Imbricated Coastal Boulder Deposits are Formed by Storm Waves, and Can Preserve a Long-Term Storminess Record

Abstract

Coastal boulder deposits (CBD) are archives of extreme wave events. They are emplaced well above high tide, and may include megagravel clasts weighing tens or even hundreds of tonnes. But do they represent storms or tsunami? Many are interpreted as tsunami deposits based simply on clast size and inferences about transport, despite the fact that there are no direct observations documenting formation of these inbricated boulder clusters and ridges. In this study, we use force-balanced, dynamically scaled wave-tank experiments to model storm wave interactions with boulders, and show that storm waves can produce all the features of imbricated CBD. This means that CBD, even when containing megagravel, cannot be used as de facto tsunami indicators. On the contrary, CBD should be evaluated for inclusion in long-term storminess analysis.

Measuring Change Using Quantitative Differencing of Repeat Structure-From-Motion Photogrammetry: The Effect of Storms on Coastal Boulder Deposits

“…CBD are also located in both western and northeast Australia [66,79], Iran [80], Oman [81], the Philippines [67,68,82], the Caribbean [71,[83][84][85][86], South Africa [87], and elsewhere. Until recently, however they received little attention: about 90% of published studies are from the last 18 years [88]. (Figure 1).…”

“…The Aran Islands are of particular interest in this context because waves generated by intense storms have recently been shown to deposit and rearrange CBD along the Atlantic-facing coasts of all three islands [65,88]. Recognition that these deposits are currenty active has made them a focus for studying the energetics and effects of high energy storms [95,96].…”

Coastal Boulder Deposits of the Neogene World: A Synopsis

“…On the other hand, boulders are regarded as precious evidence of present and ancient rocky shore facies and extreme events (such as storms, tsunamis, hurricanes, typhoons, and cyclones). This evidence has been examined by Autret et al [5], Bhatt et al [6], Biolchi et al [7], Cox et al [8][9][10], Dawson [11], Engel et al [12], Erdmann et al [13], Hearty and Tormey [14], Herterich et al [15], Hongo et al [16], Johnson et al [17,18], Kennedy et al [19], Kortekaas and Dawson [20], Lau et al [21], Olsen et al [22], Paris et al [23], Pepe et al [24], Scheffers et al [25], Schneider et al [26], Shah-Hosseini et al [27], Suanez et al [28], Terry and Goff [29], Terry et al [30], Trenhaile [31], Watanabe et al [32], and Weiss and Sheremet [33]. Most probably, the devastating catastrophes like the 2004 Indian Ocean tsunami [34] and the 2011 Tohoku tsunami [35] have fueled the interest of researchers in coastal sedimentology and, particularly, large clasts [36].…”

“…Consideration of the context of its usage in the journal articles permits outlining some characteristics of such a sedimentary formation. These include, particularly, accumulation of boulders distinguished by their large size and/or huge weight [9,10,17,18,[25][26][27], angularity with certain roundness [8], high-topography and inland occurrence [8,9,25,27], high-energy coastlines [5,8,15,17], and relevance to storm and tsunami activity [9,10,18,26,27]. It is notable that the previous works focused more on boulders individually rather than on entire deposits.…”

Finding Coastal Megaclast Deposits: A Virtual Perspective

“…Additionally, Cox et al [10] offered a novel approach for measurements of roundness of megaclasts, and, thus, the noted nomenclature development should emphasize not only on grain-size categories, but also on various morphological parameters. The second aspect of coastal megaclast deposits is linked to genetic investigations and, particularly, interpretations of the evidence of past storms and tsunamis (storm-versus-tsunami origin of megaclasts is a popular and hotly-debated topic in the modern sedimentology) [4][5][6][7][8][9][10][11][12][13][19][20][21][22][23][24][25][26][27][28]. Irrespective of which of these aspects and particular opinions to follow, finding new localities coastal megaclast deposits is of utmost importance.…”