Saturday, November 24, 2012

More from the Sampling and Structural Mapping Ground Team

by Fabian Wadsworth
16th November 2012

We’ve returned from those first three nights among the domes of Santiaguito volcano. The November expedition was divided into a summit and a ground team. While the summit team camped at Santa Maria’s peak, peering cameras over the edge to look down on the Caliente vent, the ground teams hiked to the base of the domes and looked up. Those on the ground had many objectives, however, our contingent of the ground group was focussed on sample collection and structural mapping of the dome tops.
Yan Lavallée (University of Liverpool, U.K.) and Ben Kennedy (University of Canterbury, New Zealand) coordinated a sampling campaign with a two-fold focus. Yan and student, Adrian Hornby, aimed to collect homogenous material from the active Caliente vent to use for a variety of experimental applications such as high-velocity friction experiments, high-temperature rheology characterisation, and crack-propagation and healing. Ben and student Emma Rhodes were interested in mapping the volcano’s structural information among the spines of the three ancestral vents. Yan and Ben’s interests converge on the careful description and sampling of shear zones at the spine margins. It’s in these most-deformed areas that they find the field equivalent to the experimental products from the lab including evidence for both brittle and ductile deformation mechanisms and foamy inflation. Combined, these two complementary physical studies aim to constrain the evolution of Santiaguito’s magma properties over the course of the volcano’s activity; information that feeds into the deformation models used by the monitoring ground-team.
Students Adrian and Emma are resting in Xela city for now before rejoining the hunt for spines and bombs in the coming three weeks. Their task is a big one, not least because it takes the best part of a day to hike down to the dome valley floor and it’s a demanding job to mount and descend each dome, carrying equipment, water and food each time through the isolated valleys. Armando Pineda, the volcano-guide of Guatemala, will be an invaluable aid in their field research.
Corrado Cimarelli (LMU, Germany), a Santiaguito veteran from the January excursion, collected ash samples from individual explosions at the Caliente vent. He and his group in Munich will characterise variations and try to differentiate juvenile ash from fragmented dome ash, providing a window into conduit processes at Santiaguito. The multitude of tent tops made ideal ash-capture funnels for the frequent explosions and Corrado is now expert in gentle ash-sweeping actions using his personal make-up brush.  
The walk out from the domes was punctuated by a torrential downpour on the valleys surrounding the domes which mobilised rivers and lahars down the dome-flanks and over the trail. We stood at the top of the ascent out of the valley and saw our camp of the night before flooded before it disappeared in dense rain clouds.
We all relished our time at the domes and are grateful to the wider team for accommodating us. The interdisciplinary, international focus on Santiaguito volcano is a mighty undertaking that has such a broad, ambitious scope that I am sure it will yield collaborative research connections that continue over the coming years.
Thanks everyone.

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