Overnight, I had a request in an E-Group for clarification. (NB: In response to an earlier request, I sent out a basic map of Montserrat with a few annotations to the E-Group. Available on request. You can find maps of Montserrat here and here [this being an online version of the 1: 25,000 Tourist Map] MVO has much more details and the latest hazardous/safe zone maps.)
As I am about to post this, the alarms are now sounding, 6:35 AM. Let's update when we hear more of what is happening, if necessary.
I responded to the request as below.
Notice, that as I was spell checking, a dome collapse was evidently in progress. No alarms have sounded up to the time of this posting.
I have of course removed identification of the person requesting clarification:
Thanks for the explanation and the map which I found very useful.
If I understand, you do not even go to Plymouth the capital? Has that fared badly?
It would be a useful addition to your map to indicate the areas that are now out of bounds and volcano threatened.
RESPONSE, 6:15 AM:
For the longest time, nearly everywhere South of the Belham has been off-limits [apart from tours and "holdouts" living in a hill next to the Belham]. There is also an offshore exclusion zone in the South and on the East side of the Island near the open mouth of the Crater. On land, that exclusion zone runs right up to more or less, Jack Boy Hill, the lookout point used to see the mountain.
Plymouth has been buried under debris flows since August – December 1997. It is abandoned and a tourist site.
Note, as I spell-checked this and posted, Del called me to our Kitchen window. From it and from the backyard we can see that a large reddish ash column is in our Southern Sky, 6:15 AM, maybe 15,000 – 20,000 ft, with what seems to be roaring and volcanic lightning. This seems to be a partial collapse of the dome. Please stay tuned to the news.
Currently, the upgrading to threat level 4 out of 5 meant that the tours into Plymouth are forbidden. [When I said I do not go S of St Peter's unless I have a good reason, I mean I will hesitate to go S of Lawyer's Ghaut, and most certainly will not go S of the the Nantes River [Next to Ram's Supermarket], apart from excellent reason. The line of relative safety in the hazard assessment scenarios, according to Dr Willy Aspinall (in answering public questions put to the SAC panel for the Observatory in March 2006), oscillates between those lines.]
The further warnings discussed in my earlier blog post mean that the residents in Isles Bay Hill etc are supposed to evacuate, as well as those on the rim of the Belham valley to the North, i.e. the fringes of Salem. [The big problem with that is, that in the hopefully unlikely event of a big enough sudden collapse of the rapidly growing dome leading to a spreading hot ash cloud (a la St Pierre 1902), up to hundreds of casualties could result in as little as three minutes, in the region of Salem. But, even after eleven years, no serious provision has been made to accommodate the implied up to ~ 800 evacuees from Salem.] . . . .
Looking at options and illustrative odds:
A: OPTIMISTIC SCENARIO, let's say 70% chance: Since a shift in the locus of dome growth to the NW usually lasts up to ~ 4 weeks, maybe the locus of growth will shift away to a more "safe" quadrant soon, so if nothing is done nothing would result. [But if B or C happen, dozens to hundreds of casualties could result.]
Expectation of losses: 0.7 * 0 + 0.27 * 20 + 0.03 * 200 = 11.4
B: INTERMEDIATE, let's say 27% chance, i.e. 9/10 of the remaining 30%: A large collapse leading to pyroclastic flows down the Belham but which are more or less confined to the margins of that river. If the margins are evacuated, then no casualties would occur under A or B. But if C happens, up to hundreds could happen.
Expectation of losses: 0.7 * 0 + 0.27 * 0 = .03 * 200 = 6
C: PESSIMISTIC, let's say 3% chance: A very large collapse with unconfined surge clouds similar to May 8, 1902. If an evacuation up tot he Nantes line is done, no casualties would occur. But, if no evacuation or a marginal evacuation is done, up to hundreds of casualties could easily result.
Expectation of losses: 0.7 * 0 + 0.27 * 0 + .03 * 0 = 0
Of course, the probabilities assigned and loss-levels used are crude guesstimates; for illustrative purposes only!
But, they are plainly illustrative of where A ROBUST RESPONSE lies.
The basic challenge is, that there is a perception that if one acts on a large evacuation and no major flow occurs, then there has been an "unnecessary" evacuation and socio-economic dislocation -- all with damaging effects on business values and economics.
[This is similar to the issue of what happened in Guadeloupe in 1976, where the eruption did not go beyond an initial level passed here in 1995 - 6, but where an evacuation of the western lobe of that butterfly shaped island for a year cost something like US$ 400 millions. There was a nasty public scientific quarrel over scenarios and hazards, and it was decided after a special international conference to return people to Basse Terre, and since then for 30 years, no devastating eruption has happened. IMHCO, the lack of understanding that a probability other than 1 or 0 is an index of ignorance and the need for prudence, leads to this perception. My proposal that we model based on laying out scenarios and identify a robust policy as above, is designed to reduce the risk of a scientific quarrel, and to educate the public on the range of issues and possibilities that go into the policy.]
So, we need wisdom just now -- do pray for that.
All the best