Hekla is famous for its short run-ups prior to eruption, typically the run-up involves a smattering of small earthquakes for an hour or so and then it goes boom. Pavlof has the same nasty habit of not announcing upcoming eruptions.
At beast you get a few harmonic tremor episodes in the hours prior to an eruption, and that is exactly what happened this time around. In the last 24 hours prior to onset of eruption two distinct minute long harmonic episodes happened and one Long Period charging episode.
Pavlof takes this enigmatic behavior one step further; it has no earthquakes shallower than 50 kilometers. At least that was true between 1973 and 1987 and in an area 30 kilometers out from Pavlof. This is a very unusual behavior for a highly active volcano. There are though a cluster of earthquakes that occurs at depths larger than 100 kilometers below the volcano.*
Another thing is that in 22 volcanic events in the period 1973 to 1987, 13 events where phreatomagmatic and distributed fairly evenly across the year, but the 9 magmatic events was highly constrained temporally. All of the 9 occurred between September 9 and November 20. And in one run Pavlof had a magmatic event 4 years in a row, these four eruptions was constrained even harder between November 11 and November 15, one each year.*
This little funny sequence of calendarial eruptions stopped directly after the publication of this particular paper, so it is a bit less surprising now with a late March eruption than it would have been prior to the publication.
Pavlof Volcano in the Aleutian Arc is part of an NE trending local chain of volcanoes starting at Emmons Lake Caldera that forms the Emmons Lake Volcanic Center. This volcanic center contains Pavlof Sister, Pavlof, Little Pavlof (forming a triple volcano), Double Crater, Mount Emmons, Emmons Lake Caldera and Mount Hague.
If we restrict ourselves to the Pavlofian sub-system we find that surprisingly little study has been made about this frequently erupting system. One would think that one of the most frequently erupting volcanoes on the planet with a threat rating of 96 (out of 100) would merit quite a lot of scientific study. One would be wrong to assume that, there have literally been more eruptions than studies of Pavlof itself.
And in an eye-watering neglect Little Pavlof and Pavlof Sister has not been studied at all. And here it becomes hoary, it is actually unknown when Pavlof Sister last erupted, it is believed, but not tested scientifically that Pavlof Sister was highly active up until the massive 1786 eruption. This last eruption is contested if it was Pavlof or Pavlof Sister that erupted and apparently nobody has deigned to shlog up the slope of Pavlof Sister to take samples and spend a day in a laboratory to check. To me that seems like a pretty straightforward thing to do and something that would get you a paper published.
At 23:53 UTC eruption commenced at Pavlof after the above mentioned miniscule precursor signals. This basically made any eruption prognostication impossible at the current level and type of monitoring.
At 00:18 UTC an airline pilot noticed and reported in an ash column reaching 6 100 meters (20 000 ft), and later quite a few happy passengers on passing airplanes got to photograph the eruption. The ash was dispersed northwards due to a convenient southerly wind.
Judging from earlier eruptions this eruption could last anything from a couple of days up to years and it will be time that decides the size of the eruption. Going by the looks of it we are looking at a VEI-2 or a VEI-3 if it continues for a while. Anything larger is unlikely.
Grump mode on
First of all, I would like to state that what I am writing next is not aimed at the AVO and only partially at USGS. It is mainly a rant about the foibles of politicians.
Most of the volcanoes in the Aleutian Arc are grossly understudied and many are not monitored, and those that are monitored are under-monitored on a scale that is ridiculous. This is a sad fact. A happy volcano in the Aleutian Arc has a seismometer and a GPS that works at best half the year and the volcano get a visit every year and perhaps a paper written about it every two or three years. Pavlof is such a volcano.
But a lot of volcanoes do not get even that miniscule attention, Pavlof Sister is such an example. We can drive a Panamax Supertanker through the gaps of knowledge about that volcano, and I guess it will surprise nobody when they learn that it is un-monitored.
Now most people will think that this is due to there being no people living in the area, but there are people living there even though they are pretty few.
Now remember the part of Pavlof being assigned a threat number of 96 out of 100? That is due to what occurs next to it every minute of every hour of every day across the year. And that is that an airplane flies by the volcano. This is the world’s premier flight route for all traffic between Asia and the continental US.
Now imagine that Pavlof or any other monitored or un-monitored volcano suffers a slightly larger eruption than normal at about midnight in northerly winds. Due to the airplanes flying extremely close to the chain of volcanoes you would have 1 wide-body airliner a minute suffering engine suffocation causing what the airline industry euphemistically calls a total hull-loss. In more human terms we are talking about up towards 300 people splashing into the ocean per minute.
What I described above is a worst case scenario, but sadly it is a fairly plausible one. Obviously not all airplanes would go down and it would just last a few minutes before airplanes where redirected. But it is a chilling thought all the same.
Here is something for politicians to ponder. The liability for a lawsuit per person would cover a volcanoes monitoring for ten years. So, in the long run it is far cheaper to give AVO the money it needs compared to having the FAA pay out massive amounts to grieving relatives that died unnecessarily.
And now a slightly milder barrage, I know that it is nicer to study volcanoes on Hawaii with a gin and tonic in your hand compared to freezing your butt off and getting eaten by huge bears in the Alaskan outback.
I also know that it is easier and better for the career to publish yet another useless on the comatose Yellowstone, or to spend a fortune on even more equipment there.
These might be comfortable places, but they are not the scientifically correct places to be at. I know you know this, I am just pointing it out in the open even though I know that it is easier to get grants for Hawaii and Yellowstone compared to the Aleutian Arc in the Alaskan Hinterlands. Once again it is mainly a political thing, but I have to grump a bit about it.
Update: The ash column is now reported at a height of 11 285 meters (37 000ft).
*Eruption characteristics and cycles at Pavlof Volcano, Alaska, and their relation to regional earthquake activity; S.R. McNutt