Volcano monitoring

1
Volcano monitoring

• Based on USGS Volcano Hazards program
• http//volcanoes.usgs.gov/activity/methods/index.p
  hp

2
Volcano monitoring methods

• Designed to detect and measure changes caused by
  magma movement beneath a volcano
• Rising magma typically cause
• Seismic events
• Swelling or subsidence of the summit or flank of
  a volcano
• Release of volcanic gases

3
Questions typically addressed in volcano
monitoring

• Does the current unrest involve the movement of
  magma?
• If yes, when is an eruption most likely to occur,
  if at all?
• During an eruption, what real-time warnings are
  needed to prevent loss of life and property
  damage?
• When is the eruption really over?

4
Other questions

• What is the nature of a volcano's magma-reservoir
  system?
• What is the cause of specific volcano-seismic
  events?
• How do volcanic ash clouds disperse downwind of
  an erupting volcano?
• How susceptible to massive slope failures
  (landslides) are volcanoes?

5
Monitoring method Seismicity
Magma rises into reservoir beneath volcano
Rising magma and gases exert pressure
High pressure causes rocks to break, triggering
earthquakes
6

• Earthquake activity beneath a volcano almost
  always increases before an eruption
• When magma and gases move they either cause rocks
  to break (results in HIGH-FREQUENCY earthquakes)
• Or they can cause cracks to vibrate (results in
  LOW-FREQUENCY earthquakes or continuous shaking
  called volcanic tremors)

7

• Most volcanic-related earthquakes are less than a
  magnitude 2 or 3 and occur less than 10 km
  beneath a volcano.
• The earthquakes tend to occur in swarms
  consisting of dozens to hundreds of events

8
Webicorder record for Redoubt volcano, March 27,
2009
9
(No Transcript)
10
Monitoring method Ground deformation

• The surface of a volcano often changes shape when
  magma moves beneath it or rises into its cone
• The ground can change shape by rising up,
  subsiding, tilting, or forming bulges

Illustration by B. Myers and S. Brantley
11
Methods for monitoring volcano ground deformation

• Electronic Distance Measurement (EDM)
• Measures distance between benchmarks placed on a
  volcano using electromagnetic signals
• Tiltmeters (one of the oldest methods)
• Measures changes in the slope angle or tilt of
  the ground due to magma movement

12

• Global Positioning System (GPS)
• Measures horizontal as well as vertical ground
  motions using satellite transmission
• Signals from at least 4 satellites is essential
  for accuracy
• More accurate and convenient that EDM

13
Satellite Radar Inferometry (INSAR)
14
Satellite images taken before and after
deformation are combined

• Changes in satellite-to-ground distance can be
  identified in mm scale.

Unlike other methods, INSAR technique provides
information regarding overall pattern of
deformation of a volcano