One of Gozo's best known landmarks, Dwejra's Azure Window, which is photographed by countless travellers for its unique rock formation, is slowly ceasing to exist - and pictures sent in by a reader of The Times provide dramatic evidence of this.
Francis Xavier Aloisio sent in two photographs - one taken in 1977, the other in 1999 - which expose the extent of the deterioration of the window by the natural process of erosion, assisted possibly by human intervention.
The matter was referred by The Times to George Zammit Maempel, a respected geologist in Malta and abroad, who said nobody could say exactly how much longer the Azure Window would resist the elements.
However, one thing was certain - the Azure Window was doomed to collapse and one day all that would be left of it would be its two columns, he said.
"This is the fate of all the windows. Erosion is what created them in the first place and nothing can be done to protect the Azure Window, except to prevent people from causing any harm that will hasten the process," he said.
Dr Zammit Maempel pointed out that previous abseiling activities which used to be organised from the top of the window had only served to damage the structure by placing unnecessary additional pressure on the rocks.
"The natural forces and stresses on the rock formation, coupled with the hammering of violent seas, wind and storms will continue to eat at the rock's different layers," he said.
Thousands of years of erosion by the sea have created this monumental limestone archway at Dwejra Point. In Maltese it is known as the Tieqa Zerqa.
Today the window is a magnet for photographers and a divers' dream, with hundreds of foreigners planning their holiday around a dive close to the window's breathtaking views.
The Azure Window was also prominently featured in the epic 1981 film The Clash of the Titans whose stars included sex symbol Ursula Andress. Its state is seen in the film as similar to the picture taken in 1977 by Mr Aloisio.
In a paper on 'The geology of Gozo', published in the book A Focus on Gozo, Dr Zammit Maempel wrote that compared to Malta, Gozo had a much more varied geology with greater relief contrast and more extensive outcrops of clays.
The elements - wind, water and sea - all have a destructive effect on rocks and cause weathering and erosion, yielding characteristic surface features, he wrote.
The article also points out that since the lower coralline limestone rocks are hard and well stratified, sea caves tend to have a horizontal roof. If cave formation is in a narrow headland, the opening or cave formed tends to extend to the other side, to form a window.
"Windows are doomed to collapse in time, for the wider they get, the greater the tendency for them to develop a tension crack at the middle of their lintel (the horizontal rock-bed bridging the open space), gradually leading to their collapse and the formation of an isolated column," Dr Zammit Maempel said.
Another window, which is nowhere near as well known or photographed as the Azure Window, has also developed in the lower coralline limestone at Wied il-Mielah, also in Gozo.
Dr Zammit Maempel said that both these windows have already developed the ominous median crack on their horizontal lintel, "so their fate is already sealed".