Download Monitoring Ground Deformation at Volcanoes

Monitoring Ground Deformation
at Volcanoes: Case Studies of
two New Methods—InSAR and
GPS Geodesy
Henry L. Turner
GEOL 4553/5553 Volcanology
April 7, 2009
•  Volcano monitoring techniques
•  Ground deformation associated with volcanoes:
Sources and spatial/temporal scales
•  Traditional methods for studying volcanic
ground deformation
•  New methods—InSAR and GPS geodesy
•  Case studies using InSAR and GPS geodesy
•  Conclusions
Volcano Monitoring Techniques
From http://volcanoes.usgs.gov/About/What/Monitor/monitor.html
Sources of ground deformation at Volcanoes
•  Movement of magma
Influx of magma—inflation
Outflux of magma—deflation
Injection of sills, laccoliths, and dikes
•  Changes in the local hydrothermal system
generally slow uplift or subsidence
e.g., Yellowstone caldera
•  Gravitational spreading
subsidence
•  Tectonic motion
background motion
Spatial/temporal scales of deformation
•  Movement of magma
ranges from large scale, rapid deformation near
the vent to smaller scale slower deformation distal
to the volcano
•  Changes in the local hydrothermal system
generally slow uplift or subsidence
over relatively long time scales
•  Gravitational spreading
slow subsidence
•  Tectonic motion
background motion ≤ plate rates
Traditional methods for studying
volcanic ground deformation
•  Basic Field Measurements
Fault offsets
Opening of cracks
•  Traditional surveying
Trilateration and Triangulation
Leveling surveys
Electronic Distance Measurements (EDM)
•  Tiltmeters
•  Strainmeters
From Dvorak and Dzurisin, 1997.
From Dvorak and Dzurisin, 1997.
Basic Field Measurements
Cracks in the crater floor at Mt. St. Helens. Orange line is ~1m long.
Photographs by D.A. Swanson in August 1982.
From http://volcanoes.usgs.gov/About/What/Monitor/Deformation/GrndDefrm.html
Lava Dome
Fault Scarp
Crater Floor
Measuring the distance between two
benchmarks across a thrust fault at the
base of the dome at Mt. St. Helens.
This scarp developed on the crater floor in 1981 as magma rose into
the lava dome (backgound) before erupting onto its surface.
Photograph by T. Leighley on 26 August 1981. Sketch by B. Myers
From http://volcanoes.usgs.gov/Products/Pglossary/fault_more.html
Traditional surveying
•  Trilateration
•  Triangulation
•  Leveling surveys
•  Electronic Distance Measurements (EDM)
Triangulation consists of a series of connected triangles which
adjoin or overlap each other, angles being measured from
determined fixed stations. A known base-line measurement is
required. Three examples of triangulation systems are shown below.
Trilateration uses electronic distance measuring equipment to
directly measure the lengths of the sides of triangles from which the
angles can be calculated. It is a very useful method for rough terrain
where positions can be accurately carried forward.
Leveling is the operation of determining differences of elevation
by measuring vertical distances directly on a graduated rod with
the use of a leveling instrument such as a dumpy level, transit or
theodolite. The difference in elevation between two points can
also be determined trigonometrically using vertical angles and
horizontal or inclined distances.
From http://education.qld.gov.au/curriculum/area/maths/compass/html/surveying/sutec.html
Electronic Distance
Measurements (EDM)
Mt. St. Helens
Closing distance between two benchmarks located on
the dome and at the EDM station on the crater floor
before the May 14, 1982, eruption (vertical red line).
As magma pushed the side of the dome outward, the
distance to the EDM station became smaller. The steep
curves indicate that the dome moved outward at
increasing rates right up to the eruption. For example,
the dome was moving about 2 cm/day on May 2; the
movement increased to about 200 cm/day by May 13.
From http://volcanoes.usgs.gov/About/What/Monitor/Deformation/EDMMSH.html
Photograph by R.B. Moore on 22 November 1977
Mokuaweoweo caldera,
summit of Mauna Loa
The distance between two benchmarks
located on the east and west rim of
Mokuaweoweo increased during the 1975
and 1984 eruptions of Mauna Loa. During
the onset of both eruptions (red lines),
rising magma forced the caldera apart by
about 50 cm. More was learned about the
extension and eruption processes of Mauna
Loa during this time period than in all
earlier historic eruptions.
From http://volcanoes.usgs.gov/About/What/Monitor/Deformation/EDMMaunaLoa.html
Locations of baselines that are measured in
the Long Valley Caldera, near Mammoth
Lakes, Calif., using a two-color laser distance
measuring instrument (geodimeter). The twocolor geodimeter measures distances to a
precision of 0.5 to 1.0 mm for ranges between
3 and 8 km. The locations of these baselines
are shown in relation to sources of inflation
that have been modeled using both these data
and leveling data.
Plot of the changes in length of 8 frequently measured
baselines. These baselines, which use the central station at
CASA as a common end point, have been measured
approximately 3 times each week since early 1984. The
general trend of the data is 1) a general decrease in the rate of
extension from 1983 through most of 1989, 2) an abrupt
increase in the rate of extension on several baselines to 5 cm/
yr from late 1989 through early 1990, and 3) a decrease to 2
to 3 cm/yr extension rate that has persisted since mid-1990.
From http://quake.wr.usgs.gov/research/deformation/twocolor/longvalley.html
Tiltmeters
Installing a tiltmeter on Montserrat in 1995.
From http://volcanoes.usgs.gov/About/What/Monitor/Deformation/Tilt.html
Pinnacle tiltmeters operate on the
same principle as a carpenter’s
level. At the core of each tiltmeter
is a pair of orthogonal bubble
levels with a precise
curvature.Electrodes detect
minute movements of the air
bubble within a conductive fluid as
the fluid seeks the lowest spot in
the sensor.The series 5000
tiltmeter can resolve tilt as little as
one billionth of a radian (or
0.00000005 degrees).
From http://www.pinntech.com/subs/about/pubs/series5000.pdf
Strainmeters
Sacks-Evertson single-component dilatometer schematic
How does a dilatometer work?
Magma movements, earthquakes,
and other natural phenomena deform
the volcanic edifice. This distortion
squeezes the dilatometer, which is
filled with oil. The amount of strain
is precisely measured by metering
the flow of oil into or out of the
dilatometer. Dilatometers are so
sensitive that they can easily detect
the small deformations of the Earth's
crust caused by gravitational
attractions of the sun and moon and
by the loads applied to the Earth's
surface by passing weather fronts.
From http://hvo.wr.usgs.gov/volcanowatch/2000/00_04_27.html
A. Linde’s models of single-component dilatometer data from Iceland
NB that strain signal preceded
Surface eruption by several hours!
New methods—InSAR and GPS
geodesy
SAR Interferometry (InSAR)
interferometry: interaction between superimposed wave trains
Two waves traveling that are
offset by amount, A
…A is phase difference
Use two antennae…one offset slightly closer
to surface…difference is A
One antenna transmits pulse, but returns
received by both;…difference in distance of
antennae from surface ensures that return
arrives at one antenna before other, resulting
in phase difference
interferogram…
two waves superimposed to generate one
resultant wave
resultant wave is record of
interference of two waves
may be displayed as image
by assigning gray-scale
or color spectrum to
each cycle
(crest to crest)
each cycle is an interference fringe
…image is an interferogram
because phase difference is recorded: possible to measure cm offsets
imaging geometry for a repeat-pass interferometer
one interferogram is formed with
images acquired from positions A1 and A2
(generate topography; DEM)
second interferogram is formed with A1 and A2’
if an earthquake has occurred between time 1 and time 2
additional displacement affects
the path length (surface change)
satellites at positions A1 and A2 at time 1
satellite at position A2’ at time 2
centimeter-scale differences in elevation possible to detect
topography generated from INSAR (ERS)
DEM
interferogram
Siberia
surface change from INSAR: displacement along strike-slip fault
Landers, 1993
first example
more fault ruptures…
GPS Geodesy
GPS Geodesy is a sophisticated way of
surveying using a constellation of
satellites as a “fixed” reference frame.
Positions of fixed benchmarks can be
determined at cm level accuracy.
D
Methods
•  Data acquisition
Installation of geodetic network, campaign
observations, & continuous site data
•  Data processing
SVs transmit two microwave carrier (carry information) signals
L1 (1575.42 MHz): carries navigation message; SPS code
(SPS: standard positioning service)
L2 (1227.60 MHz): measures ionospheric delay
3 binary codes shift L1 and/or L2 carrier phases
C/A code (coarse acquisition) modulates L1 carrier phase
…repeating 1 MHz pseudo random noise (PRN) code
…pseudo-random because repeats every 1023 bits or every millisecond…each SV has its own C/A code
…basis for civilian SPS
P-code (precise) modulates both L1 and L2
…long (7 days) pseudo random 10 MHz noise code
…basis for PPS (precise positioning service)
…AS (anti-spoofing) encrypts P-code into Y-code
(need classified module for receiver)
navigation message modulates L1-C/A; 50 Mhz signal ….describes satellite orbits, clock corrections, etc.
Using GPS geodesy, we can measure motions on the order of
a few millimeters per year.
This permits us to examine motion of lithospheric plates (cm/yr),
some motions related to intraplate deformation, and other types
of surface deformation (e.g. Volcanic).
How do we accomplish this?
• receivers that record both L1 and L2
• measurements acquired for minimum 2-3 days on site
• sophisticated processing that uses all GPS data in
GIPSY-OASIS II (JPL) with precise orbits & clocks
• sites are fixed spots
campaign: occupied intermittently
marked by stainless steel pin that
is epoxied into bedrock/monument
continuous: occupied permanently
receiver and antenna installed at site
Using GPS geodesy to observe intraplate surface deformation
  We use a precise point-positioning approach
Euler pole
• establish positions of individual points relative to a global
reference frame (ITRF00) using GIPSY
• re-occupy individual points after appropriate time interval,
which depends on estimates of plate deformation
• calculate changes in point positions to constrain velocities
of sites
• determine surface deformation field by comparing velocities
of sites with velocities predicted by plate velocity model
Site velocities
relative to fixed
plate
Site velocities
relative to fixed
plate
Observed site
velocities in
ITRF00
Predicted linear plate velocities in ITRF00
Surface deformation field
GIPSY
Flow Chart
Advantages of GPS Geodesy and InSAR for
measuring volcanic ground deformation
GPS Geodesy
•  High precision
•  Doesn’t require line of sight between benchmarks
•  Continuous sites operate without requiring presence of humanoids
•  Cheap
InSAR
•  Measurements made remotely—no humanoid endangerment
•  Can acquire images from numerous volcanoes
•  Entire deformation field may be imaged rather than isolated points
Limitations of GPS Geodesy and InSAR for
measuring volcanic ground deformation
GPS Geodesy
•  Sampling of deformation field limited to individual points, which
must be chosen carefully
•  Meaurements of campaign sites and installation and maintenance
of continuous sites may place humanoids in danger
•  Continuous sites may be destroyed by volcanic activity
InSAR
•  Small scale deformation may not be imaged (need >2.8 cm)
•  Difficulties in using the technique on densely vegetated or snow
covered volcanoes.
Case studies using InSAR and GPS geodesy
GPS Geodesy
•  Long Valley Caldera
•  Unzen Volcano
•  Mount Etna
InSAR
•  Long Valley Caldera
•  Mount Etna
•  Galápagos Volcanoes
•  Mount Peulik, Westdahl, Makushin, and
Okmok volcanoes, Alaska
Long Valley Caldera and Mono-Inyo Craters
Volcanic Field, California
Long Valley caldera, located at the boundary between the Sierra
Nevada and the Basin and Range Province, is one of the largest
Quaternary rhyolitic volcanic centers in North America. The
caldera is elliptical in shape and 10 by 20 miles (15 by 30 km) in
size.
The Long Valley caldera was produced by a catastrophic
eruption about 730,000 years ago. The roof above the magma
chamber collapsed, forcing 150 cubic miles (600 cubic km) of
rhyolitic magma to the surface in the form of Plinian ash
columns and associated air falls and ash flows. The volume of
ash is comparable to similar caldera-forming eruptions at
Yellowstone.
Photo from http://www.es.ucsc.edu/~anewman/research/LVC.html
Owens River Gorge Photo by R. Forrest Hopson.
Bishop Tuff
The Bishop tuff was
erupted during the
catastrophic eruption
that created Long
Valley caldera.
After the catastrophic eruption, volcanism continued on the caldera floor, producing a
thin layer of rhyolitic tephra and lava. Pressure increased within the magma chamber
and forced the overlying rocks upward, forming a resurgent dome. The resurgent dome
formed within 100,000 years after the caldera.
Eruptions 500,000, 300,000, and 100,000 years ago along the periphery of the resurgent
dome produced thick, steep-sided rhyolitic lava flows and domes. These volcanic
products are the youngest lavas to originate from the magma chamber.
Dixon et al., 1997
Newman et al., 2001
Simons and Fialko
Interferogram from a descending orbit with radar
acquisition dates of June 6, 1996, and July 12,
1998. The InSAR data reveal a domal uplift of the
Earth surface within the Long Valley caldera, with a
maximum displacement of ~10 cm in the satellite
line of sight (LOS) direction.
We invert the InSAR data for two ``endmember'' source geometries, a sill, and a
prolate finite spheroid of arbitrary
orientation. Because details of the source
geometry cannot be resolved with only
one component of the displacement field,
we include in our analysis the two-color
laser geodimeter data (data courtesy of J.
Langbein, USGS).
http://www.cacr.caltech.edu/SDA/insar.html
http://igpphelp.ucsd.edu/~fialko/
Unzen, Japan
Location: 32.75 N, 130.30 E
Elevation: 4,457, feet (1,359 m)
Photo from Steve O'Meara Volcano Watch International
Unzen is a large complex volcano made of several adjacent and
overlapping lava domes. The volcano covers much of the Shimabara
Peninsula and is east of the city of Nagasaki. In 1792, collapse of the
Mayu-yama lava dome created an avalanche and tsunami that killed
an estimated 14,524 people. Most of the people were killed by the
tsunami. After the 1792 eruption Unzen was dormant for 198 years.
The 1990 eruption was preceded by a swarm of
earthquakes that began in November 1989. A
phreatic eruption on November 17, 1990, marked
the onset of the most recent eruption of Unzen.
The eruption resumed on February 12, 1991. A
volcanic dome made of dacite lava began to grow
on May 20, 1991. The dome continued to grow
for four more years.
During this time pyroclastic flows were
frequently generated by the collapses of lava
blocks from margins of the dome. During
1991-1994, approximately ten thousand
pyroclastic flows were counted on Unzen.
Landslides also generated large pyroclastic flows
that traveled as far as 3.4 miles (5.5 km) from the
dome. On June 3, 1991, one of these pyroclastic
flows killed 43 people, including noted
volcanologists Maurice and Katia Krafft and
Harry Glicken.
Pyroclastic flows from Unzen during intense
activity on June 3-4, 1991.
Matsushima and Takagi, 2000
Horizontal displacement at FGI continuous GPS
station. The rapid expansion by the rise of magma
was observed from the end of February to the
beginning of April 1993. In mid-April the
movement was reversed, and stopped early in May.
Displacement observed from Jan 24, 1994 to Feb. 27 (35 days).
Values are horizontal/vertical displacements in unit of meter.
Wide arrows represent the directions of inflation of the Lava dome.
Etna, Italy
Location: 37.73N, 15.00E
Elevation: 10,991 feet
(3,350 m)
Looking south along the coast of Sicily to Etna. Taormina is in the foreground.
Photograph by Mike Lyvers taking during the 1993 eruption.
Bonaccorso et al., 2002
Aloisi et al., 2003
October 2002
eruption
July 2001
eruption
Massonnet et al., 1995
Hawaii
upper images: DEMS
lower image: surface change
Mt. Etna
Westdahl, Unimak Island, Alaska
Location: 54.00 N, 164.85 W
Elevation: 5,118 ft. (1,560 m)
Westdahl is a glacier-covered shield
volcano located on Unimak Island.
This volcano's most recent activity
dates back to February 1978.
Lu et al., 2000
Observed interferogram
1993-1998
Modeled interferogram for
0.5 km3 magma intrusion
The model suggests that a magma body about 8 km (5 miles) beneath
the center of the volcano expanded by about 50 million cubic meters
(65 million cubic yards) from 1993 to 1998. If the model is correct, the
summit area would have been uplifted about 17 cm.
Name:
PEULIK VOLCANO
Type:
STRATOVOLCANO WITH SUMMIT DOMES
Location:
540 KM SOUTHWEST OF ANCHORAGE
Latitude, Longitude:
57°45'N, 156°21'W
Elevation: 1474 M
From http://www.avo.alaska.edu/avo4/atlas/Peulik.htm
This interferogram represents deformation between October 1996 to September 1997. It
shows a striking bull's-eye fringe pattern centered on the southwest flank of the volcano.
Six fringes that represent about a total of about 17 cm (6.7 inches) of uplift map out the
deformation pattern in considerable detail. Other interferograms for the period from
September 1997 to September 1998 reveal one more fringe, corresponding to about 3 cm
(1.1 inches) of additional uplift.
Conclusions
•  GPS geodesy and InSAR are powerful new techniques for
monitoring surface deformation at volcanoes and can help in
forecasting eruptive activity
•  Like any method of observation, both have their limitations—
therefore, using multiple methodologies will give us the best
picture of deformation
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