Mt. St. Helen's

[Annie]

http://www.pnsn.org/NEWS/PRESS_RELEASES/MSH_09_2004.html

Mount St. Helens Notice of Volcanic Unrest
September 26, 2004 3:00 P.M., PDT
U.S. Geological Survey Cascades Volcano Observatory, Vancouver, Washington
University of Washington Dept. of Earth and Space Sciences, Seattle, Washington
Seismic activity at Mount St. Helens has changed significantly during the past 24 hours and the changes make us believe that there is an increased likelihood of a hazardous event, which warrants release of this Notice of Volcanic Unrest. The swarm of very small, shallow earthquakes (less than Magnitude 1) that began on the morning of 23 September peaked about mid-day on 24 September and slowly declined through yesterday morning. However, since then the character of the swarm has changed to include more than ten larger earthquakes (Magnitude 2-2.8), the most in a 24-hr period since the eruption of October 1986. In addition, some of the earthquakes are of a type that suggests the involvement of pressurized fluids (water and steam) or perhaps magma. The events are still occurring at shallow depths (less than one mile) below the lava dome that formed in the crater between 1980 and 1986. The cause and outcome of the earthquake swarm are uncertain at this time. Several causes are possible, but most point toward an increased probability of explosions from the lava dome if the level of current unrest continues or escalates. During such explosions the dome and crater floor are at greatest risk from ballistic projectiles, but the rim of the crater and flanks of the volcano could also be at risk. Explosions would also be expected to produce ash clouds that drift downwind at altitudes up to several thousand feet above the crater rim. Landslides and debris flows from the crater that are large enough to reach the Pumice Plain are also possible. Such events occurred at Mount St. Helens between 1989 and 1991.

We continue to monitor the situation closely and will issue additional updates as warranted, whether activity escalates or returns to background levels.

Daily updates of earthquake data and other information can be found on the WORLD WIDE WEB at URL:

http://vulcan.wr.usgs.gov/Volcanoes/Cascades/CurrentActivity/current_updates.html and http://www.pnsn.org/HELENS/welcome.html

Webicorder and spectrograph archives for this sequence - from the PNSN

Mount St. Helens Swarm Activity
Special information statement of Sep 24, 2004 10am PDT
U.S. Geological Survey Cascades Volcano Observatory, Vancouver, Washington
University of Washington Dept. of Earth and Space Sciences, Seattle, Washington

Since about 2 am PDT on the morning of 09/23 an earthquake swarm has been occurring at MSH. Through 5 P.M. PDT about 200 small (less than magnitude 1) earthquakes have been located at Mount St. Helens and many smaller events have also been recorded through this morning. The earthquakes are occurring at shallow depths (less than 1 kilometer, or 1/2 mile) mostly under the lava dome that formed between 1980 and 1986. Such earthquakes are common at St. Helens, but a swarm with this many earthquakes has not been recorded for several years, most recently on November 3-4, 2001. The probability of small landslides and debris flows in the crater may be enhanced during these periods. Such events could affect areas several kilometers (miles) north of the crater on the Pumice Plain. The probability of small steam explosions that hurl rocks a few hundred meters (yards) may also be increased during periods with increased shallow earthquakes. The cause of such shallow swarms is uncertain, but may reflect increased ground water levels with the onset of autumn rain.

Prior to the 2001 swarm, the last period of increased earthquake activity at Mount St. Helens occurred in the spring and summer of 1998 when hundreds of earthquakes per month, most smaller than M=2, were detected at depths as great as 9 kilometers (6 miles). An intrusion of magma, or molten rock, deep under the volcano and resulting increased gas pressure in the conduit that leads to the lava dome likely caused this increase in earthquakes. The current swarm is different in that the events are typically much smaller and shallower. We see no evidence that an intrusion of magma similar to that of 1998 is underway. We continue to monitor the situation closely and will issue additional Updates as warranted.

Daily updates of earthquake data and other information can be found on the WEB at URL: http://vulcan.wr.usgs.gov/Volcanoes/MSH/CurrentActivity

Webicorder and spectrograph archives for this sequence - from the PNSN

 

[Merlin1047]

The wife and I vacationed on the left coast about two years after St. Helen's blew. When we drove through the area, we were amazed at the huge piles of volcanic ash still in evidence along the roadside.

We stopped at the local airport and chartered a plane to fly us on a tour of the area. We flew to the mountain and over the crater. All that was impressive. But what was truly awesome was the utter devastation of the countryside. The only color we could see from our vantage point over the mountain to the northern horizon was grey.

 

[5stringJeff]

Seeing as how I live about 100 miles from Mt. St. Helens, I will certainly be watching this one closely.

 

[dmp]

No worries - there's not much left to come flowing down our rivers.

 

[dmp]

side note, gwb was already blamed for the hurricanes; I wonder how long before Dino Rossi is blamed for this?

 

[007]

I was just watching last night a thing about the 1980 eruption. They had the most detailed slow motion footage of the eruption I've ever seen. It was mind boogling how much of that vulcano actually blew away.

I was stationed at Nellis AFB in Las Vegas at the time, and had a friend from Walla Walla, Washington. He went up there shortly after the eruption to visit family and see the devastation, and he brought back a jar of vulcanic dust. It was really fine. It looked and felt like grey talcum powder.

 

[dmp]

I was just watching last night a thing about the 1980 eruption. They had the most detailed slow motion footage of the eruption I've ever seen. It was mind boogling how much of that vulcano actually blew away.

One reason for the slow-mo is, there was no surviving video of the actual eruption. When one goes to one of the ranger stations up there, one can see a 30? 20? minute documentary with great sound, visuals, etc.

 

[KarlMarx]

Here is something to think about. The 1980 eruption of Mt. St. Helens was about 1% of the explosive force of the largest recorded volcanic eruption (Krakatao). And there is a lot of archeological evidence to indicate that there were even bigger volcanic explosions (by several orders of magnitude) in the very distant past.

Yet, the explosive force of Mt. St. Helens is many times the explosive force of the largest nuclear weapons that have ever been produced. Furthermore, the amount of pollution in the the form of ash, gases etc from even small volcanic explosions is far greater than is produced by automobiles in a year.

 

[musicman]

Well, since the libs squeal like frightened hairdressers every time President Bush utters the name of God, Bush CAN, in fact, be blamed for Mt. St. Helen's.

Clearly, God is in flagrant violation of federal antipollution standards. Yet Bush, as always, protects his powerful friends. The bastard!