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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Investigation of at-vent dynamics and dilution using thermal infrared radiometers at Masaya volcano, Nicaragua
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Investigation of at-vent dynamics and dilution using thermal infrared radiometers at Masaya volcano, Nicaragua

机译：尼加拉瓜马萨亚火山使用热红外辐射计研究动态和稀释情况

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In order to develop a detailed understanding of the dynamics of gas puffing (gas release as a series of distinct pulses) and more sustained degassing (steady plumes of gas) during persistent volcanic degassing, measurements of gas mass flux are required in the vicinity of the volcanic vent. Masaya volcano (Nicaragua), a persistently degassing system, is an ideal location for measuring the dynamics of releases of volcanic gas in the first few seconds of their propagation. We carried out two field experiments during February 2002 and March 2003, during which thermal infrared thermometers were targeted into the degassing vent at Masaya to record thermal variations related to variations in the at-vent gas emission over short (on the order of seconds) time scales. The thermometers recorded an oscillating signal as gas puffs passed through the field of view, detailing variations in the degassing process developing over time scales of seconds. These data were processed to extract puff frequencies, amplitudes, durations, emission velocities and volumes. These data showed that, over time periods of hours, the total gas flux was stable with little variation in the puffing frequency. However, between the 2002 and 2003 data set we noted an increase in mean plume temperature, puffing frequency, puff emission velocity and puff volume, as well as a decrease in mean puff duration. These changes were consistent with a thermal data-derived increase in emitted gas flux from 4.2 × 10~7 m~3 d~(-1) to 6.4 × 10~7 m~3 d~(-1) between the two campaigns. Turbulent gas puffs entrain surrounding air, and quantifying the magnitude of air entrainment, or dilution, represents a major challenge for the measurement of total volcanic gas emissions. Our observations of small gas puffs suggest that they behave as turbulent buoyant thermals, and we use equations for mass, momentum and buoyancy, coupled with the standard entrainment assumption for turbulent buoyant flows, to estimate the gas puff dilution. The theoretically calculated dilution of 0.09 and 0.24 between emission and detection yields total SO_2 mass fluxes of 209 t d~(-1) and 864 t d~(-1) for 2002 and 2003, respectively. This compares well with UV-spectrometer SO_2 fluxes of 470 and 680 t d~(-1) for February 2002 and March 2003, respectively.
机译：为了深入了解气体喷发（以一系列不同的脉冲释放气体）和在持续的火山脱气过程中进行更持续的脱气（气体稳定羽流）的动力学过程，需要在附近进行气体质量通量的测量火山喷口。 Masaya火山（尼加拉瓜）是一种持续脱气的系统，是测量火山气体扩散最初几秒钟内释放动力学的理想场所。我们在2002年2月和2003年3月进行了两次野外实验，在此过程中，将热红外温度计对准了Masaya的脱气口，以记录与短时间内（数秒左右）的气体排放变化相关的热变化。秤。温度计在气嘴通过视场时记录了一个振荡信号，详细说明了脱气过程随秒的时间尺度变化的变化。处理这些数据以提取抽吸频率，振幅，持续时间，发射速度和体积。这些数据表明，在几个小时的时间内，总的气体通量是稳定的，并且抽吸频率几乎没有变化。然而，在2002年至2003年的数据集之间，我们注意到平均羽流温度，膨化频率，膨化速度和膨化量增加，而平均膨化持续时间减少。这些变化与两个运动之间由热数据得出的排放气体通量从4.2×10〜7 m〜3 d〜（-1）增加到6.4×10〜7 m〜3 d〜（-1）一致。湍流的气体抽吸会夹带周围的空气，并且量化空气夹带或稀释的幅度，对于测量火山总气体排放量是一个重大挑战。我们对小气团的观察表明，它们表现为湍流的浮力热，我们使用质量，动量和浮力方程，并结合湍流浮力流的标准夹带假设，来估算气团的稀释度。从理论上计算，在发射和检测之间的稀释度分别为0.09和0.24，得出2002年和2003年的总SO_2质量通量分别为209 t d〜（-1）和864 t d〜（-1）。这与2002年2月和2003年3月的紫外光谱仪的SO_2通量分别为470 t d〜（-1）和680 t d〜（-1）相当。

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