Volcanic Monitoring

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Volcanic Monitoring

Benefits of iGRAV®

High sensitivity, allows measuring typical volcanic processesas far as 30 km away from the edifice:

GWR Instruments, Inc. is introducing the iGrav Superconducting Gravity Meter as an ideal choice for continuous volcano monitoring. The iGrav will improve precision to sub-μGal levels and will eliminate drifts and scale factor variability. The iGrav will provide a high precision, continuous gravity record that is ideal for interpreting volcanic activity and correlating with other geophysical measurements.

Detection of Mass Redistribution Long Before Eruption Precursors Appear

• Magma Movements on Different Time Scales:
  • Intrusive mechanism leading to eruption
  • Magma drainage out of a reservoir, magma migration from central conduit to fractures
  • Magma storage
  • Accumulation of magma at depth, increasing pressurization in the volcanic conduit and potential for explosive eruption
  • Gas release
  • Vesiculation (density decrease) and crystallization (density increase)
  • Monitoring mass changes without significant vertical deformation (e.g. increase in CO2increases magma compressibility (Bonvalot et al., 2008))
  • The iGrav is an indispensible forecasting tool for monitoring aseismic mass changes (e.g. CampiFlegreior PhlegraeanFields, Naples)
• Volcano-groundwater Interactions:
  • Discriminating between the intrusion of magma, water and gas
  • Groundwater dynamics within a volcanic edifice (potential for slope failure, lahar generation and phreatic eruptions)
  • Hydrothermal systems (e.g. Long Valley and Yellowstone calderas, Mt Uzu, Mt Sakurajima)
• Continuous Gravity Monitoring Enables:
  • Avoiding aliasing from intermittent 4D gravity campaigns
  • Recovering functioning laws and therefore, discriminating clearly between models for sources of volcano unrest
  • Investigating short period (e.g. bubble formation and collapse in Strombolian activity) gravity changes
  • Development of an accurate surface hydrological model to achieve μGal precision
  • Precise modeling of Earth and ocean tides and atmospheric signals
  • Changes in the mechanical response of the edifice to the tidal forces
  • Providing a precise reference point to anchor microgravity surveys
• Integration and Correlation with Other Techniques:
  • Combining with GPS - Most powerful combination to separate and interpret change in gravity with expansion, deflation or stability of volcanoes’ surface
  • Combining with Absolute Gravity extends spectrum of results to years and decades for studying long term reservoir activity
  • Correlation with seismic activity and long period seismic signals

Network of iGrav®

• Allow Monitoring at Safe Distance
• Enable Discriminating Between Shallow and Deep Processes
• Horizontal Gradients Probe Mass / Density Variations at Depth Over Both Space and Time
  • Two iGrav® at distances of 1 and 10 km may allow discriminating between point sources from dyke intrusion or between shallow and deeper processes
  • One iGrav can measure the influence of a 2 x 3000 m dyke or of a 10¹² kg point source at a distance of 30 km
• A Few Strategically Positioned iGrav® will Dramatically Reduce Aliasing of Time-lapse Microgravity Surveys

Models of Volcanic Sources

As the models below show - Volcanic gravity changes range in amplitude from a few Gal to several hundred Gal depending on the size and depth of the source. Changes may occur suddenly in a few seconds or slowly over days, months or years. SGs have proven their precision and stability in distinguishing hydrological models with signal amplitudes of a few tens of Gal over a similar range of periods. The iGrav is a proven choice to monitor and separate these complex volcanic signal sources.

iGrav™ Superconducting Gravity Meter

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Volcanic Monitoring (PDF - 0.98MB)