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Nat. Hazards Earth Syst. Sci., 16, 737-756, 2016
https://doi.org/10.5194/nhess-16-737-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
16 Mar 2016
Boulder accumulations related to extreme wave events on the eastern coast of Malta
Sara Biolchi1, Stefano Furlani1, Fabrizio Antonioli2, Niccoló Baldassini3, Joanna Causon Deguara4, Stefano Devoto1, Agata Di Stefano3, Julian Evans5, Timothy Gambin6, Ritienne Gauci4, Giuseppe Mastronuzzi7, Carmelo Monaco3, and Giovanni Scicchitano3,8 1Dipartimento di Matematica e Geoscienze, Università di Trieste, Via Weiss 2, 34127 Trieste, Italy
2ENEA, UTMEA, Casaccia, Rome, Italy
3Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Sezione Scienze della Terra, Università di Catania, Corso Italia 57, 95129 Catania, Italy
4Department of Geography, University of Malta, 2080 Msida, Malta
5Department of Biology, University of Malta, 2080 Msida, Malta
6Department of Classics and Archaeology, Archaeology Centre, University of Malta, 2080 Msida, Malta
7Dipartimento di Scienze della Terra e Geoambientali, Via Orabona 4, Università di Bari, 70125 Bari, Italy
8Studio Geologi Associati T. S. T., Via Galliano 157, Misterbianco (Ct), Italy
Abstract. The accumulation of large boulders related to waves generated by either tsunamis or extreme storm events have been observed in different areas of the Mediterranean Sea. Along the eastern low-lying rocky coasts of Malta, five sites with large boulder deposits have been investigated, measured and mapped. These boulders have been detached and moved from the nearshore and the lowest parts of the coast by sea wave action. In the Sicily–Malta channel, heavy storms are common and originate from the NE and NW winds. Conversely, few tsunamis have been recorded in historical documents to have reached the Maltese archipelago.

We present a multi-disciplinary study, which aims to define the characteristics of these boulder accumulations, in order to assess the coastal geo-hazard implications triggered by the sheer ability of extreme waves to detach and move large rocky blocks inland.

The wave heights required to transport 77 coastal boulders were calculated using various hydrodynamic equations. Particular attention was given to the quantification of the input parameters required in the workings of these equations, such as size, density and distance from the coast. In addition, accelerator mass spectrometry (AMS) 14C ages were determined from selected samples of marine organisms encrusted on some of the coastal boulders. The combination of the results obtained both by the hydrodynamic equations, which provided values comparable with those observed and measured during the storms, and radiocarbon dating suggests that the majority of the boulders have been detached and moved by intense storm waves. These boulders testify to the existence of a real hazard for the coasts of Malta, i.e. that of very high storm waves, which, during exceptional storms, are able to detach large blocks of volumes exceeding 10 m3 from the coastal edge and the nearshore bottom, and also to transport them inland. Nevertheless, the occurrence of one or more tsunami events cannot be ruled out, since radiocarbon dating of some marine organisms did reveal ages which may be related to historically known tsunamis in the Mediterranean region, such as the ones in AD 963, 1329, 1693 and 1743.


Citation: Biolchi, S., Furlani, S., Antonioli, F., Baldassini, N., Causon Deguara, J., Devoto, S., Di Stefano, A., Evans, J., Gambin, T., Gauci, R., Mastronuzzi, G., Monaco, C., and Scicchitano, G.: Boulder accumulations related to extreme wave events on the eastern coast of Malta, Nat. Hazards Earth Syst. Sci., 16, 737-756, https://doi.org/10.5194/nhess-16-737-2016, 2016.
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Short summary
Along the eastern coast of Malta, the processes responsible for the transport of anomalous large boulders from the sea to the coast were analysed. The wave heights required to transport them from the sea to the coast were estimated using a hydrodynamic approach, while AMS 14C ages were determined from encrusted marine organisms. The combination of the results suggests that the majority of boulders were detached and moved by storm waves, but the occurrence of past tsunamis cannot be ruled out.
Along the eastern coast of Malta, the processes responsible for the transport of anomalous large...
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