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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Color Measurements Of Volcanic Ash Deposits From Three Different Styles Of Summit Activity At Sakurajima Volcano, Japan: Conduit Processes Recorded In Color Of Volcanic Ash
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Color Measurements Of Volcanic Ash Deposits From Three Different Styles Of Summit Activity At Sakurajima Volcano, Japan: Conduit Processes Recorded In Color Of Volcanic Ash

机译：来自日本樱岛火山的三种不同峰会活动的火山灰沉积物的颜色测量：以火山灰颜色记录的导管过程

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摘要

We measured quantitatively colors of volcanic ash deposits erupted from three different styles of summit activity (Strombolian activity, Vulcanian explosions and continuous ash venting activity) at Sakurajima volcano from 1974 to 1985. Colors of Strombolian ash samples have larger yellow components of their visible spectra (b~* values) than those of explosion and continuous venting ash samples. Colors of explosion ash samples show larger variation in both red and yellow components of their visible spectra (a~* and b~* values, respectively), while colors of continuous venting ash samples are in the narrow ranges within colors of explosion ash samples. Colors of components with lower densities than 3.1 g/cm~3 (groundmass and phenocrystic plagioclase) obtained by magnetic and heavy liquid separation methods are similar to the unseparated bulk ash samples. This result suggests that the color variations of ash deposits are mainly originated from the particles composed of groundmass. The particles can be classified into three different types of particles with different vesicularity and crystallinity (vesicular particle [VP], dense particle with vesicles [DPV] and dense particle without vesicles [DP]). Analytical results of component proportions, chemical compositions of groundmass glasses, ferrous iron contents and surface ferric materials show that (1) VP has larger yellow components of the visible spectrum (b~* values) and high ferrous iron content, and is less crystallized than the DP and DPV, (2) DP has larger red and yellow components of its visible spectrum (a~* and b~* values, respectively) and involves ferric materials on the surfaces produced by oxidation process, and (3) DPV has smaller red and yellow components of its visible spectrum (a~* and b~* values, respectively) and involves less ferric materials on the ash surfaces. Color differences of ash deposits from three different activity styles can be explained by the different mixing ratios of VP, DPV and DP. During the Strombolian activity, the VP is a main component in the ash, which is formed from relatively less degassed and crystallized magma. In the Vulcanian explosion and continuous ash venting activity, the proportions of DPV and DP in ash are larger than that in the Strombolian activity. The highly crystallized DP may correspond to a vent cap, and DPV to a magma below the cap. The color measurements of ash deposits provide information on the pre-emptive processes at the shallower levels of a conduit.
机译：我们定量测量了1974年至1985年樱岛火山从三种不同类型的顶峰活动（斯特伦伯利活动，伏尔肯人爆炸和连续排灰活动）爆发的火山灰沉积物的颜色。斯特隆伯利灰烬样品的颜色在可见光谱中具有较大的黄色成分（ b〜*值），而不是爆炸和连续排放的灰分样品。爆炸灰样品的颜色在其可见光谱的红色和黄色分量中分别显示较大的变化（分别为a〜*和b〜*值），而连续排放的灰烬样品的颜色在爆炸灰样品的颜色范围内较窄。通过磁性和重液分离方法获得的密度低于3.1 g / cm〜3的组分（地面质量和交斜斜长石）的颜色与未分离的散装灰分样品相似。该结果表明，灰渣沉积物的颜色变化主要源自由地面质量组成的颗粒。可以将颗粒分为具有不同囊泡和结晶度的三种不同类型的颗粒（囊泡颗粒[VP]，具有囊泡的致密颗粒[DPV]和没有囊泡的致密颗粒[DP]）。对磨料玻璃的成分比例，化学成分，亚铁含量和表面铁材料的分析结果表明：（1）VP可见光谱中的黄色成分（b〜*值）较大，亚铁含量较高，且结晶度低于DP和DPV，（2）DP在可见光谱中具有较大的红色和黄色成分（分别为a〜*和b〜*值），并且在通过氧化过程产生的表面上包含三价铁，并且（3）DPV具有较小的可见光谱可见光谱中的红色和黄色成分（分别为a〜*和b〜*值），并且灰分表面上的铁物质较少。 VP，DPV和DP的不同混合比可以解释三种不同活动方式产生的灰烬的色差。在Strombolian活动期间，VP是火山灰中的主要成分，是由相对较少的脱气和结晶岩浆形成的。在Vulcanian爆炸和连续排灰活动中，DPV和DP在灰中的比例大于Strombolian活动中的比例。高度结晶的DP可能对应于排气帽，而DPV可能对应于排气帽下方的岩浆。灰分沉积物的颜色测量提供了有关导管浅层的先发制人过程的信息。

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