V43A-01
Carbon Dioxide Degassing at the Crater Lake of Kelud Volcano, Eastern Java (Indonesia): Using CO2 Fluxes to Know the Input of Steam and Brine From the Hydrothermal System
The last eruption of Kelud volcano was occurred in 1990 and it contains a crater lake. Periodical surveys are carried out in geochemistry since 1993 to understand the hydrothermal system of this volcano. The lake contains near neutral waters with a pH of 6: a part of CO2 is dissolved as bicarbonates, and another part of CO2 escape through the lake as bubbles and by diffusion to the surface. From 2001 to 2006, measurements of CO2 flux emitted by the surface of the lake were performed by using the accumulation chamber method modified in order to work at the surface of a crater lake. Two statistical methods were used to process data: the graphical statistical and stochastic simulation methods. The results of graphical statistical approach permit to quantify the different degassing processes that are acting at the lake surface: one corresponding to CO2 fluxes resulting from rising bubbles close to the lake shore (from 2633 to 9072 g/m2/d); the second corresponding to CO2 fluxes from rising bubbles in the middle of the lake (from 478 to 945 g/m2/d); and the last corresponding to equilibrium diffusion of dissolved CO2 at the water-air surface (from 151 to 209 g/m2/d). Total CO2 emission rate estimated by stochastic simulation ranges from 105 t/d for 2001 to 35 t/d for 2006. Thermal energy released by the lake was estimated by using physical characteristics of the lake and meteorological data (wind speed, rainfall rate). The results of gases analysis and CO2 fluxes have provided a new constraint in the quantification of the input of steam and brine from the hydrothermal system. The thermal flux decreased from 200 MW (2001) to 60 MW (2006) and estimated inflow steam from 12 to 4 kg/s and inflow brine from 429 to 235 kg/s.
V43A-02
Study of Thermal Anomalies at Cotopaxi Volcano, 2002 to 2005
The Instituto Geofisico of the Escuela Politecnica Nacional (IG-EPN) has maintained continuous monitoring since
1977, allowing a better understanding of the volcano's baseline activity. Preliminary signs observed since 2001
of a possible reactivation of this volcano after more than a century of repose, prompted a comprehensive
seismological study and implementation of new methods of monitoring, based mainly upon a general increase
in seismic activity (VT and LP); appearance of new types of seismic signals never observed before (hybrids,
"tornillos", big LP, and tremor); an increase in the fumaroles' number and discharge, as well as a marked
thermal anomaly in the summit region. Seismic activity reached its peak in late 2001 / early 2002 and was
correlated with enhanced degassing from the crater, with vapor columns reaching some meters above the crater
level with abundant SO2 perceived. In this abstract we show evidence of the existence of a magmatic intrusion
(Troncoso, 2005), that has disturbed the hydrothermal system present in the cone and it is melting the glacier.
This has generated local population and civil defense concern. Since this stage of activity, Cotopaxi has not yet
returned to its baseline level, therefore the newly implemented technology includes periodic over flights with a
FLIR camera, which permits localization and identification of thermal anomalies. Additionally, a telemetric video
camera has been deployed in the northwest rim of the crater to identify degassing changes and its relationship
with seismic events. Finally, the IG-EPN staff perform continuous visits to the crater to observe changes IN the
ice-cap, measure temperatures and verify the presence of magmatic gases.
http:www.igepn.edu.ec
V43A-03
Aeromagnetic Anomalies and Structure of the Colima Volcanic Complex, Western Mexico.
Results of an aeromagnetic study of the region of the Colima Volcanic Complex (CVC) are presented. CVC is
constituted by a N-S range with Cántaro, Nevado and Colima volcanoes, which developed by southward
migration of activity inside the Colima rift and related to plate subduction along the Middle America trench.
Cantaro volcano does not show isolated defined anomalies associated with the summit; Nevado de Colima
volcano presents magnetic anomalies of monopolar characteristics and Colima shows a high-amplitude dipolar
anomaly normally polarized and centered on the summit cone. The aeromagnetometric survey over the adjacent
regions shows the occurrence of monopolar anomalies associated with intrusive bodies to the NW of the CVC.
The survey also reflects the shallow surface and deep geological features with high-amplitude, high-frecuency
anomalies over the volcanic units and low-amplitude, long-wavelength anomalies over the volcano-sedimentary
deposits. Our study distinguished aeromagnetic trends that have been interpreted associated to faults and/or
lithological contacts of regional characteristics that had not been reported previously. We estimate that the
magmatic chamber of the active Colima volcano is about two kilometers. Results illustrate the potential of
aeromagnetic surveys to investigate active volcanic structures with abrupt topography and difficult access.
http:www.ipicyt.edu.mx
V43A-04
2005-2006 Seismic Activity at Colima Volcano, Mexico
Colima volcano (19.51 N, 103.62 W, 3,950 m) is one of the most active volcanoes in México. It is located at the oriental end of the Mexican volcanic belt and with Nevado de Colima it forms a volcanic complex. The Colima seismic network (RESCO) has been monitoring the seismic activity since 1989 so we have records from the last four eruptions (1991, 1998-1999, 2001-2003 and 2004-2005). Since the 1998 eruption we could also measure deformation and SO2 . At the present time we are also monitoring activity with a tiltmeter network and two cameras which are continuously recording the outside activity. We also take periodically samples from springs and EDM. We present the general description of the seismicity since last eruption. Each eruption recorded from Colima volcano is different from the previous. The 2001-2003 eruption lasted for 15 months and it is considered the largest eruption (in time) of the last fifty years. It was characterized by a very low seismic activity previous to the eruption and tremors of large amplitudes never seen before during an effusive stage. The 2004-2005 eruption was characterized by a relative high rate of effusion (8-11 m3/s compared with the 4 m3 /s of that of 1998). During 2005 a series of explosions among which there were the largest ever recorded at Colima volcano occurred. After two years of mainly low intensity explosions, a new dome appeared so we are in the transition of explosive stage to effusive stage.
V43A-05
20 months of sustained changes at Turrialba volcano. Visual changes.
Turrialba Volcano (3340 m) is located at the southern end of the Mesoamerican Volcanic Arc. The summit area
has three craters aligned NE-SW: East, Central and West craters. The last active period of Turrialba Volcano
occurred between 1864-1866. During this period, the West crater of Turrialba was formed and ash falls were
reported in the Central Valley of Costa Rica. Mild to moderate fumarolic activity has been present at Turrialba
volcano, Central and West craters, since 1866.
This volcano has shown a variety of activity peaks during the last 10 years, mainly seismic swarms and vigorous
gas activity. Furthermore, at the middle of 2005 one of the greater degassing events took place provoking serious
effects on vegetation and expanding fumaroles towards the W and NW edges of the caldera. Cracks around
these sectors are releasing unestimated amounts of gas and vapor. Rapid sedimentation in the bottom of W
crater has been also reported. Enrichment of routinely sampled fumaroles make gas sampling process more
difficult. Expansion of heated ground around the W crater is accompanied by deposition of sulphur salts and other
sulphur-relative deposits.
Rapid erosion of the W crater accompanied of yet more vigorous degassing has sustained all through 2006. On
august a report was given to the national and international community due to the rapid burning and death of major
tree species. Most of dwarf vegetation and small vegetation coverage is rapidly disappearing thus affecting
directly the fragile balance between flora and fauna. Disorders in the feeding and behavior of a community of
coyotes has been observed, always related to acute impact of volcanic activity. More changes in other species that
inhabit the summit areas are expected. Moreover, pressure and impact on settlers, living in the low lands around
the volcano, is also expected.
A poster will illustrate areas of gas expansion, physical instability and sedimentation. It will also show areas
where major impact on vegetation and fauna is taking place.
http:www.ovsicori.una.ac.cr
V43A-06
Processes and Timescales of the Five Most Recent Eruptions of Fogo Volcano, Sao Miguel, Azores
Fogo Volcano is an active stratovolcano located on Sao Miguel, Azores. Fogo summit eruptions typically involve volatile-rich trachytic magmas that give rise to explosive eruptions. Within the past 5,000 years, Fogo has been the source of five eruptions: Fogo A, B, C, D, and 1563AD in chronological order (volumes from 0.05-0.7 km3 d.r.e.). In order to understand the petrogenetic processes and timescales over which magma evolves beneath Fogo volcano, a detailed petrographic, major and trace element, Sr-Nd-Pb isotope and U-series study is underway. Representative samples from the five eruptions are all trachytes, exhibiting relatively limited major element variations but large trace element variations. Element-element diagrams show that each deposit has a distinct chemical signature with the exception of the Fogo B and C deposits, which are similar to one another. Samples generally have low Sr and Ba contents and negative Eu anomalies that correlate with SiO2, indicative of compositional control by fractional crystallization of a sanidine-dominated mineral assemblage as proposed previously for the Fogo A and 1563AD deposits [1, 2]. However, fractionation of trace phases is likely responsible for differences between the five deposits in their incompatible trace element signatures. Previous studies of the Fogo A deposit have attributed 87Sr/86Sr variations (0.70490-0.70619; [2]) to syenite wall rock assimilation. The Fogo D deposit also shows 87Sr/86Sr variations (0.70491-0.70527) suggesting that similar open system process may have played a role. In contrast, Sr, Nd and Pb isotope signatures of samples from the Fogo B, C and 1563AD deposits show no variation and are similar to the unradiogenic end member of the Fogo A trachytes, consistent with closed-system evolution of these magmas. The recent detailed U-series study on the Fogo A deposit has shown that the time scale of differentiation was approximately 4.7 ky [3]. The results of U-series measurements on the remaining four deposits will allow us to constrain the time scales of differentiation and the relationship to eruptive volume. References [1] Widom et al. (1992) Contrib. Mineral. Petrol. 111: 311-328. [2] Snyder et al. (2004) J. Petrol. 45: 723-738. [3] Snyder et al. (in press) Chem. Geol.
V43A-07
Photometric Observations of Aerosol Plumes From Lascar Volcano, Chile
Lascar volcano, Chile, is the most active volcano in the Central Andes region. We conducted field campaigns at Lascar during October-November 2002 and December 2004, using a visible to near infrared Microtops II sun- photometer to measure spectral optical depths in order to infer particle size distributions of volcanic aerosols in the volcanic plume. Through this method we hope to increase the understanding of emission and conversion processes of tropospheric volcanic aerosols, specifically on atmospheric conditions similar to those at Lascar (a high volcano in a dry atmosphere). Data were collected on October 26, 28 to 31 (2002), November 5, 10, and 12 (2002), and December 2, 3, 4, and 8 (2004). We conducted Langley calibrations of the instruments during both campaigns, on 28 October 2002 and 3 December 2004. The optical properties of tropospheric volcanic aerosols were retrieved after the removal of the background optical depth. The plume optical depths for most of the 2002 data were extremely low (generally below 0.1), which is probably caused by the extreme dry conditions of the region (RH<15%). This result also shows that the plumes were very optically thin. Through the application of the Ångstrom equation and a King-type inversion, the Ångstrom coefficients (alpha and beta), the particle size distribution, and the effective radius were determined. Alpha averaged 1.5 to 1.9 for the 2002 data, which are large positive values, indicating that the particle distribution is dominated in number by small particles. The particle distribution spectra indicate bimodal distributions. The smallest radius mode is believed to be a nucleation mode consisting of particles generated by gas and aqueous phase oxidation of SO2 to H2SO4. The largest radius mode probably consists of large water droplets and/or ice. Variation in the relative size of the modes is a function of emissions and/or meteorological conditions. Preliminary results for the 2004 data show optically thin plumes, with lower plume optical depths than those of 2002.
V43A-08
Granulometric, Modal, SEM and EPMA Analyses of ashes and SO2 Emissions from Popocatépetl volcano (Mexico): Coupling Data for Identification of Eruptive Processes
Popocatépetl has being erupting effusively and explosively for the last 12 years. During this time, ash samples have been collected at several sites around the volcano, depending on the dispersion axis of the volcanic cloud. Granulometric and modal analyses have been carried out on these samples and the results allowed the construction of a data set that reveals several processes that occur before their settling at different distances from the volcano during the explosive events. We have separated the samples selecting those that come from locations at comparable distances from the vent (<47Km).This distinction allows choosing better the working fractions. After modal analyses of the samples, the most abundant fraction has been used in order to carry out SEM imaging EDS and EPMA analytical work. Starting with analyses for pumices, glasses and olivine crystals from samples obtained since 1995 (2 samples per year at least), several processes come clearer. Pumices are less abundant in comparison with other components (such as lithic fragments, crystals, and glass shards). They show little development of vesicles except for particular dates. Glass shards increased their content in the sample of the year 2000. The olivine crystals have changed their composition along the eruptive period. All this information together with SO2 emission rates are used to document processes associated to degassing processes, periods for entrance of new batches of magma, and crystal segregation.
V43A-09
Integration of video and infrasound to understand source locations and vent geometry at Erebus Volcano, Antarctica
Infrasound monitoring at Erebus volcano has enabled us to quantify eruption energetics and precisely determine
the source location of Strombolian eruptions. Since January 2006 we have operated a three-element network of
identical infrasound pressure transducers, to track explosive eruptions, triangulate source locations of the
eruptions, and distinguish activity from several vents with diverse activities. In December 2006 the network was
expanded to six identical pressure transducers with improved azimuthal distribution sited ~300 m to 700 m
from the erupting vents. These sensors have a dynamic range of +/-125 Pa and are able to record non-distorted
waveforms for almost all eruptive events.
Since January 2006, eruptions have been identified from locations within the ~40 m diameter phonolitic lava
lake, an adjacent smaller "active vent", and a vent ~80 m distant from the lava lake known as "Werner's".
Since late 2005 until the end of 2006, activity was considerably elevated at the "lava lake", from which frequent (up
to six per day) explosions were noted. These events entailed gas bubble bursts, some of which were capable of
ejecting bombs more than 1 km distant and producing infrasonic transients in excess of 100 Pa at a distance of
700 m. Activity from "Werner's" vent was much more subdued in terms of eruptive frequency and the radiated
acoustic energy, with all signals less than about 5 Pa at 700 m. Activity from the "active vent" was also observed,
though notably, these acoustic transients were extended in duration in terms of time (> 5 s to more than 30 s),
which reflects extended duration ash-venting source mechanisms, corroborated by video records.
The updated infrasound network has operated through a relative lull in eruptive intensity (November - December
2006 - January 2007). Since January 2007 more frequent and larger explosions from the lava lake have been
observed and recorded with infrasound and video. We quantify this recent upsurge in lava lake activity and
present speculative mechanisms to account for the variable eruptive behavior of Erebus lava lake.
http:erebus.nmt.edu