Underwater volcano active off Oregon coast

A volcano may be erupting off the Oregon coast, scientists say

Three hundred miles off the Pacific Northwest coast, the seafloor has been rumbling.

Over the past five months, there were hundreds of small earthquakes on most days at Axial Seamount.

Then on April 24, there was a spike: nearly 8,000 earthquakes. The seafloor level dropped more than two meters. Temperatures rose.

Scientists believe an underwater volcano is erupting.

An eruption is not a threat to coastal residents, researchers say, because the earthquakes are small, mostly magnitude 1 or 2, and the seafloor movements are relatively gradual, so they won't cause a tsunami.

The volcanic activity has no relationship to the Cascadia Subduction Zone, which scientists watch closely for signs of a much larger and more destructive earthquake.

To Bill Chadwick, an Oregon State University geologist, the eruption at Axial Seamount was not a surprise.

He had predicted it would happen this year. He predicted the previous eruption, in 2011, too.

Chadwick hopes the lessons he and his collaborator, Scott Nooner at the University of North Carolina Wilmington, learn from Axial Seamount can eventually be applied to volcanoes on land.

Land volcanoes have thicker crusts and are influenced by large earthquakes and other nearby volcanoes, among other things, so predictions are more difficult, Chadwick said.

"Axial Seamount is a pure example, if you will," he said. "It has relatively simple plumbing."

Chadwick and other scientists watch the signals at Axial Seamount in real-time via a cable laid out on the seafloor. The cable is part of the Ocean Observatories Initiative funded by the National Science Foundation. [...]

I doubt that it has nothing to do with the Cascadia Subduction Zone, since it is practically right on top of it. I presume they mean to say, that the volcano isn't signaling an imminent earthquake. As far as they can tell.

Read the whole thing for embedded links, photos and more.

     

Japanese Tsunami Debris on Oregon Coast

It's starting to arrive in greater quantities. A few Sunday's ago, I encountered my first piece. We were having a nice walk on a local beach:


It was another day in paradise. Just beautiful. Then I saw it:



A first I thought it was just an ordinary piece of rubbish. But then I saw the Japanese writing on it. It was a bottle of hairspray. It had floated in the ocean for a long time, so long that it had seaweed growing on it.

I could only wonder; had it been sitting on a shelf in a hair salon? Or on a ladies dressing table, or in someone's bathroom cabinet? Was it swept out to sea from someone's house - WITH the house? With people still in the house? All questions that can never be answered.



I left it there, bearing witness to a disaster far away, years ago. I continued my walk, and told myself I would pick it up on my way back down the beach. But on the way back, it was gone. Either someone else picked it up, or it went back to sea for a while, to remind someone else on another day.

Meanwhile, an article in the Vancouver Sun tells us that a Tsunami here would not be as bad as the earthquake that would cause it:

Monster earthquake would devastate Pacific Northwest, leaving thousands dead
But tsunami would be secondary issue for Lower Mainland, because Vancouver Island would take brunt of big wave: expert

A monster earthquake and tsunami would wreak havoc on B.C.’s west coast, but the effects would be far worse in Washington and Oregon states.

“I suspect there’d be a significant number of deaths in the Lower Mainland as a result of the shaking,” said Ronald Clowes, a crustal seismologist and professor emeritus at the University of B.C. “But the tsunami would be a secondary concern.”

Clowes spoke on Friday after researchers told Oregon legislators Thursday that more than 10,000 people could die when — not if — a monster earthquake and tsunami occur off the Pacific Northwest coast.

Coastal towns would be inundated; schools, buildings and bridges would collapse; and economic damage could hit $32 billion, the researchers said.

These findings were published in a chilling new report by the Oregon Seismic Safety Policy Advisory Commission, a group of more than 150 volunteer experts.

[...]

According to the Oregon report, the 2011 Japan quake and tsunami were a wake-up call for the Pacific Northwest. Governments have been taking a closer look at whether the region is prepared for something similar, and discovering it is not.

Oregon legislators requested the study so they could better inform themselves about what needs to be done to prepare and recover from such a giant natural disaster.

The report says that geologically, Oregon and Japan are mirror images. Despite the devastation in Japan, that country was more prepared than Oregon because it had spent billions on technology to reduce the damage, the report said.

Meanwhile, a third minor earthquake has struck off the north B.C. coast, the latest in a series that has rattled the area since last fall. [...]

I don't deny that there is a seismic hazard here. But I don't know how they can say "Oregon and Japan are mirror images". Japan has a long history of active earthquakes, which is why they are better prepared. Earthquakes in Oregon are few and far between, which is why we are not better prepared. I don't see how that makes us a "mirror image". Though I suppose if a large earthquake and resulting tsunami happen, it won't much matter what we call it.
   

Southern End of Cascadia Fault More Unstable

And thus more likely to have a quake soon:

Northwest Earthquake Risk in U.S. Looms Large: 40% Chance of Major Earthquake Within 50 Years

ScienceDaily (Aug. 1, 2012) — A comprehensive analysis of the Cascadia Subduction Zone off the Pacific Northwest coast confirms that the region has had numerous earthquakes over the past 10,000 years, and suggests that the southern Oregon coast may be most vulnerable based on recurrence frequency.

[...]

"The southern margin of Cascadia has a much higher recurrence level for major earthquakes than the northern end and, frankly, it is overdue for a rupture," said Chris Goldfinger, a professor in OSU's College of Earth, Ocean, and Atmospheric Sciences and lead author of the study. "That doesn't mean that an earthquake couldn't strike first along the northern half, from Newport, Ore., to Vancouver Island.

"But major earthquakes tend to strike more frequently along the southern end -- every 240 years or so -- and it has been longer than that since it last happened," Goldfinger added. "The probability for an earthquake on the southern part of the fault is more than double that of the northern end."

[...]

The Goldfinger-led study took four years to complete and is based on 13 years of research. At 184 pages, it is the most comprehensive overview ever written of the Cascadia Subduction Zone, a region off the Northwest coast where the Juan de Fuca tectonic plate is being subducted beneath the continent. Once thought to be a continuous fault line, Cascadia is now known to be at least partially segmented.

This segmentation is reflected in the region's earthquake history, Goldfinger noted.

"Over the past 10,000 years, there have been 19 earthquakes that extended along most of the margin, stretching from southern Vancouver Island to the Oregon-California border," Goldfinger noted. "These would typically be of a magnitude from about 8.7 to 9.2 -- really huge earthquakes.

"We've also determined that there have been 22 additional earthquakes that involved just the southern end of the fault," he added. "We are assuming that these are slightly smaller -- more like 8.0 -- but not necessarily. They were still very large earthquakes that if they happened today could have a devastating impact." [...]

This fits in with a previous post I did, "Oregon Tsunami Inundation Maps and Reports", which referenced the Gorda plate, a seismic zone that extends from Southern Oregon to Northern California. More plates, more faults, thus more activity.
     

California and Pacific North West Tsunami Risk

With all the talk about the possibility of underwater quakes just offshore of the USA's west coast causing tsunamis, I've wondered what the size of such waves might be. This article offers some estimates:

California tsunami could come with no warning

[...] Southern California could see a significant tsunami caused either by a large earthquake off Alaska or by undersea landslides spurred by smaller earthquakes off California. Northern California is at greater risk because of the Cascadia subduction zone, which runs along the Pacific Northwest coast.

Quakes off Alaska and the Pacific Northwest could create 15-foot waves in Southern California and 25-foot tsunamis in the northern part of the state, said California State Geologist John Parrish.

Tsunami inundation map of Long Beach. Click through for a larger version.And tsunamis caused by underwater landslides off Southern California could reach as high as 40 feet, although they would be localized and quick to dissipate, said Costas Synolakis, director of the Tsunami Research Center at USC.

That type of event is only expected to strike once in 2,000 or 3,000 years. But, as has happened in Japan, experts say all predictions may go out the window.

“Mother Nature is notorious for not obeying rules that we make,” Parrish said.

[...]

A quake off Alaska would give California six to nine hours lead time to clear the beaches before a tsunami struck, Parrish said. A temblor off the California-Oregon border, on the other hand, might give Northern California towns less than half an hour to prepare.

“That’s not very much time," he said, "especially if it’s 2 o’clock in the morning and you’re trying to wake up a whole town of people and get them up the hill.” [...]

I can only wonder how accurate the estimates are. No one will really know until it happens.
     

Oregon Tsunami Inundation Maps and Reports

They have had these maps for a while now, but they have been updating them based on new data. Here is one of the main sites for information:

Oregon Tsunami Clearinghouse
This site has all kinds of information. One of the links is to inundation maps:

The Tsunami Map Viewer returns a map of areas with Tsunami Evacuation Zones based on information that you enter.

The part where you enter an address, does not work for me. Below that is a search box labeled "Search By a Coastal Area". It has a drop down menu. Pick an area from the menu, and it will show you a map, with flood areas highlighted in yellow.

There are also options in the upper right corner of the map to show a satellite view or a hybrid map/satellite view. On the left is a nav-bar, you can move the map around and zoom in quite close to see photographic detail. A note in the sidebar explains:

Important Map Notes

The Oregon Department of Geology and Mineral Industries (DOGAMI), in partnership with NOAA, is developing new tsunami evacuation maps and revising current maps for the entire Oregon coast.

The anticipated date of completion of this project is 2013. The interactive map on this website depicts first generation evacuation maps developed between 1995 and 2006 that show evacuation zones in yellow based on the maximum inundation expected for a local Cascadia tsunami.

This maps on this website incorporate new information and technology gained since the 2004 Indian Ocean tsunami that have aided the development of a second generation of evacuation maps. The new maps depict the maximum extent of inundation expected for both distant tsunamis (orange) and a local Cascadia tsunamis (yellow).

Since the Japan earthquake, there have been people in the media claiming that a Cascadia quake would be very similar to the one in Japan. I believe the inundation maps are based on a 9 point richter scale quake on the Cascadia fault zone.

The map below I shows the Cascadia fault zone (It's not an inundation map; I found it on another website. Here, the yellow just marks the fault zone):



There hasn't been a large subduction zone quake in Oregon since 1700, or so geologists tell us. They also say that at that time a 10 foot wall of mud and water washed inland over low lying areas. They base their guess on fossilized remains of Indian settlements that were buried under a layer of mud in that time period (sorry, I didn't save the link). How accurate their estimate is, I couldn't say. A 10ft wave, while serious, isn't the 33 ft waves Japan had just had.

In general, there are not many quakes in Oregon. I've lived here since 2004 and have not even felt one. But they do happen occasionally. Mostly they are small, with a few exceptions.

Because Oregon is not as seismically active as Japan, I don't know how apt the comparison is. But does the lack of earthquakes here make us complacent? Perhaps.

So just how serious is the potential threat?

Earthquakes in Oregon State

[...] There are numerous fault zones in Oregon. A graphical representation is available from the University of Oregon. The information below about earthquake hazards in Oregon is exerpted from an FAQ by the Oregon Department of Geology and Mineral Industries.

Q: Is there an earthquake hazard in Oregon?

A: YES! There have been no “big” earthquakes in Oregon’s brief history, and there is no question that damaging earthquakes have been far less frequent in Oregon than in California or Washington. However, geologic research tells scientists that Oregon will some day experience big earthquakes, and the Scotts Mills earthquake of March 25, 1993, and the Klamath Falls earthquake of September 20, 1993, confirm the research. Because we are poorly prepared, the damage could be great. We are faced with a small chance of a great disaster.

Q: What about “The Big One”?

A: Geologic research in the last few years has shown that Oregon and Washington have probably been shaken by numerous subduction zone earthquakes during the last several thousand years. Subduction zone earthquakes occur when two great crustal plates slide past each other beneath the coast of Oregon and Washington. These earthquakes occur, on average, every 300-600 years, and the most recent was about 300 years ago. The subduction zone earthquakes were probably centered just off the coast of Oregon and Washington and may have been as large as magnitude 8 to magnitude 9. Such earthquakes would cause significant shaking and damage in much of western Oregon. Scientists cannot predict whether the next such event might occur in two years or 200 years.

Q: What parts of western Oregon are most dangerous?

A: Local earthquakes are most common in the Portland metropolitan area, northern Willamette Valley, and Klamath Falls area and may threaten the coast from Coos Bay south to Brookings. We simply do not know about the risk of local earthquakes in most other parts of Western Oregon. All of Oregon west of the Cascades is at risk from subduction-zone earthquakes. The amount of earthquake damage at any place will depend on its distance from the epicenter, local soil conditions, and types of construction.

Q: What about faults?

Two of the largest earthquakes in Oregon occurred in 1910 and 1993. The 1910 earthquake was the largest historical shock within the state’s boundaries at a magnitude of 6.8, but it occurred too far offshore to cause damage, whereas the damaging 1993 earthquake was the largest historical earthquake beneath the land area of Oregon, with a magnitude of 5.9. [...]

There are so many variables. And a great deal of uncertainty. Perhaps the best we can do is to be prepared for the worst, and hope for the best. At any rate, preparation can help minimize the damage and enhance the recovery, whatever the size and scope of an event, whenever it may happen.