(From Mercedario South Face base camp)
Entry to the south face route is the gully leading to the North at the base of the scree slopes that provide access to the south face of Mercedario. Follow the gully for approx one and a half hours, avoiding the steeper sections by traversing along the scree slopes to your east and west. The gully is fairly simple to ascend until you reach the lower glacier, where a thin sheet of scree on top of the ice must be carefully negotiated. There are quite a few crevasse in this area however most are filled with scree and pose no real danger. The real danger in this area is the scree slopes themselves. These slopes are highly unstable and vast areas shift with each step, take care ascending in this area.
As you reach the lower glacier, be sure to refill your water bottles from the small melt streams, this is the last liquid water on Cerro Negro.
The route follows the right hand side (east) of the couloir. Be sure not to take the western side, there are many crevasse and the rock fall danger is considerably higher on this side. You will notice from the base of the route that there is a snow field leading to up to the east, towards the summit at about 75% of the route. You are able to take this path, however you will have to negotiate small sections of steep rock and scree. It may be easier to continue directly up towards the summit ridge.
The ascent to the Rimaya or Berschgrund crevasse is on snow at about 40degrees. Switchback across the slope until you reach the crevasse, finding a suitable place to make a safe crossing. The crevasse at time of writing (December 2004) runs the width of the couloir and is approx 2m wide and with the upper lip standing about 2m from the lower. Cross to the far right of the crevasse near the rock band. You may wish to belay over this section but its not always necassary, use your discretion.
Above the crevasse is a 20m steep section of Penitentes, take care in climbing over these and head towards the middle of the couloir, the snow in this area is easier to climb than continuing up the Penitentes section. Once you are through this section, head back towards the rock band on the East side. You must take great care for the next several hundred metres, rock fall is a real threat here. The rock fall tends to start at around 7am and continues steadily until mid morning easing off at about 11am.
The route gains to about 60degrees as you reach the seracs, you may wish to belay some sections here, use the rock bands for resting if required. The seracs line the route and it will take between 5 and 7 hours to pass them. If you choose to take the snow slope to the east towards the summit, there are several false entry points, the proper entry to this slope is well above the serac line. Or continue directly to the summit ridge.
We chose to take the snow slope to the summit, this slope is very steep and quite exposed in some sections. Do not try to abandon the route via descending this slope for at its base are sheer cliffs dropping away more than 1000m to the valley floor. The slope is mixed hard ice and deep snow with a few small rock bands intersecting. The ascent of this slope is quite committing and exhausting. Work your way up towards the East side of this slope for exit to the summit ridge, you will pass through a very rocky area with deep snow and ice about 100m below the summit.
The summit is a small rocky platform approx 50m2. The reward is stunning views to the south of Cerro Ramada 6,400m, Cerro Alma Negra 6,140m, Cerro La Mesa 6,200m, Pico Polaco 6,000m and on the horizon, the massif of Aconcagua 6,965m. To the west you have an awe inspiring view of the sheer Caballito Glacier on Cerro Mercedario, a highly demanding climb, and to the North & West the 7 peaks of the Ansilta range backdropped by the plains extending beyond the horizon.
The south face route is a one day route, there are very few areas suitable for placing a camp (if any), you should leave base camp no later than 4am to begin the ascent at first light. DO NOT attempt this route any later than 7am, the rock fall hazard is too great by this time. The route gains more than 2,200m and takes between 13 and 19 hours from base camp to base camp. Be sure to take plenty of food and water with you.
South Face Descent Route / Normal Ascent Route
Descending from the summit, follow the ridge line down towards the wide snow/scree field. You will have to descend the Upper eastern flank of Cerro Negro, which is a long, steep snow and ice slope until reaching the flatter area. Continue along the flat staying clear of the edge (there are large cornices in some places) until you reach the large red valley, which is approx 500m east of base camp. Descend the eastern side of this valley, following the Guanacos trails.
Take great care this entire valley is loose scree and mud, you will see evidence of large landslides and rock avalanches here. There are many trails leading to the valley floor here, when you reach the melt water stream in the centre of the valley follow this down, switching sides as required until you see the clear trail on the western side. Follow this trail around to the west (Mercedario side) it will descend over large scree slopes ejecting you almost directly opposite base camp.
If you are ascending via the normal route, simply follow the above in reverse order. Make sure you take crampons and at least one non technical axe and trekking poles.
Be sure that you take 2 technical axes, ice screws, a couple of snow stakes, helmets and the usual equipment.
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