On the trail that connects the Logan Pass visitor center to Hidden Lake
overlook there is a shallow pond. Near Hidden Pass, it collects its
meltwater from the Continental Divide and sends it down the shallow
gorge that drains the Hanging Gardens; as a waterfall it plunges into
the upper St. Mary Valley where it becomes Reynolds Creek; joined by
other tributaries, it continues its long journey to Hudson Bay.
The surface of this pond is seldom still, for the wind treats it like a
sea. Because the water is shallow, the wave action wrinkles the bottom
mud into ripple patterns, mimicking the churning waves.
I like to come here early in the morning. Sometimes, arriving before the
wind awakes, I catch reflections of the surrounding mountains. Beyond
the low bench of Logan Pass the Garden Wall begins, running northward
with the Divide. In the eastern valley the pitched peak of
Going-to-the-Sun hunkers in the morning light like a tensed warrior. To
the south, the incisor Bearhat, beautiful cloud cutter of Hidden Lake
Valley, juts above the nearby saddle of the pass. But over this place,
standing as fresh monuments to an age of ice, tower the cliffs of
Clements and the pyramid Reynolds.
I am sitting on a wedge of red rock. Its surface exhibits a wrinkled
pattern identical to the ripples in the soft mud of the shallow pond.
The distance is not great; with a stick I could reach out and touch the
mud. Yet this represents a gulf no bird can fly, for between the ripples
of this rock and the ripples of this mud lie billions of vanished
mornings, a constellation of years.
These red, green, tan, white, black and purple bands of rock that layer
Glacier’s mountains comprise the oldest unaltered sedimentary rocks on
Earth. They were laid down in Precambrian time, more than a billion
years ago, when life was just beginning, as the deposits of an inland
sea.
For millions of years, sand, mud and carbonates washed into the ancient
sea, compressing the lower layers into mudstones and limestones,
building up a sediment thickness that may have been as much as 10,000
meters (_see_ metric conversion table on page 136).
When we look at the sharp contours of Glacier’s mountains, we see the
evidence of uplift, overthrust and glaciation. But on the geologic clock
these are recent events, a mere eyeblink of time ago. For the vast
majority of years, the rocks lay undisturbed and level beneath the sea
and land.
To understand better the tremendous time scale these rocks represent, we
need a way to visualize the vast collection of years. If we were to make
a movie of these geologic events, we would first need to determine how
many years each minute should represent. Since the Pleistocene lasted
about 3,000,000 years (its four ice ages sculpting the present muscle of
this land), let us make each minute portray a million years. To
chronicle these rocks we will then need a film 60 hours long!
Not until the fifty-seventh hour of our film will the Mesozoic lowlands
begin to bulge with the coming Rocky Mountain chain. During the long
preceding hours we would have seen little else but sea—withdrawing,
advancing, deep and shallow; yellow, green, and brown with great
colonies of algae. Unseen below the water, lava has spilled out
occasionally on the sea bottom; once, it intruded between the rock
layers below, forming the conspicuous, 60-meter-thick band of black
diorite that we see today on many mountain faces in Glacier.
During this time of initial uplift an amazing process is going on deep
underground. A major fault has developed, fracturing the buckled layers
of rock. A vast mountain plate begins to slide eastward, over-riding and
submerging the rock layers to the east and opening the wide trench that
is today the North Fork Valley. Known as the Lewis Overthrust, this
gigantic earth-force has created an unusual situation: ancient rock
strata lying atop recent rock strata.
Now less than 3 minutes of film remain. The arrival of the ice is
imminent. We look at the landscape of featureless mountains and wonder
at the dramatic difference that this last 3 million years will make. We
do not see the familiar forests and lakes, the savage peaks, and the
broad, deep valleys of this present land. These mountains are gentle,
arid, and shallow-valleyed. The vague outlines are there; we recognize
the general alignments of the drainage systems, the bloated domes from
which sharp peaks will be cut. The mountains are connected to one
another by blunt ridges and smooth saddles, and the shadows they cast
are dull, dunelike.
Suddenly the ice is there, filling the landscape, with only the
mountaintops protruding. Four times in these last 3 minutes of film the
ice sheets advance and retreat, each time leaving an altered landscape.
Strange lakes and forests fill the gaps between the glacial invasions.
Then we see the mountains we now know come into being rapidly, as if the
land were being hacked into shape by giant cleavers.
After this flicker of Pleistocene time, the film ends, the forests
return, and familiar lakes shine beneath the sun again—these lakes and
forests we had thought to be timeless.
■
Up springs the morning wind from Hidden Valley, making the nearby alpine
fir branches whiz with its passing and shattering the perfect reflection
of Bearhat Peak on the pond. From where I sit, it is a short distance to
Hidden Pass; so I leave the pond and walk to the overlook to see again
the fine basin quarried by an ancient glacier.
Hidden Lake, deep, far below, so blue, fits into its cliffed, crooked
valley like a polished boomerang. Closely ringed by ridge and
peak—distant Sperry Glacier and pointed Gunsight peering up from the
southern jumble, and broad Bearhat impossibly close—this lovely lake is
almost lost amid such sharp proclamations of rock. Its outlet gorge
gives a narrow view across the angled, hidden valleys of Avalanche and
McDonald, past the pyramid of Stanton, to the low, faraway undulations
of the Whitefish Range.
Glaciation is a cruel master of mountains, biting deeply into their bulk
and leaving sheer, spectacular contours when the glaciers disappear. The
landforms here attest to their power, everywhere exhibiting the effects
of glaciation.
In eating back the mountain headwall, alpine glaciers formed rounded
depressions, called cirques. Unlike the narrow clefts left by running
water, these broad, deep basins look as though they were made by
ice-cream scoops gouging into the rock. Hidden, Ptarmigan, Iceberg, and
Avalanche Lakes sit in well-developed cirque basins, and many mountains
are dimpled by the beginnings of other cirques—the conspicuous
amphitheater on the south shoulder of Heaven’s Peak, for example.
Occupying all major drainage systems, glaciers modified the contour of
the valleys, changing them from their narrow, stream-cut V-shapes into
broad U-shapes. Into these wide main valleys, waterfalls plunge from
higher, smaller valleys. Like rivers, flowing glaciers have tributaries.
Lacking the ice mass and cutting power of the main glaciers, these
tributary ice fingers could not bite as deeply into the bedrock. When
the ice melted, hanging valleys were left stranded high above the main
valley floor. Hidden Lake sits in one of these hanging valleys, and from
it Hidden Creek plunges 750 meters into Avalanche Basin toward McDonald
Creek.
On my many previous visits to this pass I have been too busy enjoying
the wildflowers, the weather, or the scenery to realize what an open
textbook of glaciation is everywhere displayed.
I stand here on a small saddle of a pass. Wherever glaciers met, passes,
or cols, were created. A high, notched pass like this one (or
Swiftcurrent or Gunsight) reveals recent connections. Broad, lower
passes, such as Logan, resulted where the ice early overran the mountain
ridge and had a chance to work longer.
Where two glaciers worked on opposing sides of a ridge and failed to
meet, they formed an arête—a thin, steep-walled remnant resembling a saw
blade. Another ice age would probably consume the park’s many thin
arêtes, such as the Garden Wall and Ptarmigan Wall; but it would also
create new ones from existing ridges.
Further testimony to the sculpting power of ice is presented by Mt.
Reynolds, looming to the east. The most dramatic feature of a glaciated
landscape is the pyramid-shaped mountain called a horn—and Reynolds is a
perfect example. Horns were formed when three or more glaciers cloaked
the mountain, excavating its sides toward its core and gradually
transforming its original domed shape into a sheer-sided peak. Glacier
has many remarkable horns, from the sleek spire of St. Nicholas in the
south to exquisite Kinnerly in the northern Kintla valley.
Sperry Glacier stares back at me from the flank of Gunsight. Glaciers
found in the park today are not remnants of the last ice phase, which
ended here about 8,000 years ago, but are newly formed, having come into
existence some 4,000 years ago. They reflect a cooling trend in the
present climate.
Shrinking steadily from their period of greatest extent in the middle of
the last century, these modern glaciers finally stabilized in the late
1940s and since then have shown only a slight increase in area.
Movement distinguishes glaciers from icefields, and the movement of ice
is a force on as well as a feature of a landscape. A glacier excavates
by abrading and plucking at the rock. Alternately melting and freezing,
ice at the headwalls plucks out blocks of rock. Ultimately the rocks are
deposited along the sides or at the feet of the glacier as moraine
debris. But as they move in the grip of the ice, they constantly abrade
the rock surfaces they encounter. Polished rock beds of past glaciers
show striations—grooves gouged by rock fragments imbedded in the moving
ice.
Flow rate of a glacier depends upon the thickness of the ice and the
degree of slope. Under tremendous pressure, ice becomes plastic, like
thick taffy. Unlike kilometer-thick continental glaciers, which may move
a hundred meters a day, small alpine glaciers seldom progress more than
two or three centimeters per day.
Although a glacier moves, it gets nowhere if in a state of
equilibrium—when annual melting equals annual accumulation. Snow mass
gained at the sun-shielded headwall is usually lost as melt at the
exposed snout. Glaciers such as Sexton or Weasel Collar, whose snouts
perch on cliff edges, also lose mass by calving. Thunder you hear on a
late-summer day near such a glacier may actually be the sound of ice
pushed off from the lip of a cliff.
Walking back to the visitor center, I suddenly stop where the trail
skirts the steep moraine of Mt. Clements. From the opposite side of the
moraine five mountain goats have appeared. Spotting me on the trail
below, they also halt. But before I can get to my camera they are off in
a stiff-legged gallop, running in single file along the crest of the
moraine to the distant safety of the mountain face.
Moraines are ridges of rock debris piled up along the edges and
terminuses of glaciers. Like a bracelet lying against the wall of this
mountain, the circle of steeply piled debris marks the extent of a
small, recently vanished glacier. Ghost of the power that once resided
here, a stagnant icefield lies beneath the confining walls of the
moraine. The recent accumulation of these rock fragments is a mighty
accomplishment, attesting to the force of moving ice.
_continued on p. 38_
[Illustration: The Mountains of Glacier
Lying astride the Continental Divide in the Northern Rockies,
Glacier is above all else a mountain park. The special beauty of its
lakes, streams, and forests derives from the microclimates and
varied topography and soil produced by mountain-building and
mountain-eroding forces.]
[Illustration: Overthrust Mountains
1 A hypothetical block of the Earth’s crust in the region of Glacier
National Park as it existed more than 60 million years ago. The two
layers shown actually represent many strata of sedimentary rocks.