Eruption-fed particle plumes and volcaniclastic deposits at a submarine volcano: NW Rota-1, Mariana Arc

NW Rota-1 is an active submarine volcano in the Mariana Arc with a summit depth of 517 m and an explosively erupting volcanic vent southwest of the summit at a depth of 530-560 m. During a period of ongoing explosive eruptions, particle plumes surrounded the volcano and at least 3.3 × 10⁷ m³ of volcaniclastic material was deposited on the southern flank. Particle plumes over the summit were magmatic-hydrothermal in origin characterized by ³He enrichment, hydrothermal precipitates, and low pH values. Plumes at multiple depths below the summit surrounded the volcano and were composed overwhelmingly of fresh, glassy shards of basalt. Rare anhydrite particles were present, but there was a complete absence of other hydrothermal components in the deep plume samples. These short-lived anhydrite particles indicate the source of the deep plumes is from within or very near the eruptive vent, and the mechanism for transport down the flanks of the volcano must be far faster than settling of individual particles. The deep plumes most likely originated from sediment gravity flows generated by explosive eruptions or slope failure and landslides of unstable materials that had accumulated near the eruptive vent. Suspended sediments detach from the volcano slopes at multiple depths and are transported laterally up to tens of kilometers where they contribute to fall-out deposits in distal sediments. These observations link mechanisms for the transport of volcanic ash in the submarine environment to the types of deposits common in volcaniclastic aprons and fine ash layers in distal sediments.