کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
10144955 | 1646327 | 2018 | 10 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Message in a bottle: Spontaneous phase separation of hydrous Vesuvius melt even at low decompression rates
ترجمه فارسی عنوان
پیام در یک بطری: جداسازی فاز خودبخود از ویسوویوس آب، حتی در سرعت های کم فشردگی، ذوب می شود
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
علوم زمین و سیاره ای (عمومی)
چکیده انگلیسی
Violent explosive volcanic eruptions are destructive and threaten millions of people and infrastructure. Ejected ash, pumice and gases are end-products of volcanic factories sourced deep within magma chambers and conduits. The different production stages are not directly observable. However, experimental simulation reveals different stages of dynamic volcanic processes. The starting point of explosive volcanic eruptions is determined by the phase separation of an H2O fluid from a supersaturated hydrous silicate melt. The number of formed H2O fluid vesicles per unit volume of silicate melt (VND) is a basic property that controls the efficiency of fluid-melt separation, ascent velocity and finally explosive volcanism. We performed decompression experiments at superliquidus temperatures to simulate phase separation of a single phase hydrous silicate melt during ascent with AD79 Vesuvius white pumice composition using decompression rates of 0.024-1.7 MPaâ
sâ1. The white pumice buried Herculaneum and Pompeii and is representative of other catastrophic phonolitic and trachytic explosive eruptions like the violent 39 ka Campi Flegrei and the 1815 AD Tambora eruption. Here we report a high logâ¡VND of 5.2 (in mmâ3) that is independent from decompression rate within the investigated range. Even at a decompression rate of 0.024 MPaâ
sâ1 the formation of a high VND inevitably causes rapid degassing due to short H2O diffusion distances from the melt into fluid vesicles. A decompression rate meter based on nucleation theory, which is commonly used to estimate magma ascent velocity during volcanic eruptions using VND of volcanic ejecta, cannot be adapted to explain our experimentally determined decompression rate independent VND. Alternatively, decompression induced H2O-silicate melt phase separation may be described by diffusion controlled spinodal decomposition where maximum supersaturation is reached. This process occurs spontaneously and free of activation energy if hydrous melt is driven into thermodynamic instability where the second derivative of free energy of mixing to the H2O content is â¤0. However, the decompression rate independent VND has profound consequences for the dynamics of natural polyphase hydrous magma phase separation. Even at low ascent rates spontaneous hydrous melt phase separation facilitates rapid density decrease accompanied by sudden increase of magma buoyancy triggering explosive eruptions.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volume 501, 1 November 2018, Pages 192-201
Journal: Earth and Planetary Science Letters - Volume 501, 1 November 2018, Pages 192-201
نویسندگان
Anja Allabar, Marcus Nowak,