HR: 08:45h
AN: V41B-04    [Abstracts]
TI: Infra-red Monitoring of Fumaroles at Volcán de Colima, México.
AU: * Stevenson, J A
EM: johnalexanderstevenson@yahoo.co.uk
AF: Facultad de Ciencias Universidad de Colima, Av. 25 de Julio #965 Col. Villas San Sebastián , Colima, 28045, Mexico
AU: Varley, N
EM: nick@ucol.mx
AF: Facultad de Ciencias Universidad de Colima, Av. 25 de Julio #965 Col. Villas San Sebastián , Colima, 28045, Mexico
AB: Infra-red cameras permit the remote measurement of temperatures in locations too dangerous to allow direct measurement, which is currently in a state of unrest, producing multiple explosive events each day. Since January 2006, the temperatures of three fumarole areas upon the crater rim of Volcán de Colima have been measured regularly from a distance of 5.8 km with a VarioCAM infra-red camera (wavelength 8-14 μm). Simple mathematical models demonstrate that despite the large viewing distance, and consequent large pixel size and reduced atmospheric transmissivity, changes in thermal output by the fumaroles can still be detected. Sequences of thermal images, with images taken at five second intervals, were collected on an approximately weekly basis, with the apparent temperatures of six regions of interest measured in each image. The resulting graphs show changes in fumarole apparent temperatures during each visit. Trends within individual fumarole temperature sequences are independent of the explosions. The data are then filtered to select only points from nighttime, cloud-free images and mean temperatures for each of the regions of interest are calculated. Comparison of daytime and nighttime fumarole and flank temperatures allows crude estimation of subpixel temperatures. Between January and September 2006, the apparent pixel-averaged temperatures of the hottest fumarole ranged from 30-40 °C, with maxima in mid-March and late-July. These trends are independent of flank temperature. Between October and December apparent temperatures were lower (25-30 °C), then in January 2007 they showed a sharp decline <15 °C. The trends remain when atmospheric corrections are applied to the data. There is evidence that dome growth began within the crater at the beginning of 2007 and the sharp decline in fumarole temperature may be related to associated changes in the plumbing of the upper edifice.
UR: http:www.ucol.mx/ciiv
DE: 8419 Volcano monitoring (7280)
DE: 8485 Remote sensing of volcanoes
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly