Workshop 2

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Workshop 2 Interpreting Ground Displacement Mauna
Ulu
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• 1GS135 GEOLOGICAL HAZARDS ENGINEERING GEOLOGY

SCHOOL OF EARTH ENVIRONMENTAL
SCIENCES Workshop 2 Interpreting Ground
Displacement
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Volcanic Geohazard

• Volcanic Hazards
• Monitoring

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Volcano Monitoring Methods

• Core methods
• Seismic
• Ground deformation
• Supportive methods
• Microgravity, electrical magnetic studies
• Geochemical monitoring (gas water)
• Satellite-based methods
• Global Positioning System
• Radar Interferometry
• Thermal monitoring

volcanoes.usgs.gov/About/What/Monitor/monitor.html
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Volcano Deformation

• Principles Methods
• Tilt measurement
• Tiltmeter
• Dry tilt
• Lateral displacements
• EDM (infrared laser
• microwave)
• GPS
• Vertical displacements
• Precise levelling
• Space-based
• Radar interferometry
• Laser altimetry

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Ground Deformation Sources Patterns
?h
Mogi spherical source
?h
Linear source (dyke)
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Tilt Measurement

• Early versions
• Water - tube tiltmeters
• Dry tilt levelling

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Tilt Measurement

• Borehole tiltmeters
• Provide continuous record
• Need to be insulated from T rainfall effects

Scientists install a new tiltmeter after an
eruption at Rabaul Caldera, PNG
Tavurvur Volcano erupts in background
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Tilt Measurement

• Problems
• Site specific
• No measure of absolute altitude change or
  horizontal movements

Installing a tiltmeter at Soufriere Hills
Volcano, Monsterrat in 1995
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Tilt Measurement

• Tilt Related to Puu Oo Eruptions (Kilauea,
  Hawaii)

http//volcanoes.usgs.gov/About/What/Monitor/Defor
mation/TiltKilauea.html
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Precise Levelling

• Most accurate way of deriving relative height
  changes
• First used to investigate 1910 Usu (Japan)
  eruption
• Regular monitoring tool since mid 1960s
• Involves use of a level and graduated measuring
  staff
• Time consuming and labour intensive
• Accuracies of 0.8mm over 1km possible

Etna (1989 eruption)
http//vulcan.wr.usgs.gov/Monitoring/Descriptions/
description_geodetic_level.html
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Precise Leveling the Method
a e permanent benchmarks b c d
temporary staff and instrument positions Height
difference e - a sum of all the foresights
minus sum of all the backsights
Benchmark
Turning point
Benchmark
foresight
e
backsight
d
c
b
a
Any number of turning points may be used
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Electronic Distance Measurement

• Measures horizontal distance changes in a
  network of benchmarks
• Uses laser or IR Total Stations (incorporate
  electronic theodolite)
• Light beam bounced off reflector a few kms away
• Preliminary distance read from instrument
• Corrections for T and P made to give final
  distance
• Accuracies of a few cm

http//vulcan.wr.usgs.gov/Monitoring/Descriptions/
description_EDM_meas.html
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Electronic Distance Measurement
Slope-Distance Measurements using EDM's and
Theodolites
EDM Set-up on Road100, northeast of Mount St.
Helens
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Electronic Distance Measurement
http//vulcan.wr.usgs.gov/Projects/Deformation/MSH
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Global Positioning System
Etna 1996

• Most accurate way of measuring horizontal
  position over large distances
• Utilises constellation of 24 satellites that
  beam radio signals to Earth
• Determines precise distance to satellite and thus
  position on Earth
• At least 4 satellites needed
• Accuracies of a few mm over 10s km using dual
  receiver differential GPS
• Drawbacks line of sight weather

http//vulcan.wr.usgs.gov/Monitoring/GPS/framework
.html
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GPS The Method

• One antenna (rover) is set up vertically above a
  benchmark
• Locked on to satellites 15 minutes. Data stored
  in hand-held controller

http//vulcan.wr.usgs.gov/Monitoring/GPS/descript
ion_GPS.html
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GPS The Method

• A second antenna (base) is left locked on to
  satellites at start of days work
• Rover moved on to successive benchmarks in a
  network designed to provide good spatial coverage

http//vulcan.wr.usgs.gov/Monitoring/GPS/descript
ion_GPS.html
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Integrated Monitoring Networks
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Mauna Ulu
volcano.und.nodak.edu/vwdocs/Parks/hawaii/chain_cr
ater/menu2.html
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Tiltmeter
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Mauna Ulu
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Mauna Ulu

• 1. Is the centre of ground displacement at
  Halemaumau Crater, the upper east rift zone, or
  the upper southwest rift zone? (Circle one)
• 2. Does the ground displacement pattern indicate
  uplift or subsidence? (Circle one)
• 3. What is the maximum amount of ground
  displacement?
• 4. What type of volcanic activity would you
  expect to be associated with this ground
  displacement pattern?
• 5. Where is volcanic activity likely to occur?
• 6. Why are the lines dashed for the southwest
  part of the pattern?
• 7. Are the tilt vectors useful for defining the
  centre of ground displacement?

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Mauna Ulu
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Mauna Ulu

• 1. Where is the centre of ground displacement
  located? Halemaumau Crater, the upper east rift
  zone, or the upper southwest rift zone? (Circle
  one)
• 2. Does the ground displacement pattern indicate
  uplift or subsidence? (Circle one)
• 3. What is the maximum amount of ground
  displacement?
• Answer the following questions after contouring
  the ground displacement data. Begin by contouring
  the data to define a pattern of ground
  displacement. A contour interval of 5 mm works
  best (i.e., 0, 5, 10, 15, ... 45).
• 4. Does the pattern defined by the contours
  support your answer to question 1?
• 5. Draw a line on the diagram where volcanic
  activity probably occurred.
• 6. Did you have any difficulties defining the
  south-western part of the pattern? Explain.