AIRBORNE MEASUREMENTS OF PARTICLE AND GAS EMISSIONS FROM THE DECEMBER1994 JANUARY 1995 ERUPTION OF POPOCATEPETL VOLCANO (MEXICO)

Airborne and ground-based (correlation spectrometer, cascade impactor, and photoelectric counter together with intake filter probes) measure ments are described for the volcanic emissions from Popocatepetl volca no (Mexico) from December 23, 1994 to January 28, 1995. Measurements o f SO2 restarted 48 h after the eruption onset of December 21, 1994. Ma ximum sulfur dioxide (4560 t d(-1)) plus 3.8 x 10(4) t d(-1) of partic ulate matter were ejected on December 24, 1994. The maximum rate of ej ection occurred coincidentally with the maximum amplitude of harmonic tremor and the maximum number of seismic type B events. Sulfur dioxide emission rates ranged from 1790 to 2070 t d(-1) (December 23-24, 1994 ). Afterwards, sulfur dioxide emission rates clearly indicated a consi stent decline. However, frequent gas and ash emission puffs exhibited SO2 fluxes reaching values as high as 3060 t d(-1). The emission SO2 b aseline for the period of study (February 1994-January 1995) was about 1000 t d(-1). Ejection velocity of particulate matter was approximate ly 270 m s(-1) reaching a height of about 2.5 km over the summit. The immediate aerosol dispersion area was estimated at 6.0 x 10(4) km(2) m aximum. The microscopic structure of particles (aerosol and tephra) sh owed a fragile material, probably coming from weathered crustal layers . X-ray fluorescence and neutron-activation analysis from the impactor samples found the following elements: Si, Al, Ca, S, P, Cl, K, Ni, Fe , Ti, Sc, Cu, Zn, Mn, Sr, Cr, Co, Y, Br, Se, Ga, Rb, Hg and Pb. Morpho logical analysis shows that ash samples might be from pulverized basal tic rock indicating that the Popocatepetl eruption of December 21, 199 4 was at low temperature. The microscopic structure of puff material s howed substance aggregates consisted of fragile rock, water and adsorb ed SO2. These aggregates were observed within water droplets of approx imately 1 mm and even larger. Sulfur transformations in the droplets o ccurred intensively. Volcanic ash contained 5-6% of sulfur during the first expulsion hours. Elemental relative concentrations with respect to Al show that both Si and S have relative concentrations > 1, i.e., 13.73 and 2.17, respectively in agreement with the photoelectric count er and COSPEC measurements. (C) 1998 Elsevier Science B.V. All rights reserved.