University of Auckland's Breakthrough Study on Far-Reaching Volcaniclastic Density Current Deposits from Hunga Eruption

University of Auckland Team Illuminates Hunga Volcano's Seafloor Legacy

The University of Auckland's Institute of Marine Sciences has played a pivotal role in a groundbreaking study published in Nature Communications, shedding light on the far-reaching consequences of volcaniclastic density current deposits from the 2022 Hunga Tonga-Hunga Ha'apai eruption. Led by researchers including Sally J. Watson from the University of Auckland, in collaboration with NIWA and international partners, the research reveals how these powerful underwater flows reshaped the seafloor over distances exceeding 100 kilometers, damaging critical infrastructure and decimating marine ecosystems.

This study not only advances global understanding of submarine volcanic hazards but also holds direct relevance for New Zealand, home to active volcanic arcs like the Kermadec and the Auckland Volcanic Field (AVF). As New Zealand's leading research institution in earth sciences, the University of Auckland continues to lead efforts through projects like DEVORA, enhancing preparedness for local volcanic risks.

The Cataclysmic Hunga Eruption: Setting the Stage

On January 15, 2022, the submarine Hunga Tonga-Hunga Ha'apai volcano in Tonga unleashed one of the most explosive eruptions of the 21st century, with a Volcanic Explosivity Index (VEI) of 5. The event ejected over 10 cubic kilometers of material into the atmosphere and ocean, generating atmospheric shockwaves that circled the globe twice and tsunamis that reached New Zealand shores. While aerial and surface effects were dramatic, the underwater impacts remained a mystery until detailed seafloor mapping post-eruption.

University of Auckland-affiliated researchers contributed expertise in marine geophysics to analyze pre- and post-eruption bathymetric data, uncovering the role of volcaniclastic density currents—dense, sediment-charged underwater flows—in redistributing massive volumes of volcanic debris far from the source.

Decoding Volcaniclastic Density Currents: A Step-by-Step Breakdown

Volcaniclastic density currents (VDCs), also known as turbidity currents when fine-grained, are gravity-driven flows of water mixed with volcanic particles (volcaniclastics: fragmented volcanic material like ash, lapilli, and scoria). Unlike dry pyroclastic density currents on land, VDCs form when an eruption column collapses into surrounding seawater, creating a dense slurry that sinks and accelerates downslope.

• Step 1: Eruption Collapse: Explosive magma-water interaction generates a towering plume; collapse entrains water and sediment, forming a dense head.
• Step 2: Initiation and Acceleration: The dense mixture (density 1.2-1.5 g/cm³ vs. seawater 1.025 g/cm³) flows at speeds up to 20 m/s, eroding seafloor channels up to 70 m deep.
• Step 3: Long-Runout Transport: Topography channels flows; in Hunga, they traveled >100 km, depositing lobate fans up to 22 m thick.
• Step 4: Deposition and Turbidity: Sedimentation forms graded beds; suspended fines cause prolonged high turbidity, smothering life.

This process, step-by-step modeled using Basilisk software, explains why VDCs pose stealthy threats to submarine cables and habitats.

Research Methods: Cutting-Edge Marine Science at UoA

The study's rigor stems from University of Auckland's advanced marine science capabilities. Pre-eruption multibeam surveys (2015-2017) were subtracted from post-eruption data from RV Tangaroa and USV Maxlimer, quantifying 10 km³ material removal—6 km³ from the caldera (deepened >800 m) and 3.5 km³ from flanks. Sediment cores revealed sand-sized volcaniclastic layers with Tofua arc signatures, while towed cameras documented near-total benthic invertebrate mortality except on seamount refugia. Numerical models simulated 3-4 km³ initial fluid matching observed deposits and cable breaks at 89-105 km.

Sally Watson's geophysical expertise bridged NIWA and UoA efforts, highlighting interdisciplinary collaboration key to New Zealand higher education.

Photo by Adrien Olichon on Unsplash

Key Discoveries: Volumes, Distances, and Devastation

The findings are staggering: VDCs redeposited 6.3 km³ within 20 km as uncompacted layers, eroding chutes 5-10 km long. Flows snapped 7 telecom cables, disrupting Pacific communications for weeks. Ecologically, seafloor life was obliterated over vast areas, surviving only in topographic highs like seamounts >50 km away. Turbidity lingered at 200 m depth 20 km northwest, threatening recovery.

• Caldera volume loss: ~6 km³, unprecedented observation.
• Runout: >100 km, guided by Tonga Trench bathymetry.
• Benthic impact: Mass mortality, refugia key to resilience.
• No landslides; pure column-collapse driven.

Global and Local Implications for Volcanic Hazards

With >75% of Earth's volcanism submarine, this study underscores risks to global cables (95% of data traffic) and fisheries. For New Zealand, near Kermadec Arc volcanoes, similar events could threaten undersea infrastructure.The DEVORA project, led by UoA's Prof. Jan Lindsay and Prof. Shane Cronin, models AVF phreatomagmatic eruptions producing base surges—dilute PDCs up to 5-15 km, endangering Auckland's 1.7 million residents.

Spotlight on University of Auckland's Volcanology Excellence

UoA's School of Environment houses a world-class volcanology group, with researchers like Sally Watson (marine geophysics), Shane Cronin (eruption dynamics), and Jan Lindsay (DEVORA director) driving hazard science. Their work integrates fieldwork, geochemistry, and modeling, training PhD students in cutting-edge techniques amid NZ's ring-of-fire setting. Recent DEVORA advances refine PDC scenarios for AVF, informing civil defense.

Future Frontiers: Monitoring and Mitigation

Post-Hunga, calls grow for seafloor observatories near arcs. UoA advocates real-time monitoring for VDCs, aiding NZ's submarine cable resilience. Student projects explore AVF analogs, preparing for urban volcanism. Collaborative funding via MBIE positions UoA/NIWA at forefront.

Photo by Andrew Yu on Unsplash

Careers in Volcanology: Thriving at NZ Universities

New Zealand's geohazards demand experts; UoA offers PhDs, postdocs in DEVORA. Skills in geophysics, modeling transfer to energy, environment. Explore opportunities at University Jobs NZ.

• PhD scholarships in marine volcanology.
• Postdocs on AVF hazards.
• Lecturer roles in earth sciences.

A Wake-Up Call for Submarine Vigilance

UoA's Hunga study exemplifies Kiwi ingenuity addressing global threats locally. As AVF looms, this research fortifies NZ's defenses, showcasing higher ed's societal impact. Ongoing UoA innovations promise safer volcanic futures.