Glancing now in a general way at the formation of snow-banners, we find
that the main causes of the wondrous beauty and perfection of those we
have been contemplating were the favorable direction and great force of
the wind, the abundance of snow-dust, and the peculiar conformation of
the slopes of the peaks. It is essential not only that the wind should
move with great velocity and steadiness to supply a sufficiently copious
and continuous stream of snow-dust, but that it should come from the
north. No perfect banner is ever hung on the Sierra peaks by a south
wind. Had the gale that day blown from the south, leaving other
conditions unchanged, only a dull, confused, fog-like drift would have
been produced; for the snow, instead of being spouted up over the tops
of the peaks in concentrated currents to be drawn out as streamers,
would have been shed off around the sides, and piled down into the
glacier wombs. The cause of the concentrated action of the north wind is
found in the peculiar form of the north sides of the peaks, where the
amphitheaters of the residual glaciers are. In general the south sides
are convex and irregular, while the north sides are concave both in
their vertical and horizontal sections; the wind in ascending these
curves converges toward the summits, carrying the snow in concentrating
currents with it, shooting it almost straight up into the air above the
peaks, from which it is then carried away in a horizontal direction.
Pages:
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65