As the death toll skyrockets from the tsunami that hit Southeast Asia last week, the damage from other tsunami catastrophes in Earth’s history pales in comparison. Yet Oregon has suffered from the same size and scope of tsunami that leveled parts of Southeast Asia many times in its past, said University professor of geological sciences Ray Weldon.
Students in his classes study the conflicting tectonic plates in the Pacific Ocean — the Juanda Fuca plate and the North American plate — that Oregon rests on. As the two plates collide, the North American plate stretches outward and upward, suppressing the Juanda Fuca plate underneath. Weldon’s classes, Oregon Geology, Surveying and Neotectonics, attempt to explain the collision of these two tectonic plates and the deadly results it causes.
The tsunamis that afflict the Oregon coast are usually, but not exclusively, caused by a tectonic plate on which Oregon rests that moves westward one inch per year while the Juanda Fuca plate shifts eastward, which creates tension that must be released, James Roddey, community educator at the Oregon Department of Geology and Mineral Industries, said.
“The last tsunami Oregon suffered occurred in 1700 when the populace of Oregon consisted of tribes,” Roddey said.
He added that scientists have not been able to find clear records of the magnitude of damage and any death tolls as a result of the deadly wave besides village ruins, but the fragmented records they do have come from oral history passed down by those tribes and from records in Japan, where the country experienced the catastrophic tsunami hours later.
Roddey said for a tsunami to occur, it has to be offshore and happen on the seafloor — there has to be a very large earthquake (at least 7 magnitude) or it can also be an underwater landslide. The most common tsunami, he said, is an underwater earthquake that displaces the sea floor.
Oregon’s timeline is marked by dozens of tsunamis that have been recorded in the 1,500 years scientists have been able to research, Roddey said. While there is no consistent pattern, the average interval between these tsunamis — which can reach the 9.0 magnitude earthquake seen in the Asian tsunami on Dec. 26 — is 400 to 600 years, with the longest interval lasting 1,000 years, Weldon said.
What if a tsunami were to strike today?
“The problem in Oregon is its coastal estuaries,” Weldon said, referring to towns and cities close to the ocean, such as Florence, that are without the benefit of rocky cliffs to protect them. “Florence and other towns have a risk associated with tsunamis. Properly warned, people can get away from a tsunami.”
The tsunami warnings would come first with an earthquake that would cause considerable damage, leveling buildings and destroying cars and even bridges. Injured Oregonians and those who did not escape in time would find an enemy in the inaccessibility the earthquake and tsunami would cause, isolating townspeople from the mainland, Weldon said.
“Many of the communities will be isolated, but they have to be prepared to take care of themselves and neighbors,” said Weldon. “A very minimal protection is all that’s needed until a lifeline is connected.”
Both Weldon and Roddey recommend food, water and medicine kits that can last up to a week as precautionary measures.
Tsunamis that have affected Oregon have not
always been caused by Juanda Fuca-North American plate collision. The most recent tsunami Oregon suffered came from Alaska, known as the Good Friday Alaska Earthquake, in 1964.
“The Good Friday Alaska Earthquake caused a tsunami that washed down the coast,” Weldon said. “(The tsunami) killed four people in the Oregon coast.”
Tsunamis from even farther away could cause damage. Roddey said that had the Southeast Asian tsunami not been directed toward the Indian Ocean and instead toward the Pacific, the damage could go as far as the United States coast. In those cases, people living on the coast would have hours of preparation.
“Tsunamis cross entire ocean basins,” Weldon said. “If something happened in the Philippines, we’d have 10 hours of warning.”
But the chance of a tsunami hitting Oregon any time in the near future is minimal, according to the Oregon Department of Geology and Mineral Industries, which estimates between 10 and 20 percent probability of a tsunami hitting Oregon in the next 50 years.
Professor studies Oregon tsunamis
Daily Emerald
January 4, 2005
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