The climax of the 2021-2022 eruption of Hunga Volcano (also called Hunga Tonga – Hunga Ha’apai) on the 15^th January 2022 was the most explosive volcanic eruption this century. The eruption generated pressure waves that travelled around the planet multiple times, ash clouds that reached the mesosphere, tsunamis with run-ups over 10 m and severed the subsea telecommunication cables that connected the Kingdom of Tonga to the rest of the world.

Hunga Volcano, 70 km offshore from Tongatapu, is an almost entirely submerged caldera volcano. The 2023 eruption was the most explosive in recent history, and resulted in substantial modification to the seafloor. By comparing bathymetric datasets from before the eruption with datasets acquired by this team and autonomous vehicles in the months immediately after the event, we are able to identify the impacts of the eruption on the seafloor and the processes that caused the damage to the cables and, by combining this with auxiliary datasets, provide new constraints on the speed and dynamics of volcanic triggered submarine flows.

The eruption deepened the caldera floor by 800 m, with a loss of > 6 km³ of material, while high energy submarine density flows, focussed into gullies, caused upwards of 90 m of erosion higher up the flanks and deposited large lobes of material at the bases of them. These flows travelled hundreds of kilometres from the volcano at some of the fastest speeds ever measured for submarine density flows and were responsible for the damage to the subsea cables.

During expedition MSM109 in July 2022, a new hydrothermal vent field was discovered, which is the first active field found along the 500-km-long ultra-slow spreading Knipovich Ridge. The so-called Jøtul hydrothermal field is not located on an axial volcanic ridge (AVR) but is associated with the eastern bounding fault of the rift valley. A hydrothermal plume with methane concentrations between 100-1000 nmol/L emits hot fluids into the water column above the hydrothermal field, and is being drifted north with the bottom current. These high methane emissions are likely related to interactions between magmatic intrusions and sediments of the Svalbard continental slope produce unusually high release of thermogenic methane. Further investigations during MSM109 using ROV Quest show a wide variety of fluid escape sites such as diffusive venting from sediments, as well as seepage from joints and cracks within igneous rocks. Additionally, new inactive and active mounds with abundant hydrothermal precipitates and chemosynthetic organisms were discovered. Fluids were sampled from an active black smoker emitting fluids with temperatures > 316°C, and from three other sites with venting temperatures between 8°C and 272°C. The fluids are characterized by high methane, carbon dioxide, and ammonium concentrations, as well as high ⁸⁷Sr/⁸⁶Sr isotope ratios, indicating a strong interaction of the fluids with sediments from the continental margin of Svalbard. Locations with such intense magma/sediment interactions are of particular importance for the carbon cycle, and a focus of the Bremen Cluster of Excellence "The Ocean Floor – Earth’s Uncharted Interface".

The active volcanic arcs of the Scotia- and Caribbean Plate are two prominent features along the otherwise passive margins of the Atlantic Ocean, where subduction of oceanic crust is verifiable. Both arcs have been important oceanic gateways during their formation. Trapped between the large continental plates of North- and South America, as well as Antarctica, the significantly smaller oceanic plates show striking similarities in size, shape, plate margins and morphology, although formed at different times and locations during Earth’s history.

Structural analyses of the seafloor are based on bathymetric datasets by multibeam-echosounders, including data of GMRT, AWI, BAS, MARUM/Uni-Bremen, Geomar/Uni-Kiel and Uni-Hamburg. Bathymetric data were processed to create maps of ocean floor morphology with resolution of 150-250 meters in accuracy. The Benthic Terrain Modeler 3.0, amongst other GIS based tools, was utilized to analyse the geomorphometry of both plates. Furthermore, we used bathymetric datasets for three-dimensional modelling of the seafloor to examine large-scale-structures in more detail. The modelling of ship-based bathymetric datasets, in combination with the GEBCO 2014 global 30 arc-second grid, included in the GMRT bathymetric database, delivered detailed bathymetric maps of both areas.

With the help of the fine- and broad-scale bathymetric position index, we present the first detailed interpretation of combined bathymetric datasets of the entire Caribbean, the Scotia Sea and adjacent areas, such as the South Sandwich Plate. We identified typical morphological features of the abyss, based on determination of steep and broad slopes, ridges, boulders, flat plains, flat ridge tops and depressions in various scales.

Natural marine gas hydrate deposits are one of the largest solid carbon-sequestrated reservoirs on Earth. Here we show that, remarkably, over 80 percent of all natural hydrate-bearing systems exhibit stable periodicity (i.e. periodic growth and dissolution of massive gas hydrate layers) without any external forcing such as the bottom water warming or sea level fluctuations. This stable periodicity is the manifest of the intrinsic gas hydrate system dynamics related to a complex, kinetically controlled interplay between three phases, e.g. the free gas, solid gas hydrate, and methane-saturated pore fluids. Our results state that, globally, periodic (cyclic) states are present for wide range of marine sediment type and sedimentation regimes and the length of each cycle can last from tens to hundreds of thousands of years with cyclic variations in gas hydrate concentration from 20 vol. % to 60 vol. %. Each cycle is also associated with periodic release of the free methane gas in large quantities without the presence of any external forcing. The apparent existence of the periodic states has profound implications setting hard limits on hydrate predictability and implies a systematic source of uncertainty embedded within hydrate dynamics. Moreover, the anthropogenic climate perturbations may overprint the natural gas hydrate cycle and push formerly stable hydrate reservoirs to new periodic states with large p-T-s fluctuations, thereby significantly increasing the risks of uncontrolled gas escape and geomechanical failures, or formerly periodic states towards chaotic states, making long-term predictions extremely challenging.