Activity at the Nevado del Ruiz and Cerro Machin volcanoes in Columbia seems to have subsided somewhat on the seismographs there, which, I’m sure, is something of a relief to those monitoring the situation locally. This does not mean those volcanoes are all done and will go back to sleep, they could easily resume their former seismicity and we may yet see an eruption, but things have quieted down for the time being.
Yellowstone, on the other hand, remains interesting. After the long period event reported here two days ago more seismicity has occurred and seems localized to the northeast of the caldera, in the area of the previously mentioned saturated and over-pressured fracture zone.
A pronounced seismic event appeared on the RLMT seismograph, at Red Lodge MT, and appeared far weaker on other seismographs outside Yellowstone, leading me to believe it was very close to the RLMT station or right on top of it. At the BOZ (Bozeman) seismograph for the same time period the event appears much less pronounced.
This event also did not show up on seismographs inside the park at anything like the magnitude shown here. This event at Red Lodge was followed this morning by tremor as seen after the larger event in the first graphic, and that is continuing as I write this. This event also appeared strongest at Red Lodge, which you will recall is about 70 miles northeast of the Yellowstone caldera. The long period event of the 12th also appeared strongest there. Between Red Lodge and that caldera lies the aforementioned saturated and over-pressured fracture zone. So all of this would seem to be pointing there.
Here to the right we can see that fracture zone at the northeast end of the caldera. What does all this mean? Probably magma intrusion of some manner under that fracture zone. Does it mean an eruption is coming? Not necessarily, this kind of thing can stop as quickly as it started, and such events can have hydrothermal causes as well as magmatic. Also bear in mind that the magma is about five miles down. Might it be working it’s way up to the surface? Gosh I really don’t know. It’s possible, but I can’t say that here because I don’t have the resources and knowledge of YVO, and it would be irresponsible to make such a statement without that. All I can say at this point is that this is all quite interesting. What is actually going on underground there would most likely have to be determined by means of seismic tomography, using the shock waves of quakes in the area to get an idea of what the magma chamber is doing there.
Seismographs within Yellowstone park did not register the same events anywhere near as strong as those outside the park. I’m guessing that their sensitivity is adjusted down so as to monitor closer events within the caldera, and not pick up irrelevant quakes at a distance. The closest one would be the YPK station at the far east end of the caldera, and that one showed this:
It does look somewhat like another long period event, with the characteristic slow onset and long decline. Interesting, but not enough to draw conclusions from. It’s important to remember that Yellowstone is what is termed a “restless caldera” meaning that it spends it’s geologic time uplifting and subsiding. INSAR data over time has shown ground uplift followed by subsidence there, and while the activity at Yellowstone over the last couple days is quite interesting it does not mean an eruption is in the offing.