Volcanic Hazards: A Growth Management Perspective

Patrick T. Pringle
Washington State Department of Natural Resources
Division of Geology and Earth Resources
PO Box 47007, Olympia, WA 98504-7007

Washington is home to five major composite volcanoes or stratovolcanoes: Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, and Mount Adams. These volcanoes and Mount Hood to the south in Oregon are part of the Cascade Range, a volcanic arc that stretches from southwestern British Columbia to northern California.

Although there are thousands of small basaltic or basaltic-andesitic volcanoes in the Cascade Range, the 13 major composite volcanic centers in the U.S., all part of the range, have been the focus of most hazard concerns. During the past 12,000 years, these volcanoes have produced more than 200 eruptions that have generated tephra (ejected material), lava flows, lahars (volcanic debris flows) and debris avalanches (Miller, 1990). It is important to note that other enormous debris avalanches and lahars may have been caused by intrusions of magma (not eruptions) or steam explosions at the volcanoes or by local or regional earthquakes because these flowage events do not correlate with known tephra layers.

All Washington volcanoes except Mount Adams have erupted within the last 250 years (Table 1). Mount Hood erupted in the late 1700s and into the mid-1800s (Crandell, 1980; Cameron and Pringle, 1987). However, the volcanoes do not erupt at regular intervals, thus making it difficult to forecast when a given volcano might come to life again. Although, worldwide, the risks from volcanoes are significantly lower than risks from earthquakes and landslides. The relatively long recurrence interval for volcanic hazards (decades to several centuries) combined with their great potential for destruction make them particularly insidious.

This article will focus mainly on the volcanic hazards associated with the five Washington volcanoes and Mount Hood, although other volcanic areas, such as the Indian Heaven volcanic field southwest of Mount Adams, have erupted during the Holocene (10,000 years ago to present). Also, this article briefly reviews the terminology used to communicate volcanic hazards information and provides an overview of volcanic processes and hazards in Washington State, with particular emphasis on how they relate to the Washington Growth Management Act (GMA). Additional information resources are listed at the end of the article.

Volcanic Hazards and the Planning Process
The GMA mandates comprehensive planning in some jurisdictions. This mandated planning effort includes delineation of geologically hazardous areas (including volcanic hazard areas) as the initial planning step and subsequent formulation of regulations governing development in hazardous areas. To this end, in December of 1990, the Department of Community Development (now the Department of Community, Trade and Economic Development) issued minimum guidelines for classifying volcanic hazards with respect to the GMA:

Volcanic hazard areas shall include areas subject to pyroclastic flows, lava flows, debris avalanche, inundation by debris flows, mudflows or related flooding resulting from volcanic activity.

Certain volcanic hazards, such as fallout of tephra and tsunamis, although important, were not included in the guidelines. Tephra fallout hazards, for example, are extremely widespread in volcanic terrains, and the proximal hazard zones shown in Figure 1 already include the areas that have the highest probability of destructive tephra fallout. Hoblitt and others (1987) discuss tephra hazards with respect to the siting of nuclear power plants, and Casadevall (1992, 1993) addresses the problem of volcanic ash and aviation safety.

As will be noted below, evidence for the hazardous volcanic processes mentioned in the GMA guidelines has been observed in the geologic records of various Cascade volcanoes (Crandell and Waldron, 1973; Miller, 1990). Before the cataclysmic eruption of Mount St. Helens in 1980, roughly 30 person-years had been devoted to analysis of volcanic hazards in the Cascade Range. While much has been learned about the history of the Cascade volcanoes because of these early studies, more geologic investigations are necessary in order to bring some of the older hazard assessments up to date with our current understanding of volcanic processes. Furthermore, some inconsistencies exist in the understanding of hazards from individual volcanoes because some (such as Mount St. Helens) have been studied in considerably greater detail than others (for example, Glacier Peak and Mount Baker).

Volcanic hazards are destructive volcanic processes that have a definite probability of occurring. In order to best understand the importance of considering volcanic processes and hazards in the planning process, it is helpful to briefly review the concept of risk and the magnitude of the loss. Risk can be expressed as a function of the hazard, value that could be lost (lives, property, stock, etc.) and vulnerability (generally speaking, preparedness). Using this definition, it is all too clear that the number of lives and amount of property at risk to volcanic hazards in Washington is rapidly growing as development spreads into hazardous areas, such as valleys that drain active volcanoes. While most of these communities had at least twice the population in 1990 that they had in 1950, at least one, Kent, has had a ten-fold increase!

Volcanic Processes and Hazardous Volcanic Events
The following discussion focuses on volcanic processes and hazards, particularly those mentioned in the GMA guidelines. For a more complete discussion of this topic, Chapter 2 in Tilling (1989) is an excellent reference.

Generally, composite volcanoes are associated with subduction zones. Consequently, they are found around the Pacific Rim ("Ring of Fire") and in the Mediterranean-Himalayan Belt. They are mainly characterized by the following processes, features, or aspects.

Lava Domes and Flows Lavas of higher viscosity tend to pile up and form domes because they cannot flow as readily as those having lower viscosity (such as Hawaiian basaltic lavas). The new Lava Dome at Mount St. Helens was constructed during 17 episodes of activity from 1980 to 1986 that included both intrusion of new magma into the dome and extrusion of lobes of lava onto the dome's surface and flanks. Crater Rock at Mount Hood is a remnant of a dome that was constructed by eruptions during the last 1,800 years. Hazards from lava domes include explosions and collapses. Dome collapse can produce pyroclastic flows and surges, lahars, and floods.

The main hazard from lava flows is damage or total destruction by burying, crushing, or burning everything in their paths. (However, more viscous lava flows do not typically flow far from the volcano.) Lava flows can melt snow and ice, but they generally do not produce major floods and lahars because they do not mix turbulently with snow and ice. They can, however, melt large quantities of ice, which can be released as "jokulhlaups" or glacial outburst floods.

Pyroclastic Density Currents Pyroclastic density current is a general name for various types of flows of hot gas and rock down the slopes of a volcano. These geologic processes, which include pyroclastic flows, pyroclastic surges, and lateral blasts, generally only affect areas relatively close to the volcano.

Pyroclastic flows are masses of hot (300 deg. -800+deg.C), dry pyroclastic debris and gases that move rapidly along the ground surface at velocities ranging from ten to several hundred meters per second. Typical pyroclastic flows have two components: (1) a ground-hugging, dense, basal portion (the flow); and (2) a preceding or overriding turbulent ash-cloud surge that has separated from the flow.

Direct hazards of pyroclastic flows are asphyxiation, burial, incineration, and impact. Pyroclastic flows also can generate lahars and floods by quickly melting snow and ice, can dam tributary valleys, and can start fires. Pyroclastic flows are strongly controlled by topography and are likely to be restricted to valley floors. Although most pyroclastic flows would be limited to within about 15 miles (25 km) of a volcano, Heller and Dethier (1981) noted Holocene pyroclastic flow deposits about 18 miles (30 km) from Mount Baker in the Baker Valley.

Unlike pyroclastic flows, hot pyroclastic surges, because they are less concentrated and less dense than pyroclastic flows, are not necessarily confined to valleys and can affect more extensive areas many tens of kilometers from the volcano. Hot pyroclastic surges can generate secondary pyroclastic flows. Surges are responsible for many catastrophes, including 30,000 deaths at Mount Pelee (1902) and 2,000 at El Chichon (1982). Cold, or base, surges typically result from explosive interactions of magma with water, such as that at Kilauea, Hawaii, in May of 1924 and, on a smaller scale, the post-1980 phreatic (steam) explosions on the Pumice Plain and in the crater at Mount St. Helens.

Another possible hazard from Cascade volcanoes is the directed blast. Directed blasts are very powerful, laterally directed explosions such as that at Mount St. Helens in 1980 and at Bezymianny, Kamchatka, in 1956. Blasts can affect large areas (230 mi2 or 600 km2 at Mount St. Helens).

Lahars, Lahar-Runout Flows, And Floods Lahars are volcanic debris flows ("mudflows") or rapidly flowing mixtures of rock debris mobilized by water that originate on the slopes of a volcano (Figs. 2 and 3). Most are restricted to stream valleys. Although there are many causes of lahars, two major flow types have been noted, granular and muddy.

Granular Lahars have a relatively low clay content (<4%). These flows typically begin as a flood surge that incorporates sediment and becomes a debris flow as it travels. The debris flow then rapidly transforms downstream to more diluted flow types (lahar-runout flows, floods). The many causes of these clay-poor lahars include:

Interaction of a pyroclastic density current with snow and ice

Meteorologically (rainstorm or rain-on-snow events) induced erosion of tephra (or other fragmental debris) from the slopes of a volcano

Failure of a landslide-dammed lake

Glacial outburst flood (jokulhlaup)

Muddy Lahars are relatively clayrich (>4%) and typically originate as "sector collapses" of a significant portion of a volcano. They can be triggered by earthquakes, steam explosions, intrusions, or by other destabilization (not necessarily by eruptions). Muddy lahars can have enormous volumes and flow great distances. The Electron and Osceola Mudflows at Mount Rainier and the Middle Fork Nooksack flow at Mount Baker are local examples. The volume of the Electron Mudflow has been estimated at more than 300 million yd3 (0.25 km3) and the volume of the Osceola Mudflow at more than 0.7 mi3 (3 km3) (Scott and others, 1992).

Inundation height, runout length, velocity, and duration of flood wave for lahars can vary widely. The elapsed time between events, amount of available sediment for bulking, and other factors can change the scale of the hazard from lahars. In general, relative risk decreases with distance down valley and with height above the valley floor.

Debris Avalanches are flowing mixtures of rock and soil, with or without water, that move away from a volcano at high speed. Some of these events are gigantic (>1018 m3). Since the 1980 eruption of Mount St. Helens, hummocky debris avalanche deposits have been recognized at several hundred volcanoes around the world. Some debris avalanches at volcanoes have been caused by earthquakes (Ontake Volcano, Japan, 1984). Debris avalanches are an end member of a continuum of mass-wasting processes at composite volcanoes--large lahars at some highly hydrothermally altered volcanoes, such as Mount Rainier, have undoubtedly transformed directly from debris avalanches.

Geologists now realize that this type of gigantic avalanche and those that transform into lahars occur far more frequently than previously recognized. The nature of this hazard and its relation to hydrothermal alteration and destabilization of a volcanic cone also indicate that sector collapse events (very large debris avalanches) can affect any drainage that heads on a volcano. The frequency of enormous megathrust earthquakes in the Cascadia subduction zone (13 in the past 7,600 years), as well as our increasing recognition of shallow-crustal fault zones in the Puget-Willamette Lowland and along the Cascades, amplify the need to consider this major slope-stability hazard at composite volcanoes.

The debris avalanche from Ontake Volcano (mentioned above) exemplifies this type of hazard. On September 14, 1984, a 6.8 magnitude earthquake triggered a debris avalanche that traveled about 13 km downvalley, killing 29 people. Numerous larger slope failures in the geologic record could be attributed to tectonic sesmicity. These and other uncommon events, such as the 1980 blast at Mount St. Helens, are now included in hazard assessments at composite volcanoes.

Secondary Effects of Eruptions
The secondary effects of the 1980 Mount St. Helens eruption serve as a reminder that hazards are present long after the initial eruptive activity has ceased. At Mount St. Helens, dramatic post-eruption erosion and sedimentation and the ongoing potential of floods from lakes impounded by the 1980 debris avalanche have presented costly problems. Nearly $1 billion was spent during the first 10 years after the eruption to mitigate the downstream flood hazards.

During the first 3 years after 1980, an estimated 8 million tons of tephra were washed off hillslopes into the Toutle River system. While hillslope erosion eased somewhat after 1983, erosion of the debris avalanche and the subsequent widening and incision of this drainage system by the development of a stream network resulted in a huge sediment discharge to downstream areas. The post-eruption Toutle River became one of the most sediment-laden rivers in the world. Downstream water quality and aquatic habitat severely deteriorated, and increased downstream flooding due to sediment-filled river channels jeopardized homes and roads built near the river.

Numerous natural dams were created by the debris avalanche in the North Fork Toutle River drainage. On at least five occasions from 1980 to 1982, the collapse of a dam released a small lake or pond and caused minor floods. However, public concern focused on Spirit, Coldwater, and Castle Lakes, the three largest lakes impounded by the debris avalanche. Studies by geologists in the 1980s indicated that enormous floods had resulted from the breakouts of lakes in similar settings at the volcano in pre-historic times. These types of secondary hazards could affect any volcano after an eruption or sector collapse.

Volcanic-Hazard Assessments and Hazard-Zonation Maps
Volcanic-hazard assessments for Cascade Range volcanoes provide forecasts of the type and nature of eruptions and volcanic hazards that we can expect in the future and the areas that would be affected (Crandell and others, 1975; Hoblitt and others, 1987). Some of these assessments apply to a wide variety of hazards at an individual volcano (Crandell and Mullineaux, 1978), while others apply to a more specific type of hazard, such as debris flows, and may provide detailed information about their flow processes, including travel times and volumes (Scott and others, 1992). Volcanic hazards assessments are possible because geologists have reconstructed the nature of eruptive activity or hazard by using historical records and the stratigraphic history of each of these Cascade volcanoes over the past 10,000 years. These hazards studies make the assumption that future volcanic activity at each volcano will be similar in style, scale, and frequency to its past activity.

Volcanic-hazard zonation maps (Fig. 4) designate hazardous areas around a volcano. In the past, these maps have shown relative hazard (for example, low, medium, and high), although some recent reports and maps have expressed hazards in probabilistic terms (Hoblitt and others, 1987; Scott and others, 1992). Table 2 shows an example of probabilistic hazards for lahars at Mount Rainier. A series of inundation maps based on this investigation should be available soon (Scott and others, in press).

Hoblitt and others (1987) found that the most damaging volcanic events occur within 30 miles (50 km) of a volcano. Therefore, their hazard zonation map shows a proximal-hazard zone within this 50-km radius of a given volcano (Fig.4). Because significant lahars have inundated valley bottoms at distances exceeding 50 miles (80 km) from Cascade Range volcanoes, Hoblitt and others (1987) also established distal-lahar and flood-hazard zones for the valley bottoms that extend along major drainages beyond the 50-km radius of a volcano. These zones include modern river channels, flood plains, and low terraces.

Drainages that head on a volcano are most vulnerable to proximal hazards. Other areas are less likely to be affected by all but low-probability, high-magnitude events.

Preparedness and Mitigation: Public Awareness of Volcanic Hazards
The 1980 events at Mount St. Helens have changed not only the way volcanic hazards are studied, but also public awareness of those hazards. The three most important aspects of volcanic hazards mitigation are: (1) communication of volcano-monitoring and volcanic-hazards information by geoscientists to the public, the media, and responsible agencies; (2) emergency preparedness by responsible agencies and officials; and (3) community and regional planning and land use designations that minimize the amount of risk. These three aspects are interrelated. Successful mitigation depends on the timely communication of understandable scientific information about the current state of the volcano, as well as the nature, extent, implications, and likelihood of the variety of volcanic processes possible at that volcano.

Communication of scientific information about the status of a volcano has improved mainly because geologists have observed Mount St. Helens so closely. Public demand for prompt and comprehensible technical information and the experience of working with an accessible volcano, such as Mount St. Helens, have helped scientists refine the communication process. As a result, geologists now use three types of public statements when describing volcanic activity:

Factual statements provide information but do not anticipate future events.

Forecasts are comparatively imprecise statements about the nature of expected activity (typically based on the past history and potential of a volcano and on geologic mapping).

Predictions are relatively precise statements about the time, place, nature, and size of impending activity (usually based on measurements at the volcano).

These types of public statements about Mount St. Helens and other volcanoes from Alaska to the Philippines have been accepted by the media and the public because they clarify public expectations and understanding of volcanic events and hazards.

Discussion
Hoblitt and others (1987) present an excellent compilation and analysis of volcanic hazards in Washington. They established proximal- and distal-hazards zones and summarized the existing literature on Cascade Range volcanoes. Their map (about 1:2,000,000 scale) is a general guide to areas that could be affected by hazardous volcanic processes. Other larger scale maps have been, and continue to be published (Scott and others, in press) and are essential for hazard zonation by planning agencies.

Although not a direct volcanic hazard, increased liquifaction susceptibility due to earthquakes is enhanced by the presence of thick deposits of volcanic sand and gravel and generally saturated conditions in lowland areas downstream of volcanoes (Palmer and others, 1991; Pringle and Palmer, 1992). Some valley-bottom areas are susceptible to multiple hazards. Liquefaction and related ground failure during strong seismic shaking could disrupt evacuation routes. Thus, if a large debris avalanche and (or) lahar were to be triggered by a regional earthquake with attendant liquefaction and ground failures on the valley bottom and valley walls, the combined results could be disastrous.

Summary
The Washington State Growth Management Act mandates that jurisdictions designate volcanic hazard areas in their comprehensive plans. Volcanic hazards occur with a frequency and on a scale that require that they be considered in comprehensive land-use plans where relevant.

Abundant scientific literature is available on the subject of volcanic processes and hazards. Some Washington volcanoes, such as Mount St. Helens, have been studied in great detail, while others, such as Mount Baker and Glacier Peak, have only had reconnaissance studies. As a result, volcanic-hazards investigations and hazard-zonation maps for individual volcanoes may be out of date or at scales that are too small to be useful to local planning agencies. Revised volcanic-hazards assessments and improved hazard-zonation maps are necessary for future planning and preparedness efforts.

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References for Volcanic Hazards
Mount Rainier
Crandell, D. R., 1963, Paradise debris flow at Mount Rainier, Washington: U.S. Geological Survey Professional Paper 475-B, p. B135-B139.

Crandell, D. R., 1963, Surficial geology and geomorphology of the Lake Tapps quadrangle, Washington: U.S. Geological Survey Professional Paper 388-A, 84 p., 2 pl.

Crandell, D. R., 1967, Volcanic hazards at Mount Rainier, Washington: U.S. Geological Survey Bulletin 1238, 26 p.

Crandell, D. R., 1969 [1970], Surficial geology of Mount Rainier National Park, Washington: U.S. Geological Survey Bulletin 1288, 41 p., 1 pl.

Crandell, D. R.,1971, Postglacial lahars from Mount Rainier volcano, Washington: U.S. Geological Survey Professional Paper 677, 75p.,3pl.

Crandell, D. R., 1973, Map showing potential hazards from future eruptions of Mount Rainier, Washington: U.S. Geological Survey Miscellaneous Investigations Series I-836, 1 sheet, scale 1:250,000. *Particularly informative or the latest resource for this topic or volcano.

Crosson, R. S.; Frank, David, 1975, The Mt. Rainier earthquake of July 18, 1973, and its tectonic significance: Seismological Society of America Bulletin, v. 65, no. 2, p. 393-401.

Cullen, J. M., 1978, Impact of a major eruption of Mount Rainier on public service delivery systems in the Puyallup Valley, Washington: University of Washington Master of Urban Planning thesis, 195 p.

Driedger, C. L., 1988, Geology in action--Jokulhlaups on Mount Rainier: U.S. Geological Survey Open-File Report 88-459, 2 p.

Driedger, C. L.; Fountain, A. G., 1989, Glacier outburst floods at Mount Rainier, Washington State, U.S.A. In Wold, Bjorn, editor, Proceedings of the symposium on snow and glacier research relating to human living conditions: Annals of Glaciology, v. 13, p. 51-55.

Fiske, R. S.; Hopson, C. A.; Waters, A. C., 1963, Geology of Mount Rainier National Park, Washington: U.S. Geological Survey Professional Paper 444, 93 p.

Frank, D. G., 1985, Hydrothermal processes at Mount Rainier, Washington: University of Washington Doctor of Philosophy thesis, 195 p.

Moxham, R. M.; Crandell, D. R.; Marlatt, W. E., 1965, Thermal features at Mount Rainier, Washington, as revealed by infrared surveys: U.S. Geological Survey Professional Paper 525-D, p. D93D100.

Mullineaux, D. R., 1974, Pumice and other pyroclastic deposits in Mount Rainier National Park, Washington: U.S. Geological Survey Bulletin 1326, 83 p.

Mullineaux, D. R.; Sigafoos, R. S.; Hendricks, E. L., 1969, A historic eruption of Mount Rainier, Washington: U.S. Geological Survey Professional Paper 650-B, p. B15-B18.

National Research Council, 1994, Mount Rainier--Active Cascade volcano: National Academy Press, 114 p.

Pringle, P. T.; Palmer, S. P., 1992, Liquefiable volcanic sands in Puyallup, Washington correlate with Holocene pyroclastic flow and lahar deposits in upper reaches of the Puyallup River valley [abstract]: Geologic Society of America Abstracts with Programs, v. 24, no. 5, p. 76.

Scott, K. M.; Pringle, P. T.; Vallance, J. W., 1992, Sedimentology, behavior, and hazards of debris flows at Mount Rainier, Washington: U.S. Geological Survey Open-File Report 90-385, 106 p., 1 pl. (To be released as U.S. Geological Survey Professional Paper 1447-C.) *Particularly informative or the latest resource for this topic or volcano.

Scott, K. M. Vallance, J. W.; Pringle, P. T., [in press], Debris flows, debris avalanches, and floods, at, and downstream from Mount Rainier, Washington: U.S. Geological Survey Open-File Report 92-654.

Swanson, D. A.; Malone, S. D.; Samora, B. A., 1992, Mount Rainier-- A Decade Volcano: Eos (American Geophysical Union Transactions), v. 73, no. 16, p. 177, 185-186.

Swanson, D. A.; Malone, S. D.; Casadevall, T. J., 1993, Mitigating the hazards of Mount Rainier: Eos (American Geophysical Union Transactions), v. 74, no. 12, p. 133.

Mount St. Helens
Collins, B. D.; Dunne, Thomas, 1988, Effects of forest land management on erosion and revegetation after the eruption of Mount St. Helens: Earth Surface Processes and Landforms, v. 13, no. 3, p. 193-205.

Crandell, D. R., 1987, Deposits of pre-1980 pyroclastic flows and lahars from Mount St. Helens volcano, Washington: U.S. Geological Survey Professional Paper 1444, 91 p., 1 pl.

Crandell, D. R.; Mullineaux, D. R., 1978, Potential hazards from future eruptions of Mount St. Helens volcano, Washington: U.S. Geological Survey Bulletin 1383-C, 26 p.

Foxworthy, B. L.; Hill, Mary, 1982, Volcanic eruptions of 1980 at Mount St. Helens--The first 100 days: U.S. Geological Survey Professional Paper 1249, 125 p.

Hoblitt, R. P., 1990, Current perspectives on the 18 May 1980 lateral blast deposit at Mount St. Helens, Washington [abstract]: Geoscience Canada, v. 17, no. 3, p. 126.

Lehre, A. K.; Collins, B. D.; Dunne, Thomas, 1983, Post-eruption sediment budget for the North Fork Toutle River drainage, June 1980-June 1981. In Okuda, S.; Netto, A.; Slaymaker, O., editors, Extreme land forming events: Zeitschrift fur Geomorphologie, supplement band 46, p. 143-163.

Lipman, P. W.; Mullineaux, D. R., editors, 1981, The 1980 eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, 844 p.

Manson, C. J.; Messick, C. H.; Sinnott, G. M., 1987, Mount St. Helens--A bibliography of geoscience literature, 1882-1986: U.S. Geological Survey Open-File Report 87-292, 205 p.

Mullineaux, D. R., 1986, Summary of pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington State, USA: Bulletin of Volcanology, v. 48, no. 1, p. 17-26.

Pallister, J. S.; Hoblitt, R. P.; Crandell, D. R.; Mullineaux, D. R., 1992, Mount St. Helens a decade after the 1980 eruptions--Magmatic models, chemical cycles, and a revised hazards statement: Bulletin of Volcanology, v. 54, no. 2, p. 126-146.

Pringle, P. T., 1993, Roadside geology of Mount St. Helens National Volcanic Monument and vicinity: Washington Division of Geology and Earth Resources Information Circular 88, 120 p.

Scott, K. M., 1988, Origins, behavior, and sedimentology of lahars and lahar-runout flows in the Toutle-Cowlitz River system: U.S. Geological Survey Professional Paper 1447-A, 74 p.

Scott, K. M., 1989, Magnitude and frequency of lahars and lahar runout flows in the Toutle-Cowlitz river system: U.S. Geological Survey Professional Paper 1447-B, 33 p.

U.S. Forest Service, 1992, Mount St. Helens contingency plan 1992--Gifford Pinchot National Forest: U.S. Forest Service, 1 v.

Yamaguchi, D. K., 1983, New tree-ring dates for recent eruptions of Mount St. Helens: Quaternary Research, v. 20, no. 2, p. 246-250.

Miscellaneous References
Bolt, B. A.; Horn, W. L.; MacDonald, G. A.; Scott, R. F., 1977, Geological hazards--Earthquakes, tsunamis, volcanoes, avalanches: Springer-Verlag, 330 p.

Casadevall, T. J., 1992, Volcanic hazards and aviation safety: Federal Aviation Administration Aviation Safety Journal, v. 2, no. 3, p.917.

Casadevall, T. J., 1993, Volcanic ash and airports--Discussions and recommendations from the Workshop on Impacts of Volcanic Ash on Airport Facilities: U.S. Geological Survey Open-FIle Report 93-518, 52 p.

Dunne, Thomas; Smith, J. D.; Wigmosta, M. S., 1983, Field evidence for the flow properties of the Toutle valley mudflows: U.S. Bureau of Reclamation, 2 sheets microfiche [146 p.]; U.S. National Technical Information Service PB 86-157138.

Ewert, J. W.; Swanson, D. A., 1992, Monitoring volcanoes--Techniques and strategies used by the staff of the Cascades Volcano Observatory, 1980-1990: U.S. Geological Survey Bulletin 1966, 223 p.

Eisbacher, G. H.; Clague, J. J., 1984, Destructive mass movements in high mountains--Hazard and management: Geological Survey of Canada Paper 84-16, 230 p.

Fairchild, L. H., 1985, Lahars at Mount St. Helens, Washington: University of Washington Doctor of Philosophy thesis, 374 p.

Fairchild, L. H., 1986, Quantitative analysis of lahar hazard. In Keller, S. A. C., editor, Mount St. Helens--Five years later: Eastern Washington University Press, p. 61-67.

Higgins, J. D.; Naik, Bijayananda; Mills, S. V.; Copp, Howard; Roberson, J. A., 1983, The mechanics of mudflows: Washington Water Research Center Report 51, 116 p.

Lopez, D. L.; Williams, S. N., 1993, Catastrophic volcanic collapse-- Relation to hydrothermal processes: Science, v. 260, no. 5115, p. 1794-1795.

Norris, R. D., [in press], Seismicity of rockfalls and avalanches at three Cascade Range volcanoes--Implications for seismic detection of hazardous mass movements: Seismological Society of America Bulletin.

Nuhfer, E. B.; Proctor, R. J.; Moser, P. H., 1993, The citizens' guide to geologic hazards: American Institute of Professional Geologists, 134 p.

Palmer, S. P.; Pringle, P. T.; Shulene, J. A., 1991, Analysis of liquefiable soils in Puyallup, Washington: In Proceedings--Fourth International Conference on Seismic Zonation, Stanford, California, 1991: Earthquake Engineering Research Institute, v. 2, p. 621-628.

Stine, C. M., 1990, Annotated bibliography, volcano-deformation monitoring: U.S. Geological Survey Open-File Report 90-47, 29 p.

Tanaka, Janet, 1986, The other side of the volcano--Social aspects of volcanic activity: Volcano News, no. 25/26, p. 1-8.

Wigmosta, M. S., 1983, Rheology and flow dynamics of the Toutle debris flows from Mount St. Helens: University of Washington Master of Science thesis, 184 p.

Wood, C. A.; Kienle, J., editors, 1990, Volcanoes of North America: Cambridge University Press, 354 p.