Extensive earthquake-triggered landslide(s) primed by recent major volcanic eruption

We aim to document an eruption-primed, but seismically-triggered submarine landslide for the first time through rapidly-acquired new seafloor data.

Event: Extensive damage to the Tongan domestic subsea telecommunications cable on the 29th June 2024 caused the second major internet outage in the Ha'apai and Vava'u island groups in <3 years. The cable owner reported damage to 23 km of the subsea cable, 16 km east of Hunga volcano (which produced the most explosive volcanic eruption this century, causing cable damage in January 2022). Unlike 2022, there was no evidence of volcanic activity in the region at the time of the break. Instead, the first interruption to data traffic occurred 40 minutes after a 5.7Mw earthquake, 25 km WSW of the volcano. We hypothesise that the earthquake caused remobilisation of thick volcanic deposits emplaced on the volcano flanks during the 2022 eruption, generating one or more significant submarine landslides. This is supported by the existence of landslide signals interpreted from regional seismic monitoring data shortly after the earthquake and the unusually long length of cable damaged/buried.



Significance: Submarine landslides pose a hazard to critical cables that carry >99% of digital data traffic globally and vulnerable seafloor communities. However, they remain poorly understood due to a paucity of surveys that capture the evolution of slopes - particularly in seismic and volcanic regions. The remobilisation of volcanic material following a volcanic eruption is a currently unrecognised risk for both subsea infrastructure and other secondary hazards. Such remobilisation likely explains cable damage in other volcanic regions, not connected directly to an eruption, including at Kick 'Em Jenny Volcano in 2015 and La Soufriére in 2021. Similar processes may also occur in other non-volcanic but seismically active settings with sudden high sediment delivery. We seek to understand the pre-conditioning and triggers for major submarine landslides, and the processes by which they transport material, to support ongoing research at Hunga volcano, benefit communities, government/industry stakeholders beyond the South Pacific, and support more resilient telecommunications networks.



Justification for Urgency: There is an urgent need to survey the area associated with this cable-breaking event. If such a survey was delayed, then the landslide scar may be buried/reworked. However, the cable damage occurred at water depths between 1500 and 1700 m, making the region inaccessible to anything but a large vessel. This project will use data acquired by the cable repair vessel, collected within a month of the event, and supplement a scheduled research expedition that will occur within a year. Given typical lead times and costs for ships, this represents both exceptionally good value, and also the fastest realistic response to an event in deep water.



Approach: Hunga Volcano was mapped in 2015/16 and in 2022 (post-eruption), providing a unique time series dataset. We will acquire new seafloor data to map the evolution of the edifice and surrounding slopes following a major eruption, to identify the likely sources of the landslide(s). We will test whether the source for failure(s) was from suddenly-emplaced material on the flank of Hunga volcano or from adjacent slopes, which were also mantled with sediment from the eruption. Sediment cores will be logged, scanned and geochemically-analysed to fingerprint sources of material and landslide dynamics. Findings will be disseminated to stakeholders through workshops and publications, to assess previously-unrecognised hazards in similar settings worldwide.