Boulder accumulations related to extreme wave events on the eastern coast of Malta
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 mapp...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-03-01
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| Series: | Natural Hazards and Earth System Sciences |
| Online Access: | http://www.nat-hazards-earth-syst-sci.net/16/737/2016/nhess-16-737-2016.pdf |
| Summary: | 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Conversely, few tsunamis have been recorded in historical documents to have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.
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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.
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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) <sup>14</sup>C 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 m<sup>3</sup> 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. |
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| ISSN: | 1561-8633 1684-9981 |