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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Detailed analysis of particle launch velocities, size distributions and gas densities during normal explosions at Stromboli
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Detailed analysis of particle launch velocities, size distributions and gas densities during normal explosions at Stromboli

机译：在Stromboli正常爆炸过程中对粒子发射速度，尺寸分布和气体密度的详细分析

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摘要

Using high frame rate (33 Hz) thermal video data we describe and parameterize the emission and ascent dy-namics of a mixed plume of gas and particles emitted during a normal explosion at Stromboli (Aeolian Islands, Italy). Analysis of 34 events showed that 31 of them were characterized by a first phase characterized by an initial diffuse spray of relatively small (lapilli-sized) particles moving at high velocities (up to 213 ms~(-1); average 66-82 ms~(-1)). This was followed, typically within 0.1 s, by a burst comprising a mixture of ash and lapilli, but dominated by larger bomb-sized particles, moving at lower exit velocities of up to 129 m s~(-1), but typically 46 m s~(-1). We interpret these results as revealing initial emission of a previously unrecorded high velocity gas-jet phase, to which the lapilli are coupled. This is followed by emission of slower moving larger particles that are decoupled from the faster moving gas-phase. Diameters for particles carried by the gas phase are typically around 4 cm, but can be up to 9 cm, with the diameter of the particles car-ried by the gas jet (D) decreasing with increased density and velocity of the erupted gas cloud (p_(gas) and U_(gas)). Data for 101 particles identified as moving with the gas jet during 32 eruptions allow us to define a new relation, whereby U_(gas) = U_(parcital) + a [ρ_(gas) √D]~b. Here, U_(partical) is the velocity of bombs whose motion is decoupled from that of the gas cloud, and a and b are two empirically-derived coefficients. This replaces the old relation, whereby U_(gas) = U_(partical) + k √D; a relation that requires a constant gas density for each eruption. This is an assumption that we show to be invalid, with gas density potentially varying between 0.04 kg m~3 and 9 kg m~3 for the 32 cases considered, so that k varies between 54m~(1/2)s~(-1) and 828m~(1/2)s~(-1) compared with the traditionally used constant of 150 m~(1/2)s~(-1).
机译：使用高帧频（33 Hz）的热视频数据，我们描述并参数化了在Stromboli（意大利风神群岛）正常爆炸期间散发的气体和颗粒的混合羽流的发射和上升动力。对34个事件的分析表明，其中31个事件的特征在于第一阶段，该阶段的特征是初始扩散喷雾以高速（最高213 ms〜（-1）；平均66-82 ms 〜（-1））。随后通常在0.1 s内进行一次爆发，​​爆发包括灰烬和青金石的混合物，但以较大的炸弹大小的粒子为主，以较低的出口速度（最高129 ms〜（-1），但通常为46 ms〜）移动（-1）。我们将这些结果解释为揭示了先前未记录的高速气体喷射相的初始发射，并与lapilli耦合。随后发出的是运动较慢的较大颗粒，这些颗粒与速度较快的气相分离。气相所载颗粒的直径通常约为4 cm，但可以达到9 cm，而气体喷流（D）携带的颗粒直径随喷出的气体云的密度和速度增加而减小（ p_（gas）和U_（gas））。被确定为在32次喷发期间随气体射流移动的101个粒子的数据使我们能够定义一个新的关系，其中U_（气体）= U_（局部）+ a [ρ_（气体）√D]〜b。在此，U_（partical）是炸弹的速度，其运动与气体云的运动解耦，而a和b是两个根据经验得出的系数。这取代了以前的关系，即U_（gas）= U_（partical）+ k√D;每次喷发需要恒定气体密度的关系。这是一个假设，我们证明是无效的，在考虑的32种情况下，气体密度可能在0.04 kg m〜3和9 kg m〜3之间变化，因此k在54m〜（1/2）s〜（-之间变化1）和828m〜（1/2）s〜（-1），而传统使用的常数为150 m〜（1/2）s〜（-1）。

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