I've often heard it repeated that the whole area in and around the vast caldera is deforming and rising alarmingly (when compared to the surrounding lands) but I've had trouble finding the measurements and/or studies explicitly showing this.
Please know that I am not saying it's not true or disputing any person's belief in an impending eruption. But, does anyone have any links, names of studies, or names of researchers? I really
do want to delve a little deeper.
I also know that some areas of land are still "rising" (quebec) or "sinking" (midwest) after the last glacial period affected the crust/upper mantel so I'd like to learn more about the details in this particular area.
As to what look like harmonic tremors. My armchair based understanding is this: to see a steady constant thrum can mean that magma is possibly on the move but it doesn't necessarily mean it's going up. It can be moving out/down/away/draining/shifting. Nothing on this planet is static. Other data (like temp readings, deformation measurements, etc) are required to estimate direction, or if it is
magma on the move and not something else. It can also be wind, road thrum, or sensor noise (which you'll see cleaned up ounce a sensor rig is serviced which will then reoccur again after a period of weeks to months later.) Sudden tremors can be bedrock settling, mining explosions, even construction or road activity. The area is crisscrossed with roads, tourist development/activity, and ongoing and extremely active geothermal activity, etc.
Relying on just the seismographs for a picture of the area (or any area) can be a bit misleading. There have been cases that planes, falling trees, and geothermal drilling have been recorded on the seismographs. That's all really cool but probably quite maddening for the people monitoring them.
I've also read in vulcanologist literature that if something shows up on a single seismograph but doesn't show up on any of the others, especially one's relatively nearby, it often - but not always - indicates it to be external and unrelated noise of some kind.
I guess the working assumption for those who study this stuff is that due to the shear size of the chambers below the caldera that any movement of magma would show up on most, if not all, of the regional sensors.
But then again, we have never monitored a caldera system of this size and makeup through to an active eruptive stage. Assumptions, data, and experience from "smaller" volcanoes might not carry over well to an entity the size of Yellowstone.
Interesting times for sure.
And speaking of interesting, it would be very interesting to see what the GRACE project
comes up with (releases
) when it measures gravity anomalies in the caldera region over time. I'm not sure if the resolution is high enough, though it should
be since it has recently measured changes in the mass of underground aquifer
systems in India.
"It is said that your life flashes before your eyes just before you die. That is true, it's called Life." Terry Pratchett
(Skeptic. But not of PO.)