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showing 10 items of 21658 documents
H2O-content and temperature limit the explosive potential of rhyolite magma during Plinian eruptions
2019
Abstract Recent rhyolite eruptions on Earth have demonstrated their capacity to produce a multitude of hazards, including ash formation lasting months and impacting the large reaches of the southern hemisphere. Nevertheless, the underlying mechanisms driving these eruptions are not yet fully understood. Magmatic volatiles, especially H2O, dictate whether volcanic eruptions proceed explosively or effusively. Experimental evidence for the role played by H2O in driving explosive fragmentation is rare, in particular in the eruption of rhyolitic magma. Here we show that when hydrous rhyolitic obsidians from Chaiten Volcano (Chile) are experimentally heated above their glass transition temperatur…
Lightning-induced weathering of Cascadian volcanic peaks
2020
Abstract The process of meteorological lightning-induced modification of coherent volcanic rocks is examined by geochemical, textural, and experimental analysis of fulgurites from South Sister volcano, Oregon Cascades, USA. Lightning's effects on volcanic target rocks was simulated with an arc-welding device in order to reproduce the geochemical and textural features of natural fulgurites and to constrain temperatures of melting and devolatilization behavior during lightning strikes. Melting of volcanic target rocks produces melts of exceptional compositional diversity, ranging from those with pure mineral compositions (e.g., diopside and plagioclase), resulting from congruent melting react…
Insights into magma and fluid transfer at Mount Etna by a multiparametric approach: A model of the events leading to the 2011 eruptive cycle
2013
[1] Since the second half of the 1990s, the eruptive activity of Mount Etna has provided evidence that both explosive and effusive eruptions display periodic variations in discharge and eruption style. In this work, a multiparametric approach, consisting of comparing volcanological, geophysical, and geochemical data, was applied to explore the volcano's dynamics during 2009–2011. In particular, temporal and/or spatial variations of seismicity (volcano-tectonic earthquakes, volcanic tremor, and long-period and very long period events), ground deformation (GPS and tiltmeter data), and geochemistry (SO2 flux, CO2 flux, CO2/SO2 ratio) were studied to understand the volcanic activity, as well as…
Passive vs. active degassing modes at an open-vent volcano (Stromboli, Italy)
2012
Abstract We report here on a UV-camera based field experiment performed on Stromboli volcano during 7 days in 2010 and 2011, aimed at obtaining the very first simultaneous assessment of all the different forms (passive and active) of SO 2 release from an open-vent volcano. Using the unprecedented spatial and temporal resolution of the UV camera, we obtained a 0.8 Hz record of the total SO 2 flux from Stromboli over a timeframe of ∼14 h, which ranged between 0.4 and 1.9 kg s −1 around a mean value of 0.7 kg s −1 and we concurrently derived SO 2 masses for more than 130 Strombolian explosions and 50 gas puffs. From this, we show erupted SO 2 masses have a variability of up to one order of mag…
Late Paleozoic Ice Age glaciers shaped East Antarctica landscape
2019
International audience; The erosion history of Antarctica is fundamental to our understanding of interlinks between climate and glacier dynamics. However, because of the vast polar ice sheet covering more than 99% of Antarctica land mass, the continental surface response to glacial erosion remains largely unknown. Over the last decade the subglacial topography of Antarctica has been imaged by airborne radar surveys. These studies revealed high and complex sub-glacial relief in the core of the East Antarctic shield, interpreted as resulting from rifting episodes and low long-term erosion rates, or repeated large-scale glacial retreats and advances. In East Antarctica, thermochronology studie…
Vegetation and environmental changes in tropical South America from the last glacial to the Holocene documented by multiple cave sediment proxies
2019
Abstract δ 18 O values in speleothems have been utilized to document past changes in South American monsoon intensity. However, changes in regional vegetation and ecosystems have not been part of this discussion, and other cave proxies such as speleothem δ 13 C values, a useful proxy for vegetation reconstruction, have been neglected due to interpretive complexities. Here we report δ 13 C values and 87Sr/86Sr ratios in stalagmites, together with XRF-derived elemental chemistry, δ 13 Corg values and carbon content from a sedimentary profile from the same cave where the stalagmites were collected. In combination with a previously published δ 18 O record, this enables us to clarify climate and…
Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari massif: an integrated geodynamic and petrological modelling approach
2017
The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from ∼2.4 GPa to ∼4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India–Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure–temperature–time (P–T–t) path has been derived from thermomechanical simulations tailored for E…
Porites corals from Crete (Greece) open a window into Late Miocene (10Ma) seasonal and interannual climate variability
2006
Variations in the biotic composition of marine shallow water carbonates document global climatic changes. However, a discontinuous stratigraphic record and uncertainties regarding the ages limit the significance of shallow water carbonates as palaeoclimatic archives on geological time-scales. Notwithstanding these deficits, the environmental information stored in the skeleton of reef biota is a unique source of information that resolves seasonal to interannual climate variability in geological time. Application of the method to corals from carbonate rocks is usually restricted to the past 130,000yr, because the aragonite skeleton undergoes rapid diagenetic alteration. Consequently, reconstr…
Multiple positive normalized solutions for nonlinear Schrödinger systems
2018
We consider the existence of multiple positive solutions to the nonlinear Schr\"odinger systems sets on $H^1(\mathbb{R}^N) \times H^1(\mathbb{R}^N)$, \[ \left\{ \begin{aligned} -\Delta u_1 &= \lambda_1 u_1 + \mu_1 |u_1|^{p_1 -2}u_1 + \beta r_1 |u_1|^{r_1-2} u_1|u_2|^{r_2}, -\Delta u_2 &= \lambda_2 u_2 + \mu_2 |u_2|^{p_2 -2}u_2 + \beta r_2 |u_1|^{r_1} |u_2|^{r_2 -2} u_2, \end{aligned} \right. \] under the constraint \[ \int_{\mathbb{R}^N}|u_1|^2 \, dx = a_1,\quad \int_{\mathbb{R}^N}|u_2|^2 \, dx = a_2. \] Here $a_1, a_2 >0$ are prescribed, $\mu_1, \mu_2, \beta>0$, and the frequencies $\lambda_1, \lambda_2$ are unknown and will appear as Lagrange multipliers. Two cases are studied, the first …
Moroccan speleothem and tree ring records suggest a variable positive state of the North Atlantic Oscillation during the Medieval Warm Period
2013
We present a magnesium (Mg) and strontium (Sr) record from an aragonitic speleothem (Grotte de Piste, Morocco, 34°N; 04°W) providing a reconstruction of effective rainfall from 619 to 1962 AD. The corresponding drip site was monitored over 2 yr for drip water Mg/Ca and Sr/Ca ratios. Results show evidence for prior aragonite precipitation, which can explain negative correlations between speleothem Mg and Sr concentrations. The data shown here have important climate implications concerning the evolution of the North Atlantic Oscillation (NAO). A comparison of the stalagmite data from Grotte de Piste with an updated tree ring based drought reconstruction from Morocco and other NAO related pro…