Cook Inlet volcano could trigger tsunami
Researchers model wave's impacts on Kenai Peninsula
Date: May 28, 1997
ANCHORAGE, Alaska—Rising 4,200 feet from the lower west side of Alaska's Cook Inlet, Mount Saint Augustine is one of the state's most active volcanoes. Better known for plumes of ash that disrupt air traffic around Anchorage, Saint Augustine has attracted the attention of scientists who study tsunamis—large ocean waves created by volcanoes and earthquakes.
One of those scientists is Elena Troshina. As a graduate student at the University of Alaska Fairbanks, Troshina created a computer visualization model of a tsunami that occurred in 1883. The wave was created when the north side of the volcano's dome collapsed into the sea. The tsunami traveled 51 miles across the inlet and partially flooded the small fishing village of English Bay.
"There are records that say on that day the air became black and foggy and it began to thunder," said Troshina. "Then an hour later four tidal waves came and raised sea levels by about 20 feet and partially flooded the village."
Since then, four other eruptions have spewed lava and rocks onto the slopes of the volcano. Scientists believe material on the summit now is so steep and unstable that another tsunami-producing landslide is possible. "There was great public concern in 1986 when the volcano erupted," said Troshina, "At that point the dome was already unstable. But it didn't collapse. Now it looks like the next eruption may collapse this dome."
Following the last eruption, the Alaska Sea Grant College Program, a federal-state marine research agency in Fairbanks, commissioned UAF scientists to model the impact of the 1883 tsunami on English Bay. Juergen Kienle from the Geophysical Institute and Zygmunt Kowalik from the Institute of Marine Science calculated the volume of material that slid into the sea, the initial creation of the tsunami wave, and the propagation of the wave across Cook Inlet. Troshina employed mathematical formulas that consider ocean depth and local topographical features to model the wave as it moved across Cook Inlet and flooded English Bay. Based on her model, the tsunami took just 53 minutes for the first 20-foot wave to hit the village.
In addition, Troshina modeled the impact on Homer Spit of a tsunami originating from a collapse of the east side of the volcano. She will present the models May 30 at the American Geophysical Union's session on coastal hazards in Baltimore, Maryland. The models will be used to help officials predict what might happen should future landslides and tidal waves occur.
"We know the volcano has a history of dome-building eruptions and then sudden collapses that cause tsunami waves," said Ron Dearborn, director of Alaska Sea Grant. "This model allows emergency planners to understand and plan for the risks."
Troshina says the model will be especially useful to scientists and emergency planners because different scenarios can be plugged into it to see how various waves may affect lower Cook Inlet communities.
"In the model you can consider landslide velocities from 10 meters per second to 100 meters per second," said Troshina. "You can look at the whole range of results from different avalanches."
According to the model, a landslide on the volcano similar to the one that occurred in 1883 would direct most of the tsunami's energy at Anchor Point. This is a region of high bluffs that would absorb the force of the wave, Troshina said. Most at risk from another collapse of Saint Augustine's dome would be Homer Spit, a peninsula that juts about four miles into Kachemak Bay that is a popular summertime tourist attraction.
"A lot depends on how much material ends up in the water from the collapse of the volcano's dome," said Troshina. "At high tide it can be a danger. It could flood Homer Spit if enough material crashed into the water at high tide. If something happens there it will be a problem just to leave the spit, to organize an evacuation."
Because the Kenai Peninsula shoreline offers protection, Anchorage is not at risk from a tidal wave generated by a collapse of the Saint Augustine dome.
The Alaska Tsunami Warning Center and the Alaska Volcano Observatory coordinate their efforts to alert coastal residents of possible dangers. Thomas Sokolowski is the chief geophysicist at the Alaska Tsunami Warning Center.
"There have been a number of landslide-generated tsunamis in Alaska," said Sokolowski. "We had at least five confirmed landslide-generated tsunamis during the 1964 earthquake that shook up two-thirds of the state. So in this respect her work helps us understand the kind of wave action that can be generated from them and their run-up onto shore."
A video that depicts the 1883 tsunami and its impact on English Bay is being completed by the Alaska Sea Grant Program and the visualization lab at the University of Alaska Arctic Region Supercomputing Center. It will be used to inform emergency planners and citizens about the cause and possible effects of a tsunami triggered by a landslide on Mount Saint Augustine.
The Alaska Sea Grant College Program is a marine research, education and outreach service headquartered at the University of Alaska Fairbanks, School of Fisheries and Ocean Sciences. It is funded by the National Oceanic and Atmospheric Administration in partnership with the state of Alaska and private industry.
Photos of the 1986 Mount Saint Augustine eruption as well as other images, topographic maps, and detailed information about the volcano can be seen on the Alaska Volcano Observatory's Augustine web page.
Alaska Sea Grant press releases and links to other fisheries and oceanographic material can be found at http://seagrant.uaf.edu/.
Alaska Sea Grant Homepage