Department of Earth Sciences, Durham University, South Road, Durham, DH1 3LE, UK.
Department of Geology & Geophysics, SOEST, University of Hawai'i at Mānoa, Honolulu, HI, 96822, USA.
Sci Rep. 2018 Jun 15;8(1):9179. doi: 10.1038/s41598-018-27065-1.
Spatter is a common pyroclastic product of hawaiian fountaining, which typically forms vent-proximal ramparts or cones. Based on textural characteristics and field relations of spatter from the 1969 Mauna Ulu eruption of Kīlauea, Hawai'i, three spatter types were identified: (1) Primary spatter deposited as spatter ramparts and isolated cones during the peak of episode 1; (2) Late-stage spatter comprising dense, small volume, vent proximal deposits, formed at the end of episode 1; (3) Secondary spatter preserved in isolated mounds around tectonic ground cracks that we interpret to have formed by the disruption of overlying lava. We propose that not all spatter deposits are evidence of primary magmatic fountaining. Rather, deposits can be "secondary" in nature and associated with lava drain-back, disruption, and subsequent ejection from tectonic cracks. Importantly, these secondary pyroclastic deposits are difficult to distinguish from primary eruptive features based on field relations and bulk clast vesicularity alone, allowing for the potential misinterpretation of eruption vents, on Earth and in remotely sensed planetary data, thereby misinforming hazard maps and probabilistic assessments. Here, we show that vesicle number density provides a statistically-robust metric by which to discriminate primary and secondary spatter, supporting accurate identification of eruptive vents.
喷溅物是夏威夷火山喷发的常见碎屑产物，通常形成近喷口的堤堰或锥体。基于夏威夷基拉韦厄火山 1969 年 Mauna Ulu 喷发的喷溅物的纹理特征和野外关系，确定了三种喷溅物类型：（1）原发性喷溅物，在 1 期喷发高峰期作为喷溅堤堰和孤立的锥体沉积；（2）晚期喷溅物，由密集的小体积、近喷口的沉积物组成，形成于 1 期喷发末期；（3）次生喷溅物，保存在构造地裂缝周围的孤立土丘中，我们认为这些土丘是由上覆熔岩破裂形成的。我们提出，并非所有的喷溅物沉积都是原生岩浆喷发的证据。相反，沉积物可能是“次生的”，与熔岩回流、破裂以及随后从构造裂缝中喷出有关。重要的是，仅根据野外关系和大块碎屑的气泡度，这些次生火山碎屑沉积物很难与原生喷发特征区分开来，这使得在地球上和遥感行星数据中对喷发口的潜在误解，从而导致灾害图和概率评估的错误信息。在这里，我们表明，气泡数密度提供了一个统计上可靠的指标，可用于区分原发性和继发性喷溅物，从而支持对喷发口的准确识别。
