Ground-based Thermal Observations of Gas Pistoning at Pu'u O'o

Three IR-sensitive (8 to 14 micron) radiometers situated on the north rim of Pu'u O'o provide University of Hawaii and HVO with real-time telemetered thermal time-series (2 Hz) data. During the past two years, these instruments have targeted the crater floor as well as various hornitos and pit vents to monitor fluctuations in eruptive activity, understand cycles in the ongoing eruption, and investigate linkage of various vents. Between June 18th and July 23rd, 2002, our system recorded spectacular thermal signals associated with `gas pistoning' at one of the Pu'u O'o central pit vents. This pistoning is characterized by discrete and vigorous gas jets (possibly ballistic-laden) that recur regularly at intervals ranging from 2 to 10 minutes. The thermal intensity of these pulses produces radiation equivalent to a blackbody at 400 degrees C, a marked contrast to the background that radiates at only 20 degrees C. Central vent gas pistoning rarely occurs as an isolated pulse. Instead, our thermal records show intervals of quasi-continuous gas emission (mean equivalent blackbody temperature 100 degrees C) alternating with sequences of ten or more gas piston pulses. Between July 16th and July 21st, 2002 the central vent activity was nearly dominated by pistoning, with as many as 300 individual pulses occurring in succession over 12 hour periods. The onset of this period of elevated gas pistoning appears to coincide with a series of lava flows (detected by our radiometers) that erupted from the central crater pit vent starting on July 11th. We hypothesize that pistoning is a stable mode of degassing for volatile-rich basaltic magmas with particular supply rates and conduit geometries. Our current work focuses on forward modeling of eruption phenomena to produce various thermal signals (both gas pistoning as well as lava flow emplacement/cooling curves). The end goal is to convert our thermal records to calibrated temperature-time waveforms that will be used to constrain mass transport estimates.