Seismic Signature of the Azure Window Collapse, Gozo, Central Mediterranean

Galea, Pauline; Bozionelos, George; D’Amico, Sebastiano; Drago, Aldo; Colica, Emanuele

doi:10.1785/0220170115

Cited by 12 publications

(21 citation statements)

References 17 publications

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“…During the storm of 7-9 March 2017, strong north-westerly winds reached speeds of c. 72 km h -1 off Gozo's northwest coast generating wave heights of up to 3 m and these factors combined to cause the arch to collapse (Galea et al 2018).…”

Section: November 2014mentioning

confidence: 99%

“…At 09:32:11 LT on 8 March and to the surprise of local people and scientists, the stack collapsed with a 'loud whoomph' into the sea below, with scientists estimating that c. 38 million kg of rock was involved (Anon 2017b;Caruana 2017;Galea et al 2018). Following a report by Gatt (2013) fines were levied and fences and later security officers were hired to protect the arch from continued erosion from tourist foot-fall and tourists from the dangers posed by the rapidly eroding arch (Satariano and Gauci 2019).…”

Section: November 2014mentioning

confidence: 99%

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A Multi-Hazard Historical Catalogue for the City-Island-State of Malta (Central Mediterranean)

Main

Gauci

Schembri

et al. 2021

Preprint

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The city-island-state of Malta is traditionally viewed as a low-hazard country with the lack of a long historical catalogue of extreme events and their impacts acting as an obstacle to formulating evidence-based policies of disaster risk reduction. In this paper, we present the first multi-hazard historical catalogue for Malta which extends from the Miocene to 2019 CE. Drawing on over 3,500 documents and points of reference, including historical documentary data, official records and social media posts, we identify at least 1,526 hazard events which collectively have caused the loss of at least 661 lives. Recognising that historical materials relating to Malta are complicated by the presence of a strong temporal bias, we establish a four-point reliability indicator and apply this to each of the 1,062 recordings, with the result that some 78 % show a high degree of reliability. For an island state where there are significant gaps in the knowledge and understanding of the environmental extremes and their impacts over time, this paper addresses and fills these gaps in order to inform the development of public-facing and evidence-based policies of disaster risk reduction in Malta.

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Section: November 2014mentioning

confidence: 99%

Section: November 2014mentioning

confidence: 99%

A Multi-Hazard Historical Catalogue for the City-Island-State of Malta (Central Mediterranean)

Main

Gauci

Schembri

et al. 2021

Preprint

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“…In aerial digital photogrammetry, the camera is generally installed on Unmanned Aerial Vehicles (UAVs), aeroplanes, or satellites (Li et al 2003). The recent advancements both in terms of technology and software developments have given a boost to such applications in several fields (e.g., Colica et al 2017;D'Amico et al 2017;Galea et al 2018;Remondino et al 2011;Casella et al 2017;Menegoni et al 2019;Westoby et al 2012). Primarily, photogrammetry has been used in geosciences for the reconstruction of landforms; for example, digital elevation models (Fonstad et al 2013), topographic and surface models (Heng et al 2010), and geomorphological investigations (Chandler 1999;Lane 2000;Grosse et al 2012;Menegoni et al 2019;Wu et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Using unmanned aerial vehicle photogrammetry for digital geological surveys: case study of Selmun promontory, northern of Malta

et al. 2021

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In recent years, we have been witnessing the widespread use of low-cost, increasingly high-performance Unmanned Aerial Vehicles, or UAVs, equipped with a large number of sensors capable of extracting detailed information on several scales and in an immediate manner. This study was motivated by the need to perform a geological survey in an area with difficult physical access, and to compare the results with those from conventional surveys. Here we used a Multirotor UAV equipped with a high definition RGB camera and the digital photogrammetry technique to reconstruct a three-dimensional model of the Selmun promontory, located in the northern part of the island of Malta (central Mediterranean Sea). In this area, the evident cliff retreat is linked to landslide processes involving the outcropping geological succession, characterized by the over position of stiff limestones on ductile clays. Such an instability process consists of a lateral spreading associated with toppling and fall of different-size rock blocks. Starting from the 3D model obtained from the UAV-photogrammetry, a digital geological-structural survey was performed in which we identified the spatial geometry of the fractures that characterize the area of the Selmun promontory by measuring strike, dip and dip direction of the fractures with semi-automatic digital tools. Furthermore, we were able to measure the size and volume of singularized rock masses as well as cracks, and their sizes were mapped in a GIS environment that contains a large number of digital structural measures. It is the first application of this type for the Maltese islands and the results obtained with this innovative digital methodology were then compared with those of the traditional field survey of the same area acquired during a previous campaign. This study demonstrated how the innovation of digital geological surveying lies in the possibility of mapping areas and geological features not detectable with traditional methods, mainly due to the high risk associated with the stability of the cliff or, more generally, the inaccessibility of some sites, therefore allowing the user to operate in safety and to detect in detail the most remote rocky outcrops.

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“…Sustainability 2021, 13, 12538 2 of 21 toring methods (geophysical, structural, gemorphological, photogrammetric) in a single site: the Wied il-Mielaħ Window (Figure 1d), located 5 km north-west of Victoria, (Gozo-Malta; Figure 1a-c). The stability and conservation of the window have been a primary concern of local authorities, since the famous Azure Window has collapsed [1,2]. As often happens over the years, the structure has progressively deteriorated; consequently, due to climatic events, water infiltration has led to an increase in humidity and rock degradation.…”

Section: Introductionmentioning

confidence: 99%

“…The development of these studies, focusing on preventing structural failure of the roof, has a very important application in natural heritage protection. The stability and conservation of the window have been a primary concern of local authorities, since the famous Azure Window has collapsed [1,2]. As often happens over the years, the structure has progressively deteriorated; consequently, due to climatic events, water infiltration has led to an increase in humidity and rock degradation.…”

Section: Introductionmentioning

confidence: 99%

Stability Assessment and Geomorphological Evolution of Sea Natural Arches by Geophysical Measurement: The Case Study of Wied Il-Mielah Window (Gozo, Malta)

et al. 2021

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The Wied il-Mielaħ Window (Gozo–Malta) is a limestone natural arch on the north-western coast of the island of Gozo in Malta. It is located at the end of the Wied il-Mielaħ valley north of the village of Għarb. This natural arch is less well known than the Azure Window, which collapsed in March 2017 following a heavy storm, but notwithstanding, it is an imposing and important natural monument too. In the past, the Wied il-Mielah valley was responsible for discharging wastewater from the surrounding localities to the Mediterranean directly at the Wied il-Mielah Window. The sewage flag was often clearly visible underneath the archway into the open sea. The natural features of the arch provide an outstanding touristic attraction. To avoid what happened to the Azure Window, a methodology for the evaluation of the collapse hazard, combining passive seismic, ground penetrating radar (GPR), geological/geomorphological surveys and mine engineering methods, is here proposed. In this study, a methodological approach was applied, based on the following: (i) passive seismic method to study the physical–mechanical characteristics of the rock mass that constitutes the window; (ii) GPR method in order to demonstrate the conservation state (i.e., the intensity of fracturing); (iii) geological/geomorphological surveys in order to obtain a crack pattern; and (iv) scaled span empirical analysis in order to evaluate the stability of the arch. The calculation of the safety factor, with a static method, gave a value equal to 3.75 with a probability of collapse of the marine arch within 50 and 100 years.

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Seismic Signature of the Azure Window Collapse, Gozo, Central Mediterranean

Cited by 12 publications

References 17 publications

A Multi-Hazard Historical Catalogue for the City-Island-State of Malta (Central Mediterranean)

A Multi-Hazard Historical Catalogue for the City-Island-State of Malta (Central Mediterranean)

Using unmanned aerial vehicle photogrammetry for digital geological surveys: case study of Selmun promontory, northern of Malta

Stability Assessment and Geomorphological Evolution of Sea Natural Arches by Geophysical Measurement: The Case Study of Wied Il-Mielah Window (Gozo, Malta)

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