A model for wet aggregation of ash particles in volcanic plumes and clouds: 2. Model application
A model for wet aggregation of ash particles in volcanic plumes and clouds: 2. Model application
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DOI：
10.1029/2009jb007176
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发表时间：
2010-09-01
影响因子：
3.9
通讯作者：
Macedonio, G.
中科院分区：
文献类型：
--
作者：
Folch, A.;Costa, A.;Macedonio, G.
颗粒聚集的发生对火山灰的输运和沉积有显著的影响。聚集过程是复杂的，可能在不同的条件下发生，也可能发生在羽流的多个区域和灰云中。在配套文件中，Costa等人。开发了一个基于分形关系的聚集模型，以描述颗粒被纳入灰聚集体的速率。该模型包括火山云中存在的岩浆和大气水的影响，并表明，聚合率取决于初始粒径分布的特性。聚集模型包括两个参数，分形指数D-f，它描述了聚集过程的效率，和聚集体沉降速度校正因子psi（e），它影响远端质量沉积最大值形成的距离。这两个参数的调整使用所观察到的存款的功能。在这里，这个聚合模型中实现的CNOL 3D火山灰运输模型，并应用于1980年5月18日圣海伦火山和1992年9月17日至18日火山口峰喷发。对于这两次喷发，D-f（2.96-3.00）和psi（e）（0.27-0.33）的优化值表明，火山灰聚集体的体积密度为700-800 kg m（-3）。该模型提供了一个更高程度的协议比以前的完全经验聚集模型，并成功地再现了沉积特征的存款调查在很大范围内的规模，包括位置和厚度的次极大值。
The occurrence of particle aggregation has a dramatic effect on the transport and sedimentation of volcanic ash. The aggregation process is complex and can occur under different conditions and in multiple regions of the plume and in the ash cloud. In the companion paper, Costa et al. develop an aggregation model based on a fractal relationship to describe the rate particles are incorporated into ash aggregates. The model includes the effects of both magmatic and atmospheric water present in the volcanic cloud and demonstrates that the rate of aggregation depends on the characteristics of the initial particle size distribution. The aggregation model includes two parameters, the fractal exponent D-f, which describes the efficiency of the aggregation process, and the aggregate settling velocity correction factor psi(e), which influences the distance at which distal mass deposition maxima form. Both parameters are adjusted using features of the observed deposits. Here this aggregation model is implemented in the FALL3D volcanic ash transport model and applied to the 18 May 1980 Mount St. Helens and the 17-18 September 1992 Crater Peak eruptions. For both eruptions, the optimized values for D-f (2.96-3.00) and psi(e) (0.27-0.33) indicate that the ash aggregates had a bulk density of 700-800 kg m(-3). The model provides a higher degree of agreement than previous fully empirical aggregation models and successfully reproduces the depositional characteristics of the deposits investigated over a large range of scales, including the position and thickness of the secondary maxima.