In this companion study to Simons et al. (Bull Volcanol 82, 2020a), we examine Strombolian style explosive activity at Yasur (Vanuatu) over 11 weeks via seismic, thermal-infrared and visual observations. In part 1 of this study (Simons et al., Bull Volcanol 82, 2020a), we investigated the link between variations in the surface expression and style of volcanism at Yasur in relation to vent, shallow conduit and shallow magma reservoir processes. Now, in part 2, based on the database of 4998 explosions, we describe, define and classify Yasur’s Strombolian eruption styles and magnitudes, and compare and contrast to Stromboli and other similar centres. The styles of most of Yasur’s explosions fit with other known Strombolian eruptions, but they are 2–3 times more frequent and with higher average eruption heights than at Stromboli. Observed activity at Yasur also produced more ash than at Stromboli. The most powerful eruptive periods are dominated by type 2a explosions (ballistics and ash) and type 2b (ash-dominated) explosions. A new type of Strombolian style explosion was observed at Yasur and is here termed a type 3 explosion. They occur when vents are buried by a thick cap of loose, poorly sorted pyroclastic breccia. Type 3 explosions begin as a series of emergent ash-rich jets that rupture and fountain from the breccia cover, generating prolonged jetting of ash to form vigorous low plumes. The loose breccia cover apparently dissipates the violent early phase of the explosion. The greatest hazard of type comes from their occurrence with little warning from a smooth crater floor without an apparent vent and after longer than typical intervals between eruptions. The findings extend the observed range of Strombolian explosion styles and imply that surficial vent cover and burial may influence gas slug stability and contribute to variations in ash and ballistic output.

中文翻译：

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瓦努阿图亚苏尔火山喷发方式和规模的时空变化：第 2 部分——扩展斯特龙博利火山喷发分类

在西蒙斯等人的这项伴随研究中。（Bull Volcanol 82, 2020a），我们通过地震、热红外和目视观测在 11 周内检查了 Yasur（瓦努阿图）的 Strombolian 式爆炸活动。在本研究的第 1 部分（Simons 等人，Bull Volcanol 82, 2020a）中，我们研究了 Yasur 火山活动的地表表达变化和类型与喷口、浅层管道和浅层岩浆储层过程之间的联系。现在，在第 2 部分中，基于 4998 次爆发的数据库，我们描述、定义和分类 Yasur 的 Stromboli 喷发类型和规模，并与 Stromboli 和其他类似中心进行比较和对比。Yasur 的大部分喷发风格与其他已知的 Stromboli 喷发相吻合，但它们的频率是 Stromboli 的 2-3 倍，平均喷发高度也更高。在 Yasur 观察到的活动也比 Stromboli 产生了更多的灰烬。最强大的喷发期以 2a 型爆炸（弹道和火山灰）和 2b 型（以火山灰为主）爆炸为主。在 Yasur 观察到一种新型的 Strombolian 型爆炸，这里称为 3 型爆炸。当通风口被厚厚的松散、分类不良的火山碎屑角砾岩盖掩埋时，就会发生这种情况。第 3 类爆炸开始于一系列涌出的富含灰烬的喷射流，从角砾岩覆盖层破裂和喷泉，产生长时间的灰烬喷射，形成强烈的低羽流。松散的角砾岩覆盖层显然消散了爆炸的早期猛烈阶段。最大的危险来自于它们在没有明显通风口的光滑火山口底部几乎没有警告的情况下发生，并且喷发之间的间隔时间超过了典型的间隔。