Augustine volcano as tsunami
By Ned Rozell
January 31, 2007
On October 6, 1883, someone wrote this entry in the Alaska Commercial
Company logbook at a trading post at English Bay, Alaska, about
50 miles northeast of Augustine volcano:
"This morning at 8:15 o'clock, 4 tidal waves flowed with
a westerly current, one following the other . . . the sea rising
20 feet above the usual level. At the same time the air became
black and (foggy), and it began to thunder . . . it began to
rain a finely powdered brimstone ash."
Augustine volcano viewed
from Homer Spit in September 2006.
Photo courtesy Tom Harnish and Alaska Volcano Observatory.
Augustine, which erupted explosively at the beginning of 2006,
also erupted in 1883 but with a dramatic difference: part of
the mountain tumbled into the sea in a giant landslide. That
landslide caused a tsunami that crossed lower Cook Inlet and
hit the southernmost Kenai Peninsula.
Because the tsunami happened at low tide in an area with some
of the largest tidal ranges on Earth, the 20-foot high wave flooded
areas only slightly above the high tide line. Researchers think
the damage from the 1883 tsunami was limited: some low-lying
shelters flooded, and a few kayaks floated away.
The 1883 eruption of Augustine and the resulting tsunami intrigue
Jim Beget, a scientist with the Geophysical Institute at the
University of Alaska Fairbanks and the Alaska Volcano Observatory.
He traveled to Augustine volcano as recently as last summer to
gather evidence of the 1883 event he read about in the old logbook.
On the island, Beget found driftwood scattered high on shore
above the beaches, beyond the point where severe storms might
deposit wood. Using that wood and deposits of marine mud, sea
shells, and beach sand found within the soil of the island, Beget
figured that the 1883 waves on Augustine Island reached a maximum
height of more than 50 feet near where the giant volcanic landslide
entered the sea. Traveling around Cook Inlet, Beget found deposits
from the 1883 tsunami along the coast near Mt. Illiamna, the
village of Nanwelak (formerly the English Bay of the Alaska Commercial
Co. journal), and the town of Homer.
The 1883 tsunami happened because the north side of the mountain
that is Augustine volcano collapsed into the sea. Since then,
the volcano has healed the scar, filling it with lava during
eruptions in 1935, 1963, 1976, 1986, and again in 2006.
"Augustine gets higher and higher and higher with each eruption,"
Beget said. "In 2006, it added another new dome."
Some active volcanoes accumulate enough material that they get
to a collapse point. That's what happened to Augustine in 1883,
and has happened to a few other volcanoes over time. Though have
been about a dozen recorded collapses of Augustine in the last
2,000 years, people didn't think of giant landslides from volcanoes
as much of a hazard until 1980.
"When St. Helens collapsed, it was a big surprise to most
people," Beget said. "Now we realize it's not that
Scientists at the Alaska Volcano Observatory now watch Augustine
and other Alaska volcanoes for signs of a pending implosion,
such as earthquakes and changes in shape of the mountain they
can detect with global positioning system receivers cemented
into its flanks.
Beget and Zygmunt Kowalik of the Institute of Marine Sciences
at UAF recently authored a paper in which they confirmed travel
times of an Augustine-generated tsunami calculated by computer
model. The model calculated that a tsunami would reach Homer
in about 75 minutes. Travel time to Anchorage would be around
four hours, but only small waves would reach that far up Cook
Inlet. Beget and Kowalik also found that because of sea floor
characteristics, tsunamis would be larger along the Illiamna
coastline and near Nanwelak, Homer, and Anchor Point.
Depending on the state of the daily tides in Cook Inlet, a tsunami
from Augustine would either be catastrophic or an interesting
footnote to another eruption.
"If it happens at low tide, we'll consider ourselves lucky,"
This column is provided
as a public service by the Geophysical Institute, University
of Alaska Fairbanks, in cooperation with the UAF research community.
Ned Rozell [email@example.com]
is a science writer at the institute.
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