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From Dôme de la Lauze to Trifides: warm-up. From Dôme de la Lauze (3568m), you reach Col de la Lauze (3512m) and diagonally traverse to the right towards the northeast, under Pic de la Grave and Pointe Marie-Louise. Pass above a serac bar and descend the northeast slope via a steep (40°) but little exposed wall. You can then reach the Trifides ski lift without difficulty.
Upper part of Grand Couloir: Pointe Trifide - Glacier du Vallon. This part has a very alpine access. Below the top of the Trifides ski lift, you reach the crest which connects Col des Ruillans to Pointe Trifide. To reach the corridor, go up the rocks of the ridge for a few meters in the direction of the Pointe (East). Descend this straight corridor which shrinks towards the bottom (40° for 200m) to reach Glacier du Vallon. You can avoid this part by directly accessing Glacier du Vallon from the top station of Col des Ruillans (3211m): just head completely north on the classic Vallons de la Meije route and traverse to the right (East) as soon as possible.
Lower part of Grand Couloir des Trifides (Trifides 1): under Glacier du Vallon. This corridor is clearly visible from the tram cars. It is important to locate it well and to observe the skiing conditions (powder, hard, lumpy snow...) as well as the continuity of the snow cover and number of skiers. Binoculars are useful. Staying to the right in the broad scoop of Glacier du Vallon, you reach a characteristic shoulder (3050m) which dominates a north facing funnel-shaped doline. This is the entry to Grand Couloir (lower part). Shortly after, in an elbow on the left, the corridor narrows and forms a steep pitch (from 40 to 45°) sometimes badly snow covered. With weak snow cover, you have to jump or...climb back up!). After the corridor is more regular (35°) but its line is curved towards the right. Skiing on hard snow therefore generally ends in the left bank rocks....
Variants of the lower part. They are all more technical and more exposed. Falls prohibited! - Couloir de l'épaule (Trifide 0). Before reaching the shoulder 3050, pull to the north to reach the rock ridge. Then take the northeast side slopes intersected with rocks to reach the base of Grand Couloir. - Couloir Médian (Trifides 2). At the shoulder, traverse horizontally towards the right (East) and cross a small ridge passing between rocks. Descend it (40°, narrow at the top sometimes with rocky slab outcroppings) until around 2900m. From there, either traverse on the left (north) to reach the end of Grand Couloir, or continue in the main part. The end of the corridor is cut by a rock band. A weak point on the left bank makes it possible to traverse to reach the main part of the corridor and from there easily to the moraine. - Couloir to the South (Trifide 3). Before the shoulder, traverse on the right (east) under the rocks resulting from Pointe Trifide (3090m). You then reach a broad snow slope suspended above the bars. Descend it diagonally to the right and leave on the right via a broad ledge. At the end of this is the final corridor (45°), which is not always entirely snow covered. Check it out before you take it otherwise you may be in danger of being blocked on the last rock band!