Mt Arthur - New Zealand

HTG Ellis Basin (South Island) Expedition, Jan 1-11 2002

Ghar Parau Foundation Expedition Report

Mount Arthur and the Twins in north west Nelson are host to some of the longest and deepest caves in New Zealand. Of particular note is the Ellis Basin system, currently ranked New Zealand's second longest (28km) and second deepest (750m). The upper part (Tomo Thyme) contains two major stream passages heading uphill under the Twins. In 2001 the Hamilton Tomo Group put a small but highly successful expedition into the field. As well as prospecting below the South Twin, this team also pushed Twin Traverse Tomo towards the Ellis Basin system streams, but unfortunately the route became too tight at –350m. Nevertheless it is now New Zealand's eighth deepest cave, and if it had connected to the Ellis Basin system would have created an 1100m+ deep system. In 2002 a new expedition was planned with the twin objectives to prospect the other side of the North Twin from Twin Traverse Tomo and push the upstream passages in Tomo Thyme. Participation in the second expedition was supported by a grant from the Ghar Parau Foundation.

The 2002 expedition ran from January 1–11, with a base camp located next to the Tomo Thyme entrance. We had on average 18 people in camp. Despite poor weather, we were pleased that both objectives were largely completed. Unfortunately though, no new entrances into the Ellis Basin system were located, nor did we discover anything as significant as Twin Traverse Tomo the previous year. For the first objective only two shaft systems were found to get past the usual problems of alpine karst (snow plugs and scree). Although it is likely they connect with the Ellis Basin system since they carry strong inward drafts, both end in impassable passages similar to Twin Traverse Tomo. For the second objective, good upstream progress was made in Tomo Thyme from –250m by bolting, until time ran out. A number of additional outstanding leads in Tomo Thyme were also followed up and surveyed.

Additional funding for CPC participation was obtained from the CPC special projects fund (£600).

Sponsorship in the shape of extra baggage allowance was obtained from Singapore Airlines and Malaysian Airlines.

Postscript

In 2010 a team led by Kieran McKay pushed 3010 to a connection with Tomo Thyme, thereby creating New Zealand's first 1000m+ deep system.

Mike Bertenshaw at a junction at the start of Black Sheep Highway in Tomo Thyme.

Blue helictites at the end of Black Sheep Highway.

Shaft systems explored in 2002 in the upper Ellis basin karst field on the North Twin.

Scales are all metres.

View looking SW over the Ellis Basin karst from NZ grid ref M27 825 971. The North Twin is the summit in cloud. Twin Traverse Tomo lies behind the ridge indicated. The distance from Tomo Thyme to the North Twin is about 1km.

Post expedition fun: Tom Chapman descending the 175m entrance pitch of Harwood's Hole, Takaka Hill.

Adapted from CPC Record 68, 37-45 (Oct 2002).