V34A-01
Acoustic Remote Sensing of Volcanic Eruptions in Washington, Ecuador, and Colombia: New Tools for Covering Observational Gaps
Some volcanoes, particularly near population centers or in developed countries, have well developed ground- based monitoring systems. Yet there remain large portions of Earth's surface, particularly in remote areas or less-developed countries, where local ground-based surveillance systems are sparse, fragile, or non-existent. The Acoustic Surveillance for Hazardous Eruptions (ASHE) project aims to develop and evaluate the capability to use low frequency sound to provide robust, low-latency notifications of volcanic eruptions over large regions. We describe current field deployments of several small, autonomous infrasound arrays in Washington State (since October 2004) and Ecuador (since January 2006). The arrays in Washington have detected diverse eruption signals from Mount St. Helens, and the arrays in Ecuador have captured eruptions from Tungurahua and Sangay Volcanoes, as well as Galeras in Colombia. These stations send continuous real time data to a central facility where automatic analysis techniques for eruption detection are being prototyped. Plans are in place to send automated notification products on a test basis to a participating ICAO-designated Volcanic Ash Advisory Center for comparison and possible integration with their existing warning systems. These notifications would be coupled with more detailed real-time data products (presently provided in designated web pages), and could be used by responsible agencies to assess hazard and disseminate updated information.
V34A-02
The Summer 2006 Volcanic Crisis of Tungurahua, Ecuador: No Lessons Learned
More than 250 volcanoes are exposed in the Ecuadorian part of the Northern Andean Volcanic Zone of which the 5019 m a.s.l. high Tungurahua, is one of the seventeen considered active volcanoes in the country. The Tungurahua volcanic complex is located in the Eastern metamorphic belt and is made up of three different edifices. The actual active stratovolcano, Tungurahua III, is build up above debris-avalanche deposits of the last sector collapse and contains also series of lavas of either andesitic affinities, which reached in past VEI's of 3 while the occasionally dacitic lavas have been associated with eruptive phases reaching VEI's of up to 4. The growth of the steep-sided volcano is based on eruptive phases with the repeated generation of ash falls, lahars, lava and pyroclastic flows demonstrating a frequency of approximate once per century, lasting each up to a decade. The volcano remained relatively dormant until 1993 when seismic activity gradually increased, while in August of 1999 after some 80 years of rest, Tungurahua III entered into a new eruptive phase lasting up to date, now eight years of continuous activity. The new magmatic, andesitic activity was characterized mainly by strombolian types of explosions, gas, ash and tephra emissions covering usually the southwestern area of the volcano and occasionally minor lahars due to the accumulation of ash on the flanks of the volcano. Since the beginning of the new eruptive activity in late 1999, the volcano exhibited different eruptive cycles, usually every 12 to 18 months up to the spring-summer of 2006. Between the 10th to the 16th of May a new eruptive cycle started with the usual ash showers due to the high frequency of phreatic and strombolian explosions of which one reached a height of 19km. Shortly later after an apparent calmness, a 15 km high eruptive column produced the very first pyroclastic flows (and minor lava flows), which descended on the western volcanic flank reaching small villages. About a month later, the strongest eruption since the reactivation of Tungurahua in 1999, with a VEI of 3, produced some 20 pyroclastic flows, which covered a big part of the western volcanic flank, killing seven persons in a previously stated safe zone and devastating at least five small villages, destroying some 20,000 hectars of cultivated land. This eruption of the 16th to the 17th of August of 2006, which had a very high social and economic impact, covered a huge area of Ecuador of which ash and gas clouds reached a length of at least 800 km and a width of some 200 km mainly towards the western side of the volcano. Since 1999 as result of the volcanic activity, authorities changed frequently the alert levels between yellow, moderate orange and orange, which leaded to one evacuation of some 26,000 persons from the foothill-situated, but due natural barriers protected city of Banios and some other nearby minor villages in the volcano area in October 1999. Due to the failed prediction of a major event, people went back violently three months later despite the orders of the authorities. Later in 2006 due to the presence of the first pyroclastic flows, a few hundred people fled from their homes situated in the western flank of the volcano and after the eruption of the 16th to the 17th of August 2006, some 5,000 people of the same area fled or were evacuated into refuge camps in the surrounding of the volcano. Promised and assured financial assistance by different ministries for the relocation of the public, never reached the affected families. New previously unpublished photographic and video material as well as statistics of the interviewed, affected public will be shown within this presentation.
V34A-03
The 2002-2003 and 2007 eruptions at Stromboli (Italy): A geochemical monitoring approach
Stromboli volcano is famous worldwide for its persistent mildly explosive activity (e.g. "Strombolian activity"). These intermittent explosions usually occur at intervals of 10-20 minutes, throwing glowing scoriae, ash and solid blocks to heights up to a few hundreds of meters. This "normal" activity is episodically interrupted by lava effusions and by more violent explosions, called "major explosions" and "paroxysm". The last explosive paroxysm occurred on April 5, 2003, during an effusive phase of the volcano which began on December 28, 2002, as well producing a slope collapse and consequent tsunami. Although the volcano geophysical monitoring net-work had been strongly reinforced after the eruption onset, no sign has been recorded in the seismic activity or in the ground deformation, heralding the impending large explosion. Some significant geochemical changes were instead observed in the fumarolic crater area and in the thermal water of shallow wells located near the coast, suggesting that relevant inputs of magmatic gas into the shallow aquifer occurred both before the eruptive onset and the following explosive paroxysm. These thermal waters look therefore as a promising target for the geochemical monitoring of Stromboli as a connection likely exists with deeper gas releasing systems, such as the volcano magma chamber and, possibly, a deep seated geothermal reservoir. On the basis of the acquired experience during the 2002-2003 eruption we have improved our geochemical network with remote continuous stations to measure dissolved CO2 in the thermal well and plume SO2 fluxes. A preliminary results of ongoing eruption starting by February 27, 2007 are also showed.
V34A-04
Volcano Relaxation Following Great Dome Collapses: Impact on Magma Volume Retrievals From Geodetic Monitoring at Soufriere Hills Volcano, Montserrat, West Indies
Large dome collapses can induce a significant stress release on volcanic edifices. We used 3D Finite Element Method (FEM) analysis to assess the effect of the July 12-13, 2003 dome collapse at Montserrat on the edifice (i.e. ground deformation due to elastic relaxation). The edifice geometry was derived from a high-resolution Digital Elevation Model whereas the dome geometry was estimated from recorded observations. We used linear and isotropic elastic properties for the FEM structural analysis of the edifice response and simulated the dome collapse by the cancellation of gravitational body forces in the dome domain. Results of our numerical modelling show that a significant amount of observed ground deformation is due to the edifice elastic relaxation. Direct interpretation of ground deformation as solely due to magma input into the shallow magma chamber and/or overpressurization due to volatile exsolution would therefore be greatly over-estimated. Here we quantify the ground deformation due to the edifice relaxation and discuss our model implications for volcano deformation monitoring and magma volume retrieval.
V34A-05
WATER SOLUBILITY IN FORSTERITE AND ENSTATITE: A KEY FOR UDERSTANDING MANTLE RHEOLOGY
The temperature dependence of solubility of H2O in forsterite and enstatite has been studied experimentally using two different starting compositions in the system MgO-SiO2- H2O to produce the parageneses per+fo+fluid and fo+en+fluid (per = MgO; fo = Mg2SiO4; en = MgSiO3). All experiments were run at 2.5 GPa for at least 24 hours, with temperature varied from 1000 to 1400 °C. Recovered samples were examined for the types of H2O substitution and their quantification by FTIR spectroscopy and SIMS. In the per-buffered experiments, peaks in fo at 3612, 3589, 3566, 3555, 3533 and 3480 cm-1 were identified, which are related to silica vacancies due to low silica activity. In the en-buffered experiments, the IR spectrum of fo shows two peaks at 3160 and 3220 cm-1 in addition to those present in the per-buffered experiments. These peaks indicate Mg vacancies. Peak intensities decrease with increasing temperature in both the per- and en-buffered systems, showing that water solubility is inversely proportional to temperature in fo. For en, two peaks at 3360 and 3060 cm-1 were found. These peaks are close to the peaks in fo at 3160 and 3220 cm-1 that are associated with higher silica activity, suggesting that H2O only substitutes in en by a Mg vacancy mechanism. The H2O content of en increases with increasing temperature. The results imply that the partitioning of H2O between olivine and orthopyroxene in the mantle is a very strong function of temperature. Because of their much higher H2O contents, pyroxenes control the water budget of the upper mantle, but olivine controls its rheology. Cooling of the mantle will transfers H2O from orthopyroxene (and presumably clinopyroxene) into olivine. We calculate that transfer from pyroxenes increases the H2O content of olivine by a factor of 2.5 for a 100 °C decrease in temperature. Since H2O causes marked weakening in olivine, this increase in H2O may "dampen" the effect of decreasing temperature on mantle viscosity, so that the net effect of secular cooling on mantle convection may be much less than currently estimated.
V34A-06
Diamond of Possibly Metallurgical and Seismic Origin: PART 3: Additional Specimens and a Proposal Calling for adjusted Methodologies for Diamondism
Per Giamn [1,2,3], additional or potential specimens have been sought after. Examination was made of known
specimens located in the proximity of iron ores, a number with template-like or proportionate (the larger bodies of
diamond associated with the larger bodies of iron)arrangements.An exercise was made to illustrate my theory by
utilizing a hypothetical iron ore in the Democratic Republic of Congo, Tanzania, respectively, which is seismically
induced by recent real seismic events into diamond-bearing. If I were to suggest that the study of a number of
major phases, for instance the olivines, pyroxenes, feldspars, oxides, sulfides, be based upon data of small (the
top 1 of 1,000,000) number of large sized grains only and from limited geographical regions, ages, modes of
occurrence only, I would be confronted with (i) enormous opposition since such methodology would impede
mineralogy, which is a form of generally specimen-based science; and questions of (ii) what the purposes may
be in such a deviantly unusual pursuit? What is being achieved by knowing omission of the majority of specimen
population? (iii) A simpler and fairer solution is not unavailable. (iv) What is wrong with underaddressed average
and small sized grains especially most of them workable with current analytical instruments except those
extremely fine grained; (v) Placing greater importance to grains of lager economic value is historically common
among the most topical economic minerals, yet not necessary. For instance, the platinum group elements
(PGE)is pluralistic. Research of PGE has been a rigorous institution based not solely upon ingot-sized grains; (vi)
Is this not a clear manifestation of prejudice and misrepresentation, endemic blind excessive blatant
sensationalism and objectification of basic science? There is no rational basis. Yet the knowledge of diamond is
based primarily upon a small number of morbidly obese specimens irrepresentative of the real diamond
population. A realistic, noniconic, nonstereotyping specimen population of primarily fine grains is needed. My
theory accomodates (1) broad compositional ranges;(2) present or historical specimens; and (3)valid on a grain
by grain scale as well as regional scale. A great nember of metallic elements are broadly similar to iron in crystal
structure, phase equilibria, range of stoicheometry of solid solutions, and properties. Under favorable conditions,
they could be as likely as iron to proceed to generate carbon. This expand to a great number of potential source
metal for diamond. Further multiplying this number by alloying and centering (of lattice points) variations, the
number of potential source could be vast. Above mentioned exercise is expendable to, for instance, Cr, Ni or other
metals. This could provide for a missing link between diamond in stable craton and other diamonds.
1 Giamn,
M., Diamond of possibly metallurgical and seismic origin in an alloy from the debris after earthquake Taiwan
PART I,2004 Eos AGU Spring.2 Giamn, M. submitted to GCA. 3 Giamn, M., PART II (Thermal) past is present.
V34A-07
Controls on Porphyroblast Size Along a Regional Metamorphic Field Gradient
Garnet-bearing schists from the Waterville Formation of south-central Maine provide an opportunity to examine the factors governing porphyroblast size over a range of metamorphic grade. Three-dimensional sizes and locations for all garnet porphyroblasts were determined for three samples along the metamorphic field gradient spanning lowest garnet through sillimanite grade, using high-resolution X-ray computed tomography. Comparison of crystal size distributions to previous data sets obtained by stereological methods for the same samples reveals significant differences in mode, mean, and shape of the distributions. Quantitative textural analysis shows that the garnets in each rock crystallized in a diffusion-controlled nucleation and growth regime. In contrast to the typical observation of a correlation between porphyroblast size and position along a metamorphic field gradient, porphyroblast size of the lowest-grade specimen is intermediate between the high- and middle-grade specimens' sizes. Mean porphyroblast size does not correlate with peak temperatures from garnet-biotite Fe-Mg exchange thermometry, which would be expected if porphyroblast sizes were strongly affected by post-crystallization annealing (Ostwald ripening), as previously proposed for these rocks. Robust pseudosection calculations fail to reproduce the observed garnet core compositions for two specimens, indicating that these calc-pelites experienced metasomatism. For each of these two specimens, Monte Carlo calculations suggest potential pre-metasomatism bulk compositions that replicate garnet core compositions. Pseudosection analyses coupled with semi-quantitative pressure-temperature paths allow the estimation of the critical temperatures for garnet growth: ~472° C for the lowest-garnet-zone and middle-garnet-zone specimens, and ~492° C for the sillimanite-zone specimen. Porphyroblast size appears to be determined in this case by a combination of the critical temperature for the garnet forming reaction and variations in the rates of nucleation and heating. Numerical simulations of thermally accelerated, diffusion-controlled nucleation and growth for the three samples closely match measured crystal size distributions. These observations and simulations suggest that previous hypotheses linking the temperature at the onset of porphyroblast nucleation to the resulting crystal size can only partially explain the observed textures. Also important in determining porphyroblast size are the heating rate and the distribution of favorable nucleation sites.
V34A-08
Experimental Studies of the P-T-H2O Near-Liquidus Phase Relations of Basaltic Andesite From North Sister Volcano, High Oregon Cascades: Constraints on Lower-Crustal Mineral Assemblages
North Sister Volcano, in the central Oregon High Cascades, is a large, mafic stratovolcano that has erupted a remarkably compositionally limited range of basaltic andesite (53-55 wt.% SiO2) for over 300 ka. Other workers have suggested that these "monotonous" lavas are generated by mantle melts that undergo deep crustal magmatic processes within "deep crustal hot zones" (DCHZ), where the parental melt composition is modified and buffered by reaction with lower-crustal rocks. However, the nature of the lower-arc crust is not well known and a better understanding of the pressure, temperature, composition, and water content of the lower-arc crust is necessary to help constrain these processes. The goal of our study is to elucidate the deep crustal lithology that is involved in the production of mafic arc magmas. We have used hydrous, high pressure experiments to provide P-T-H2O and compositional constraints on the possible lower-crustal mineral assemblages beneath North Sister Volcano. Inverse approach high pressure experiments were conducted using a basaltic andesite from North Sister Volcano, in order to map the water-undersaturated liquidus surface from 5-20 kbar, 1000-1350°C, and 0-15 wt.% H2O. These experiments identify permissible crustal mineral assemblages and compositions with which the North Sister basaltic andesites may have equilibrated in the deep crust before ascent as homogeneous magmas. The liquidus is saturated with plagioclase from 5-15 kbar and 0-5 wt.% H2O, augite from 10-20 kbar at all water contents, garnet above 18 kbar at all water contents, spinel from 5-10 kbar with 10-15 wt.% H2O, and amphibole from 10-20 kbar with 10-15 wt.% H2O. Combining our experimental results with examples of tectonically exposed lower arc crust, trace element geochemistry, geophysical constraints, and melt inclusion volatile contents, we have determined that a mafic granulite at ~12 kbar (~40 km) and 1175°C is the most probable lithology involved in deep crustal processes beneath North Sister Volcano, and the resulting melts contain ~3.5 wt.% dissolved H2O. Although our inverse approach experiments cannot constrain the mode of the plagioclase + augite in the granulite, using measured distribution coefficients from our experimental run products, we conclude that the assemblage with which North Sister basaltic andesites equilibrated in the DCHZ was greatly dominated by augite.