After 12 hours Saturday, West Coast emergency management agencies canceled a tsunami advisory following an underwater volcanic eruption near Tonga in the Pacific Ocean.
While the Washington coastline saw minimal impacts from the tremors, it was a reminder of past Pacific tsunamis and the potential earthquake and tsunami of the Cascadia subduction zone.
The South Pacific eruption on Friday evening spewed ash, steam and gas, according to satellite images, and a sonic boom could be heard from Alaska, according to the National Weather Service.
Waves of about 2.7 feet hit the Tonga coast, according to Associated Press and the U.S. West Coast was hit by remnants of reverberation throughout Saturday.
The National Weather Service reported that the California coast saw the highest recorded waves, peaking at 4.3 feet in Port San Luis. The Pacific Northwestern and Alaskan coastlines saw smaller impacts of less than 2 feet waves.
A tsunami advisory was issued for the U.S. West Coast on Saturday morning at 5 a.m. from the National Tsunami Warning Center.
An advisory is issued when waves are expected to reach between 1 and 3 feet, and directs people to stay out of the water and away from the shore due to strong currents and higher than normal waves.
In Washington, the advisory included the entire Pacific coast as well as the Strait of Juan de Fuca and the San Juan Islands, Grays Harbor, Willapa Bay and the Columbia River as far as Cathlamet.
The tsunami waves were unlikely to create any significant surge into the Puget Sound, said Harold Tobin, director of the University of Washington’s Pacific Northwest Seismic Network.
Pierce County Emergency Management told residents to prepare for stronger currents during the afternoon high tide.
There was no recorded earthquake, but the volcano explosion itself was a seismic event, Tobin said. The U.S. Geological Survey reported that the eruption caused tremors equivalent to that of a magnitude 5.8 earthquake.
Emergency management agencies across the West advised people to stay away from the beaches, ports and harbors.
Pacific County’s Emergency Management Agency said many were ignoring official direction.
“Droves of people are driving out onto the beach. This is not a spectator event. Please stay off the beach,” the emergency agency’s Facebook post said.
Has this happened before?
Tobin believes this is the first Pacific-wide tsunami alert from a volcanic eruption in this century.
The seismologist said the last time Washington felt similar impacts was in 2011. A magnitude 9.0 earthquake struck the Pacific Ocean near Japan’s main island, Honshu on March 11, 2011. The seismic event triggered a tsunami with waves reaching as high as 30 feet. More than 200 miles of the Japanese coast was flooded, including the Fukushima nuclear power plant.
It was the largest earthquake ever recorded in Japan, and the fourth largest in the world since 1900.
The tsunami in Japan brought higher waves to the West Coast and eventually some debris, according to News Tribune archives. Nine months after the tsunami, debris floated a few miles from Neah Bay, the northwest tip of Washington.
Could a stronger tsunami hit Washington?
About 80-miles off the West Coast lies the Cascadia subduction zone, where one of the Earth’s tectonic plates slides under another. Experts have estimated that the last time the fault ruptured was in 1700, triggering a slightly larger earthquake than 2011. For the last three centuries, the fault zone has remained silent.
The subduction zone could rupture at any time or continue to be dormant for another two centuries. A full rupture of the fault could be felt for 775 miles from Northern California to Vancouver Island, Canada, according to the latest tsunami hazard maps from the Washington State Department of Natural Resources released on Jan. 10.
An earthquake would provoke tremors in the ocean, causing massive waves along the Western coastline. The department’s models estimate that the first tsunami wave would arrive at La Push within 10 minutes from the start of the earthquake shaking. The first wave is modeled to exceed 30 feet and reach much of the Pacific coast within 30 minutes.
“Tsunami wave inundation would likely continue over 8 hours and remain hazardous to maritime operations for more than 24 hours,” the state agency’s blog said.
The tsunami waves would travel into the Salish Sea to the Puget Sound. Waves are expected to reach the Port of Seattle 2 hours and 20 minutes after the initial tremors cresting at seven feet high, according to DNR hazard maps. The Port of Tacoma is estimated to see 3.5-foot waves about 2 hours and 40 minutes after the first fault tremors.
Washington is adding two new 80-foot escape towers: one in Westport and another near Tokeland.
The Washington Emergency Management Division previously told The News Tribune that the Washington coast needs dozens of these structures for safe evacuations.
Driving may not be as available as many hope during a tsunami.
“You’re going to have severe damage to bridges, to roadways, fires, liquefaction, trees and telephone poles falling down,” Maximilian Dixon, the geologic hazards supervisor, told The News Tribune. “You’re going to have folks that are potentially panicking, getting into accidents. So the likelihood of someone being able to find their car keys, get into their car and have a clear path to drive to safety is very, very low.”
