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contents
Page
The changing landscape of 12-60 million years ago 3
Thumbnail biography of Mount Rainier 11
Results of recent eruptions 12
Why glaciers? 23
Work habits of glaciers 25
Yesterday’s glaciers 29
Landslides and mudflows—past, present, and future 35
The volcano’s future? 42
Further reading in geology 43
Frontispiece. Eunice Lake, northwest of Mount Rainier.
Figure Page
1. Outcrop of sandstone and shale in the Puget Group 6
2. Outcrop of welded tuff in the Stevens Ridge Formation 8
3. Granodiorite looks like granite 9
4. Geological cross section of Mount Rainier 10
5. An old lava flow which forms Rampart Ridge 13
6. Columns of andesite at the end of an old lava flow 13
7. Layers of pumice on the floor of a cirque 14
8. Generalized distribution of some pumice layers 16
9. Breadcrust bomb enclosed in a mudflow deposit 19
10. Pumice layer C, which consists of light-brown fragments 20
11. The recent lava cone lies in a depression 21
12. Two ice streams meet to form Cowlitz Glacier 23
13. Glacier-smoothed and grooved rock 26
14. A lake lies behind an end moraine of Flett Glacier 27
15. Recessional moraines on the valley floor of Fryingpan Creek 28
16. Extent of glaciers between 15,000 and 25,000 years ago 30
17. Lateral moraine at Ricksecker Point 31
18. Rock-glacier deposit at The Palisades 33
19. Hummocky end moraine in front of Emmons Glacier 34
20. Avalanche deposits in the White River valley 37
21. The northeast flank of Mount Rainier 39
Table
1. Characteristics, sources, and ages of pumice layers, Mount
Rainier National Park 17
2. Summary of important geologic events in the history of Mount
Rainier National Park 41
The Geologic Story of
Mount Rainier
By Dwight R. Crandell
[Illustration: Map of Cascade Range]
WASHINGTON
Seattle
Tacoma
CASCADE RANGE
Mount Rainier
Mount Adams
Mount St Helens
OREGON
Portland
Mount Hood
_Crater Lake_
Ice-clad Mount Rainier, towering over the landscape of western
Washington, ranks with Fuji-yama in Japan, Popocatepetl in Mexico, and
Vesuvius in Italy among the great volcanoes of the world. At Mount
Rainier, as at other inactive volcanoes, the ever-present possibility of
renewed eruptions gives viewers a sense of anticipation, excitement, and
apprehension not equaled by most other mountains. Even so, many of us
cannot imagine the cataclysmic scale of the eruptions that were
responsible for building the giant cone which now stands in silence. We
accept the volcano as if it had always been there, and we appreciate
only the beauty of its stark expanses of rock and ice, its flower-strewn
alpine meadows, and its bordering evergreen forests.
Mount Rainier owes its scenic beauty to many features. The broad cone
spreads out on top of a major mountain range—the Cascades. The volcano
rises about 7,000 feet above its 7,000-foot foundation, and stands in
solitary splendor—the highest peak in the entire Cascade Range. Its
rocky ice-mantled slopes above timberline contrast with the dense green
forests and give Mount Rainier the appearance of an arctic island in a
temperate sea, an island so large that you can see its full size and
shape only from the air. The mountain is highly photogenic because of
the contrasts it offers among bare rock, snowfields, blue sky, and the
incomparable flower fields that color its lower slopes. Shadows cast by
the multitude of cliffs, ridges, canyons, and pinnacles change
constantly from sunrise to sunset, endlessly varying the texture and
mood of the mountain. The face of the mountain also varies from day to
day as its broad snowfields melt during the summer. The melting of these
frozen reservoirs makes Mount Rainier a natural resource in a practical
as well as in an esthetic sense, for it ensures steady flows of water
for hydroelectric power in the region, regardless of season.
Seen from the Puget Sound country to the west, Mount Rainier has an
unreal quality—its white summit, nearly 3 miles high, seems to float
among the clouds. We share with the populace of the entire lowland a
thrill as we watch skyward the evening’s setting sun redden the
volcano’s western snowfields. When you approach the mountain in its
lovely setting, you may find something that appeals especially to
you—the scenery, the wildlife, the glaciers, or the wildflowers. Or you
may feel challenged to climb to the summit. Mount Rainier and its
neighboring mountains have a special allure for a geologist because he
visualizes the events—some ordinary, some truly spectacular—that made
the present landscape. Such is the fascination of geology. A geologist
becomes trained to see “in his mind’s eye” geologic events of thousands
or even millions of years ago. And, most remarkable, he can “see” these
events by studying rocks in a cliff or roadcut, or perhaps by examining
earthy material that looks like common soil beneath pastureland many
miles away from the volcano.
Our key to understanding the geology of Mount Rainier is that each
geologic event can be reconstructed—or imagined—from the rocks formed at
the time of the event. With this principle as our guide, we will review
the geologic ancestry of this majestic volcano and learn what is behind
its scenery.