1. Volcano Monitoring with GPS
An Alaskan Example
Maite Agopian (EarthScope National Office)
Shishaldin (ESNO)

2. Augustine by Read, Cyrus (AVO/USGS) Veniaminof by Alto, Joyce (AVO/USGS) Pavlof by Almandmoss, Nahshon (AVO/USGS)
Alaska contains over 130 volcanoes and volcanic fields
which have been active within the last two million
years. Of these volcanoes, about 90 have been active
within the last 10,000 years (and might be expected to
erupt again), and more than 53 have been active
within historical time (since about 1760, for Alaska)

3. Image courtesy of the AVO/ADGGS// by Schaefer, J. R. G.; Cameron, C. E.; Nye, C. J.

4. Image courtesy of the NASA (Unimak Island, Alaska, United States - September 1992)
UNIMAK ISLAND
Westdahl Volcano
Shishaldin Volcano

5. Wesdhal Volcano
Image courtesy of AVO/USGS // Read, Cyrus
Westdhal Volcano is a field volcano. The size of the postulated ancestral cone is about 19 x 30 km at sea level, making it one of the
largest volcanoes in the Aleutian Islands be it a stratovolcano or a shield. The entire ancestral cone has been extensively dissected
by erosion, with the northeast-facing slopes steeper and of greater relief than the other slopes.

6. Westdahl eruption 1991
Westdahl Volcano last erupted between Nov. 29 1991–Jan. 15 1992, before monitoring began.
Image courtesy of AVO/USGS // Read, Cyrus
Image courtesy of AVO/USGS

7. Description of
the eruption
A steam and ash
cloud rising to more
than 6 km above
Westdahl volcano
was first reported by
commercial pilots on
routine flights along
the Aleutian Island
chain on November
29, 1991.
Image courtesy of AVO/USGS

8. Many pits, craters, and gaping cracks were visible in the
ice adjacent to the fissure.
Image courtesy of AVO/USGS

9. In addition to ash and steam venting, spectacular lava
fountains along the lower few kilometers of the fissure
fed a lava flow that extended 7 km from the vent and was
as much as 1.5 km wide at the front and 5-10 m thick.
Image courtesy of AVO/USGS

10. Stormy weather conditions prevented direct observation
of the vent area for most of December, 1991, but pilots
reported a constant steam plume, usually mixed with ash,
punching through the weather cloud cover.
Image courtesy of AVO/USGS

11. Residents of False Pass, the
nearest permanent settlement,
90 km NE of Westdahl Peak,
also reported thunder-like
rumbling sounds, the
occasional smell of sulfur, and
light ashfalls on November 30,
December 16, 25, and 26 -
evidence that the eruption was
still continuing.
By January 15, there was no
sign of a vertical plume or any
other eruptive activity.
(report by McGimsey and others ; 1995, AVO)

12. MONITORING VOLCANOES IN AK

13. Alaska Volcano Observatory (AVO)
The Alaska Volcano Observatory (AVO) is a joint program of the United States
Geological Survey (USGS), the Geophysical Institute of the University of Alaska
Fairbanks (UAFGI), and the State of Alaska Division of Geological and
Geophysical Surveys (ADGGS). AVO was formed in 1988, and uses federal,
state, and university resources to monitor and study Alaska's hazardous
volcanoes, to predict and record eruptive activity, and to mitigate volcanic
hazards to life and property.

14. Volcanic Monitoring
Changes to a volcano's ground surface (volcano
deformation) appear as swelling, sinking, or
cracking, which can be caused by magma, gas,
or other fluids (typically water) moving
underground or by movements in the earth's
crust due to motion along faults. Often, this
deformation is very small in magnitude—a few
centimeters (inches) or less—and so can only be
detected and monitored with very sensitive
instruments.

15. AVO uses different types of data to monitor
volcanoes for signs of unrest or eruptive activity.
Remote sensing
Ground vibration Camera Deformation

16. Using GPS to monitor Volcanoes
GPS antenna
inside of dome
Tripod legs are cemented 10 – 30 feet into the ground
Image courtesy of UNAVCO

17. How does it work?
Image courtesy of UNAVCO

18. A high precision GPS antenna is
much bigger than a cell phone
42 cm (~16.5 in)
32cm(~12.6in)
Image courtesy of UNAVCO

19. Anatomy of a GPS Antenna
• Antenna
• Signal
Amplifier
• Choke ring
(to dampen
unwanted
signals)
• Antenna
mount
• Dome
• Power &
signal cable
• Tripod
supports
19
Image courtesy of UNAVCO

20. SANDBOX ACTIVITY
Image courtesy of EARTHSCOPE

21. Activity: How do GPS work?
• Make your mini GPS monument
• Demonstration (using the sand box): How
does GPS work to pinpoint location?

22. For Teachers/Educators
• Watch the full GPS_ActivityDemo_Part1&2
(IRIS): https://youtu.be/s_CeiMjO5Pc

23. How GPS Works - Basics
• Satellites broadcast their
name and position in space.
• The GPS ‘listens’ only.
• GPS antenna collects the
satellite signals and sends
the signals to the GPS
receiver
• GPS receiver calculates the
GPS antenna to satellite
distance.
23

24. How GPS Works - Basics
To locate the GPS receiver:
o Three satellites for rough
location
o Fourth satellite corrects
time errors, improving
location accuracy.
Position can be calculated within to a
millimeter.
24
Networks of GPS sensors can track three-
dimensional movements of the ground
surface even at rates of less than 1 millimeter
(1/25 inch) per year.

25. High precision GPS Corrects
Some of these Sources of Error
25
Some GPS Error Sources
• Satellite orbits
• Satellite and receiver clock errors
• Atmospheric delays
– Ionosphere
– Troposphere
• Multi-path (reflections of signals off other objects)
• Human errors (trained staff)

26. Activity: Inflation/Deflation
• How to GPS work demonstration
• Be a field engineer (build and deploy)
• Be a scientist (make your hypothesis,
observe, measure and record your data)
• Discuss your conclusions
Image courtesy of Earthscope

27. RECAP
• By looking at data from a single receiver over a period
of time, scientists can determine whether the ground
surface has moved (deformed). By combining the data
collected from a GPS network, it is possible to get a
larger view of which areas of the volcano's surface are
moving as well as the speed and direction of
movement.
• This large-scale picture of volcano deformation can be
used to construct a model of what is happening
beneath the surface—for example, the location of any
magma reservoirs or active faults.

28. Other monitoring options
• Ground deformation can also be measured with
satellite radar interferometry (InSAR). Though not
as accurate as GPS, the satellite measurements
have the advantage of broad spatial coverage.
• The combination of GPS and InSAR is especially
powerful because the two data sets complement
one another's strengths and weaknesses.

29. Extended exploration
Explore and discuss
other methods of
monitoring volcanoes
Remote sensingGround vibration Camera

30. Using Real Data Sets
Understanding Time Series and
Velocity Vectors

31. Understanding GPS time series plots
3 separate plots :
– North
– East
– Height
*Vertical scales
vary
X-axis: Time
Y-axis: Distance
GPS has moved
(mm)
Loss of data set
Snow effects
Image courtesy of UNAVCO

32. Loss of data sets have different causes…
Image courtesy of UNAVCO

33. Weather
Image courtesy of UNAVCO

34. Fauna
Image courtesy of AVO

35. Hazards (eruptions, landslides,
earthquakes)
Image courtesy of UNAVCO

36. Large battery banks to power through
the long winter
Image courtesy of UNAVCO

37. Up
Down
How to read a time series?
N
E
+
+
-
-

38. Which Direction is the GPS moving?
It is going down : South
It is going down: West
Slightly up (barely)
For information only. The
Height data set will not be used
in this activity.

39. How much is it moving?
-1.31
-2.55
N
E
??
Total Velocity Vector

40. Using the Pythagorean theorem
-1.31
-2.55
N
E
??
√(-2.552)+ (-1.312)= 2.86
The annual velocity for this
station is 2.86 mm /year

41. Check your answer
http://www.unavco.org/software/visualization/GPS-Velocity-Viewer/GPS-Velocity-Viewer.html
All PBO GPS data set
(location, station
information, picture, time
series, etc.) can be freely
accessed on UNAVCO’s
Visualization tools.

42. PBO Network on the Aleutians

43. PBO Network on Unimak Island

44. Westdahl Volcanic GPS Network
Find your station!

45. Graph the GPS velocities

46. Check your answer

47. Final Questions
1. Describe the overall movements observed
2. What volcanic process could be leading to
these movements on Westdahl volcano?
3. If you were in charge of issuing warnings
would you tell people an eruption was likely
to happen soon? Why or why not?
4. What other types of volcanic monitoring
would you recommend and why?