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The Rainier volcanic hazards detection system has been growing

Tags: earthquakes

Aerial view of a volcano with the top covered in snow and surrounded by clouds.
Mt. Rainier. (Credit: Max Bender, Unsplash.)

Volcanoes are typically known for their explosive eruptions, hot lava, and blankets of ash, but they are not the only hazards to be on the lookout for. Other risky events can be associated with volcanoes, such as lahars, which are fast-traveling sludgy mixtures of ash and water that can devastate a landscape in minutes. The Mount Rainier active stratovolcano in the Seattle-Tacoma metropolitan area of Washington state presents such a risk. 

Image of a volcano, Mt. St. Helens, in the background, with what appears to be an eroded river-like feature in the foreground. This is a lahar.
Landscape scoured and filled by lahars at Mt. St. Helens in Washington state. (Credit: Mike Dierkin, Unsplash.)

Lahars are one of the most deadly volcanic hazards. Because they are fast moving, evacuation efforts must be timely. They often move down drainages and valleys along rivers where towns and communities are often located. Around Mount Rainier these flow paths follow the Carbon River and Puyallup River that lead directly to metropolitan areas. Lahars would impact the nearest small towns within a matter of 10 to 15 minutes, and would reach the larger metropolitan area within 50 to 60 minutes. Mount Rainier is also glaciated at the top and often covered with snow for most the year, which provides ample water for ash and debris to mix with, forming the lahar. Moreover, lahars aren’t always associated with a volcanic eruption – they can be triggered by unstable rock on the flank of the volcano giving way and causing a landslide. Being able to monitor for both lahars and landslides with a dense network of detectors and robust transmission to emergency services could save thousands of lives. 

A colorful two-paneled map showing the locations of detection instruments with black and red triangles on a topographic map of the Mount Rainier area. The metropolitan area of Tacoma is highlighted in yellow towards the upper lefthand corner. The bottom panel shows a bar graph indicating the number of detection equipment over a range of years.
Top: Map of the Mount Rainier area with detection stations. Bottom: Type of instrument and number installed per year. (Credit: Maher et al. 2024; Seismological Research Letters.)

To address the lahar risk, the Cascades Volcano Observatory and the Pierce County Emergency Services established the Rainier lahar detection system (RLDS) in the 1990s in order to detect lahars within 5 to 10 minutes after they occur and subsequently alert downstream communities of their impending arrival. The RLDS of the 1990s included acoustic flow monitors, which are geophones transmitting at only a few frequencies once every 10 minutes. While helpful, given that lahars are fast-moving, this is not fast enough for timely warning. In 2016, the Cascades Volcano Observatory and Pierce County began upgrading the RLDS—an effort detailed in a recent paper in Seismological Research Letters.

Since then, 25 new stations have been established in valleys and drainages along the northwestern flanks of Mount Rainier in the direction of the Tacoma metropolitan area. These stations operate in the broadband and continuously transmit so that data is always received in real time. Three new stations were installed along the Puyallup and include tripwires, which will break during the passage of a lahar and send an alert to emergency services. Additionally, there are now three seismic stations and a telemetry station that host webcams updated hourly. 

Four-paneled image showing photographs of new detection equipment. They are housed in little huts with solar panels on the roofs.
Station setups in the RLDS. Panel (a): The hut style enclosure around instruments at stations. Panel (b): Box and swingset style enclosure. Panel (c): Infrasound sensor in a water-resistant tub. Panel (d): Infrasound sensor covered in an aluminum mesh. (Credit: Maher et al. 2024; Seismological Research Letters.)

Though the RLDS seems to serve a very specific purpose of lahar detection, it actually helps the Cascades Volcano Observatory with general earthquake and volcanic hazards monitoring of Rainier. Due to the additional stations now installed on Mount Rainier’s edifice, the network sensitivity of the broader monitoring system has been increased. It is also more sensitive to smaller earthquakes, which can help study the broad West Rainier Seismic Zone near the volcano. This is an area that experiences earthquakes unrelated to the volcanic activity of Rainier proper, and is thus of broader tectonic processes in the Cascades. Studying this zone with the additional seismometers installed as part of the RLDS provides an opportunity for geophysicists to understand this unique area and the mechanisms that promote earthquake seismicity. The upgrade of the RLDS to broadband also makes monitoring more robust and can help with detection of lower-frequency, longer-period seismic signals. The addition of infrasound arrays can also help identify and characterize explosions that may be triggered.

A two paneled figure showing seismicity in the study area captured by stations. Orange circles show detected earthquakes in a region called the West Rainier Seismic Zone which is on the western flank of the volcano. Blue circles show seismic activity that are associated with the volcano. The size of the circles corresponds to magnitude, with the largest typically being M3. The bottom panel shows events per month as a filled line chart, and also the distribution of events per depth. The distributions are color-coded orange for the West Rainier Seismic Zone and blue for general volcanic events.
Seismic events captured by RLDS. (Credit: Maher et al. 2024; Seismological Research Letters.)

Other types of hazards can be studied on the volcano, too. Mass movements like landslides and avalanches can also be detected and are useful for testing out the RLDS because they occur at a higher frequency than lahars. For example in 2023, an avalanche was detected on the western flank of Mount Rainier by one of the seismic stations in the RLDS array. 

A figure showing seismic and infrasound detection of an avalanche, as well as the trajectory of flow.
Left: Instrumental detection of avalanche on the slope of Mount Rainier. Right: Trajectory and time series of avalanche.

The upgrade of the RLDS system will help the Seattle-Tacoma metropolitan area better respond to future lahar threats more quickly while also providing sufficient network sensitivity to study hazards on the volcano.