Greville Harbour, D'Urville Island, Tasman Bay, New Zealand. Throughout the world, boulder-cobble beaches are commonly associated with high-energy wave environments. However, in eastern Tasman Bay, numerous boulder-cobble beaches are situated in relatively low-energy wave environments, which have persisted throughout the Holocene. These beaches are exposed only at low tide and forma shallow dipping platform that extends seaward for several hundred metres to depths over 20m. Clast counts indicate that the beaches consist of poorly-moderately sorted boulders, cobbles and pebbles, but some boulders are actually greater than 1 m in diameter. These beaches do not fit a world-wide relationship between beach-face slope and particle size.
The boulder-cobble beaches appear to be remnants of ridges that have eroded in situ. Essentially, the beach is the erosional debris of the ridge that can be seen in the center distance of the photo. The remnants of the eroding ridge have been modified by sea level rise and waves, which can move boulders inshore but not consistently along shore. The overall shape and position of the beaches are mostly a product of antecedent geology with minor modifications caused by coastal processes. (Photograph taken July 2020 by Warren Dickinson, Earth Sciences, Victoria University,Wellington, New Zealand.)
Greville Harbour, D'Urville Island, Tasman Bay, New Zealand. Throughout the world, boulder-cobble beaches are commonly associated with high-energy wave environments. However, in eastern Tasman Bay, numerous boulder-cobble beaches are situated in relatively low-energy wave environments, which have persisted throughout the Holocene. These beaches are exposed only at low tide and forma shallow dipping platform that extends seaward for several hundred metres to depths over 20m. Clast counts indicate that the beaches consist of poorly-moderately sorted boulders, cobbles and pebbles, but some boulders are actually greater than 1 m in diameter. These beaches do not fit a world-wide relationship between beach-face slope and particle size.
The boulder-cobble beaches appear to be remnants of ridges that have eroded in situ. Essentially, the beach is the erosional debris of the ridge that can be seen in the center distance of the photo. The remnants of the eroding ridge have been modified by sea level rise and waves, which can move boulders inshore but not consistently along shore. The overall shape and position of the beaches are mostly a product of antecedent geology with minor modifications caused by coastal processes. (Photograph taken July 2020 by Warren Dickinson, Earth Sciences, Victoria University,Wellington, New Zealand.)
