A group of Vietnamese and British researchers have suggested caves at the world heritage site Phong Nha Ke Bang in central Vietnam be closed to tourism for a while in order for the stalactites to recover.
The gate to the Phong Nha-Ke Bang caves of central Vietnam.
Two British researchers and four geographers from Vietnam National University in Hanoi said tourism to the caves in the central province of Quang Binh have helped alleviate poverty in the area since opening in 1990.
But they said it was a lucky few who had the chance to see the caves back then, when the stalactites had yet to lose their colors, become dry or covered by moss due to constant illumination required for tourists to see them.
Tourism has had a negative impact on the caves, they said at a recent Vietnam Studies conference in Hanoi.
"The lighting system has caused many stalactites not to be fresh anymore, many masses have become dry," professor Nguyen Quang My said.
"Direct impact from tourists has peeled the cover of the floor at fossilized caves, and caused the underground sand to lose their porous quality.
"Several unreasonable settings in the caves also made them look unnatural and no longer pristine," My added.
The researchers, who said the more than the 500-million-year-old caves are manifestations of grand ecological system with great biodiversity, suggested scientific methods to keep them intact.
Howard Limbert, from the British Cave Research Association, who was the first Westerner to explore the Phong Nha caves and made them known worldwide, including Son Doong as the world's largest cave, said any modern development at the caves must be done in a way which minimizes negative environmental impact.
Any necessary construction needs to be made with natural materials like wood, the power of the lights need to be reduced or there should be no lights and only footpaths should be illuminated, he said.
But before all that, the researchers said the caves need to be closed now, and then regularly, to give time for the natural environment to recover.
Phong Nha-Ke Bang National Park was recognized a UNESCO world heritage site in 2003 for its unique beauty, biodiversity and geological diversity.
But the system of 300 different grottoes and caves was explored years earlier by British scientists, who made it well-known for world records, including the longest underground river, the broadest and most beautiful sand beaches, and the most spectacular stalagmites and stalactites.
UNESCO said in its world heritage assessment that the cave system "displays an impressive amount of evidence of the Earth's history. It is a site of very great importance for increasing our understanding of the geologic, geomorphic and geo-chronological history of the region."