Study reveals how topography influences emplacement of small-volume pyroclastic flows

phys.org | 5/9/2019 | Staff
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The emplacement of small-volume ( less than 0,1km3) pyroclastic flow is strongly controlled by topography, according to a new study by researchers of the Institute of Earth Sciences Jaume Almera of the Spanish National Research Council (ICTJA-CSIC) and the University of Barcelona. The paper has been published in the journal Sedimentology.

The work focused on the study and characterization of the Arico ignimbrite, located in the southern slopes of the Las Cañadas volcanic complex (Tenerife, Canary Islands). These rock formations were originated by the deposition of a 670,000-year-old pyroclastic flow.

Guajara - Emission - Zone - Cloud - Mix

Guajara was the emission zone of this cloud, which was made up of a mix of hot gases, volcanic ashes and rock fragments. The cloud showed fast downslope movement, and was finally deposited in the valleys of the southern zone of the island, forming the studied ignimbrites.

"It is well known that pyroclastics flows are density currents controlled by the gravity and thus they tend to flow through valleys or depressed topographical zones," explains Joan Martí, researcher at ICTJA-CSIC and first author of the study. "Now, we have been able to demonstrate that, besides the slope, the emplacement of small-volume pyroclastic flows is controlled by the shape of the channel through which they flow. The bedrock morphology, obstacles, sudden slope variations or changes in the channel width are some of the topographical drivers that influence the emplacement and deposition of these types of pyroclastic flows."

Team - Fieldwork - Barranco - Ovejeros - Total

To do this, the team conducted fieldwork in the Barranco de los Ovejeros where they found and described a total of 57 outcrops. In this valley, the ignimbrite deposits are well exposed. Researchers studied the lithology, stratigraphy and the sedimentological features of the ignimbrite outcrops. They also measured the slope of the previous ground, depth and width of the channels that guided the transport and the final emplacement of...
(Excerpt) Read more at: phys.org
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