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Geomorphology and Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Giovanni Barrocu, Saeid Eslamian
The following situations may occur: An upstream tectonic block of a watershed is uplifted: a knickpoint in the river profile indicates a local base level, from which erosion proceeds upstream. Consequently, The general base-level remains stable: significant erosion upstream and increased deposition downstream, with possible coastal plain formation, depending on the erosion balance between river and sea.The general base is lowered: activated erosion and downcutting of coastal plain and terraces formation, whereas headward erosion continues upstream of the knickpoint, which recedes towards the source.Subsidence of a coastal tectonic block or sea-level rise occurs due to deglaciation (changing climate). There is Erosion upstream of the knickpoint and deposition downstream: coastal plain and delta advancement, depending on the load.The danger of floods in the coastal plain with temporary or stable humid areas consisting of coastal ponds of fresh and brackish water and swamps.
Quaternary uplift and fault movement near Waitomo, North Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2023
The only process likely to have had sufficient energy to cause the large collapses inside the cave is seismically generated ground shaking, probably associated with the adjacent Okohua fault (Figures 5 and 6). The Waipa fault is unlikely to be the source because to reach Ruakuri Cave evidence of its movement would first have to be transmitted upstream through the Glowworm Cave which contains no signature from this event. Minimum vertical displacement can be estimated from the 5 ft waterfall (1.5 m) in the subterranean Okohua Stream, a knickpoint now about 300 m upstream from the resurgence (Figure 6), although its height would have reduced in the process of upstream migration from perhaps an initial 2 m. Outside the cave, collapse debris lines the foot of the cliff for about 70 m towards the southwest where it blocks the entrance to Holden’s Cavern, a former cliff-foot resurgence passage of the Waitomo Stream. Further to the southwest, the rockfall obscures the entire cliff face.
Landscape evolution of the Blue Mountains revealed by longitudinal river profiles and Cenozoic basalts and gravels
Published in Australian Journal of Earth Sciences, 2020
Two phases of uplift are suggested by the geodynamic models. The initial uplift continued through to ca 80 Ma and is interpreted to be due to the cessation of subduction under eastern Australia and the subsequent opening of the Tasman Sea. The Divide formed during this time and the uplift was followed by a period of relative tectonic quiescence until the second phase of uplift commenced. This is inferred to be related to the northward movement of the Australian plate and is progressively younger towards the south of the eastern highlands. Czarnota et al. (2014) suggested that the second phase of uplift is due to crustal movement over a thermal anomaly in the mantle, which also led to volcanism along the eastern highlands. Alternatively, Müller et al. (2016) and Salles et al. (2017) proposed that the uplift relates to crustal interaction with the large Pacific mantle upwelling. In both scenarios, the modelling of river erosion shows that with the second phase of uplift, knickpoint retreat was initiated in rivers such as the Shoalhaven and Macleay, which flow east off the Divide. Czarnota et al. (2014) also suggested that development of the Great Escarpment began at this time. In the vicinity of the central highlands of NSW, the second phase of uplift began at ca 30 Ma (Czarnota et al., 2014, figure 15g, h; Salles et al., 2017, figure 10c).
Structural and morpho-tectonic evidence of Quaternary faulting within the Moutere Depression, South Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2018
Francesca C. Ghisetti, Mike R. Johnston, Paul Wopereis, Richard H. Sibson
The longitudinal profile of the Motueka River has been constructed using elevations from the New Zealand 8 m Digital Elevation Model (LINZ Data Service). The profile (Figure 11A) has a typical concave up shape, with the major gradient change (from average slope of 4.6% to average slope of 0.7%) across the W-FFS, where it superposes the Eastern Province basement rocks onto the Moutere Gravel. The transition to the lowest downstream slope (0.2%) occurs at the junction with the Motupiko River and does not coincide with any lithological boundary. The incised sinuous pattern of the Motueka River within the granites may result from progressive downcutting of an antecedent river through a sequence of now eroded Moutere gravels that covered the presently uplifted units of the Median Batholith. The regular shape of the profile is interrupted by a number of gradient changes (knickpoints). These are especially evident at the intersection with the W-FFS and within its hanging wall region. Other knickpoints along the section of the Motueka River that sharply deflects from S- to NW flow may mark the capture of an older drainage in the Red Hills that is now part of the upper stretch of the river (Figure S3). Within this steepened area the river is strongly incised, with erosion possibly driving the upstream migration of knickpoints (cf. Burbank and Anderson 2001). The only knickpoint in the river across the Moutere Gravel occurs at its junction with the Motupiko River (Figure 11).