Infrared radiation thermometry of guatemalan volcanoes

A Barnes PRT-5 radiation thermometer was used to obtain apparent surface temperatures of two Guatemalan volcanoes from land-based stations from 500 to 4000 meters distant. Isotherms of apparent surface temperatures, drawn on photographs of the volcanic terrain under study, delineate areas of fumarolic activity and active domal upgrowth. The excess radiant heat emitted from Pacaya Volcano is calculated from apparent surface temperatures corrected for atmospheric absorption of infrared radiation and for the adiabatic cooling of the atmosphere with altitude. The excess radiant heat data indicate that the lava flow extruded in June 1969 had completely solidified by December 1969. This calculation is consistent with theoretical estimates of the cooling of an extrusive lava sheet by conduction. Similar calculation of excess radiant heat emission shows the depth of the magma chamber underlying the Santiaguito Volcanic Dome to be 11 meters. This depth is consistent with field observations. Corrections are made for surface emissivity on Pacaya Volcano and the isotherms of real surface temperature plotted. Consideration is given to the times required for the equilibration of a geothermal gradient following the upward movement of a magma.