Friday, January 12, 2007

Montserrat Update, 7: Jan 12 2007 -- a correction and comments on the credible implications of the new MVO pictures

I have updated at the MC Online E Group as follows.

Kindly note the correction, and the discussion on the credible implications of the photos now at MVO's site :


First, a bit of correction:
it seems that the Lime-Kiln Bay/Salem Police station line was more a matter of "being considered" than likely at this point to be implemented on the ground.

Second, comments on the photos:

The new photos available at the MVO site, illustrate what pyroclastic flows look like, what they do and what could plainly all-too-easily now happen. For, given the wide, flat U of the valley and the smoothening posed by the Jan 8 flows, as it is now only a matter of debates and scenarios over how far further large flows will go relative to "our" models. [Let us pray that they do not come!]

Note in particular the photo here in the MVO photos of the week page , and how wide open it shows us that Salem is to a longer, bigger, spreading flow. (This is what Dr Willy Aspinall -- the lead person for the SAC on estimating hazards and risks through expert elicitation -- warned of. That possibility is the basis for the pessimistic scenario in earlier comments posted here, and here and here in a blog.)

NB: It is also reasonable to again point out that since the MVO's revised estimates on the deposits are in the range 3 - 5 Mn cu m, the model runs may be a bit over-conservative on run-out lengths for real-world flows of a given size. [ Maybe the friction terms are given a tad too much force?

At any rate, taking the 3 - 5 mn cu m revised estimate, a flow possibly as small as 60% of the model size ran out to the sort of point that a model 5 mn cu m flow was expected to run out.

That flow has now also doubtless smoothed the way for further ones to follow.

So, using a very crude simple proportionality model, it is reasonable to warn that a flow of size 5 - 8 mn cu m could therefore potentially do serious and costly damage in Salem and Environs. Especially, if it spreads out across and possibly beyond the fairly shallow U of the Belham valley at that point.

Thus, prudence should be our guide; as previously noted.


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