Gouffre de la Pulpite Irréversible
Northing: 45.314053° Easting: 5.855845° Altitude: 1,900 m
How to find it
Follow the waymarked GR9 from the Col du Coq past the Trou du Glaz onto the plateau above. At the signposted junction follow the path up towards the summit. After about 350 metres there is an obvious spoil heap 40 metres on the left, which marks the location. Note that one source on the web give the altitude as 1,790 metres - this is incorrect.
Further information
Having been identified as a potential entrance from below, Gouffre de la Pulpite Irréversible was dug open in 2010. It has two fully equipped (traverse lines and pull-through chains) routes which connect with the lower storey of Trou du Glaz, the first of which enters from high above Lake Shaft, and the other enters from a meander at the top of P60 (also known as Puits Charles).
The name refers to pulpitis, a dental condition which can result in necrosis creating cavities in the very heart of the tooth…
Pulpite - Trou du Glaz (via Puits Lac)
This is the original and most direct route, and is used for commercial caving. It is not a long traverse, but is flood prone so should be avoided in times of wet weather and snow melt. The narrow entrance shaft is short and broken into three sections, and drops into about 100 m of meander, 20 m of which has been blasted and is restricted (the Tortue Ninja). It enters the impressive Salle du Dôme des Écrins from which a succession of short pitches lead to the main feature, a 145 metre shaft (Puits du Lac) dropped in three stages - 85 m, 20 m, and 40 m. This lands in the main passage in Trou du Glaz below the Lantern shafts. From here, it is possible to exit through Trou du Glaz (4 to 5 hours) by ascending the permanently rigged Puits de l'Ogive into the Trou du Glaz upper story, or join one of the standard through trips from Trou du Glaz.
The best account of the route available on the web is a route guide by Charlie Rivoire of Emergence-spéléo, written in the same style as those of the Spéléo Secours Isère. It has been loosely translated by the author (use at your own risk).
A survey of the passages between Puits du Lac and the bottom of the entrance shafts, with a cross section, is available in the original exploration report by Olivier Dutel in Scialet 38, downloadable from here.
Pulpite - Trou du Glaz (via Puits de l'Erreur 255)
This traverse was made possible when two lines of exploration converged, the first from a meander leading off from the top of P60 in the lower storey (also called Puits Charles), and the second from within Pulpite itself. Once down the Pulpite entrance shaft, the 'upstream' passage is followed (away from Tortue Ninja). It's a complex route which includes a P50, a P80 (Puits de l'Erreur), a P52, and a 400 metre long meander disconertingly named "Y'en a marre!" ("I've had enough!"). The traditional Trou du Glaz route is met at the top of P60.
The traverse is one of the hardest of those documented on this site. It typically takes five to eight hours, and requires 2*55 m of rope. It is fully described in a Spéléo Secours Isère guide (a loose translation by the author is available here, use it at your own risk).
There is an account of the exploration of the connection written by Thibud Galai in Spéléo Magazine 124 (December 2023), available on bone fide request.