Decadal‐scale gravel beach evolution on a tectonically‐uplifting coast: Wellington, New Zealand

Abstract

Uplift of the shoreline in tectonically‐active areas can have a profound influence on geomorphology changing the entire process dynamics of the coast as the landforms are removed from the influence of the sea. Over decadal timescales it is possible for the landforms to return to their pre‐earthquake condition and this paper examines the re‐establishment of mixed sand and gravel beaches on the coast of Wellington, New Zealand, subsequent to an uplift event in 1855. Over 60 topographic profiles were surveyed, seven sets of aerial photographs from a 67 year period were mapped and sediment size analyses conducted in order to quantify the nature of beach change following uplift, and associated relative sea level fall. These data were supported by surveys using ground penetrating radar. It is found that uplift raised the gravel beaches out of the swash zone thereby removing them from the littoral zone. Intertidal rocky reefs which occur between each embayment were also uplifted during the same event and completely interrupted the longshore transport system. Continued input of gravel material to the littoral zone allowed beaches to re‐establish sequentially along the coast as each embayment was infilled with sediment. This reconnection of the embayments with the longshore drift system is associated with the beach planform being initially drift dominated during infill but then switching to swash alignment once the embayment becomes infilled. This has resulted in shoreline accretion of over 100 m in some places, at rates of up to 4 m/yr, covering shore protection works built in the past few decades. The ability of the shore to adjust back to its pre‐uplift condition appears to be a function of the accommodation space created during uplift and the rate of sediment supply. Copyright © 2012 John Wiley & Sons, Ltd.

Evolucion geomorfologica y vegetacion costera de playa Palmeras, Parque Nacional Natural Isla Gorgona, Pacifico Colombiano

“…En ambientes costeros de márgenes convergentes el transporte de sedimentos y la geomorfología pueden estar fuertemente influenciados por movimientos verticales donde movimientos cosísmicos pueden hacer cambiar la tendencia de una playa de depositacional a erosiva (Olson et al, 2012). Este tipo de movimientos se ha documentado para la costa continental del Pacífico colombiano (Correa & González, 2000), donde un terremoto en 1991 generó subsidencia que agravó las tasas de erosión de las playas.…”

Geologically controlled sandy beaches: Their geomorphology, morphodynamics and classification

“…For a beach to become relict, a change in base level is required to strand the beach above the reach of modern marine processes, which can be eustatically, glacio-isostatically or tectonically driven (Blackburn et al, 1967;Kidson and Wood, 1974;Sprigg, 1979;Huntley et al, 1993;Alonso and Pagés, 2007;Benedetti et al, 2009;Trenhaile, 2016). Raised beaches are particularly common in tectonically active areas where instantaneous base level change strands beaches so that they can no longer be reworked by contemporary marine processes, such as Turakirae Head (McSaveney et al, 2006) and Wellington (Olson et al, 2012) in New Zealand and Kujikuri, Japan (Tamura et al, 2008). Some geologically controlled beaches are described as 'perched beaches' with various definitions of 'perched' existing from both the geomorphological and engineering literature.…”

The formation of beaches on shore platforms in microtidal environments

“…They also form at the rear of platforms in storm‐dominated environments of England (Robinson, ; Paris et al , ) and at the base of cliffs which are impacted regularly by tropical cyclones such as on Niue (Kennedy et al , ; Marsters and Kennedy, in press). Gravel beaches are also found at the base of eroding cliffs in New Zealand (Olson et al , ) and on either side of the English Channel (Paris et al , ; Regard et al , ).…”