ALBERT

Description: Seamounts can provide conduits for the entry and exit of hydrothermal fluids in ocean basins. However, only a few ridge flank hydrothermal systems that discharge through seamounts have been discovered, all located on relatively young crust. We have retrieved samples from 126 m.y. old Henry Seamount, an extinct volcano near the youngest Canary island of El Hierro, that provide evidence for Holocene low-temperature hydrothermal fluid discharge. This is the first documented finding of such activity at the Canary archipelago. The samples include shells from vesicomyid clams

Description: Tens of thousands of submarine volcanoes, so-called seamounts, with heights of more than a few hundred meters, exist in the world ocean. The Cape Verde archipelago is of volcanic origin and includes several prominent seamounts, which can give important information on the origin of submarine intraplate volcanism.

Description: Villarrica is one of the most active volcanoes in Chile and is presently characterized by continuous degassing, high-level seismicity and a persistent lava lake within its crater. Three stationary NOVAC-type scanning Mini-DOAS UV spectrometers for the quantification of SO2 fluxes were installed at the volcano in March 2009. Seismic stations used for this study include the OVDAS (Observatorio Volcanológico de los Andes del Sur) volcano monitoring network, and 7 dedicated short period and broadband seismometers that were deployed in the region for more than one year. We have registered several cases of correlation between SO2 fluxes and seismic activity (LP events). Seismic events have in several cases been followed by an increase in degassing activity. The response seems to occur on two different time scales. Regional earthquake events in 2009 and 2010, and the 2011 Araucania event which occurred on January 2 and had a magnitude of 7.1, were followed by strongly increased degassing activity at Villarrica 2-4 days later, interpreted as due to increased bubble nucleation in the magmatic system at depth. The large Maule earthquake on February 27, 2010 with a magnitude of 8.8 had little immediate effect, but was followed several weeks later by an immense increase in degassing activity of about one order of magnitude compared to the baseline level. We speculate that this was a result of changing stress fields in the lower crust and at mantle depths caused by the Maule event, possibly changing melting conditions temporarily. Numerical models based on seismic, petrologic and gas flux data are used to demonstrate the feasibility of the time-lag between seismicity and degassing. We thus aim at gaining insight into the interface between magmatic and volcano-tectonic processes, especially factors playing a role for the onset of volcanic unrest. www.ifm-geomar.de

Description: Seamounts can provide conduits for the entry and exit of hydrothermal fluids in ocean basins. However, only a few ridge flank hydrothermal systems that discharge through seamounts have been discovered, all located on relatively young crust. We have retrieved samples from 126 m.y. old Henry Seamount, an extinct volcano near the youngest Canary island of El Hierro, that provide evidence for Holocene low-temperature hydrothermal fluid discharge. This is the first documented finding of such activity at the Canary archipelago. The samples include shells from vesicomyid clams 〈18.6 k.y. old, massive barite, and trachytes that are pervasively barite metasomatized. Sulfur, oxygen, and strontium isotope ratios of barite indicate that the fluid contained residual sulfate from microbial reduction at the recharge site and reacted with basement rocks. Recharge probably occurred at basement outcrops of El Hierro's submarine flank at 25–30 km distance, the driving force for hydrothermal circulation through old crust being provided by increased basal heat flow from Canary magmatism. The data show that island flanks may provide important recharge sites for seawater circulation and that even old and small seamounts can contribute to heat and mass exchange between ocean crust and seawater.

Description: OS11C-06 As well as providing well-localized samples, Remotely Operated Vehicles (ROVs) produce huge quantities of visual data whose potential for geological data mining has seldom if ever been fully realized. We present a new workflow to derive essential results of field geology such as quantitative stratigraphy and tectonic surveying from ROV-based photo and video material. We demonstrate the procedure on the Charles Darwin Seamounts, a field of small hot spot volcanoes recently identified at a depth of ca. 3500m southwest of the island of Santo Antao in the Cape Verdes. The Charles Darwin Seamounts feature a wide spectrum of volcanic edifices with forms suggestive of scoria cones, lava domes, tuff rings and maar-type depressions, all of comparable dimensions. These forms, coupled with the highly fragmented volcaniclastic samples recovered by dredging, motivated surveying parts of some edifices down to centimeter scale. ROV-based surveys yielded volcaniclastic samples of key structures linked by extensive coverage of stereoscopic photographs and high-resolution video. Based upon the latter, we present our workflow to derive three-dimensional models of outcrops from a single-camera video sequence, allowing quantitative measurements of fault orientation, bedding structure, grain size distribution and photo mosaicking within a geo-referenced framework. With this information we can identify episodes of repetitive eruptive activity at individual volcanic centers and see changes in eruptive style over time, which, despite their proximity to each other, is highly variable.

Description: ABSTRACT FINAL ID: V44C-02 Villarrica is one of the most active volcanoes in Chile and is presently characterized by activity from open continuously degassing conduit. The twohundred meter diameter crater contains a persistent lava lake which has a diameter of approximately ten meters. For the quantification of SO2 fluxes three stationary NOVAC-type scanning Mini-DOAS UV spectrometers were installed at the volcano in March 2009. To validate the ground-based gas measurements we compared them to thermal anomalies detected by the MODVOLC algorithm which is provided by the Hawai'i Institute of Geophysics and Planetology (http://modis.higp.hawaii.edu). The MODVOLC algorithm (WRIGHT et al., 2002) uses data from the space-based Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the National Aeronautics and Space Administration’s Terra and Aqua platforms and it exhibits the possibility to monitor volcanic heat sources. Although it was not intended to detect low intensity activity from open vent degassing, we find that in the case of Villarrica the detected thermal anomalies seem to originate from the heat carried by the gas phase. Additionally we have registered correlation between SO2 fluxes and thermal activity during the whole period of our ground-based gas-monitoring. Thermal anomalies detected by the MODVOLC algorithm coincide with observed periods of increased gas flux, enabling us to estimate gas fluxes indirectly from thermal data. Wright R. et al. (2002) Remote Sensing of Environment 82, 135-155