Sedimentation and stratigraphy from pyroclastic gravity-driven flows (sponsored by IAS) (co-organized)
|Convener: G. A. Douillet|
Pyroclasts are emitted during explosive volcanic eruptions and are rapidly transported by a variety of gravity-driven flows. These include pyroclastic density currents (PDCs), debris flows, or lahars, which leave a wide spectrum of sedimentary signatures. A better documentation and understanding of the sedimentary record and its link to the flow dynamics is the key for more accurate predictive analysis, with consequences for over 500 million people living in areas directly at risk from volcanic activity.
The number of variables impacting pyroclastic deposition is significant and depends both on the source conditions and type of transport. This includes initial velocity, temperature, particle supply (with different textures, shapes, composition, from porous pumice to dense crystalline fragments) and grain size distributions at the vent. Flows can travel over large distances, confined or not, encounter obstacles, or experience changes in slope and nature of the bed. Pore fluid may range from insignificant to dominant, while the load and flow parameters can demonstrate considerable heterogeneity spatially and temporally within a flow.
Within the deposit, grain-size can range between blocks of up to several meters in diameter, lapilli of a few centimetres, and ash down to the micron scale. Facies can be well or poorly sorted, massive or stratified, demonstrate a range of different grading structures, and contain a variety of cross-stratification patterns. Depositional units evolve within an isochron and over time, volumes can vary by orders of magnitude and the stratigraphic architecture frequently contains overlapping, amalgamated, truncated or hiatus boundaries.
This range of variables and scales, the widespread deposit preservation and accessibility, and the variety of flow styles means that the study of volcanogenic sedimentation can have significant relevance for other research fields, including the study of snow avalanches, turbidity currents, debris flows, and other types of granular transport. We seek studies using field, numerical, experimental, or theoretical approaches to understand the link between the flow itself and its sedimentary signature. Documentation and analyses of cross-bedding patterns, deposit architecture and sequence stratigraphy, as well as comparison between PDC deposits and other environments are of great interest. The session aims at fruitful interaction between sedimentologists with different backgrounds in addition to volcanologists using different approaches, in order to better understand the transport, sedimentation processes and stratigraphy of pyroclastic sediments.