Understanding clast dispersal from subaqueous volcanism is hampered by uncertainty in the source and extent of seafloor deposits. Extensive sampling in situ of seafloor deposits from the 2012 submarine eruption of Havre volcano provides an ideal opportunity to assess subaqueous dispersal. The 2012 Havre eruption produced 14 lavas/domes, a pumice raft, and three seafloor clastic deposits. At Havre the source of clastic deposits can be confidently identified, and deposit thickness, grain size, and distribution are also well-constrained. We examine a seafloor deposit termed subunit 3 (S3) generated in the 2012 Havre eruption to investigate dispersal of fine lapilli and ash, and the eruption conditions that generated this deposit. Subunit 3 is the third from bottom of four subunits that make up the Ash with Lapilli unit. Subunit 3 is composed of ash with highly elongate shapes, unique within the 2012 Havre deposits. It thickens and coarsens toward Lava G, also generated in the 2012 eruption, located on the southwest wall of Havre caldera. Lava G is the only lava produced during the 2012 Havre eruption that has a glassy carapace with elongated vesicles and a fibrous texture. We infer the source of unit S3 is Lava G, due to the spatial pattern of deposit thinning and fining away with distance from this lava, and the morphological and microtextural similarity of ash with the Lava G carapace rock. Grain size and transport distance of ash from S3 are used to test a simple 1D model addressing both clast dispersal by a buoyant thermal plume above an explosive eruption, and by penetrative convection during effusive lava emplacement. Comparison of calculated maximum dispersal distances with grain size and transport distance show that a jet forming eruption generating a turbulent plume is required to generate S3. We suggest that S3 was generated by hybrid explosive-effusive activity during the effusion of Lava G. Using model results we calculate maximum clast dispersal distances across a range of grain sizes for both dispersal mechanisms. The calculated maximum clast dispersal distance has wide implications globally for interpretation of ash deposits from subaqueous eruptions.

海底沉积物来源和范围的不确定性阻碍了对水下火山作用的扩散的理解。广泛采样原位从2012年阿弗尔火山海底火山喷发中获取的海底沉积物为评估水下扩散提供了理想的机会。2012年的阿弗尔火山喷发产生了14个熔岩/穹顶，浮石筏和3个海底碎屑沉积物。在阿弗尔，可以确信地确定碎屑沉积物的来源，并且也很好地限制了沉积物的厚度，粒度和分布。我们研究了在2012年哈弗尔火山喷发中产生的称为亚单元3（S3）的海底沉积物，以调查细青金石和灰分的散布以及产生该沉积物的喷发条件。子单元3是构成带有Lapilli的Ash单元的四个子单元中从底部的第三个。子单元3由高度伸长的灰烬组成，在2012年阿弗尔矿床中是独一无二的。它也向2012年喷发时产生的熔岩G变粗和变粗，位于阿弗尔破火山口的西南墙上。熔岩G是在2012年阿弗尔火山喷发期间产生的唯一熔岩，其玻璃状甲壳具有细长的囊泡和纤维质地。由于沉积物稀疏化和远离该熔岩的细化的空间模式，以及灰与熔岩G甲壳岩的形态和微观结构相似性，我们推断单元S3的来源是熔岩G。来自S3的灰分的粒径和运移距离用于测试一个简单的一维模型，该模型解决了爆炸性喷发上方的浮力热羽流和熔岩冲积过程中的穿透对流问题，从而实现了碎屑的扩散。将计算出的最大分散距离与晶粒尺寸和传输距离进行比较，结果表明，生成湍流羽流的射流爆发需要生成S3。我们认为，S3是由熔岩G的散发过程中的混合炸药-喷发性活动产生的。使用模型结果，我们为两种散布机制计算了整个粒度范围内的最大碎屑散布距离。计算出的最大碎屑扩散距离在全球范围内对水下喷发产生的灰分沉积物的解释具有广泛的意义。