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Cover

Summary

Introduction

Geologic setting of Crater Lake

Reawakening of Mount Mazama

Potential hazards from an eruption beneath Crater Lake

    Factors controlling explosivity of eruptions in bodies of water

    Pyroclastic surges

    Ballistic blocks and other hazards of eruptions in the lake

    Proximal hazard zones for explosive eruptions

Hazards of silicic eruptions outside the caldera

Hazards of lahars (volcanic debris flows) and their runout flows

    Potential for lahars at Crater Lake

    Definition of lahar hazard zone

    Potential size and flow velocity of lahars at Crater Lake

Regional volcanism

    Probability of a future volcanic eruption

    Hazard zones for regional volcanoes

Events of high consequence but low probability

    Another large volume or caldera-forming eruption?

    Sudden gas release from Crater Lake

    Catastrophic flood or lahar from drainage of Crater Lake

Protecting Crater Lake National Park and surrounding communities from volcano hazards

Earthquakes

    Seismicity

    West Klamath Lake fault zone

    Slip rate and recurrence interval of the WKLFZ

    Maximum earthquake on the WKLFZ

    Cascadia subduction zone

    Volcanic earthquakes

Landslides may cause large waves on Crater Lake

    Subaqueous landslides

    How large must an earthquake be to trigger landslides?

    Waves generated by landslides into the lake

    Waves generated by earthquakes

Preparing for an earthquake affecting the Crater Lake region

Acknowledgments

References

Glossary

Illustrations

Plate 1. Map showing hazard zones, faults, and volcanic vents in the Crater Lake region .......... In pocket

Figure 1. Map showing faults and volcanic vents in the Crater Lake region

2. Generalized geologic map of Mount Mazama and vicinity

3. Geologic map of Crater Lake caldera floor

4. Map showing earthquake epicenters and magnitudes

Tables

Table 1. Volume and flow properties of a hypothetical lahar at Crater Lake based on events at Mount St. Helens, Washington, and Raupehu Volcano, New Zealand

2. Numbers of known basalt, basaltic andesite, and andesite volcanic vents and eruptive episodes outside Crater Lake caldera and exclusive of Mount Mazama between approximately latitudes 42°48’ and 43°05’

3. Seismicity in the vicinity of Crater Lakre, Oregon

4. Fault offsets (down-to-the-east) and average long-term slip rates along Annie Spring and Red Cone Spring faults

5. Maximum earthquake magnitudes in the Crater Lake region

6. Approximate minimum areas, thicknesses, and volumes of probable landslides at Crater Lake

* Technical terms which appear in bold italics in this report are defined in the glossary. A more comprehensive glossary, descriptions of types of volcanic activity in the Cascades, and more information on volcanoes can be found at the USGS Cascades Volcano Observatory World Wide Web site. URL: http://vulcan.wr.usgs.gov The book by Decker and Decker (1989) gives an illustrated, non -technical overview of volcanoes. The book by Francis (1993) is more technical and includes many case histories.