Observations of the incipient and penultimate stages of Holocene marine terrace development

Abstract

Flights of Holocene marine terraces are useful for reconstructing past earthquakes, but coastal erosion can remove terraces from the landscape, potentially leading to incorrect estimates of earthquake magnitude and frequency. Relatively little effort has been afforded to studying terrace erosion processes, and this paper presents the first field evidence that we are aware of documenting terrace erosion rates. Two case studies from New Zealand provide a unique opportunity to observe the beginning and end phases of terrace development. We present downwear and backwear erosion measurements, showing that both sets of processes are important. Microerosion meter measurements from Kaik oura Peninsula, South Island, confirm that downwear processes are modifying new marine terraces that were created when the

Changes in shore platform wetting and drying cycles following the 2016 Kaikōura earthquake: Implications for incipient marine terrace evolution

“…Of the surveyed platforms post‐uplift, only KM4 and KM6 have multiple intertidal field sites that are still active within the long‐term erosion monitoring programme (Dickson et al, 2022; Kirk, 1977; Stephenson et al, 2019). KM6, a poorly bedded mudstone, has three active MEM monitoring sites within the intertidal zone (a subset of the data presented in Table 5).…”

“…Contrasting results are found for limestone platforms. At KM4, the four intertidal MEM monitoring sites on indurated Amuri limestone have decreased erosion rates (Dickson et al, 2022; Stephenson et al, 2018), despite an increase of 73% in annual wetting and drying cycles and a 214% increase in drying hours. On limestone platforms, wetting and drying effects are less destructive as an isolated weathering process, and limestone is more vulnerable to salt weathering and chemical pitting (Alves et al, 2021; Beck & Al‐Mukhtar, 2014).…”

“…The formation of marine terraces from Holocene co‐seismic uplift, their longevity in the contemporary environment, and vulnerability to denudation provides insight into the potential of such landforms to act as records of Holocene palaeo‐earthquakes (Litchfield et al, 2020; Pedoja et al, 2014). However, within suites of marine terraces, there may be ‘missing’ terraces (Dickson et al, 2022; Howell & Clark, 2022; Litchfield et al, 2020; Matsumoto et al, 2021). Combining the model of wetting and drying cycles with observations of erosion rates on the platform at Kaikōura, it is evident that contemporary processes are relevant to elucidating landform preservation and determining if post‐uplift changes in wetting and drying cycles can remove incipient marine terraces.…”

“…Of the surveyed platforms post-uplift, only KM4 and KM6 have multiple intertidal field sites that are still active within the long-term erosion monitoring programme (Dickson et al, 2022;Kirk, 1977;…”

“…Uplifted platforms are exposed to sub‐aerial weathering and, if still at low elevations, they are also exposed to erosion by waves and wetting and drying cycles (Kennedy & Beban, 2005; Matsumoto et al, 2021). There has been little opportunity, however, to observe waves, tides, and sub‐aerial weathering on recently uplifted shore platforms to understand the erosional processes that operate immediately following uplift (Dickson et al, 2022; Stephenson et al, 2017). The most potent erosion agent is water, which controls mechanical and chemical weathering processes, as well as enhancing erosion through wetting and drying cycles (Hall & Hall, 1996).…”