During the 1978 Royal Geographical Society Expedition, the first cavers to explore Deer Cave stated, “This is undoubtedly one of the world’s speleological wonders, for our survey showed that the monstrous passage was 174m wide and 122m high in one section. It is nowhere less than 90m wide and high and it passes right through the mountain for a distance of one kilometre.”
The 1978 expedition report came to the following conclusion; “…it is a strong contender for the title of the largest cave passage in the world.”
As time went on it became clear that Deer Cave did indeed contain the largest genuine cave passage in the world. A further survey in 2009, undertaken by the Hoffman Institute of Western Kentucky University, confirmed the dimensions.
The 2009 survey effort increased the known passage length to 4.1 kilometres and connected Langs Cave, another show cave within the park, to the Deer Cave System. The maximum cross sectional area was in the large southern passage. This was documented at 169m wide with a ceiling height of 125m. The northern passage registered the greatest ceiling height at 148m with a cross sectional width of 142m. The main entrance of Deer Cave was measured at 146m and the Garden of Eden Entrance was measured to be 140m in width. The survey revealed the existence of an un-ascended 305 meter high aven in the roof of the upstream passage. The highest elevation roof passage was measured at 226m above the main cave trail.
Best of all, this speleological wonder can be seen by all visitors to Gunung Mulu National Park. It is only a short walk from the accommodation at Park Headquarters along a raised plank walk to the great cave entrance. Every evening a spectacular natural event takes place here, when millions of bats leave their roosts and exit the cave in great snaking streams across the sky, on their way to distant feeding grounds.
In early 2009, a team caving in Vietnam claimed to have discovered an even greater cave passage, Hang Son Dong. This was excitedly published in newspapers and National Geographic film and magazine became interested. The Vietnam discovery quickly became an accepted truth as the ‘world’s largest cave’, but the expedition never managed to produce any factual evidence to demonstrate that Hang Son Dong was as large as Deer Cave. It later transpired that the largest part of the cave was a surface doline and the cross sectional area had a height quoted from one part of the cave and a width from another. Perhaps the best judgment came from two explorers who traveled directly between the two caves. In their separate opinions there was no part of Hang Son Dong that was bigger than the main passage of Deer Cave. Undoubtedly both are magnificent caves.
The truth of the matter is that there is no accepted measure for the largest cave passage, all is subjective opinion. At the best there is a single cross sectional measure at the widest/highest part. To be definitive a set of criteria would need to be established by which large passages could be compared. This would have to include setting a length over which the passage was measured and then defining average dimensions or a volume, perhaps by laser scanning techniques. Most importantly, it would be necessary to agree a set of rules as to what constitutes a ‘passage’ in the first place otherwise Nasib Bagus (Sarawak Chamber) would surely be the largest passage in the world at 700m long, 400m wide and 100m high. Along with Api Chamber, at 300m long, 200m wide and 120m high, these great chambers are just large sections of a collapsed passage. So, if we exclude these types of chambers then we should be careful what passage elements we do include such as junctions, skylights, avens, alcoves and cross rifts which all distort the true dimensions of a borehole-like passage.
Unlike the longest cave in the world, where one cave stands out way above the rest, the largest known passages of Deer Cave, Gebihe System, Hang Song Dong, Gruta do Janelao etc. are more difficult to compare. As it was in 1978 it is the same today, Deer Cave is still a strong contender for the title of the largest cave passage in the world.