Mount Rainier – Living Safely With a Volcano in Your Backyard

Mount Rainier towers over Seattle’s growing suburbs and Tacoma, Washington, rising more than 3 miles (14,410 feet) above sea level. Over the course of a year, about two million visitors explore Mount Rainier National Park to see the volcano, glaciers, forested ridges, and alpine meadows. The volcano’s elegance, though, is deceiving.

Mount Rainier is considered to be one of the most hazardous volcanoes in the United States, in regards to a USGS assessment. It has been the location of numerous eruptions and volcanic mudflows (lahars), which have excavated valleys and buried vast regions that are now densely populated. USGS researchers are collaborating with the National Park Service, local communities, and emergency managers to help people live more safely alongside the volcano.

An Active Volcano at Rest In Between Eruptions

Mount Rainier, the tallest summit in the Cascade Range, is an erupting volcano that is currently dormant between eruptions. Its monument, crowned by snow and 25 glaciers, was built up over 500,000 years by unknown eruptions. It last erupted in 1894-95, when bystanders in Seattle and Tacoma witnessed minor summit explosions. The next eruption of Mount Rainier could be comparable or larger. It may produce volcanic ash, lava flows, avalanches of extremely hot rock, and volcanic gases, known as “pyroclastic flows.”

Some of these occurrences rapidly melt snow and ice, causing gushes of meltwater to pick up loose rock and form rapidly flowing slurries of mud and stones known as “lahars.” Unlike lava flows and pyroclastic flows, which are unlikely to move over ten miles from the volcano’s summit and remain within Mount Rainier National Park, the most significant lahars can travel even further and approach Puget Sound.

Volcanic ash will be spread downwind, typically to the east, far from the major population areas of Puget Sound. Volcanic ash plumes in the air can endanger planes in flight and severely disrupt air travel operations. Although rarely life-threatening, volcanic ash after-fallout on the ground can cause problems for communities, disrupt utility and transportation networks, and necessitate significant clean-up costs.

Lahars Represent the Greatest Risk

Lahars pose a larger threat to Mount Rainier than lava flows, volcanic ash fall, or other volcanic phenomena because certain prospective lahar courses are densely inhabited and feature critical infrastructure such as highways, ports, bridges, and pipelines. Lahars look and act like flowing concrete, destroying or burying most man-made structures in their path. Earlier lahars, that most likely raced 45 to 50 miles at a time and were at least one hundred feet thick, were most likely restricted in valleys surrounding the volcano. They flattened and extended downstream, slowing to 15 to 25 kilometres in an hour. Past lahar deposits can be found throughout every valleys that originate on Mount Rainier’s sides.

Exactly How Hazardous is Mount Rainier?

Mount Rainier has erupted far less frequently and violently in recent centuries than its more well-known neighbor, Mount St. Helens. However, Mount Rainier’s closeness to big population centers in valleys prone to lahars renders it a significantly greater hazard to life and property than Mount St. Helens for the following reasons:

Population and development are at risk: Within Mount Rainier’s lahar-hazard zones, about eighty thousand individuals and their places of residence are at risk. These areas are home to critical infrastructure such as major highways and utilities, as well as economically significant industries, hydroelectric dams, and big ports.

Lahar size and frequency: Massive lahars have reached the Puget Sound lowland at least once per between five hundred and one thousand years over the previous generations. Smaller streams that did not extend into the lowland occurred more frequently. Assume that future massive lahars occur at rates equivalent to the past. In such circumstance, a lahar has a one-in-ten chance of reaching the Puget Sound bog lowland during the average human lifespan.

There might be little or no warning: According to USGS experts, at least one of Mount Rainier’s recent massive landslide-generated lahars may have happened when the volcano was quiet and not giving the warning indicators typical of an active and erupting volcano. The only caution in such an uncommon situation could be a rumor that a lahar is now ongoing.

Two Sorts Of Lahars

Mount Rainier can cause two types of lahars that could endanger nearby valleys:

Lahars caused by melting water: Mount Rainier contains approximately one cubic mile of glacial ice, which is more than all of the volcanoes located within the Cascade Range together.Throughout earlier eruptive occurrences, pyroclastic flow and other events caused rapid melting of snow and ice, resulting in several lahars. Such lahars would be preceded by occurrences that signaled an impending eruption.

Lahars caused by landslides: Earthquakes can be caused by molten rock (lava) seeping inside a volcano and weakening it, as occurred at Mount St. Helens.Helens in 1980, or by severe earthquakes. They could also be caused by the eventual failure of rocks weakened by the action of acidic fluids. Magma emits chemicals and heat, which leads to hot, acidic groundwater which may hydrothermally transform rough volcanic rock into a weak, clay-rich rock as time passes. When chunks of water-saturated clay-rich rock slip away, they quickly change into a lahar.

Fortunately most of Mount Rainier’s massive landslides occurred during eruptive events and were most likely produced by magma intrusion or explosive explosions shaking the volcano, the start of at least one, the 500-year-old Electron lahar, may not have been caused by eruptions. This lahar deposited deposits up to 20 feet thick and buried an old-growth forest near Orting today.

Are Landslides Possible in All Regions of the Volcano?

Because it possesses the most weakened clay-rich rock at high altitude, Mount Rainier’s west face, including the head of the Puyallup River, has the greatest potential for unleashing huge landslides that become far-traveled lahars. For consequently, the Puyallup River valley and, to a lesser degree, the Nisqually River basin, which both include some of the damaged rock, are the areas which are most susceptible to such calamities.

Tahoma, Washington Height on the east side of the volcano, as well as numerous additional cliffs and steep gradients, can fall short in landslides, such as one that traveled several miles in December 1963. However, such events are too small to cause lahars. Lahars caused by eruptions, unlike landslides, might flow down any of Mount Rainier’s valleys.

Long-Term Effects of Lahars

Lahars bury valley floors with deposits of rocks, sand, and mud several feet to tens of feet thick. These deposits disintegrate quickly when rivers and streams improve their channels, dumping a large amount of debris downstream over the course of years to decades.

As a result, downstream valley floorings that were previously unaffected by a lahar may experience increasing flooding and eventual burial by remobilized material. Extensive layers of sandy silt from Mount Rainier have been discovered in recent study projects, including the Port of Seattle along the Green and Duwamish River valleys. This silt was rapidly eroded from lahar deposits caused by eruptions around 1,000 years ago. The lahars, nevertheless, did not reach much farther than Auburn, roughly twenty kilometers south of metropolitan Seattle.

Debris Flows Endanger Mount Rainier National Park Regions

Almost every year, water released from glaciers or runoff from heavy rains combines with boulders and sediment to generate “debris flows” that disrupt valleys on Mount Rainier’s sides. These debris flows act similarly to lahars. However, they are typically so little that they rarely spread beyond the volcano’s base and only harm sensitive areas within Mount Rainier National Park’s limits.

Debris flows are most common in autumn and summer, while glaciers produce enormous quantities of meltwater and heavy rains can fall on sparsely vegetated, snow-free zones with plentiful loose debris. Because debris flows endanger park visitors and infrastructure, notably trails, bridges, and roads, Mount Rainier National Park educates employees and tourists about the hazards of debris flows and how to avoid them by staying away from valley floors.

Past Lahars Provide Clues Regarding Future Hazards

On valley bottoms, lahars deposit extensive layers of rocks, mud, and logs. Geologists use this and other evidence to assess future hazard potential and identify locations in river basins leading up to Mount Rainier that could be inundated by future lahars. A particular explosion or huge landslide would not touch all valleys, and not all lahars in a valley would be sufficiently significant to fall within hazard-zone limits.

Counties and communities at Mount Rainier’s base use lahar hazard regions identified by the USGS to lead the creation of hazard-area regulations in comprehensive land-use plans..

Lahar Warning System Minimizes Risk

Because of the increased potential of lahars caused by lanslides on Mount Rainier’s west face, the USGS, Pierce County Department of Emergency Management, and the Washington State Emergency Management Division devised a lahar warning system

A detecting element is made up of arrays of screens that capture the ground vibrations caused by a lahar. Computerized data analysis determines the presence of a flowing lahar and sends an automated notice to emergency response services. Following that, emergency managers can undertake necessary reaction steps. Notification processes, evacuation routes, and public education programs are established and maintained by city, county, and state agencies.

Assume a massive lahar formed in the upper Puyallup River valley without the usual antecedents that indicate volcanic activity and eruption. In that case, it might arrive in Orting as soon as 40 minutes after ringing the first warning. Time may be of the essence, and successful mitigation will undoubtedly rely on effective notice of those at risk, public comprehension of the issue, and rapid citizen response. This automated lahar detection and alerting system decreases but does not eliminate risk in lahar paths..

Monitoring and Emergency Preparation Are Ongoing

The USGS continuously monitors Mount Rainier and analyses potential volcanic activity hazards in collaboration with the Pacific Northwest Seismic Network at the University of Washington. Volcanoes frequently show indicators of unrest, such as increased seismicity (earthquakes), volcanic gas emissions, and volcano swelling, days to months before an eruption.

When unrest is detected, scientists will contact emergency management officials and enhance monitoring efforts.

The Mount Rainier Volcanic dangers Reaction Plan, which was created in partnership with local, county, state, and federal officials, is now available online. During a volcanic emergency, the plan describes firms’ responsibilities as well as the way they will interact with each other and the wider public.

What Should be Done If a Lahar or Debris Flow Threatens

Knowing the features of debris flows and lahars is the best thing to do. Relocating to high elevation above the valley level is the only way to secure safety and security during a lahar, according to experience from throughout the world. Look for signals of approaching debris flow–earth shaking and roaring sound–when trekking in valleys on Mount Rainier’s inclines in late summer during heavy rains–and go up the valley wall to higher land. The exact same thing is true for lahars; however, because they affect greater areas, people must evacuate vulnerable locations before lahars approach. Volcanic unrest usually always precedes lahars, thus people will be warned when there is an elevated risk in many cases.

Read the original article on Geology.com.