Review and direct evidence of transgressive aeolian sand sheet and dunefield initiation

Abstract

The multiple hypotheses which exist to explain the initiation of transgressive aeolian sand sheets and dunefields, are reviewed and discussed. Direct evidence supporting many of these hypotheses is largely lacking. In South Australia, the Younghusband Peninsula coastal barrier extends ~180 km and predominantly comprises transgressive and parabolic dunefields. The 42 Mile Crossing area on the barrier is undergoing significant erosion at variable rates of 0.5 to 5.0 m/yr, and a new transgressive aeolian sand sheet has rapidly developed in ~1 year and is extending landwards at an average rate of 13 m/yr. This research provides unequivocal evidence that large‐scale shoreline and dunefield erosion does lead to the development of a new transgressive aeolian sand sheet (and eventual dunefield) phase thereby demonstrating an initiation mechanism that is likely linked to future sea level rise and climate change. We also show that the initiation process, and, in particular, the subsequent rate of sand sheet transgression occurs at an incredibly rapid rate (+100 m in 8 years). Plain Language Summary Coastal sand dunes border many of the world's coastlines and are highly adapted to local climate and conditions. How coastal dunes transition from predominantly vegetated and stable systems to wind‐blown sand sheets and dunefields transgressing prior terrain is a research area of pressing relevance due to forecasts of sea level rise and climate change. The factors or triggers that are considered to initiate transgressive aeolian sand sheets and dunefields are reviewed. The formation and evolution of a new transgressive aeolian sand sheet phase triggered by large‐scale shoreline erosion in South Australia is presented. According to the results from historical and satellite images, local shoreline erosion began in the late 1970s and has continued at highly variable rates. We show that once the foredune was removed, the high scarp created by wave erosion of the relict, vegetated transgressive dunefield destabilized and was then eroded by wind processes leading to the rapid development of a transgressive aeolian sand sheet. The initiation and evolution of the sand sheet provides an excellent example of how dunefields might respond to future sea level rise and climate change.

Post‐wildfire coastal dunefield response using photogrammetry and satellite indices

“…The fires of 2019/2020 burned coastal dunefields across KI, altering the vegetation cover on both semi‐stabilised and fully vegetated dunefields. Fire has been suggested to be a potential initiation mechanism for dune transgression in the literature (Barchyn & Hugenholtz, 2013; Filion, 1984; Filion et al, 1991; Hesp et al, 2022; Matthews & Seppälä, 2013), but following the severe fires of the Black Summer season of 2019/2020, the dunefields of this study clearly show a trend of stabilisation. The dune sites studied here are representative landscapes of burnt dunefields across KI (Figure 1), with results illustrating the post‐fire response of semi‐stabilised foredune–blowout complexes (sites A and B) and previously stabilised parabolic dune/transgressive dunefield sites (sites A, B and C).…”

“…The fires of 2019/2020 burned coastal dunefields across KI, altering the vegetation cover on both semi-stabilised and fully vegetated dunefields. Fire has been suggested to be a potential initiation mechanism for dune transgression in the literature (Barchyn & Hugenholtz, 2013;Filion, 1984;Filion et al, 1991;Hesp et al, 2022;Matthews & Seppälä, 2013) that is used here to demonstrate the progression of these dunefields as they return to a post-fire state.…”

Decadal coastal evolution spanning the 2010 Maule earthquake at Isla Santa Maria, Chile: Framing Darwin's accounts of uplift over a seismic cycle

“…Possibly in this area, the dune advanced further due to the wind shadow resulting from the closer position of the cliff to the beach. Therefore, we propose that analogous processes as those inferred during relative sea-level rise (Brooke et al, 2015;Hesp, 2013;Hesp et al, 2022) have affected the beach during the decade after the 2010 earthquake as a result of 32 cm of land subsidence (Inset in Figure 1c), which fuelled the coastal system with a large volume of available sediment for beach accretion.…”

“…Sea‐level rise often leads to coastal erosion (Bruun, 1962), which eventually delivers significant volumes of sediment to the beach (Brooke et al, 2015; Hesp, 2013; Hesp et al, 2022). In South Australia, a new transgressive eolian sand sheet, and eventually a dune field, was a result of the high onshore sediment supply observed during the 2010s as a consequence of sea‐level rise induced by climate change (Hesp et al, 2022). In another example, erosion induced by a 0.5–1.0 m coseismic subsidence during the 2004 Sumatra earthquake supplied sediment to build a particularly high beach ridge 2 years after the earthquake (Monecke et al, 2015).…”

“…The pre-earthquake dune development at TCUE could respond to a positive balance of eolian sediment input from the southwest, which in turn would depend on other processes, including ISM experienced interseismic subsidence, at an average rate of 10 mm/year between 1835 and 2010, causing a fast relative sea-level rise (Wesson et al, 2015). Sea-level rise often leads to coastal erosion (Bruun, 1962), which eventually delivers significant volumes of sediment to the beach (Brooke et al, 2015;Hesp, 2013;Hesp et al, 2022). In South Australia, a new transgressive eolian sand sheet, and eventually a dune field, was a result of the high onshore sediment supply observed during the 2010s as a consequence of sea-level rise induced by climate change (Hesp et al, 2022).…”