2
Monitoring submarine volcanic eruptions and drifting icebergs in the South Pacific Ocean Olivier Hyvernaud CEA/DASE, Laboratoire de Géophysique BP 640 — Tahiti, French Polynesia ([email protected]) COMMISSARIAT A L’ENERGIE ATOMIQUE Monowai volcano, Kermadec arc, was discovered in 1977 : a patch of brown and turbulent water was observed by Royal New Zealand Air Force. The summit of the seamount is now 130m deep. Since 1988, the Laboratoire de Géophysique, CEA/DASE, uses its ‘T Phase’ sta- tions to monitor closely the submarine hydroacoustic activity of the seamount. Hydroacoustic paths from source TO RSP stations and IMS hydrophones. Many T waves marked out the drift and the progressive crumbling of B15A. Finally, on December 27, at 03:22, an unusual swarm of T waves indicated that knife-shaped B15A was breaking up into 4 pieces. We found that the most of the hydroacoustic events where generated by B15A, but some of them came from small pieces accompa- nying the giant. In February and March 2008, we detected the last events from small melting pieces. The source mechanism of these hydroacoustic events was not clearly known, but the locations and some anomalies of ampli- tude suggested that the sources were due to cracks at the periphery of B15A. Since May 24, 2002, Monowai volcano is in constant activity. Several Sea Beam surveys have shown at least two dramatic changes of the volcano : in May 24, 2002, a very strong T wave was associated with a SE sector col- lapse. A second slide was identified on the SW slope between 2004 and 2007 but could not be associated with a strong T wave because the RSP network was shadowed by the edifice. Since 2002, cyclic collapses and regrowth of the volcano generates episodic swarms of T waves of different shapes and origin: hour-long tremors, subma- rine explosive activity, very shallow volcano-seismic earthquakes. The continuous real-time seismic recordings of RSP Network enable to follow all the stages of Monowai erup- tion. IMS H03N hydrophones are occasionally very useful to constrain the localization of particular Monowai sources and to reduce the size of error ellipse. At present, Monowai is still continuing sending out T waves. LDG has frequent contacts with the Institute of Geological and Nuclear Sciences of New Zealand to keep them informed. RSP Network records numerous T waves from Antarctic icebergs. During summer 2008-2009, we particularly stu- died the giant iceberg B15A. The parent iceberg of B15A calved off the Ross Ice Shelf in 2000, and broke up into several pieces. B15A, 27 x 122km, the size of Long Island, NY, slowly moved in the Ross Sea, broke Drigalsky Ice Tongue in 2005 and began to drift in the Pacific towards north in mid 2008. In October 2008, it was near 56°S, 167°W. Between November an February, we detected 798 hydroacoustic events coming from Pacific-Antarctic Ocean, and 412 events were located with RSP and H03N data. The T phases were very short, with a weak to me- dium amplitude. They were different from T phases of colliding icebergs. K. Stuart, from MERS Lab, BYU., pro- vided us with accurate Qscat tracking positions of B15A, and LAADS, NASA, made available high resolution images of Terra and Aqua MODIS instrument. These data gave us the opportunity to track closely the drift and final breaking-up of this icy giant. Hydroacoustic source locations (orange circle) during December 2008 with error ellipses, track of B15A in red, and known QScat positions (MERS Lab.) in December (green stars). In yellow, the QScat position of a son of B15A. B15A on Dec 25, 2008 with many located hydroacoustic sources. Image Terra MODIS, LAADS, NASA. H03N Hydrophones waveforms from Monowai. RSP ‘T Phase’ stations waveforms from Monowai. H03N RAR PMO&VAH TAOE TBI RKT MEH PPT MONOWAI Monowai seamount in 2004(Chadwick et al, 2008). Hydroacoustic activity of Monowai since 2002 : cumulated number of events. Landslide on the SE slope. RSP Network Ton ga Tr en ch Lo uisv ille Ridge So uth America Volcanic Activity : Drifting Icebergs : Chadwick, W. W., Jr., I. C. Wright, U. Schwarz-Schampera, O. Hyvernaud, D. Reymond, and C. E. J. De Ronde (2008), Cyclic eruptions and sector collapses at Monowai Submarine Volcano, Ker- madec Arc: 1998-2007, Geochem. Geophys. Geosyst., Q10014, doi:10.1029/2008GC002113. May 5, 2009 May 5, 2009 1.5Pa 1.5Pa 1.5Pa 2μ/s .8μ/s .2μ/s 3μ/s 1μ/s .4μ/s .4μ/s .15μ/s B15A on Dec 4, 2008 with a located hydroacoustic source at 01:29 UTC. Image Terra MODIS, LAADS, NASA. B15A on Dec 29, 2008 with located hydroacoustic sources at 18:42 and 15:55 UTC. Image Terra MODIS, LAADS, NASA.

Monitoring submarine volcanic eruptions and drifting ... · MEH PPT MONOWAI Monowai seamount in 2004(Chadwick et al, 2008). Hydroacoustic activity of Monowai since 2002 : cumulated

  • Upload
    others

  • View
    2

  • Download
    0

Embed Size (px)

Citation preview

Page 1: Monitoring submarine volcanic eruptions and drifting ... · MEH PPT MONOWAI Monowai seamount in 2004(Chadwick et al, 2008). Hydroacoustic activity of Monowai since 2002 : cumulated

Monitoring submarine volcanic eruptions

and drifting icebergs in the South Pacific Ocean

Olivier Hyvernaud

CEA/DASE, Laboratoire de Géophysique

BP 640 — Tahiti, French Polynesia ([email protected])

COMMISSARIAT A L’ENERGIE ATOMIQUE

Monowai volcano, Kermadec arc, was discovered in 1977 : a patch of brown and turbulent

water was observed by Royal New Zealand Air Force. The summit of the seamount is now

130m deep. Since 1988, the Laboratoire de Géophysique, CEA/DASE, uses its ‘T Phase’ sta-

tions to monitor closely the submarine hydroacoustic activity of the seamount.

Hydroacoustic paths from source TO RSP stations and IMS hydrophones.

Many T waves marked out the drift and the progressive crumbling of B15A. Finally, on December 27, at 03:22, an

unusual swarm of T waves indicated that knife-shaped B15A was breaking up into 4 pieces. We found that the

most of the hydroacoustic events where generated by B15A, but some of them came from small pieces accompa-

nying the giant. In February and March 2008, we detected the last events from small melting pieces. The source

mechanism of these hydroacoustic events was not clearly known, but the locations and some anomalies of ampli-

tude suggested that the sources were due to cracks at the periphery of B15A.

Since May 24, 2002, Monowai volcano is in constant activity. Several Sea Beam surveys have shown at least two

dramatic changes of the volcano : in May 24, 2002, a very strong T wave was associated with a SE sector col-

lapse. A second slide was identified on the SW slope between 2004 and 2007 but could not be associated with a

strong T wave because the RSP network was shadowed by the edifice. Since 2002, cyclic collapses and regrowth

of the volcano generates episodic swarms of T waves of different shapes and origin: hour-long tremors, subma-

rine explosive activity, very shallow volcano-seismic earthquakes.

The continuous real-time seismic recordings of RSP Network enable to follow all the stages of Monowai erup-

tion. IMS H03N hydrophones are occasionally very useful to constrain the localization of particular Monowai

sources and to reduce the size of error ellipse.

At present, Monowai is still continuing sending out T waves. LDG has frequent contacts with the Institute of

Geological and Nuclear Sciences of New Zealand to keep them informed.

RSP Network records numerous T waves from Antarctic icebergs. During summer 2008-2009, we particularly stu-

died the giant iceberg B15A. The parent iceberg of B15A calved off the Ross Ice Shelf in 2000, and broke up into

several pieces. B15A, 27 x 122km, the size of Long Island, NY, slowly moved in the Ross Sea, broke Drigalsky Ice

Tongue in 2005 and began to drift in the Pacific towards north in mid 2008. In October 2008, it was near 56°S,

167°W. Between November an February, we detected 798 hydroacoustic events coming from Pacific-Antarctic

Ocean, and 412 events were located with RSP and H03N data. The T phases were very short, with a weak to me-

dium amplitude. They were different from T phases of colliding icebergs. K. Stuart, from MERS Lab, BYU., pro-

vided us with accurate Qscat tracking positions of B15A, and LAADS, NASA, made available high resolution

images of Terra and Aqua MODIS instrument. These data gave us the opportunity to track closely the drift and

final breaking-up of this icy giant.

Hydroacoustic source locations (orange circle) during December 2008

with error ellipses, track of B15A in red, and known QScat positions

(MERS Lab.) in December (green stars). In yellow, the QScat position of a

son of B15A.

B15A on Dec 25, 2008 with many located hydroacoustic

sources. Image Terra MODIS, LAADS, NASA.

H03N Hydrophones waveforms from Monowai.

RSP ‘T Phase’ stations waveforms from Monowai.

H03N

RAR

PMO&VAH

TAOE

TBI RKT

MEH PPT

MONOWAI

Monowai seamount in 2004(Chadwick et al, 2008).

Hydroacoustic activity of Monowai since 2002 :

cumulated number of events.

Landslide on the SE slope.

RSP Network

Tonga Trench

Louisville Ridge

South America

Volcanic Activity :

Drifting Icebergs :

Chadwick, W. W., Jr., I. C. Wright, U. Schwarz-Schampera, O. Hyvernaud, D. Reymond, and C. E. J. De Ronde (2008), Cyclic eruptions and sector collapses at Monowai Submarine Volcano, Ker-

madec Arc: 1998-2007, Geochem. Geophys. Geosyst., Q10014, doi:10.1029/2008GC002113.

May 5, 2009

May 5, 2009

1.5Pa

1.5Pa

1.5Pa

2µ/s

.8µ/s

.2µ/s

3µ/s

1µ/s

.4µ/s

.4µ/s

.15µ/s

B15A on Dec 4, 2008 with a located hydroacoustic source at

01:29 UTC. Image Terra MODIS, LAADS, NASA.

B15A on Dec 29, 2008 with located hydroacoustic sources at

18:42 and 15:55 UTC. Image Terra MODIS, LAADS, NASA.

Page 2: Monitoring submarine volcanic eruptions and drifting ... · MEH PPT MONOWAI Monowai seamount in 2004(Chadwick et al, 2008). Hydroacoustic activity of Monowai since 2002 : cumulated