Eastern slopes, under the influence of Continental air masses,
receive less annual precipitation. West Glacier’s annual average is
66.5 cm. Babb, a small town east of the park, averages 49.3 cm.
Frequent high winds east of the Divide further reduce moisture
through evaporation.
Exposed to Arctic air masses flowing down from Canada, locations
east of the Divide also suffer more severe winter conditions than do
protected western valleys. Average January temperature is -5°C at
West Glacier, -8° at Babb.
Moreover, 80 percent of the winter days in the western portion of
the park are overcast, a condition almost identical to that of
Seattle, Wash. This serves to moderate winter temperatures and to
minimize evaporation.]
[Illustration: Moss campion and mountain forget-me-not colonize a
fellfield. Fellfields are rocky alpine sites that are slightly less
than 50% bare rock, interspersed with such plant pioneers as cushion
plants, mosses, and lichens.]
[Illustration: High lakes generally occupy cirque basins. These
depressions in the valley bedrock, quarried by glaciers, are deepest
near the headwall where ice thickness was greatest. Cold and deep,
and ice-free only weeks each year, tarns cannot support vascular
plants or vertebrates. Iceberg Lake, shut off from the sun most of
the year by the encompassing 1,000-meter walls of Mt. Wilbur and the
Ptarmigan Wall, is never completely free of ice.]
[Illustration: Lake McDonald, 16 kilometers long, 2 kilometers wide,
and 134 meters deep, is the largest lake in the park. Its basin is
the classic U-shaped glacial valley. Forested lateral moraines on
either shore gently rise 600 meters above lake level.
Going-to-the-Sun Road snakes along the eastern shore, and Logan Pass
lies near the center of the photograph, behind the peaks of the
Lewis Range.]
[Illustration: Subjected to the drying and shaping effects of wind
both winter and summer, this Douglas-fir, growing in the prairie
community near St. Mary, will attain neither the symmetrical shape
nor the great size of the Douglas-firs growing in moister, more
sheltered sites on the western slopes of the Continental Divide.]
[Illustration: Freeze-and-thaw cycles continually fracture and
loosen rocks along joints, making them subject to removal by the
actions of water, gravity, and avalanche. The resulting fans of rock
debris (talus cones) indicate the extent of erosion since the
withdrawal of the Pleistocene glaciers.]
[Illustration: Although moving water is an agent of erosion—the
primary destructive force of mountain masses—it also permits life.
Even small watercourses, such as this freshet, abound with plant and
invertebrate life.]
[Illustration: Going-to-the-Sun Mountain, towering above the St.
Mary Valley, from the trail to Siyeh Pass. The coniferous forest at
its base and the alpine tundra plants at its summit are closely
juxtaposed in space; but if these two communities grew at the same
elevation they would be separated by thousands of kilometers. Hiking
from St. Mary Lake up to Siyeh Pass is going, in effect, from
Montana to the Arctic Circle; but here the life zones are compressed
and sharply divided rather than extended and overlapping.]
[Illustration: Setting moon and snow shelf near the summit of
Heavens Peak. Note stratification of Precambrian sediments.]
[Illustration: Western redcedars line the shores of Lake McDonald.
Because of prevailing air currents from the Pacific coast, winters
in the protected western valleys are moist and comparatively mild,
and this deep body of water freezes over an average of only one
winter in four.]
[Illustration: Moose often follow the spring snowmelt upwards to the
headwaters of drainages. This bull will remain at Thunderbird Pond,
at the base of Brown Pass, until autumn, when it will return to its
Waterton Valley wintering ground.]
[Illustration: Because of the high reproductive capacity of insects
and small mammals, if all their offspring survived the earth’s plant
life would be consumed within one year. This is prevented by natural
controls such as predation and parasitism. The American kestrel
(“sparrow hawk”) feeds primarily on large insects and on small
rodents such as the meadow vole here.]
[Illustration: Gray jays are found in the deep coniferous forests of
the park. In some parks gray jays, or “camp robbers,” loiter about
campgrounds and picnic areas begging or stealing food. In Glacier,
however, they are seldom noticed as they search out seeds, berries,
and insects.]
[Illustration: A generalized predator, the coyote will eat almost
anything, from berries to carrion. When man eliminated most of the
coyote’s enemies and competitors, including the wolf, grizzly, and
cougar, it enlarged its range to fill the void. Intelligent and
social, the coyote thrives despite man’s persecution. Although most
numerous in the prairie community, it ranges up to timberline.]
[Illustration: The spruce grouse is a year-round resident of the
spruce/fir and lodgepole communities. It forages on the ground for
seeds and insects, in winter turning to needles. Several other
species of grouse occupy different habitats in Glacier.]
[Illustration: Chipmunks are found in every community, from prairie
to tundra, in Glacier. Each of the park’s three very similar species
has its preferred habitat. The diurnal counterpart to nocturnally
active mice, which have the same diet of seeds, berries and
occasional insects, chipmunks adapt easily to the presence of people
and become nuisances if encouraged by handouts. Feeding rodents is
dangerous and is harmful to them. By altering their diets and
blunting their cautious instincts, daily exposure to “free lunches”
makes the animals less fit to face the harsh realities of their
natural environment.]
[Illustration: Unlike whitetail deer, which remain in lowland areas
all year, mule deer range upward into high meadows during the
summer. The bucks, especially, are wanderers and travel together.
Velvet antlers, worn during the time of summer sociability, presage
the autumn contests to come.]
[Illustration: The checkerspot butterfly belongs to the most diverse
group of animals on the planet—the insects, whose importance can
hardly be overestimated. They not only help recycle nutrients in the
living community and provide an abundant food base for other
lifeforms, but are instrumental in pollinating most of the earth’s
terrestrial plants.]
[Illustration: Alpine vegetation must be able to survive freezing
temperature during the growing season, since winter conditions are
possible even in summer. Early bloomers, such as the glacier lily,
endure repeated snowfalls during the unstable weather conditions of
June.]
[Illustration: Unlike mountain goats, these bighorn rams will desert
the alpine zone at the approach of winter; they will join other
bighorns congregating in the lower valleys.]
[Illustration: In November bighorn sheep rams end their summer-long
isolation from the ewes, move down from the higher slopes, and begin
a bloodless but taxing ritual of strength and endurance to determine
the harem master. The sharp reports of clashing horns may carry for
kilometers, and the contests continue for weeks until the dominant
ram emerges. (Note the Many Glacier hotel complex in the valley
below.)]
[Illustration: Hummingbirds, like shrews and other small-bodied,
warm-blooded animals, exist at the theoretical thresh-hold of life.
Because of their small size, body volume is not large enough in
relation to surface area to prevent a rapid loss of body heat. To
compensate for this, metabolic rates must be high; food is rapidly
processed and used up. Thus, since fat reserves are not practical on
such small animals, they must eat at frequent intervals.
Two species of hummingbirds—the rufous and the calliope—are found in
Glacier. Pictured is a female rufous (which weighs about the same as
a dime) landing on its lichen decorated nest to feed its two young
on a protein-rich mixture of nectar and small insects.]
[Illustration: The insect-eating yellowthroat prefers moist
habitats. Unlike many of its treetop-dwelling relatives, this tiny
(10-11 cm.) warbler is usually seen near or on the ground.]
[Illustration: Bands of bighorn ewes and lambs do not summer as high
as the rams and are often encountered in the scrub-forest zone. Note
the gnarled limber pine in the foreground of this photograph taken
on the south face of Altyn Peak.]
Reaching the mountain wall, the goats scramble upward to a ledge,
sending scree streams pouring from several clefts. Encountering a
narrow, steep snowbank, they do not hesitate but continue across the
slope. Above the rock fingers of this peak the gathering clouds grow
black. A sudden crack of thunder hurries me down the trail.
Although geologically young, the Rocky Mountains in Glacier are composed
of soft sedimentary rocks that are easily assailed by the many agents of
weathering and erosion. If not rejuvenated by continual uplift, these
magnificent peaks will glimmer but briefly in the long memory of the
planet.
Already the sharp countenance of this land is being softened by the
ongoing forces of erosion. Chief among these is water, which attacks the
mountains everywhere. In addition, frost action continually exploits
rock fractures, breaking down blocks of rock into talus and scree.
Avalanche and rockfall sweep down the slopes. Layers of softer rock
erode quickly, undercutting more resistant rock and creating overhangs
which gravity, in time, will collapse.
The lashing rain catches me on this sun-and-storm-contested pass. Ice,
gravity, wind, and especially water—all attack a land that dares the
clouds.