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Monitoring of Thermal Features at Mount St. Helens

By analyzing thermal features of an erupting volcano scientists can better understand active volcanic processes.

FLIR (forward looking infrared monitoring instrument) mounted on no...
FLIR (forward looking infrared monitoring instrument) mounted on nose of helicopter with Mount St. Helens in the background.

Thermal imaging data, especially when used together with other monitoring techniques (such as seismicity, GPS measurements, and gas emissions), helps to determine the nature of potential volcanic hazards.

During the 2004-2008 eruption of Mount St. Helens, Cascades Volcano Observatory staff monitored volcanism with a helicopter-mounted thermal infrared (TIR) camera side-by-side with an optical camera. CVO staff conducted observation flights from twice daily at the onset of the eruption to several times a week during later dome extrusion (weather permitting). The thermal surveys differentiated hot from cold eruptive events and structures and helped delineate the eruption sequence.Thermal imaging showed that the crater dome grew as a series slowly extruding lava spines. Observations during the 2004-2008 eruption of Mount St. Helens include:

  • Steam rather than magma drove early explosive phases (October 1-5).
  • Broad areas around the dome warmed significantly during days immediately before lava spines emerged.
  • Thermal imaging highlighted active faults and structures associated with spine growth.
  • Thermal imaging helped scientists identify locations on the dome that were cool enough for monitoring instruments, like seismometers and GPS receivers.

Thermal sensors on satellites that orbit the earth were less successful as monitoring tools because these instruments were so much farther from source than helicopter-based thermal cameras and therefore view a much larger area than thermal-imaging solutions at close range to the volcano.

Thermal infrared monitoring techniques can be implemented both rapidly and safely since crews can operate at a safe distance and need only a thermal camera. Thermal infrared technology is improving rapidly and will likely prove even more useful during future eruptions of Mount St. Helens.


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