Preservation and Destruction of Holocene Marine Terraces: The Effects of Episodic Versus Gradual Relative Sea Level Change

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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

Section: Discussionmentioning

confidence: 94%

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

Dickson

Omidiji

Litchfield

et al. 2022

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“…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.…”

Section: Discussionmentioning

confidence: 99%

“…Recent numerical modelling by Matsumoto et al (2021) has suggested that a marine terrace formed during earthquake uplift might be more likely to be preserved if the preceding earthquake uplift event was smaller than the tidal range of the coastline. This non‐intuitive result arises in their model because downwearing of a shore platform that has been uplifted only a small amount allows it to be unified with the newly uplifted seafloor, creating an expansive shore platform that is more likely to be preserved as a terrace when it is next uplifted.…”

Section: Discussionmentioning

confidence: 99%

“…The formation of marine terraces from Holocene coseismic 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).…”

Section: Preservation Potential Of Incipient Marine Terracesmentioning

confidence: 99%

“…Holocene marine terraces along tectonically active plate margins provide a record of past co‐seismic uplift preserved as flights of low‐relief terraces (Berryman et al, 2018; Litchfield et al, 2020; Ota et al, 1996; Uesawa & Miyakawa, 2015). 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).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Horton

Stephenson

Dickson

2022

Self Cite

Co-seismic uplift of Kaik oura Peninsula in 2016 has substantially reduced the number of wetting and drying cycles that occur on the shore platforms and the newly uplifted incipient marine terraces. A simple empirical model incorporating field and laboratory measurements was used to determine the number and frequency of wetting and drying cycles. The mudstone supratidal terraces are vulnerable to material disintegration and slaking through sustained drying, and occasional sweeping by storm waves.Overall, wetting and drying cycles have decreased on six of eight field transects, between À8% and À148%, resulting in prolonged drying of the supratidal terraces following uplift (upwards of a 29% increase in annual drying hours). We conclude that accelerated rates of denudation due to enhanced drying post-uplift are likely to return sections of the incipient mudstone terraces to their former intertidal pre-uplift state, potentially removing evidence of the co-seismic uplift event. Terrace preservation, however, will likely be highly variable between locations depending on its inherited morphology, lithological vulnerability, and the timing of any future tectonism.

Holocene marine terraces as recorders of earthquake uplift: Insights from a rocky coast in southern Hawke's Bay, New Zealand

Litchfield

Morgenstern

Clark

et al. 2022

On rocky tectonic coasts, data from Holocene marine terraces may constrain the timing of coseismic uplift and help identify the causative faults. Challenges in marine terrace investigations include: (1) identifying the uplift datums; (2) obtaining ages that tightly constrain the timing of uplift; (3) distinguishing tsunami deposits from beach deposits on terraces; and (4) identifying missing terraces and hence earthquakes. We address some of these challenges through comparing modern beach sediments and radiocarbon ages with those from a trench excavated across three terraces at Aramoana, central Hikurangi Subduction Margin, New Zealand. Sedimentary analyses identified beach and dune deposits on terraces but could not differentiate specific environments within them. Modern beach shells yielded modern radiocarbon ages, regardless of position or species, showing age inheritance and habitat is likely not an issue when dating shells on these terraces. By integrating terrace mapping, stratigraphy, morphology, and radiocarbon ages we develop a conceptual model of coastal uplift and terrace formation following at least two, possibly three, earthquakes at 5490-5070, 2620-2180, and 950-650 cal. yr BP. A high step and time gap between the upper two terraces raises the possibility that at least one intervening terrace is completely eroded. The trench exposure also showed that terrace stratigraphy may differ from that inferred from surface geomorphology, with apparent beach ridges being of composite origin and draping of younger beach deposits on the outer edge of a previous terrace. Dislocation modelling and comparison of marine terrace and earthquake ages from $4 km south and ≤ 73 km north confirms that the most likely earthquake source is the nearshore, landward-dipping, Kairakau Fault. Alternative sources, such as multi-fault ruptures of the Kairakau-Waim arama faults or Hikurangi subduction earthquakes, and/or a combination of the two are also possible and should be examined in future studies.