I dont see that he is "self arresting" as the ice axe seems to be just 'in hand' rather than in use. To me it looked more like he was just leaning forward in the act of going up hill and the rear leg has come against the natural compression of the snow at the end of his stride. The snow condition looks like it is quite stable ( at least from memory of working in the high country in the 60's) so the ice axe looks to be in hand because it is just as easy to carry it that way. My first thought on seeing the pic was military and the rifle is in hand for that reason but looks to have been used as a balancing "aid" as well. JMHO.