Waves, coastal boulder deposits and the importance of the pre-transport setting

The pre-transport environment of a coastal boulder along with its shape, size and density determines the height of wave required for it to be transported. Different forces act on sub-aerial boulders as opposed to submerged boulders when struck by a wave. Boulders derived from joint bounded blocks on shore platforms predominantly experience lift force and require a wave of greater height to be transported than boulders in other environments. No one equation is applicable to determine the height of palaeo-waves responsible for depositing a field or ridge of imbricated coastal boulders. A range of equations and their derivation is presented here which can be applied to the respective pretransport environment of a boulder. Such an approach is necessary when attempting to reconstruct the frequency and magnitude of past coastal wave hazards and for differentiating between tsunami and storm wave deposited boulder fields. (C) 2003 Elsevier Science B.V. All rights reserved.