Natural Hazards Observer
| September 2004 | Volume XXIX | Number 1 |
Disasters Waiting to Happen . . . Fifth in a Series
Mount Rainier:
A Threat Becomes a Reality
Listening, Watching, and Waiting
It was a clear day in March 2010 when Delia grabbed a NOAA weather radio off the store shelf with a sigh of relief. Delia's family lived on a farm on the Puyallup River floodplain seven miles south of Orting, Washington, and a trip into town meant a 15-minute drive. As she and her mother stood in line, Delia noticed that two people in front of them had weather radios and there was a man at customer service asking about them.
As she stepped outside into the spring afternoon, Mount Rainier towered above her, a plume of steam rising from its snow-covered summit. The small stream of vapor looked peaceful at the moment, but had been darker and more turbulent in previous days as steam explosions blasted fragments of old lava and ash hundreds of feet into the air. For three days, the constant plume had been a reminder of the volcano's increasing unrest. The thirteen-year-old worried about what might happen based on scientists' warnings that landslides or snowmelt during eruptions could produce destructive volcanic mudflows (lahars) in the river valleys with headwaters on Mount Rainier.
As days turned into weeks, Delia grew tired of hearing the same talk everywhere. The four million people of western and central Washington State could view continuous steam explosions rising from the summit and the news was filled with reports about the volcano. U.S. Geological Survey (USGS) scientists and their colleagues reported that the noticeably increasing amounts of carbon dioxide and sulfur dioxide were indicators of rising magma. They broadcast pictures of seismometers, tiltmeters, and global positioning satellite (GPS) devices. Volcanologists explained how the cubic mile of snowpack and glacier ice on Mount Rainier would be melted by eruptions and described how a debris avalanche could trigger a lahar. Based on monitoring data, scientists raised the volcano alert level to the highest level below an actual volcanic eruption and displayed maps showing areas likely to be affected by lahars, ashfall, lava, and pyroclastic flows.
Emergency managers issued repeated warnings that people should move to high ground, at least one hundred feet above the valley floor. Pierce County Department of Emergency Management (DEM) announced evacuation routes and instructed residents on what to do during an emergency. They also explained the acoustic flow monitors (AFMs) installed in the Carbon and Puyallup Valleys to detect approaching lahars and send signals to trigger sirens in communities downstream. Emergency managers advised residents, especially those who lived beyond the sirens' range, to purchase weather radios. It seemed like everywhere Delia went people were listening to their radios and waiting.
The Waiting is Over
Because it was so cloudy, no one witnessed the debris avalanche that broke away from the upper west flank of Mount Rainier on the afternoon of April 29, 2010. What began as an avalanche transformed into a lahar, and a muddy mass poured into the valley of the Puyallup River, eroding stream banks, incorporating trees, rocks, and human-made structures into its flow. The mixture rumbled down the river valley at about 30 miles an hour, triggering the AFMs.
It was 2:10 p.m. when the AFM alarm sounded. In school, Delia's teacher recited instructions: "Okay, students, line up. Over the footbridge and up the hill. No running, no pushing; we have plenty of time. Remember the drills." The classes flowed down the hall and through the exit doors.
Unlike during the drills, the students could hear a roar in the distance, like the rumble of a train. In front of Delia, students sprinted toward the Carbon River Lahar Evacuation Bridge, the result of an Orting community fundraising effort to get citizens across the river to high ground. The procession of students passed quickly over the bridge and along a trail 200 feet above the valley floor. Another half-mile of walking brought them to waiting buses that transported them to an emergency center.
The lahar, still 15 miles upriver and 60 feet thick, tore through commercial timberland. When it reached the Orting-Kapowsin highway bridge south of town, the lahar was briefly slowed by the bridge before lifting it from its foundation and continuing on to engulf 23 small farms along the Puyallup River. Seven miles south of town, the lahar spread into the widening valley and lost momentum. Three miles south of Orting, thirty-four minutes after the warning sirens started, the mudflow came to a stop.
The Aftermath
At the emergency center, Delia watched as parents picked up her schoolmates. Like most of those still at the center, Delia ate her dinner while watching the news and fighting the sinking feeling that her family's farm was gone. She knew that her mother's office in Tacoma was on high ground, but waiting alone only made her worry more.
On television, a USGS scientist described events of the day with a Washington State geologist and the director of DEM, explaining that water draining from the lahar would combine with rainfall runoff and lead to serious flooding during the coming weeks. Maps of predicted flood zones were displayed along with a video that showed the lahar raging down the valley, trees collapsing into it like a sequence of falling dominoes.
Finally, Delia's mother arrived and wrapped Delia in a warm hug. Their house and everything they owned was gone, but her family was safe.
The news continued to give every detail of the volcano's activity, with messages from the USGS, Washington State Emergency Management Division, the American Red Cross, and local fire and rescue agencies. The volcano continued to show signs of impending eruption and crews were sent to repair the damaged AFMs.
During the two days after the lahar, water that drained from the lahar upstream flooded homes built on the 100-year floodplain of the Puyallup River and made the highway between Orting and Kapowsin impassable and sections of the Port of Tacoma waterfront unusable. Port authorities began emergency dredging, and, as the floods receded, cleanup began under the shadow of the restless volcano.
Danger Returns
The number of earthquakes beneath the volcano soon accelerated, heralding the arrival of magma at the summit one afternoon. A column of ash-a cloud of tiny, sharp fragments of cooled magma-rose to an altitude of 24,000 feet, spreading eastward with the prevailing winds and forcing aircraft in the region to change routes to avoid exposure to the ash. Sea-Tac Airport and smaller airports in eastern Washington closed for 12 hours to reduce the likelihood of aircraft damage, and the backlog of flights was felt around the world. National Weather Service meteorologists tracked the threatening ash plume as far east as the Dakotas.
That evening, airborne volcanologists noted a red-hot lava pool rising in the volcano's crater, overtopping the rim and spilling down the steep mountain slopes. Lava flows fifty to one hundred feet thick cooled on the upper slopes. As the lava spilled onto the steep flanks of the volcano, the flanks collapsed, producing pyroclastic flows, avalanches of hot rock fragments and gases. The flows melted the snow and ice and again formed lahars in the Puyallup, Nisqually, and White River valleys. The sirens sounded once more in Orting.
All is Quiet
A week later, the eruptions had halted. The slopes of the mountain, formerly white with snow, were dark and a scar was clearly visible on the northwest side. Darkened streaks showed where lahars had traveled down the slopes and into the valleys below. The news reports detailed the economic loss of structures, roadways, bridges, hydropower generation, water supply systems, and productivity, but Delia knew that things were not so bad. Even after losing her home, she knew that what really mattered was that many lives had been saved by advance warnings and evacuations.
Thanks to the warnings, more than 200 people were saved during the initial debris avalanche and lahar in the Puyallup Valley. Had that lahar gone through Orting, more than 10,000 would have been saved. Intensive volcano monitoring during the subsequent eruptions and lahars, coupled with close cooperation among scientists, public officials, and the media, saved countless other lives.
This Invited Scenario was written by Tania Larson of the U.S. Geological Survey (USGS) in consultation with Carolyn L. Driedger, Willie Scott, and Cynthia Gardner of the USGS Cascades Volcano Observatory.
Internet Resources
http://volcanoes.usgs.gov/
The Mount Rainier Mudflow Warning System was installed as a joint project between the USGS Cascades Volcano Observatory and Pierce County Emergency Management. General information about the USGS Volcano Hazards Program can be found here as well.
http://vulcan.wr.usgs.gov/
Information about Mount Rainier Hazards, including the Mount Rainier Hazards Assessment conducted by USGS is available here.
http://emd.wa.gov/index.htm
The Mount Rainier Response Plan written by the interagency Mount Rainier Volcano Hazards Work Group is found on this Web site.