasi, Volcanic Rocks and Soils, 2016
Vicki G. Moon, David J. Lowe, Michael J. Cunningham, Justin B. Wyatt, Willem P. de Lange, G.J. (Jock) Churchman, Tobias Mörz, Stefan Kreiter, Max O. Kluger, M. Ehsan Jorat
The stratigraphic sequences in the Tauranga area of the Bay of Plenty are complex, but an overall stratigraphy recognizes several broad units that are well exposed in the present scarp of the Bramley Drive failure at Omokoroa where the sequence is very thick (Figure 2). Most of the deposits derive from caldera volcanoes in the Taupo Volcanic Zone (see Briggs et al., 2005; Wilson et al., 2009) southeast of Tauranga (Figure 1). At the top are Holocene and Pleistocene tephras representing the most recent eruptives and modern pedological soil horizons; the base of this unit comprises the Rotoehu Ash deposited c. 50,000 years ago (Briggs et al., 1996; Danisik et al., 2012). The Rotoehu Ash lies on a very distinctive dark reddish-brown clay-rich paleosol formed on the Hamilton Ash beds. (Paleosols are defined here as pedogenic soils on a landscape, or of an environment, of the past.) These beds are composed of a series of weathered tephra deposits with intercalated paleosols ranging in age from c. 0.08 to 0.34 Ma (Lowe et al., 2001). At Bramley Drive the Hamilton Ash beds reach a total thickness of ~9 m; this thickness is variable around the region. The Hamilton Ash beds lie on top of another very well developed, dark brown clay-rich paleosol which marks the top of the so-called Pahoia Tephra sequence – a poorly defined composite sequence of primary pyroclastic and reworked rhyolitic volcaniclastic materials ranging in age from approximately 0.34 to 2.18 Ma (Briggs et al., 1996). The Pahoia Tephras are part of the Matua Subgroup, a widespread, complex unit that occurs throughout the Bay of Plenty (Pullar et al., 1973; Briggs et al., 1996, 2006), and which includes pyroclastic deposits of both fall and flow origin, lacustrine, estuarine, and (rare) aeolian sedimentary deposits, lignites, and fluvially reworked volcanogenic materials. At the Bramley Drive site, the Pahoia Tephras include at least six units that attain a combined thickness of > 12 m. These units are underlain by a weakly-welded ignimbrite provisionally identified as Te Puna Ignimbrite (0.93 Ma) (Gulliver and Houghton, 1980; Briggs et al., 1996, 2005). In turn, the ignimbrite is underlain by a lignite deposit at shore platform level.
Learning from a Well-documented Geotechnical Cold Case: The Two Towers of Bologna, Italy
Published in International Journal of Architectural Heritage, 2022
I. Bertolini, M. Marchi, G. Gottardi
Bologna’s historic centre is located in the high Po Plain, in the northern foothills of the Apennines. Its geographical position, slightly elevated, corresponds to the core of the interfluve of the Savena and Reno Rivers. Nonetheless, recent geological studies (Amorosi et al. 2014b) demonstrated that the major river beds of Reno and Savena never reached this area, as attested by the lack in the subsoil of the town of thick fluvial-channel bodies. As a consequence, the geological architecture of the shallowest deposits within the mediaeval walls of the town results from the depositional processes of a network of small creeks and canals (Meloncello, Ravone, Aposa and Fossa Cavallina, in Figure 5), rather than that of the major Reno and Savena Rivers. The sedimentation processes in these coalescing alluvial fans are characterized by low and very low hydraulic energy and the resulting subsoil is mainly composed of fine grained soil (clay and silt mixtures), whereas sandy lenses are rare and the gravels roof deep well over 100 m below the ground level. In addition, the local geological history, characterized by paleoclimate changes, is recorded in the alluvial deposits in the alternation of paleosols and non-pedogenized silty clay deposits (Amorosi et al. 2014b; Bruno et al. 2013). Paleosols are ancient exposed soil layers formed from the interaction with the lithosphere, biosphere and atmosphere, which were buried and incorporated into the geological record. Pedogenetic modifications potentially record a number of physical, biological, chemical and climatic information on the past conditions near the Earth surface. More information on the encountered paleosols can be found in Section 5.2.