Mount Rainier: Active Cascade Volcano (1994)

Mount Rainier is one of about two dozen active or recently active volcanoes in the Cascade Range, an arc of volcanoes in the northwestern United States and Canada. The volcano is located about 35 kilometers (km) southeast of the Seattle-Tacoma (Washington) metropolitan area, which has a population of more than 2.5 million. This metropolitan area is the high-technology industrial center of the Pacific Northwest and one of the commercial aircraft manufacturing centers of the United States. The rivers draining the volcano empty into Puget Sound, which has two major shipping ports, and into the Columbia River, a major shipping lane and home to approximately a million people in southwestern Washington and northwestern Oregon.

Mount Rainier is an active volcano. It last erupted approximately 150 years ago, and numerous large floods and debris flows have been generated on its slopes during this century. More than 100,000 people live on the extensive mudflow deposits that have filled the rivers and valleys draining the volcano during the past 10,000 years. A major volcanic eruption or debris flow could kill thousands of residents and cripple the economy of the Pacific Northwest. Despite the potential for such danger, Mount Rainier has received little study. Most of the geologic work on Mount Rainier was done more than two decades ago. Fundamental topics such as the development, history, and stability of the volcano are poorly understood.

Studies of the geologic history of Mount Rainier and other Cascade volcanoes suggest that major volcanic hazards, volcano-related events that pose threats to persons or property, are likely to include the following:

• Volcanic eruptions. The eruption of lava flows and tephra (particulate materials such as ash).

• Edifice failure. The gravitational collapse of a portion of the volcano.

• Glacier outburst floods (jökulhlaups). The sudden release of meltwater from glaciers and snowpack or from glacier-dammed lakes on the edifice.

• Lahars, or debris flows, and debris avalanches. Gravitational movement of commonly water-saturated volcanic debris down the steep slopes of the volcano and into nearby valleys.

Mount Rainier is capable of eruptions of small to very large magnitude, as measured by the Volcanic Explosivity Index of 4 to 5 that has been tentatively assigned to the explosive eruption that occurred between 30,000 and 100,000 years ago. Based on past activity, the most likely future eruptive event at Mount Rainier is the extrusion of a lava flow at the summit, possibly accompanied by tephra eruptions. Lava flows would likely be restricted to valley floors within or a short distance outside of Mount Rainier National Park, where they would destroy roads, buildings, and other fixed installations. The sluggish motion of these flows would probably permit people to evacuate safely from areas at risk, so little loss of life would be expected. However, steam columns and nighttime reflections of the glowing surfaces of lava flows from clouds could be visible from the Seattle-Tacoma metropolitan area, possibly creating an unwarranted sense of impending crisis.

Explosive eruptions from Mount Rainier could send clouds of tephra high into the atmosphere where they would be carried laterally by prevailing winds before settling to the ground. This tephra could be a major hazard to crops and other vegetation, poorly built structures, and machinery. The prevailing winds in western Washington are from southwest to northeast, so tephra from Mount Rainier would normally be carried away from the Seattle-Tacoma metropolitan area. Less frequently, winds blow from east to west, and at such times tephra could be scattered over

much of Puget Lowland. This would disrupt commerce, travel (including flights at Seattle-Tacoma International Airport), and the daily lives of hundreds of thousands of people.

Major edifice failures, glacier outburst floods, and lahars could occur in the absence of volcanic eruptions because of the inherent instability of the volcanic edifice. Mount Rainier is a high volcano (4,392-meters above sea level with approximately 3,000 m of relief) that contains about 140 cubic kilometers (km³) of structurally weak and locally altered rock capped by about 4.4 km³ of snow and ice, all of which stand near the angle of repose. Ground shaking during an earthquake, or ground deformation due to intrusion of magma into the edifice, could cause the gravitational failure of a large sector of the volcano, producing catastrophic avalanches and debris flows and possibly triggering an eruption. Glacier outburst floods and lahars can also occur during heavy rainfalls or transient heating events that melt the snow and ice cover on the volcano.

Damage caused by debris flows could be substantial. Geologic mapping of surficial deposits in Mount Rainier National Park has shown that numerous debris flows have entered the rivers draining the volcano over the past several thousand years. The largest known debris flow from Mount Rainier, the Osceola Mudflow, traveled down the White River drainage system a distance of approximately 110 km about 4,500 to 5,000 years ago and transported at least 3 km³ of rock debris, burying parts of the Puget Lowland that are now heavily populated. In the past 45 years, about two dozen debris flows and outburst floods have occurred at Mount Rainier, the majority in the Tahoma Creek-Nisqually River drainage. These debris flows traveled downstream as far as 16 km from their origin on the volcanic edifice.

Coordinated research that involves both geoscientists and social scientists should be undertaken to determine potential magnitudes and frequencies of potential hazards, their human and economic impacts, and strategies for using such information effectively to mitigate risk as part of this Decade Volcano Demonstration Project. A plan to achieve these objectives is outlined in this report.

Regional studies are needed to address the formation and development of Mount Rainier within the Cascade volcanic arc environment. Of particular importance in this context are studies that address the following:

• tectonic processes that control the locations of volcanic vents;

• regional stress fields and their effects on volcanism, faulting, and seismicity;

• the crustal deformation field caused by magma injection, subduction, and glacial loading; and

• ages, distributions, and characteristics of tephras, lavas, and lahars.

Studies of the Mount Rainier edifice are also needed to address the development of the volcano in order to predict its future behavior. Of particular importance are studies that address these topics:

• the structure of the volcanic edifice and underlying crust;

• the history of edifice growth and failure;

• the geometry of hydrothermal and groundwater systems; and

• distributions of hydrothermally altered rocks.

A high degree of feedback between local and regional studies and between individual projects and investigators should be employed as part of the strategy for this Decade Volcano Demonstration Project. This project should be coordinated with ongoing research programs of federal, state, and academic scientists and should include the following elements:

1. Geologic mapping. Mapping the spatial and temporal distributions of eruptive and intrusive rocks, faults, hydrothermal alteration zones, surficial deposits, springs, fumaroles (vents that emit steam and other gases), and glaciers should be undertaken as part of the effort to understand the development of the Cascade volcanic arc and Mount Rainier edifice.

2. Petrologic and geochemical studies. Petrological and geochemical studies of Tertiary and Quaternary (particularly Holocene) rocks should be undertaken to address the physical characteristics and evolution of the magma system through time, to help establish stratigraphic relations among eruptive products, and to provide the basis for reconstructing patterns of hydrothermal alteration.

3. Geophysical surveys. Geophysical surveys should be undertaken to elucidate the structure of the volcanic edifice and underlying crust, including distributions of magma, intrusive bodies, faults, hydrothermal and groundwater systems, and glacier ice.

4. Lahar studies. Detailed mapping, including mapping of buried lahars, should be carried out to reconstruct the spatial and temporal distributions of these flows and to obtain volumetric estimates for each flow event.

5. Edifice stability assessment Research on edifice stability should focus on mapping the distributions of hydrothermally altered rocks, faults, and dikes, which are mechanically weak and prone to failure. Research should also focus on the delineation of the hydrothermal system and the process of wallrock alteration, particularly beneath the glaciers that cover the edifice.

A program of volcano monitoring should be established at Mount Rainier to identify anomalous activity that could serve as an early warning of the occurrence of volcanic hazards such as eruptions, edifice collapse, and lahars. This monitoring program should include plans for the collection of adequate baseline data to provide a background of values with which to contrast anomalous behavior.

Monitoring should involve the following techniques, which have been developed and tested over the past several decades at active volcanoes around the world:

1. Seismic monitoring, using the present network of seismometers, to detect the movement of magma, glaciers, and rock on or beneath the volcano. The network should be upgraded with a minimum of two, three-component instruments to allow for the precise location of events on the edifice.

2. Ground-deformation monitoring, to detect edifice creep or the underground movement of magma. To this end, the present network of geodetic stations should be expanded with additional stations established at higher elevations on the edifice, and this local network should be integrated into the regional network. These local and regional networks should be monitored using real-time, continuous Global Positioning System (GPS) or they should be resurveyed using GPS at frequent intervals.

3. Monitoring hydrothermal activity, to detect changes in the composition or rates of emission of gases and fluids from the edifice. A program of fluid and gas sampling should be initiated to monitor the hydrothermal system on the volcanic edifice.

4. Monitoring changes in surface appearance, to detect changes in the snow and ice cover on the volcano. This monitoring should include visual observation, photogrammetry, infrared heat emission, and radar imagery.

5. Stream monitoring, to detect floods and lahars after they have formed and are moving downslope toward populated areas. To this end, a network of sensors tied into the existing seismic network should be installed in the major drainages on the volcanic edifice to detect the formation and movement of lahars.

Communities in the region must seek ways to reduce or mitigate risk to life and property from volcanic hazards while maintaining the strong economic base that derives in part from the desire of people to live, work, and play around the volcano. Effective risk mitigation can be successfully executed only within the context of a comprehensive strategy to understand the volcano. The success of mitigation efforts requires that the

hazards themselves are well understood through a program of coordinated research as outlined in this report; that they can be recognized through effective monitoring before they reach a critical level; that warning of their occurrence can be communicated clearly, accurately, and quickly to public officials; and that public officials can and will act to put the appropriate risk-mitigating measures into operation.

The important elements of an effective mitigation program are these:

1. Communication is essential among the many groups that live and work around the volcano:

• Within the scientific community, to coordinate and disseminate research on the volcano. To this end, a Mount Rainier Hazards Information Network should be established on the Internet to disseminate past, current, and planned research and information on mitigation measures.

• Between scientists and responsible authorities, to provide precrisis information about volcanic hazards, and warnings of impending hazards. An emergency-response plan should be developed so that scientists involved in monitoring can provide responsible authorities with accurate and timely warnings of impending hazards and can keep officials informed during such events.

• Between scientists and the public, to inform the general public about the nature of volcanic hazards, people and property at risk, and options for risk reduction. Scientists should work with educators and National Park Service staff to develop and distribute high-impact educational materials, to provide presentations at schools and public meetings, and to develop displays on volcanic hazards and emergency response for visitors to Mount Rainier National Park.

• Between responsible authorities and the public, to communicate timely and accurate information and warnings about volcanic hazards to the public. Authorities should develop plans for such

communication and test those plans in simulated precrisis and crisis situations.

2. Planning and implementation of risk-mitigation measures should involve scientists, government, business, and citizens and should be coordinated and, where appropriate, integrated with other planning activities in the region. Several measures, including the following, should be considered for implementation in order to significantly reduce risk from volcanic hazards to people and property:

• analyses to identify regions and populations at risk;

• land use planning and economic incentives to discourage inappropriate use of high-risk areas; and

• engineering solutions to mitigate risks, where possible, from specific volcanic hazards.

An important contribution of geoscientists in these efforts should be the identification of areas at risk through the development of hazard maps, which are spatial representations of risk from hazards such as lava flows and debris flows. Geoscientists should work cooperatively with planners, engineers, social scientists, and legal professionals to ensure that these hazard maps contain appropriate data, presented in usable formats for risk-mitigation efforts.

Traditionally, natural scientists participate in mitigation efforts up to the point of public debate, providing information about hazards and, occasionally, about their effects on people. Social scientists, on the other hand, rarely become involved in the early stages of hazard studies. The U.S. Geodynamics Committee believes that more effective strategies could be developed and implemented if both groups work together, starting with geologic investigations and continuing throughout debate and implementation of mitigation measures. Similarly, social scientists, geoscientists, planners, engineers, citizens, and decision makers should work together, from hazard assessment through implementation, if the populations around Mount Rainier are to coexist in reasonable safety with the volcano.

Implementation of the Mount Rainier Decade Volcano Demonstration Project is the responsibility of the scientific community, which should develop a plan to carry the project forward. This implementation plan should provide guidance on:

• priorities for research and monitoring activities based on scientific significance and value to risk-mitigation efforts;

• funding for research and monitoring activities deemed to be of high priority;

• mechanisms for coordinating the efforts of scientists to avoid unnecessary duplication, particularly in the use of instrumentation or collection of samples from wilderness and other environmentally sensitive areas with limited access; and

• mechanisms for balancing the needs of scientists for access, samples, and data with the needs of federal and state agencies to fulfill their research, public safety, and land-management missions.

To be effective, monitoring efforts will require continuity in funding, management, personnel, and facilities that can best be provided by federal and state agencies with responsibilities for volcano and hazards research. Nongovernment scientists should be encouraged to participate in monitoring activities in both data collection and advisory capacities, and the scientific community should have free and immediate access to monitoring data.

Many of the research, monitoring, and mitigation activities described in this report will require access to Mount Rainier National Park and surrounding Forest Service and private lands for field work, sample collection, and installation and operation of scientific instruments and telemetry equipment. Much of this land is environmentally sensitive and is designated as wilderness area. Research and monitoring activities must be designed to minimize impacts to the environment. Consultation with Park Service and Forest Service staff for work on federal land and with

state personnel for work on private lands must begin at the design stage of all projects in order to assure compliance with existing regulations.

Park Service and Forest Service staff can make significant contributions to the research and monitoring efforts outlined in this report. They are in a position to notice subtle changes in the volcano that might not be apparent to visiting scientists or the general public. They can make regular visual observations of snow, ice, and rocks on the volcanic edifice; assist with the collection of data; and, where appropriate, assist with inspections and routine maintenance of instrumentation. Cooperation between researchers and Park Service and Forest Service staff is essential to the successful implementation of this project.