Avacha Volcano.

Avacha volcano

The volcano walk is on a single trail, where members can walk as far as they wish and then return down the same trail. People can walk at their own pace, but should avoid walking alone; in case of accidents as trivial as a sprained ankle, it is essential to be in groups of at least three. The camp is at an altitude of about 950 m, and Avacha's summit is at 2741 m. The climb to the rim of the summit crater involves a climb of nearly 1800 m. An easier option is to aim to reach the shoulder on the old crater rim, which offers a lovely stretch of scenic walking, and requires a climb of about 1100 m.
The Avacha trail crosses the stream near camp and then heads up pyroclastic slopes, where stream sections expose stratified lapilli tuffs; these become steadily steeper. There are increasingly good views back to the splendid andesite cone of Koryaksky; this rises to 3456 m and is scored by deep gullies, but its current activity is limited to a few small fumaroles.
The steep part of the trail ends where it turns onto a gently rising shoulder, which provides the delightful walk on an easier gradient. The shoulder is the rim of the early crater, formed when the main mass of the old summit slipped in a gigantic landslide down towards the coast,  followed immediately by a massive lateral blast and eruption. The old has been nearly filled and obliterated by the growth of the new summit cone. It is surfaced with loose cinders which lie over partially welded pyroclastic flows; some sections of channel are filled with lava with rubbly tops to individual flows.
On the ancient crater rim, there is an old vulcanologist'. The newer summit cone rises above, and its northern slope overlaps and buries the old caldera rim, so that the easy shoulder does not continue round. Andesites on the ridge and above have 4 mm augite and 2 mm feldspar phenocrysts. There are views south to the andesite cone of Viluchinsky and beyond to the complex peaks of Mutnovsky and the rounded shield volcano of Gorely; to the north lie the old degraded cones of the Zhupanovsky volcanoes.
The trail to Avacha's summit starts up some snow fields, but then winds up the steep cinder cone. Its surface is mainly loose, red, oxidized tephra, with areas of airfall ashes, and there are some exposures of the underlying welded pyroclastics.
Ascending a volcano.

The summit crater yawned hundreds of meters deep until 1991, when it was filled with andesite lava. The black lava now forms a gentle dome - it is the fresh top of a classic plug dome. Steam rises through its fissured surface, and there are even more fumaroles and solfataras round its edge, at the contact with the crater walls of red pyroclastics. Walk round the rim to the left; giant crescent flow ribs mark the lava's surface where it moved sluggishly east and flowed over the lowest point on the old crater rim. It flowed for a kilometer down the volcano flank, but was so viscous that it came to rest on an angle of nearly 45. Climbing over the blocky andesite is not easy, but a little scrambling reaches some active vents lined with sulphur crystals. The rim to the right overlooks slopes of sulphur deposits, but soon reaches the lava overflow. There are fine views of Koryaksky and all points beyond.
The descent of the summit cone is on a straight steep down-trail alongside the zigzag up-trail; it requires an element of bold scree running, with considerable care where areas of welded tephra tend to promote spectacular somersaults.