“There was quite a substantial breeze coming out. A substantial breeze normally would signify a substantial cave.” A nice piece of Brit understatement about what is a late-breaking entry for a wonder of the world: Vietnam’s Hang Son Doong, the largest cave system on the planet by volume, stumbled upon by jungle logger Ho Khảnh in 1991 and only surveyed in 2009. The stupefying shots here of towering limestone buttes, skylight dolines and sodden subterranean rainforest look computer-generated, like something from Avatar.
Another visitor points out that where other caves echo each other, Hang Son Doong feels like nothing else on Earth. Predictably, this exceptionalism has dollar signs spinning in the eyes of the Vietnamese government and big business, who are sizing up the grotto for a cable car transit system. Alastair Evans’s slightly ungainly documentary (we only get the history of the cave’s discovery 20 minutes from the end) very thoroughly details the campaign to preserve Hang Son Doong in its natural state in the context of Vietnam’s breakneck economic boom in the period since it was discovered.
There’s a noticeable colonial gulf in the gap between tourists, researchers enjoying the cave and the local porters – which Evans, devoting a section to the latter, is evidently aware of. But a second kind of colonialism isn’t so easily dismissed: that of ecologically minded westerners and urban Vietnamese telling rural people who have only just emerged from penury to go easy on the development. Quảng Bình province, where Hang Son Doong is situated, was Vietnam’s poorest, levelled by American bombing and barely redeveloped until the 1990s.
Campaigners – often targets for violent repression by the government – are pinning their hopes on the so-far responsible urbanisation of Phong Nha, the hub for visits to Hang Son Doong. But more than one person in this scrupulous but depressing film concludes that high-density planning and mass tourism in the region are inevitable, the flows of capital as mighty and unstoppable as the water that gouged out the cave. The sublime views feel a bit consolatory after that.
• A Crack in the Mountain is released in cinemas on 26 May.
