Image: Mount Etna Boils Over As Seen From Space
After maintaining a low simmer for ten months, Italy's Etna volcano boiled over on February 19-20, 2013, with three outbursts in 36 hours. According to the Italian Istituto Nazionale di Geofisica e Vulcanologia, each outburst (paroxysm) featured "emission of lava flows, pyroclastic flows, lahars, and an ash cloud."
The Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite captured Mount Etna on February 19 at 9:59 a.m. Central European Time, about 3 hours after the end of the first paroxysm. The false-color image combines shortwave infrared, near-infrared, and green light in the red, green, and blue channels of an RGB picture. This combination makes it easier to differentiate between fresh lava, snow, clouds, and forest.
In the image, fresh lava is bright red, as the hot surface emits enough energy to saturate the instrument's shortwave infrared detectors but is dark in near-infrared and green light. Snow is blue-green because it absorbs shortwave infrared light, but reflects near-infrared and green light. Clouds made of water droplets (not ice crystals) reflect all three wavelengths of light similarly and appear white. Forests and other vegetation reflect near-infrared more strongly than shortwave infrared and green, and so appear green. Dark gray areas are lightly vegetated lava flows, 30 to 350 years old.
Abrams, M, Bianchi, R, and Pieri, D. (1996 December) Revised Mapping of Lava Flows on Mount Etna, Sicily. Photogrammetric Engineering & Remote Sensing. 62(12), 1353-1359.
Cooperative Institute for Research in the Atmosphere. (n.d.) Snow/Cloud Discriminator (3-color technique)--Basic Information. Accessed February 20, 2013.
Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania. (2013, February 19) Etna and Stromboli update, 19 February 2013. Accessed February 20, 2013.
Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania. (2013, February 20) Etna update, 20 February 2013. Accessed February 20, 2013.
Etna's Explosive Last Three Days (Eruptions Blog)
Tour of the Electromagnetic Spectrum (NASA Mission: Science)
NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team. Caption by Robert Simmon.
Instrument: EO-1 - ALI