The southern side of Sumantri is the only aspect of the peak that is not guarded by tremendous cliffs. It also holds the remnant ice of the North Wall Firn. An ascent of these slopes makes for a magnificent and varied outing with a combination of hiking, scrambling, and enjoyable glacier travel. The ice is melting fast so anyone wishing to do this route should do so as close to the present time as possible.
This route and peak make a wonderful addition to a climb of Carstensz Pyramid, and is highly recommended for anyone desiring a little more than the standard trip up that peak. The views are magnificent (weather permitting) and the climbing varied. The final summit block looks daunting, especially when covered in fresh snow, but turns out to be merely a highly entertaining scramble.
The route starts at the Carstensz Pyramid base camp. See the main peak page for information regarding arrival to this point.
The red line is the suggested route. Green indicates a possible alternative approach.
There is one lake right next to the Carstensz base camp and a lake to the east with a narrow bit of land between the two. Begin the climb by walking between these two lakes and then continuing up the valley past a third lake on the right to the base of a wide and loose gully (shown in green on the picture). This can be used as an approach to the glacier, but looks to be less desirable than the route suggested below. Instead of taking this wide approach, continue up the valley keeping at its very bottom past a small pond that nearly stretches from one vertical wall to another. There is just enough room on either side to allow passage while staying on dry land.
Once past this small lake, be looking for the first significant talus cone lining the left side of the valley. It is perhaps 500 meters up the valley and has a distinct trail up its left margin. This is the key to easily reaching the glacier. Climb up the talus cone, and then the gully and slopes above. The route is regularly cairned and works its way in a fairly straight line up the prominent gully system to the toe of the glacier. There is one place where two possible routes options present themselves - each cairned and each usable. They rejoin about a hundred meters higher up.
The route follows the red.
On the summit block traverse.
Once at the base to the glacier, put on crampons and romp up the enjoyable ice slopes above. There are sections with large crevasses to keep things varied and interesting. Trend to the left as you ascend so as to be approaching Sumantri rather than Puncak Jaya which is on the right (and can also be easily climbed from this point). Near the top of the glacier the gradient increases as you climb up and over a broad bulge, then decreases again upon arrival at the high point to the ice.
Work north from the high point of the ice to the rocks beyond. There may be crevasses to navigate. In June of 2010 there was a narrow snow ridge to go along as well.
Summit view to Puncak Jaya (left) and East Carstensz.
The summit block looks like it can be surmounted on its right side, however, the crack beneath this route grows quite wide and deep and the rock quality looks poor. For these reasons, this option is not recommended. Instead, traverse right across the front (South) side of the summit block on an obvious ledge. This looks to be highly exposed and potentially dangerous if covered in snow but this is not the case due to extremely positive holds in the rock. Once across this traverse, follow the weaknesses and shallow gullies up to a final steep wall beneath the summit. Once again, this final passage is significantly easier than it looks. Scramble up to the frighteningly exposed summit and peer down the massive cliffs on the back side. There is a route here if anyone is so inclined...
Descend the ascent route.
Crampons and an ice axe or ski poles.
We brought a rope but did not use it. If there were to be a period of heavy snows, a rope could be desirable on the glacier.
View west from the col between Sumantri and Puncak Jaya.
The summit of Puncak Jaya is an easy glacier walk from Sumantri. Descend to the saddle between the two peaks, then climb the shorter, flatter summitted Puncak Jaya. Once again, the high point is now on rock not ice as was the case back in the day. According to the altimeter that was on the watch that I had, the left (west) summit of this broad peak is one meter higher than the right (east) summit. The east summit has some really cool deep cracks in it though and is worth the effort, however.
In June of 2010, the Amungme had placed a number of lines indicating the edge of their land within the approach gully. It is advisable that you have their approval before crossing these lines.
"Working rule number twenty-three: Go through the motions anyway; you might get lucky."