The Azure Window at Dwejra is unlikely to collapse in short order, although rock fall will persist, a geological study commissioned by the Environment Ministry has found out.

The window – and its stability – has been the subject of several previous studies, but Environment Minister Leo Brincat remarked that he felt the need to commission a fresh study since the existing work had been somewhat inconclusive.

The study was carried out by geologist Peter Gatt, through Geoscience Consulting, with the aim of analysing the stability of the scenic natural arch – which, as historical photos show, has sustained a number of rock falls over the past few decades. Since 1981 the void underneath the arch has actually doubled in size.

Ultimately, natural arches are relatively short-lived geological features, and the Azure Window will face the same fate faced by many others in the past: the arch will collapse and the pillar will become a stack. The nearby Fungus Rock is actually an example of this inevitable process.

But Dr Gatt’s report emphasises that the Dwejra area can be considered to be a unique geological site even if the arch was not present. There are at least six circular sinkholes along this part of the west Gozo coast – even more may exist offshore – the result of collapses resulting from the dissolution of underlying gypsum through the infiltration of water.

The most obvious of these sinkholes is the famed inland sea, while the nearby Dwejra Bay – where Fungus Rock lies – and the Berwin sinkhole in between are also fairly evident. Erosion has claimed much of the area, and the remaining three sinkholes are not as easily discerned.

In light of this finding, Dr Gatt argues that the Dwejra and Azure Window area should be declared a “geopark” to protect its unique geological features. Furthermore, he maintains, the site should be reconsidered as a candidate for listing as a UNESCO World Heritage Site.

As for the arch itself, the use of rock bolts has been brought up, in the past, as a possible way of securing the arch and prolonging its life-span.

But Dr Gatt maintains that large rock bolts intended to secure the entire arch were not recommendable, as there was insufficient stable rock for such bolts to adhere to in order to support the arch. He does note that small blocks at the edge of the arch, which are prone to rock fall, may be bolted, but points out that such intervention can be dangerous due to these blocks’ precarious location and the installation of machinery over the arch.

The dramatic collapse of a large chunk of rock at the edge of the arch last year is arguably the most significant recent evidence of the continuing rock fall, but Dr Gatt actually finds out this was unlikely to affect the arch’s stability, since the span of the bridge remained the same. However, the condition of the base of the pillar, which is being undercut by sea waves, remains unknown.

The arch was considerably thicker a few decades ago, and Dr Gatt notes that it is made of two distinct layers of rock, within the lower coralline limestone formation (zonqor) of the Maltese islands.

The lower layer is more prone to collapse: around 90% of it has disappeared in the past three decades, and the rest is expected to follow over the next few years. But the upper layer is more resilient: although rock falls do take place, these tend to consist of small chunks of rock. This was evidenced, for instance, in a rock fall that took place only last March.

Three blocks of rock have been identified for potential collapses: one is not likely to affect the arch, one would actually lessen its load, and one may affect the stability of the overlying arch in its area. In light of such risks, the report recommends that the existing prohibition of swimming and navigation underneath the arch should be maintained.

Dr Gatt also identifies extension cracks which have been occurring in the southeast part of the arch as a potential risk factor, and is recommending the installation of crack meters which would take monthly measurements.

But ultimately, he predicts that future rock failure along the arch will continue to happen in a piecemeal fashion, with the collapse of rock up to 1 metre across – as opposed to a dramatic instantaneous collapse.

“The Azure Window natural arch is relatively stable and will continue to remain so for a number of years. However, rock fall will persist,” Dr Gatt states in his conclusions.

On his part, Mr Brincat said that it was now up to the ministry’s technical advisors to look into the recommendations made, he said, adding that the ministry’s aim – with all such reports – was to ensure that all recommendations found to be practical are followed up.

He also stressed that the aim was to create a report that was not only fit for experts in the field, but one that could also be easily analysed and scrutinised by the general public. The report is in the public domain, and is available online.