Fabric Analysis of Unconsolidated Pyroclastic Density Current Deposits

Document Type

Student Presentation

Presentation Date



College of Arts and Sciences



Faculty Sponsor

Brittany Brand


Pyroclastic density currents (PDCs) are gravity-driven mixtures of hot volcanic material and gas often produced during explosive volcanic eruptions. PDCs are extremely hazardous and difficult to analyze in real time. Therefore, we use their deposits to better understand PDC flow dynamics. Previous work proves that particle orientation and deposit fabric can provide information about flow direction and internal flow processes. We collected 19 samples of unconsolidated PDC deposits generated in the 1980 Mount St. Helens eruption and lithified these samples using a sodium silicate vacuum impregnation technique. Once solidified, the samples were cut in three planes: horizontal (map view), parallel to flow, and perpendicular to flow. These faces were analyzed using FabricS, a software that automatically measures particle orientation and statistically determines fabric strength. Analyses of the horizontal plane show mean particle orientations that correlate well with previous estimates of Mount St. Helens PDC flow directions. This study demonstrates that these techniques can constrain flow direction in outcrops without contextual information. Future analyses will provide information on particle transport mechanisms and further insights into flow rheology. Understanding PDC flow dynamics will allow for more accurate numerical modeling, and thus better hazard assessment, of these dangerous volcanic flows.

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