Earthquake!
 

There was a small earthquake at around 11:40. Discuss.

Weird. I didn't notice, but I am in G'ville. How big?

It felt huge to me. It was only 8 miles south of Truckee - Mag 4.8. It felt larger though because it lasted so long. We had books fall of shelves and the whole house moved for about 4 seconds. Me no likey!

Was the epicenter in the lake?

Thats nuts. Is there a danger of the volcano blowing?

Me and Eric B were sitting around up at Stead, both of us felt it. Mike K was sitting right next to us, but he was moving around or something and didn't notice. I thought I moved away from that crap...

I didnt feel it but my head is still shaking from being at NASCAR all day :)

Our little meet and drive felt it. We were having a picnic up at Stumpy medows resevoir off of wentworth springs road and the table shook like a big semi truck or train just went by... But of course since there were no trains or semis near by, we figured it was an earthquake :p

I was still in bed, and it felt like my girlfriend was climbing in with me. I soon realized that she wasnt in the room when the door closed and the top of my apartment started rattling.


They say the Reno area has a major quake(7.8+) every 50 years or so. I think we are do.

Carnage out there... quakes freak out the wildlife. I saw several deer, 2 dogs, and a buncha critters on the side of the road. :(

The epicenter was between the lake and Truckee.

What Volcano?

Isn't Lake Tahoe sitting in the caldera of a dormant volcano?

I'm pretty sure that Lake Tahoe was formed by glacial deposit. The Mammoth Lakes area is basically one huge caldera. That place is gonna blow someday.

Unless I am mistaken, the Sierras are tectonic in origin, not volcanic. Not to say we don't have geothermal springs and vents, but I think the volcanos tend to be more solitary at weak points in the plates rather than where they ram together. Shasta and the 4 up north, Bachelor, Hood, St Helens, and ?Rainier?

Don't know about Mammoth. I would have said it was part of te Sierras, not volcanic, but don't know it's history.

Mammoth is most certainly a volcano. There is an active volcano watch there by the US Gelogical Survey. Its active too, most eruptions are from the geologicly recent history (like 200-600 years ago). I did some googling, and yeah, Tahoe isn't a volcano, even though it really looks like one.

The Sierra's are tetonic in origin, but there is also magma under these hills. Isolated pockets of magma, and in some cases (like the Long Valley Caldera), active volcanos.

Dean you sound interested in this sort of thing. If so, you should drive down 395 to the mamoth area. There are a ton of dormant and extinct volcanoes down there and a self guided tour along 395 that explains the evolution of that area. Mammoth ski area is actually a young semi-active volcano. They had to evacuate the ski area a few years back because she was making some noise and letting off steam.

That's pretty scary stuff.
Good info though :)

There's also a lot of cool volcanic history stuff in Tehama County. The enitre county was once an active volcano. Lassen is the biggest part of what's left. Cool stuff.

Yes thats true. The sierras are a result of the Pacific plate and North American plate colliding. There is volcanic activity as mentioned due to previous or currently active hot spots, and well since technically there is magma under everywhere anyway theres bound to be volcanos here or there that manage to seep up through the plates. The pacific rim (ring of fire) which im sure all of us learned about some time in school includes Lassen, Mamoth, etc. and is a result of tectonic activity. Granite, being a Plutonic Igneous rock type is actually directly formed from magma however Granite unlike extrusive volcanic rock, stays under ground for quite some time before reaching the surface.

Oh, I just found this on the usgs website, shows all the recent california activity:

http://earthquake.usgs.gov/recenteqs...-125.-115.html

When I think of West coast volcanoes I think of the high density in the northwest in the Cascade range. I recalled Shasta, and now I am reminded it is Lassen that is the southern most volcano in the that bunch.

I forgot about the 4 or so we have in the southwest...

and now a link to a website to a guy that makes "indie" electronic music from field recordings from things like volcanic vibrations. While taping nature and calling it electronic music isn't new it's still pretty brutal to listen to even in 2005! You would think geothermal audio recordings would make a good dance track.

http://fonik.dk/bio.html

Yeah, that's where i'm from. Lassen and Shasta are both volcanos, If your driving down highway 33 (iirc) you can see all the debree from lassens eruption, like 35 miles away! It was huge!

Lassen, Shasta, and the rest of the Cascades are composite volcanoes. All the big ones (i.e. the ones with snow...) are concidered dormant, not extinct. All are closely monitored by the USGS and various University researchers for tremor activity, gas levels, and bulging. Shasta, by the way, experiences gas release and bulging constantly. Tremor activity would likely be linked to dike intrusion (just hope it's deep). Lassen's last eruption was in the late 1800's if I remember correctly. Any of those peaks could easily go Mt. St. Helens on us with just weeks/months of notice.

The Mammoth region has a long history of local vocanism, as Nick points out. The Long Valley caldera is for all purposes an extinct volcano. The catastrophic eruption that deposited the Bishop Tuff formation was a once-recorded event, although it did spread ash to South Dakota. Yellowstone was a similar situation, and the likelihood of a recurring similar event at either of these locations is judged to be extremely minute (for one thing, we'd need the build-up of thousands of cubic kilometers of magma in one area --- something we might notice --- plus the fact that the time span between such events is hundreds of thousands of years, IIRC). Around the rim of the caldera, however, several small intrusions have created other formations since the caldera eruption (such as Glass Mountain, Mammoth Mountain, the various Domes, and the Inyo Craters). The Mono Crater chain, a horizontal dike leading north from the caldera to the north side of Mono Lake, has had the most recent activity, with eruptions of < 1 cubic km or so in volume occuring every 250-500 years. If I remember correctly, the last one is estimated to be Negit Island at ~300 years ago.

Mammoth Mountain itself is currently experiencing shallow dike intrusion, which seems to be small in scale. Gas leakage, sporadic tremor activity, and deformation have all been recorded there in the last 30 years. Every so often it seems to act up and scare the heck out of the real estate developers.

If you look at the USGS quake map here, http://quake.usgs.gov/recenteqs/Maps/119-38.htm
you will notice that there is a constant cluster of shallow, small quakes/tremors (I believe that a "quake" is tectonic in origin, whereas a "tremor" is caused by the fluidic movement of a magma body through rock) east of Tom's Place (under Mt. Morrison/Convict Lake area I think). This is what the USGS is paying closer attention to currently. There are no recent vents in that locale, as far as I know, with Mt. Morrison being mostly comprised of the metamorphic "Morrison Roof Pendant" formation (that is the much older rock under which the Sierra batholith intruded), and the various valleys being glacial in origin.

Another volcanic event in the Mono Crater chain, or even Mammoth Mountain, that stays within the same size limits as all the rest in recent history will, under the right wind conditions, spread ash as far as Hawthorne, Bridgeport, or Bishop.

Earthquakes in our area, like the one in Truckee, are tectonic in origin and simply the result of fault slippage. Occasionally we have a big one in Nevada, but most often they stay below 4.0. Notice on the USGS quake map all the major fault lines in the Great Basin. These are not faults like the San Andreas due directly to plate contact, but rather are the result of crustal expansion that formed the Basin & Range in the first place.



Yikes, is that my longest post evAr?

edit: does my spelling need work or what?

Nice. Geology is awesome :D

I should have studied it more when I was in college.

Speaking of live ones, there is an active volcano in Mexico where my lab has a long-term tree-ring study area. While it has been steaming for a while, they recently have had a huge increase in activity....I wonder how our instruments are doing.....

http://www.ucol.mx/volcan/imagen.htm

I've been down there a couple times to do maintainence and climb some other Mexico volcanoes:

Scotty is on my team for geology trivial persuits....

If any of you have not seen been to St Helens since it blew, I encourage you to do so.

Though I'm sure mother nature has recovered quite well, (She was well on her way 5 or so years ago when I was there last) the devistationis is just amazing...

The size of the trees that were just snapped like matchsticks is amazing, as is the lake that is no longer there...