Soufriиre Hills Volcano, Montserrat and the CALIPSO Project Material by Barry Voight and Glen Mattioli Presented by M. Garces

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Soufrière Hills Volcano, Montserrat and the
CALIPSO ProjectMaterial by Barry Voight and Glen
MattioliPresented by M. Garces
NSF Infrasound Workshop, July 24-25, 2003,
Waikoloa, Hawaii
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Montserrat

• Soufriere Hills, Montserrat, West Indies ,
  Lesser Antilles volcanic arc
• Location 16.7N, 62.2W, Elevation 3,002 feet
  (915 m)

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Dome collapse on July 12-13, 2003

• In the early hours of Sunday morning (July
  12/13th) there was a major dome collapse at the
  Soufrière Hills Volcano Montserrat. This was the
  largest event to date in the 8 year volcano
  crisis and was 1.5 times larger than the previous
  collapse of July 29th 2001.
• Mattioli the dome collapsed on july 12th
  culminating in a sub-plinian to plinian eruption,
  which dumped 12 cm of ash _at_ 6.5 km from the dome
  (where i was staying). the next morning we had a
  vulcanian explosion that dumped 6.5 cm pumice at
  the same location
• The seismograph network recorded 58 rockfall
  signals, 3 long-period rockfalls, 24 long-period
  earthquakes, 84 hybrid earthquakes, 1
  volcano-tectonic earthquake and 3 explosions
  signals. A complex mixture of signals was
  captured during the collapse event.
• The Soufrière Hills Volcano on the Caribbean
  island of Montserrat began erupting in 1995.The
  activity of the volcano is monitored by the
  Montserrat Volcano Observatory, which has been
  managed by the BGS under contract to the UK
  Department for International Development (DFID).

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Montserrat PFs
February 2003 View towards west
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Montserrat Risk Map

• Small island, forested on the tips away from the
  dome

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The CALIPSO ProjectCaribbean Andesite Lava
Island Precision-Geodetic Seismic Observatory

• Principal Investigators
• Penn StateUniv. Barry Voight and Derek Elsworth
• Univ. of Arkansas Glen Mattioli
• Carnegie Inst. Alan Linde and Selwyn Sacks
• Duke Univ. Peter Malin and Eylon Shalev
• Non-US partners
• Bristol Univ. Steve Sparks
• Montserrat Volcano Observatory
• 1.8 M in funding from NSF-EAR Continental
  Dynamics and Instrumentation and Facilities
  Programs plus 190 K from U.K. NERC

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CALIPSO Sites

• AIR StudiosAIR, Olveston OLVS, Geralds
  GRLD, Trants TRNT have borehole
  strainmeters, 3 component seismometers,
  tiltmeter, and GPS.
• AIR also has a 3-comp surface broadband (Guralp)
  and Bruel Kjaer 4193 microphone (12 mV/Pa, 70
  mHz to 20 kHz).
• A similar system was installed at TRANTS but it
  was near the shore and too noisy with breaking
  waves, so it was reinstalled at HARRIS.
• AIR and HARRIS were operational during the
  recent lava dome collapse and explosions on 12-14
  July, but the data have not been retrieved

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CALIPSO Sites

• Microphones and broadband seismometers at AIRS
  and HARR
• 2 extra channels at AIRS and HARR
• Need sensors, cables, and wind filters!

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• CALIPSO Borehole Observatory
• Sacks-Evertson single component dilatometer (10-9
  strain)
• Nearly broadband 3 component seismometer (2 Hz
  to 1 kHz)
• Pinnacle Systems short-baseline electronic
  tiltmeter
• Ashtech µ-Z code-phase CGPS w/ choke ring antenna

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Grouting in strainmeter at Air Studios - Jan. 03
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Temporary data acquisition started at each site
upon BH completion using IRIS-PASSCAL Refteks
with on-site download every month
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CALIPSO Instrument Package Schematic
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CALIPSO Wind Speed at St Georges Hill
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CALIPSO Wind Direction at St Georges Hill
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CALIPSO Architecture
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CALIPSO Summary of activity
Besides the info previously sent there is a
seismic net operated by MVO, with 5 3-comp BBs
and 3 other short period V-comp stations. The
seismic events (Miller et al GRL 1998 v 25)
include VT (rock fracture) earthquakes, not now
so common, long period events (dominantly1-2 Hz),
rockfalls/pyroclastic flows with several
subclasses (gt2-8Hz 2-8 Hz plus component1-2Hz
and with precursory 1-2Hz energy starting before
rockfall). The LPs are sometimes subdivided into
so-called 'hybrid' events, and low-frequency
events (shallower), although there appears to be
a continuum between events so classified. The LP
seismicity has ben interpreted to result from
resonance of interface waves at the walls of a
fluid-filled conduit, with the trigger poorly
understood. Preliminary acoustic data suggest
that acoustics could help to understand some
aspects of the process. For example a Setra 276
pressure transducer was in operation for limited
times. The next figure shows a delay between
start of rockfall seismic signal and pressure
pulse is gt10 sec, and with the dome and sensor
2km apart, the acoustic wave could arrive in
lt6sec. So although the two are linked, the
seismic signal is not gas-venting at the
surface. Up to now no pressure sensor has been
employed when long-period rockfalls were being
recorded, so the relative timing of the LP phase
and gas release is unknown, and it is not known
whether the seismic disturbance or gas release
starts the rockfall. Further acoustic work could
shed light on rockfall triggering dynamics.
Similar work could be performed on explosion
seismic signals, related to Vulcanian explosions
(as occurred a few weeks ago). Likewise, the path
of pyroclastic flows could theoretically be
tracked by acoustics, which is a useful potential
method for hazards mitigation particularly when
the volcano is in clouds, or at night.
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CALIPSO

• Seismic and acoustic records

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Photo of dome in Dec. 02 on a rare clear day. By
July 2003 the dome had grown to gt230 M m3 and
had not collapsed significantly for 2 years!!
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July 2003 Dome Collapse
July 12th, 2003 - Dome collapse begins at 9 AM
AST By sunset, pyroclastic flows are getting
more energetic and now routinely reach the sea
at the Tar River delta. NB white is steam while
gray is co-ignimbrite ash cloud.
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Trants Borehole Seismic and Strain Records for
July 12th Sub-plinian to Plinian event at 11 PM
AST
Seismometer 200 Hz (803 PM to 1213AM AST)
Strainmeter 50 Hz (842 PM to 1242AM AST)
Although Trants site was impacted by ash during
the culminating event of the July12th dome
collapse, the CALIPSO BH instruments
functioned throughout the eruption.
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The morning after at Sea Dreams in Olveston, 12
cm of ash and 6.5 cm pumice fragments!
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First visit to Air Studios on July 14th - 12.5 cm
of ash and 6 cm mud in crypt NB infrasound
microphone under ash, but CALIPSO was still up!
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CALIPSO Air Studios site after cleanup on July
14th
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