Ranier Earthquake

[Jake]

http://cnn.netscape.cnn.com/news/story.jsp?photoid=20041005ORDR102&idq=/ff/story/0001%2F20041109%2F1944291680.htm&sc=1110

[gslater]

So they're saying that this quake was "centered one mile below the surface of Rainier's crater".

 

Let's see: 14,200 (ish) - 5280 is about 8920 or so, so that means they're saying the quake came from inside the mountain a little below the level of Muir. It's been quite a while since I've taken any geology, but that seems to be kind of an unlikely source of the rumbling, unless the mountain is a lot more active than I had thought...

[sobo]

...but that seems to be kind of an unlikely source of the rumbling, unless the mountain is a lot more active than I had thought...

 

Rainier is, in fact, considered an active volcano. It is not at all considered "dormant" by geologic standards.

 

More info from PBS here.

 

Excerpt:

 

"In the Cascade Range in the Pacific Northwest, the home of Mount St. Helens, geophysicists are continuously monitoring a number of other volcanoes that have erupted within the past two centuries, including Mount Shasta, Mount Hood, Lassen Peak, and Mount Rainier. "There is a lot of concern about Mount Rainier because it is so close to Seattle and capable of damaging mudflows," says geologist Mary Reid of the University of California at Los Angeles."

[Norman_Clyde]

I would be very surprised if the epicenter were above Cascade crest level. That would suggest magmatic intrusion at that same elevation, which would suggest imminent eruption (at least, based on extrapolation from the recent Mt St Helens info in the paper). I wonder if it were really about a mile beneath the average surface level around the mountain, which would put it at about sea level. Interesting development either way.

[Jake]

http://www.geophys.washington.edu/recenteqs/Maps/122-47.htm

 

If you look at the map it shows two quakes on Sunday for Ranier. Both about a mile deep and 1 mile south of the mountain. Beats me how accurate this really is (location quality says "good"). But as Norman_Clyde says, interesting either way.

[ryland_moore]

Typically depth is measured from the point below the epicenter (the surface). If this is true, then the earthquake's epicenter occurred above Camp Hazard (due North) at around the 12,500' level. The depth of 0.9 miles would be from this point, meaning that the quake occurred around the 7,700' level, or somewhere near the same level of the Van Trump Glaciers but probably a mile or two into the mountain.

[TeleRoss]

X marks the spot according to this map. Depth of 1mi. below the surface, which would be at about 7,000'. Interesting.

web page

[Alasdair]

That would suggest magmatic intrusion at that same elevation, which would suggest imminent eruption

Jesus Dude you sound like king 5 news! No it does not mean imminent erruption, or really much of anything, other than there was an earthquake. An isolated earthquake such as this one with no further quakes afterward is very normal in a dormant volcano. If there really was any sort of magma movement they would know it, and there would have been a hell of a lot more earthquakes from areas deeper than this. Look back at the data from the 1980 St. hellens erruption, and the erruption of Piatubo. There was months of earthquakes prior to erruption, and in both cases the magma was tracked up by steadily shallower quakes. This set of quakes is more likely due to a lack of any new heat in the system and contracting rocks breaking due to cooling. In otherwords it may signal less activity in the near future.

[ryland_moore]

Alsadair is right. Picture an object when it heats up, it expands. When it cools down, it contracts. Now if a volcano continues to cool then technically the mountain can "contract." With all of the weight that makes up Rainier, earthquakes can and do occur from the mountain "settling" or "contracting".

[Norman_Clyde]

In my previous post I was not meaning to suggest that an eruption was imminent, but was implying skepticism about the earthquake occurring so high into the mountain. This was because the only sources of seismic activity I knew of were movement along a fault, which should not occur high up in a volcano, and magmatic intrusion, which could happen in Mt. Rainier but would be expected to start deep. But now I understand!

[iain]

Just admit it, you were calling for a cauldron of seething lava