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The Geology of Crater Lake National Park, Oregon With a reconnaissance of the Cascade Range southward to Mount Shasta by Howell Williams




Book cover, The Geology of Crater Lake National Park, Oregon



   Suggested Excursions


Discovery and Early Exploration

The Foundations of Mount Mazama

   The Pre-Cretaceous Bedrocks

   Cretaceous Formations

   Eocene Formations

   The Western Cascade Volcanic Series

        Age of the Western Cascade Series

        Rocks of the Western Cascade Series

        Climate and Flora

   Intrusions and Volcanic Necks in the Western Cascades

   Earth Movements of the Close of the Miocene

   The High Cascades Between Mounts Shasta and Mazama

       The Volcanic Cones

       The lntracanyon and Associated Fissure Flows

   The Union Peak Volcano

       Limits of the Volcano

       The Main Shield

       Parasitic Cinder Cones

       The Summit Cone

       The Summit Plug

   Other Pre-Mazama Lava Within the Park

The Structural Setting of Mount Mazama

The Main Andesite Cone of Mount Mazama

   Nature of the Floor and Size of the Cone

   Building of the Main Andesite Cone

   Nature of the Lavas

   Interbedded Andesitic Pyroclastic Rocks

   Solfataric Areas and Vents


       Dacite Dikes

       Andesite Dikes

Mount Scott

The Earlier Dacite Eruptions

   The Southern Dacite Flows and Domes

   The Eastern  Cluster of Domes and Flows

Inter-andesitic Dacite Pumice on the Caldera Walls

The Northern Arc of Vents

   The Watchman Dike and Flow

   The Hillman Cone

   The Sentinel Rock Flow and Vent

   The Dacite Flow of Llao Rock

   The Grouse Hill Dome and Flow

   The Cleetwood Flow

   Dacites of Redcloud and Cloudcap

The Parasitic Scoria Cones of Mount Mazama

   The Older Cones

   The Younger Cones

       Bald Crater

       Desert Cone

       Red Cone

       Forgotten Crater

       Crater Peak

       Diller Cone

       Southeast Comer Cone

       Cavern Creek Cone

       The Pumice Flat Cones

       Cones outside the Park

Timber Crater

The Wineglass Welded Tuff and Associated Pumice

The Formation of Mount Mazama Just before Its Destruction

The Climax: Culminating Explosions of Pumice and Scoria

   The Main Pumice Fall

       Distribution and Thickness

       Lithology of the Main Pumice Fall

       Volume of the Pumice Fall and Its Magma Equivalent

       Relation of the Pumice Fall to the Pumice Flows

   The Glowing Avalanches: Pumice and Scoria Flows


       The Lack of Sorting

       The Paucity of Stratification

       Abundance of Charred Logs

       Double Character of the Deposits

       Content of Lithic Fragments

       Erosive Action of the Flows

       "Fossil Fumaroles"

   Detailed Description of the Individual Flows

       The Annie Creek Flows

       The Sun Creek Flows

       The Sand Creek Flows

       The Rogue River Flows

       The Castle Creek Flows

       Other Flows down the West Slope of Mazama

       Flows down the North Slope

       Flows down the East Slope

   Volume of the Pumice-Scoria Flows

   The Last Weak Explosions

   Total Volume of Material Erupted During the Culminating Activity of Mount Mazama

The Origin of the Caldera

   How Much of Mount Mazama has Disappeared?

   Diller's Collapse Theory

   Smith and Swartzlow's Explosion Theory

   A Preferred Theory

Comparison of Crater Lake with Other Calderas

The Caldera Floor

The Age of Crater Lake

The Relation of Ancient Man to Crater hake

Post-caldera Eruptions

   Wizard Island

The Glaciation of Mount Mazama

   Evidences of Early Glaciation on the Caldera Walls

       Cloudcap Bay

       The Northeast Wall, from Grotto Cove to Cleetwood Cove

       Cleetwood Cove to Pumice Point

       Steel Bay

       Llao Rock

       West Wall of the Caldera, from Llao Rock to Eagle Cove

       South Wall of the Caldera, from Eagle Cove to Kerr Notch

       Danger Bay and Sentinel Rock

   Direction of Glacial Striae on the Caldera Walls

   Summary of Glacial Evidences on the Caldera Walls

   Evidence of Glaciation Outside the Caldera

       The Munson Valley or Annie Creek Glacier

       The Sun Creek Glacier

       The Kerr Valley Glacier

       Glaciers of Mount Scott

       The Bear Creek Glacier

       Glaciers on the North Slope of Mazama

       Glaciers on the West Slope of Mazama

       The Castle Creek Glacier

       The Rogue River Glacier

       The Union Peak Glaciers

Changes of Water Level in Crater Lake

Microscopic Petrography

   Lavas of the Union Peak Volcano

       Lavas of the Main Cone

       Intrusions near Bald Top

       The Micronorite Plug of the Union Peak Volcano

   Pre-Mazama Lavas in the Northwest Corner of the Park

   Andesites of Mount Mazama and Scott

       Basic Inclusions in the Andesites

       Andesites of the Hillman Vent

       Andesites of the Phantom Vent and Cone

       Alterations of the Mazama Andesites

   The Southern Dacite Flows and Domes

   The Younger Dacite Flows

       The Llao Dacite

       The Grouse Hill Dacite

       The Cleetwood Dacite

       The Redcloud Dacite

       Dacites of Cloudcap and Scott Bluffs

       Dacites of Anderson Bluffs

   Domes and Flows East of Mount Scott

   Welded Dacite Tuffs (Ignimbrites)

   Timber Crater Lavas

   Cinder Cones and Associated Flows

       Crater Peak

       Diller Cone

       Cones Bordering Pumice Flat

       Desert Cone and Bald Crater

       Red Cone

       Forgotten Crater

       Wizard Island


       Dacite Dikes

       Andesite Dikes

   Pumice and Scoria of the Climactic Eruptions

       Dacite Pumice

       Basic Scoria



List of Illustrations


I. Crater Lake viewed from the west

2. Reconnaissance geologic map of the Cascade Range, northern. Ca. and southern Oregon

3. Geologic map of Crater Lake National Park

4. Fig. I. The Union Peak volcano

    Fig. 2. Looking south from Mount Bailey to the rim of Crater Lake

5. Fig. I. Mount McLoughlin from the north

    Fig.2. Looking north toward Crater Lake from near Fort Klamath

    Fig. 3. Model of Crater Lake

6. Dutton Cliff and Phantom Ship

7. Fig. I. Phantom Ship

    Fig. 2. Dacite dike on the caldera wall beneath Llao Rock

8. The west wall of Crater Lake

g. Fig. I. Mount Scott from the west

    Fig. 2. Mount Scott and parasitic domes

10. Redcloud Cliff

11. Fig. I. Pumice Point

      Fig. 2. Hillman Peak from the south

12. Fig. I. The Llao Rock dacite flow

      Fig. 2. West edge of the Llao Rock flow

13. Fig. I. Looking north across the Pumice Desert

      Fig. 2. Forgotten Crater

14. Fig. I. Timber Crater and the rim of Crater Lake

      Fig. 2. Deposits on top of Sentinel Rock

15. Fig. I. Welded dacite tuff (ignimbrite) forming the brim of the Wineglass

      Fig. 2. Llao's Hallway

      Fig. 3. Charcoal logs in deposits of a pumice flow

16. The Pinnacles, Sand Creek canyon

17. Fig. I. Columnar scoria flow

      Fig. 2. "Fossil fumarole" in Castle Creek canyon

      Fig. 3. Pumice deposits on Diamond Lake highway '

18. Fig. I. Mount Mazama immediately before the collapse of the summit

      Fig. 2. Mount Mazama immediately after the collapse of the summit

19. Fig. I. A channel among the bedded pumice deposits

      Fig. 2. Washed and bedded pumice deposits

      Fig. 3. View from Kerr Notch

20. Aerial view of the cone of Wizard Island

21. Fig. I. The southeast wall of the caldera, and Wizard Island

      Fig. 2. Lava flows on Wizard Island

22. Fig. I. Typical glacial striae on the caldera rim near Discovery Point

      Fig. 2. Mount Mazama at the time of maximum glaciation

23. Panorama of the caldera wall: Cloudcap Bay

24. Panorama of the caldera wall: Grotto Cove

25. Panorama of the caldera wall: Palisades and Roundtop

26. Panorama of the caldera wall: Cleetwood Cove

27. Panorama of the caldera wall: Pumice Point

28. Panorama of the caldera wall: Steel Bay

29. Panorama of the caldera wall: Watchman to Llao Rock

30. Fig. I. Section on the caldera rim

      Fig. 2. Sentinel Rock

31. The southeast wall of Crater Lake


1. Paleogeographic maps of Oregon

2. Map of the Cascade Range

3. Sections across the Cascade Range

4. Block diagram of the Union Peak volcano

5. Block diagram of the Crater Lake region

6. Map of the region east of Crater Lake National Park

7. Sections on the caldera wall

8. Sections on the caldera rim

9. Map and section of the Watchman flow

10. Map and section of the Llao Rock flow

11. Map and sections of the Grouse Hill dacite dome and flow

12. Section across the Cleetwood dacite flow

13. Profiles through Mounts Shasta, Rainier, and Adams, and Crater Lake

14. The forms of Mounts Shasta, Rainier, and Adams compared with the remnant Mount Mazama

15. Panorama of Mount Mazama from the southwest

16. Map showing distribution and thickness of Crater Lake pumice

17. Size distribution of samples of pumice fall

18. Size distribution of samples of pumice fall

19. Samples of pumice fall north and northeast of Crater Lake

20. Samples of pumice fall east and southeast of Crater Lake

21. Samples of pumice fall

22. Samples of pumice fall and flow

23. Map of pumice, drift, rock outcrops. and main glacial striae

24. Size distribution of samples of pumice flow

25. Histograms of pumice deposits

26. Histograms of pumice-scoria flows in Annie Creek canyon

27. Block diagram of Crater Lake, looking northeast

28. Block diagram of Crater Lake, looking southwest

29. The evolution of Crater Lake

30. The floor of Crater Lake

31. Glacial striae and deposits on the rim and walls of Crater Lake

32. Variation diagram of the Crater Lake rocks

33. K-mg diagram for the Crater Lake series



Photograph by 116th Photo Section, Washington National Guard

Crater Lake viewed from the west

   Plate 1. The Watchman, one of the Northern Arc of Vents, rises on the caldera rim in front and to the left of Wizard Island. To the north (left) rises Hillman Peak, connected by a ridge with the parasitic cinder cone known as Forgotten Crater. Next to the left is the great dacite flow of Llao Rock. Continuing along the caldera rim, the white-topped cliff is Pumice Point, beyond which lies Cleetwood Cove, overlooked by the Cleetwood dacite flow. Farther on, where the caldera wall is low, are the thick andesite flows of the Palisades and Roundtop, which rest on glacial deposits. The conspicuous V-shaped cliff on the distant wall is formed by the Redcloud dacite flow; beyond it rises Mount Scott. The numerous hills on the outer slopes of Mount Mazama, behind Mount Scott, are parasitic dome of andesite and dacite. Still farther away is the interior plateau, thickly covered a with the deposits of pumice flows (nuées ardentes).





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