(USGS - Hawaiian Volcano Observatory) and Daniele Carbone

V21B-2771 A foamy lava lake at Kīlauea Volcano, Hawai‘i
Michael P. Poland (USGS - Hawaiian Volcano Observatory) and Daniele Carbone (Istituto Nazionale di Geofisica e Vulcanologia, Catania, Italy)
CONTINUOUS GRAVITY AT KĪLAUEA
gravimeter
housing
solar
panel
Hawaiian
Volcano
Observatory
N19˚ 30'
HAWAI‘I ISLAND
summit
caldera
W155˚ 00'
Kamoamoa
fissure eruption
gravimeter
Halemaʻumaʻu
Crater
summit
eruptive vent
Hawai‘i Island
thermal camera
Kīlauea
Caldera
gravimeter
Puʻu ʻŌʻō
Crater
rift
t
s
ea e
zon
N19˚ 20'
battery
box
W155˚ 10'
10 km
250 m
On March 5, 2011, the lava lake
within Kīlauea’s summit vent
drained as magma withdrew from
beneath the caldera to feed a
fissure eruption on the east rift
zone. The lava level was
monitored by a thermal camera
and the continuous gravimeter.
wall of
Halema‘uma‘u
Crater
Halema‘uma‘u
Crater
G-721
former high
lava mark
LaCoste & Romberg gravimeter G-721 is installed on the floor of Kīlauea Caldera near the rim of Halema‘uma‘u Crater. Data
are recorded on a serial datalogger and stored locally.
200
small lava pond
250
200
150
100
50
0
-50
980
Lava level (m a.s.l.)
940
920
900
880
860
840
820
800
-400
200
Gravity change (μGal)
Gravity change (μgals)
Lava level was estimated from continuous
views of the lava lake by a thermal camera
on the rim of Halema‘uma‘u Crater. Lake
draining began at about 2 PM HST—just
after the start of an intrusion along the east
rfit zone (based on seismicity and
deformation). The level dropped by ~150 m
in <24 hours. Data courtesy Matt Patrick.
960
-200
-600
-800
-1000
150
100
50
0
-50
-100
04 March 2011
12.00 HST
February 2011
March 2011
April 2011
Example three-month time series from gravimeter G-721. The long-term gravity signal reflects a combination of mass
change, solid Earth tides, environmental factors, and instrument drift.
Halema‘uma‘u Crater
0
Thermal camera
Higher lava level
05 March 2011
00.00 HST
05 March 2011
12.00 HST
06 March 2011
00.00 HST
Continuous gravity data, corrected for solid
Earth tides, mass loss from the 1.5-km-deep
contracting magma reservoir, and ground
subsidence (determined from GPS). The
decrease in gravity tracks the drop in lava
level, implying that the gravity change is due
to mass removal from the lava lake. Spikes
are caused by local earthquakes.
The lava level drop over time and the geometry of the vent are
known from visual observations, so it is possible to calculate
the lava density needed to fit the gravity signal.
Schematic cross section through
Halema‘uma‘u Crater showing the
geometry of the lava lake in early
2011. Sketch is based on visual
observations, courtesy Tim Orr.
lava
lake
200m
Model of
lava lake
200m
m
0
14
970m a.s.l.
Changeable level of
overhang base
floor of
Halema‘uma‘u
Crater
GPS data from a station collocated with the
continuous gravimeter. Gray line gives 30 s
positions, and red line is low-pass filtered.
Data indicate subsidence coincident with
the start of lava lake draining. Subsidence
is due to volume loss from a source about
1.5 km beneath the east margin of
Halema‘uma‘u Crater.
300
-100
0
Schematic cross section
through Halema‘uma‘u Crater
Gravimeter
Changeable lava level
(Left): The Kamoamoa fissure eruption occurred during March 5–9, 2011, on Kīlauea’s east rift zone. Photo by Tim Orr.
(Right): Near-vertical FLIR image from a helicopter of Kīlauea’s summit vent on March 8, 2011, after lava had drained and the
level had dropped by about 150 m. Photo by Matt Patrick.
Elevation changes (mm)
G-721 is a LaCoste & Romberg gravimeter with an Aliod
feedback system. Data are recorded every 0.5 s, including
gravity, instrument temperature, voltage, long level, and
cross level. The gravimeter is collocated with a GPS station.
We constructed a model of the lava lake and changed the
model lake height to match the thermal camera observations.
We then calculated the gravity effect of the changing lake
level, varying the lake density to fit the gravity data.
rim of summit
eruptive vent
1 km
Image acquired by NASA’s Advanced
Land Imager, Earth-Observing-1 satellite.
LAVA LAKE DENSITY
Model of lava lake. Geometry is
based on visual observations of
the vent (overhanging top is
probably only a few meters thick).
Model consists of 224 vertical
square-based (10×10 m)
parallelepipeds with changeable
height. The gravity effect of each
parallelepiped is calculated and
the total effect is obtained by
summing their contributions.
Lava level changes are simulated
by changing the height of the
“active” parallelepipeds. Using
the lava level determined from the
thermal camera, we perform a
direct calculation aimed at
assessing the value of lava
density that yields the best fit to
the gravity changes.
Bottom (800m a.s.l.)
160m
RESULT: The gravity change can be modeled by
-3
an average lava lake density of 800 kg m .
200
Gravity change (μGal)
N
W155˚ 20'
so
u
rif thw
tz e
on st
e
Since the summer of 2010, the USGS Hawaiian Volcano
Observatory (HVO) has operated a continuously recording
gravimeter on the rim of Kīlauea’s summit eruptive vent.
MARCH 5, 2011, LAVA LAKE DRAINAGE
150
100
50
0
-50
Gravity data, corrected for tides, subsurface
mass loss, and vertical deformation (black
line), can be approximated from the lava
lake draw down assuming an average lava
density of 800 kg m-3 (red line). All gravity
data fall within a 600–1000 kg m-3 envelope
(light red field).
600 kg m -3
1000
kg m -3
800 kg m-3
-100
04 March 2011
12:00 HST
05 March 2011
00:00 HST
05 March 2011
12:00 HST
06 March 2011
00:00 HST
Although surprisingly low, the modeled density is consistent
with that of clasts ejected from the vent (Carey et al., 2012).