Explosive Volcanism in the Deep

Can a volcano be explosive in the deep sea? What about violent? What about mildly aggravated?

Historically, we’ve assumed the answer to be no. Explosive eruptions were thought to be absent at depths below the critical point for seawater around 3000m. Combine this with the lack of evidence for a pyroclastic deposit [rock materials formed by fragmentation as a result of volcanic action] below 3,000m. On top of that add the hypothesis that mid-ocean-ridge basalts do not possess the volatility to produce impressive eruptions at high pressures.

A group of researchers report this week in Nature provide evidence of pyroclastic deposits on the Gakkel ridge in the Arctic Basin at 4000m. In the abstract the authors note a large area “blanketed” with deposits including bubble wall fragments.

Well…that raises some questions.

Figure 2: a, Frame grab from a high-definition video camera taken on the south side of Duque’s hill (see Fig. 1 for location). About 10 cm (visually estimated and confirmed during sampling) of pyroclastic material is piled atop a high-standing, weathered, pillow feature. The exoskeleton of an as yet unidentified species of hexactinellid sponge23 is visible in the foreground. b, High-definition video frame grab of talus blocks possibly representing ejecta from a vulcanian explosion on Oden volcano (see Fig. 1 for location). c, Glassy, granular, pyroclastic material. d, Bubble wall fragment from pyroclastic deposit.