Large boulders along Alam El Rom rocky beach on the Mediterranean coast of Egypt as evidence for high-energy WavesMagdy Torab, Noura Dalal, Nourhan Nour An accumulation of large boulders was recently discovered along the rocky coast of Alam El Rom area located east of Marsa Matruh city between 3 & 7 km, and west of Alexandria city of about 280 km, on the Mediterranean coast of Egypt, in an area exposed to N and NW wave regime. This study measures the size, shape, position, pre-transport setting and long-axis orientation of 292 boulders found on 5 separated positions along the study area. We have investigated the megablocs on the study coastline, the volumes of the blocks have been calculated and main morphometric characteristics measured (orientation of the long axis, volume, distance from the coast etc.). The energy necessary to transport these blocks is presently being modelled. Present research suggests that the maximum number of blocs is around 12m3 and the maximum distance from the coastline around 45 m. We used wave transport equations as well as statistical analysis of boulders in order to determine both extreme events using the significant wave height and period of maximum observed storms and historical tsunamis along the study area as a part of The Egyptian Mediterrean Coast. These megablocs were deposited by the sea waves during winter storms or by paleo tsunami mega waves and most of these boulders were uprooted from the marine platform and distributed within 55 m of the shoreline, are found up to 4 m above present mean sea level. Most boulders are rectangular, with sharp, broken edges, most blocks consist of limestone and sandstone fragments up to 14 m3 in volume and 43 ton in weigh, some of these blocks were observed by local people to have moved after strong winter storms. The objective of this work is defining systematic characterisation of the high-energy depositional contexts working both on the type of storm or paleo tsunami deposit and the different geomorphological contexts, and to reconstruct the history of megabloc deposition along the study area, using chronostratigraphy methodology, it will aid in evaluating the risk of submersion in an area that is affected by storms and tsunamis. The consequences on the occupation of the coastline are important, such as the destruction of Alexandria's ancient lighthouse. Our future work on the same area will be Dating of mega blocks characteristic of high-energy events (storms or tsunamis) using fixed marine bioconstructions. We wish to evaluate sedimentological impacts and natural hazards associated with these events (submersion, coastal mobility, erosion, high-energy impacts). The primary results show that both possible processes (storm and tsunami waves) can deposit these boulders, specially the Mediterranean coast of Egypt has recorded a number of seismic or tsunami events during the Holocene (tsunamis of 23 AD, 365 AD, 746 AD, 881 AD, 1202 AD, 1303 AD, 1870 AD and 1908 AD attested at Alexandria (east of the study are for about 290 km) for example by the archaeological excavations and historical sources, (Guidoboni et al., 1994). |
