Questions and Answers about

Montserrat Volcanic Eruptions

From lead@candw.ag 
Mon Feb 24 10:42:03 1997
Date: Sun, 23 Feb 1997 22:36:25 -0500
From: David Lea 
To: 'MONTSERRAT E-MAIL GROUP' 
Subject: Ask the Scientist

Via MNI-INFO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Dear Group,
    Here's two more questions that have been asked, and now answered by
Dr. Angus Miller.

Question I've been wondering...  If the volcano on Montserrat has become
active as a result of tectonic plate activity, then there must be other
"pressure release" points in the area. Are there any other volanic
activity increases in the area, or if not, are any expected? Are other
areas of Montserrat at risk of becoming active?

Answer:
There has been no recorded increase in volcanic activity around Montserrat.
 It's particularly interesting that the soufriere areas around the volcano
have not shown changes.  Most of that monitoring program has stopped now
because of safety considerations, but regular sampling of the Galway's and
Gages soufrieres was carried out for many months, and no changes from the
pre-eruption states were detected.

In 1966-67, the last "seismic crisis" before the current eruption,
temperature increases were recorded at the soufrieres.  But it seems that
the current eruption has not appreciably altered the zones that are feeding
the springs. In previous episodes, as the magma was making it's way towards
the surface, it must have changed the conditions at the source area of the
water and steam that comes out at the soufrieres.

Can the other volcanoes on Montserrat become active?  No!  The magma
beneath Montserrat has a clear pathway to the surface at Soufriere Hills. 
It would take a lot of energy and time to intrude magma into one of the
old and cold volcanic centre
...........................................................................

Question  Are the grounds for delimiting the risk zones purely
geological, or also partly political?

Answer:
Volcanologists work with hazard and risk maps.  Hazard mapping determines
simply which areas might be affected by volcanic activity, for example
which valleys might experience pyroclastic flows, how far rocks of a
certain size might be ejected in an explosion.

Risk mapping takes societal considerations into account to determine the
risk to human life.  The airport is an interesting case, and many questions
have been asked about why the airport is safe but Spanish Point is not. 
It's pretty simple- the danger to the airport comes from intense volcanic
activity (greater than September 17) that would develop over many hours. 
The airport is only occupied in day time, and people could move from there
to safe, high ground in a matter of minutes.  

The main danger with Spanish Point is of activity that develops in a short
time period, especially at night, that cuts off escape routes or makes
driving impossible, therefore trapping people in areas that then become
more dangerous.
....................................................
....................................................
Finally, some interesting figures:

Delta is 600 m out to sea and 1300 m north to south at it's widest point
Volume of delta is 15 million cubic metres
Current dome volume is about 42 million cubic metres, and growing at about
3 cubic metres per second.  This is the largest the dome has ever been
(previous maximum was about 30 million, prior to 17 September explosion).
About 60,000 seismic events have been recorded by the seismic network since
the start of the eruption in July 1995.

Angus Miller

     Many thanks to Dr. Miller for taking some time from his schedule to
answer our questions. You can send your questions to me and I will forward
them to the MVO. 

David Lea
. . . The Electronic Evergreen, courtesy of GEM Radio Network

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