کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
6427701 1634723 2016 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Experimental volcanic ash aggregation: Internal structuring of accretionary lapilli and the role of liquid bonding
ترجمه فارسی عنوان
تجمع خاکستر آتشفشانی تجربی: ساختار درونی لادلی و تغییر نقش باند مایع
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم زمین و سیاره ای (عمومی)
چکیده انگلیسی


- We apply fluidized bed techniques to aggregate volcanic ash and analogue material.
- NaCl is used as a natural binder in concentrations found on natural volcanic ash.
- We study the effect of humidity on the amount of aggregates produced per time.
- We study the effect of PSD on external shape and internal structuring of aggregates.
- Internal structures of natural accretionary lapilli are reproduced.

Explosive volcanic eruptions can release vast quantities of pyroclastic material into Earth's atmosphere, including volcanic ash, particles with diameters less than two millimeters. Ash particles can cluster together to form aggregates, in some cases reaching up to several centimeters in size. Aggregation alters ash transport and settling behavior compared to un-aggregated particles, influencing ash distribution and deposit stratigraphy. Accretionary lapilli, the most commonly preserved type of aggregates within the geologic record, can exhibit complex internal stratigraphy. The processes involved in the formation and preservation of these aggregates remain poorly constrained quantitatively. In this study, we simulate the variable gas-particle flow conditions which may be encountered within eruption plumes and pyroclastic density currents via laboratory experiments using the ProCell Lab System® of Glatt Ingenieurtechnik GmbH. In this apparatus, solid particles are set into motion in a fluidized bed over a range of well-controlled boundary conditions (particle concentration, air flow rate, gas temperature, humidity, liquid composition). Experiments were conducted with soda-lime glass beads and natural volcanic ash particles under a range of experimental conditions. Both glass beads and volcanic ash exhibited the capacity for aggregation, but stable aggregates could only be produced when materials were coated with high but volcanically-relevant concentrations of NaCl. The growth and structure of aggregates was dependent on the initial granulometry, while the rate of aggregate formation increased exponentially with increasing relative humidity (12-45% RH), before overwetting promoted mud droplet formation. Notably, by use of a broad granulometry, we generated spherical, internally structured aggregates similar to some accretionary pellets found in volcanic deposits. Adaptation of a powder-technology model offers an explanation for the origin of natural accretionary pellets, suggesting them to be the result of a particular granulometry and fast-acting selective aggregation processes. For such aggregates to survive deposition and be preserved in the deposits of eruption plumes and pyroclastic density currents likely requires a significant pre-existing salt load on ash surfaces, and rapid aggregate drying prior to deposition or interaction with a more energetic environment. Our results carry clear benefits for future efforts to parameterize models of ash transport and deposition in the field.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volume 433, 1 January 2016, Pages 232-240
نویسندگان
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