Mt. St. Helen's - After Cycle Updates

[dgavin]

Three more minor quakes here, 2 yesterday, one today so far. Still no evidence for any magma movement. The Baja 5.1 earthquake at 9:47am today was picked up nicely on the St. Helens siemographs however.

[Inclusa]

Ok. We possibly cannot say "extinct" volcanoes.

[Tobin Dax]

Yesterday it was rocked by a 4.3 magnitude Quake (Felt in Portland, Vancouver and other regional towns) followed by various aftershocks, some of which were also felt.

This is what my mother called a "rumble"? Okay, they might not have felt it (too far south, probably), but that's a decent little quake.

[Gillianren]

Ok. We possibly cannot say "extinct" volcanoes.

Actually, we can. There are places where there were volcanoes caused by mantle plumes past which the plate has drifted. There simply isn't anything to power those volcanoes anymore. However, no one who knows anything about vulcanology would even consider the idea that Mount St. Helens, or Mount Rainier, or any of the other volcanoes up and down our coast, are extinct. I think they've even decided Mount Mazama can't even be considered extinct.

[dgavin]

Actually, we can. There are places where there were volcanoes caused by mantle plumes past which the plate has drifted. There simply isn't anything to power those volcanoes anymore. However, no one who knows anything about vulcanology would even consider the idea that Mount St. Helens, or Mount Rainier, or any of the other volcanoes up and down our coast, are extinct. I think they've even decided Mount Mazama can't even be considered extinct.

No, Mt. Mazama (Crater Lake) is most definately NOT extinct. It's eruption was only 7000 years ago. Water temperature measurements indicate a sharp 3.89c temperature increase at the floor of the lake, indicating that the lake is being warmed by heat from the volcano.

That eruption was a VEI 7 (rather forceful for a single stratovolcano) so it's likely that it would take some time for the magma chamber to refill itself after that caldera collaspe eruption.

Mt. Jefferson however might be considered extinct, as there hasn't been any signs of activity at it for some 50,000 years. But even that one still has some active hydrothermal systems, and is only considered dormant.

As you said, extinct usualy means the the volcano has moved past the source of the magma that fed it. Quiet volcanoes in and around an active magma system are considerted Inactive (Had Eruption in last 1000 years) or Dormant (Last eruption > 1000 years)

[dgavin]

Three more earthquakes since last report, smallish from 1 - 2 magnitude. USGS officially saying that it's from tectonic stresses and is not magma related. Two of the quakes were under the mountain this time (moved south) but as it's still along that slip/strike fault that isnt unexpected.

[dgavin]

Nothign but windstorms on the siesmographs last few days. Likely this episode of fault earthquakes is over.

[dgavin]

A small earthquake today, and what appears to be harmonic tremors on the siemographs at Helens and Hood both starting about 10am this morning.

However after checking more these tremors seem to be originating around the Newberry Caldera region. It doesn't appear to be volcanic tremors, nor wind storms. My best guess here is slow sliping like motion at a fault.

[dgavin]

Another small quake, and more of the harmonic like reading at various stations.

While it is windy today, I've compared about 6 siesmographs from oregon to washighton that ahve the same reading, and the patterns of strong to week peeks match up on most. If it was wind the patterns would be different due to the differences in localized wind gusting.

Considering the same pattern is showing up from northern Washington Siesmographs, to Southern Oregon ones, at this point I would say the readings are of a deep slow movement of the plates, or the magma, in the melt boundy zone of the Jan-De-Fuca/American subduction zone itself.

It's still possible it could be wind related readings, will know better once we have a few more calm days here. Granted, there was almost no wind yesterday during the periods of it's readings according to NOAA data for Redmond Or.

[dgavin]

St. Helens have been quiet since last report. USGS is indicating the Cascades at Background levels of activity.

As to the other siesmograph readings there is a major windstorm going on now at Newberry, and it's definately showing a different pattern then the ones seen before.

I've attached yesterdays siesmograph, showing the windstorms at the bottom, and the other readings at the top.

Hopefully someone may recognize the patten of the readings at top, all I really know is at best, just guesses.

[dgavin]

Mystery Solved on the odd siemographs readings.

The top style that has been going on for a while is just wind without rain, the one on bottom that is more famlliar, is wind -and- rain.

The Rain adds a high freqency component to the wind signatures. Considering it usualy is always raining in oregon, I haven't seen the other signature before where there is no rain, but only a lot of wind.

NOAA still indicates periods of calm during the low-feq only readings, however I checked some additioanal weather archives and found windy conditions recorded.

So on the above sample I posted, lookign at a wind storm in the morning and a rain/wind storm in afternoon.

I don't have an good explaination as to the day where I matched the pulse freqency (Strong/weak patterns) of them between siesmograph stations. It may be that was a day where the winds had regional 'gusts' instead of localized ones.

[jlhredshift]

dgavin, The traces certainly go to the sensitivity of the seismographs, but I was wondering, there are many times here in the Midwest that lighting accompanies wind and rain, like two nights ago. If the lightning is close enough the BOOM shakes the whole house, like two nights ago. Have you seen examples of lightning in the traces?

[Gillianren]

Considering it usualy is always raining in oregon, I haven't seen the other signature before where there is no rain, but only a lot of wind.

It is, but more importantly, it is usually (at least at this time of year) raining in Washington. Where, incidentally, we don't reliably get lightning.

[Tobin Dax]

It is, but more importantly, it is usually (at least at this time of year) raining in Washington. Where, incidentally, we don't reliably get lightning.

That's pretty much true in western Oregon, too. Growing up, I rarely experienced a thunderstorm like those I've been through in Illinois and Kentucky.

[dgavin]

dgavin, The traces certainly go to the sensitivity of the seismographs, but I was wondering, there are many times here in the Midwest that lighting accompanies wind and rain, like two nights ago. If the lightning is close enough the BOOM shakes the whole house, like two nights ago. Have you seen examples of lightning in the traces?

I haven't sene them on the newer webicorders yet, but there are plenty of Lightning examples samples from older AS-1 type siesmographs I have looked at.

I'll keep that in mind to check the next time a lightning storm blows through these parts.

[dgavin]

Intresting events at St. Helens, 3 minor quakes today, and a huge avalanche was recorded eailier this week. The 3 quakes are at the 8km-11km depths, placing them in/around the mid/main magma chamber. Nothing to worry over when they are that deep.

There was also a nice avalanche picked up on the siesmographs at Mt. Hood today too.

[Swift]

Spring thaw causing the avalanches?

[Gillianren]

Possibly. Here in Olympia, the temperature hasn't dipped below freezing in the last two weeks.

[dgavin]

Were starting to get the wetter heavier snows, as opposed to the light powders seen during the coldest part of season. When you put heavy damp snow on lighter drier powder, I think you get prime avalance conditions. Most of the mountains are still in the 18-28f temp range, so thawing probably doesn't account for much of the avalances yet.

There was another avalanche today at St. Helens, but a small one.

[Swift]

From National Geographic

Volcanologists have created the first ever 3-D simulation of the cataclysmic eruption of Mount St. Helens, which happened 31 years ago this month.

The model backs up current ideas about what led to the 1980 blast, which killed 57 people. The real news, though, is that the simulation could save lives in the future by helping researchers predict how dormant volcanoes may lose their tempers.

....


Soon after the Mount St. Helens eruption, scientists began trying to decipher why the disaster zone was so widespread and extended so far north.

One theory suggested that a single, sustained jet of volcanic material had shot out of the loosened north face at supersonic speeds. Later research determined that the eruption was sloppier—more like a grenade blast.

But when the grenade scenario was plugged into older, 2-D simulations, the virtual eruption failed to properly re-create the St. Helens-area devastation.

Those models looked at the physics of the explosion and the effects of the surrounding topography on falling ash and debris as separate factors—and ignored gravity's influence altogether, according to the authors of the new study.

The new model, however, factored in all these dynamics in 3-D. The new element, gravity—which created faster ash-and-gas flows by pulling debris more rapidly downhill—was found to be key in re-creating the scorched region.

The result is the first simulation of the Mount St. Helens eruption to match the blast's speed and the actual damage boundaries, the researchers say.

[dgavin]

Nice Find Swift!

[Tobin Dax]

Very cool. Thanks, Swift.

[dgavin]

I'm still having trouble finding new imagry of lowit falls and the galcier toes advancment. After two years without any new images for the area, I'm assuming that USGS pulled the camera equipment out after they downgraded St. Helen's to condition green.

It's sort of a shame as the evolution of erosion activity at St. Helen's seems as important as it's eruptions are.

[dgavin]

Yesterday there was a very low level (intensity) Vocanic Tremor at St. Helens, starting abruptly around 5:30 am PST, and contining on with less intensity until the late evening. It was picked up at 4 out of 5 of the area's siesmographs, and also at Mt. Rainier's siesmograph station.

This appears to something of the order of a shifting of magma in St. Helens lower magma chamber as opposed magma moving through rock in a chimney from the upper chamber. It had a very distictive signature that looked more like wind storm readings, expect it started without any build up, and then slowly dwindled in intensity over time, and the recorded winds was only in the 5-10mph category and not able to produce such a prominent reading.

My guess here is again, that something caused the magma in the lower chamber, to shift or churn around. Possible it was a partial chamber collapse as there were 2 avalance like readings on some of the siesmographs just before this happened.

[Gillianren]

Could there have been avalanches? We're having unusual-for-us weather around here.

[dgavin]

It's possible the two events before the tremors were, but the tremor part lasted for near 9 hours, I've never heard of an avalance lasting that long.

[Gillianren]

True enough.

[dgavin]

Oh wow, I was right and wrong, it was definately somethign moving...but it wasn't magma...

It was a stream nearing flood stage! Which explains it's long long duration. I'm assuming it's in the lowitt falls area but webcams still obscured so can't visually verify.

[Gillianren]

Yes, that makes sense as well!

[Tobin Dax]

That fits with the news that I've been hearing.