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Extraordinary, but deadly: The hazards of submarine volcanoes

By James Dalziel | January 28, 2022

After the recent eruption of the submarine Hunga Tonga-Hunga Ha’apai volcano, James Dalziel outlines the hazards and impact this will have on communities, and the wider reaching consequences
Climate|Environmental Risks|Marine
Climate Risk and Resilience

The recent eruption of the submarine Hunga Tonga-Hunga Ha’apai volcano has gained international attention after dwarfing previously observed activity in the area, with the most readily observable impacts including magma and volcanic gases blasting an ash plume over 20km high and 260km in diameter before being distributed even further by wind. The event has served to illustrate the many varying hazards associated with submarine volcanoes and, as the situation continues to unfold, is highlighting how natural perils become human and environmental risks on a local, regional, and even global scale.

Coincident and compounding perils: Volcanic ash, tsunami waves, and possible landslides

Volcanic ash is a hazard that many are well aware of, with the 2010 eruption of Eyjafjallajökull in Iceland in particular causing widespread disruption to aviation across Europe. But in addition to the wider-reaching financial implications of ash clouds causing airlines to change flight paths, issue delays and ground aircraft for risk of damage – something we’ve been researching with MITIGA Solutions – there can be far more deadly consequences for the local population. Following the Icelandic eruption, agriculture took a major hit with destruction of pasture and animals having to be kept indoors or even prematurely slaughtered to avoid ingesting ash covering the fields. Crops are also often impacted, with acid leachate burning leaves and fruit, and stressing root systems. In Tonga and other island communities surrounding the volcano, one of the most immediate hazards from ashfall is the contamination of drinking water. This is further compounded by seawater contamination and debris infiltration, caused by tsunami waves inundating low-lying coastal areas. Clean, safe, water is not only a key necessity for the population and descending aid community, but also for industry on the islands from an operational perspective. Ashfall on the runway of Tonga’s main Fua’amotu airport also presents problems for incoming aircraft delivering aid and supplies, as it has to be manually removed before any flights can land.

The eruption and the resulting tsunami have tested the early warning systems of several countries

The risks presented by tsunamis are also known all too well, with events such as the 2004 Indian Ocean and 2011 Tōhoku tsunamis devastating areas around the Pacific and helping spur advances in monitoring, early warning systems, and coastal defenses. However, this tsunami is somewhat unique; while both the 2004 and 2011 events were caused by large magnitude earthquakes, this is one of the estimated 5% of tsunamis to be caused directly by a volcanic eruption. This is a dubious honour it shares with the 1883 eruption of Krakatoa, which itself caused widespread devastation around much of the Indian Ocean.

The eruption of the Hunga Tonga-Hunga Ha’apai volcano and the resulting tsunami have tested the early warning systems of several countries, including the United States, Japan, Peru, and New Zealand, and although so far the global impact of these tsunami waves has been relatively minor compared to past events, the local impact for the Kingdom of Tonga has been far more severe. Limited contact from the islands affected has produced photographs showing chunks of seawall strewn across roads and inland areas, dramatic videos of waves lapping against windows of buildings have surfaced through news outlets, and aerial photography shows extensive damage to buildings and infrastructure. The extent of damage to ports and docks and the main international airport, and the time and materials needed to make them serviceable, will be central to planning and implementing the recovery efforts.

Initial observations suggest that the tsunami was caused by explosive eruption of the volcano itself, with sonic booms heard as far away as Fiji, New Zealand, and Alaska, and an atmospheric pressure wave thought to have travelled twice around the world being clearly recorded on national as well as local meteorological instruments. However, it is also possible that a submarine landslide or collapse of the larger Hunga caldera is partly responsible for the tsunami. Although yet to be proven, some scientists believe initial evidence points towards this type of collapse causing damage to the subsea communications cable connecting Tonga to Fiji and the rest of the world. Preliminary data suggests a break in the 827km-long cable approximately 37km offshore of Tonga’s capital Nuku’alofa, close to the site of the eruption. Another break was noted in a domestic cable running north from Tonga to the islands of Pangai and Neiafu, approximately 47km offshore and also running close to the volcano.

In a world increasingly reliant on technology and connectivity, this kind of disruption can have multiple impacts ranging from local to the global arena. Damage to subsea cables can result in disruption to internet connectivity, and increasing utilization of offshore power generation means the potential risk of blackouts in some areas. However, cable damage from events such as earthquakes, submarine landslides and volcanic eruptions can be far more serious for smaller island nations, disrupting the principal method of communication and leaving satellites as the only remaining option for contacting the outside world. In the case of the Hunga Tonga-Hunga Ha’apai eruption, volcanic ash is also affecting satellite communication, making it near-impossible to ascertain the full extent of infrastructure damage and human impact for planning relief strategies. The presence of ash in the air and on runways, as well as danger of further eruptive episodes, has frustrated efforts to use aircraft to survey damage done by ashfall and tsunami waves, and cast uncertainty over plans to provide supplies and medical aid. To complicate matters further, the risk of spreading Covid-19 to the as-yet uninfected population of Tonga is also a risk that shall impact relief efforts.

These compounding risks serve to highlight that while modelling and early warning systems are very useful, there will always been sudden and unexpected events, especially in a rapidly (by geological standards) changing climate, and not just in the middle of the Pacific. It is therefore just as important that resilience strategies include response mechanisms for the “unknown unknowns”, and be aimed at building resilience (i.e., upskilling individuals, establishing monitoring and response protocols etc.) at individual, community, and institutional levels. WTW is undertaking research into these broader disaster and climate risk management strategies, such as the Climate and Resilience Hub’s involvement with a project discussing “Consultancy for enhancing action on comprehensive climate change risk management in the Pacific Region”.

The sheer scale and violence of this submarine volcanic eruption has made it a terrifying spectacle watched the world over, and although not currently as internationally devastating as some natural disasters in recent history the impact to local communities and economic growth is likely to be severe and long-lasting.

Science for resilience

It is important to note that there is no guarantee that this will be the worst of the crisis, as geological evidence of previous activity at the Hunga caldera approximately 1,000 years ago suggests there were multiple separate eruptive episodes. If this were to happen again with the current eruption, further activity may create more wide-reaching risks for the Pacific basin in the weeks, months, or even years ahead.

By quantitative modelling of natural disasters and stress-testing qualitative scenarios of risk and loss, we can help build resilience to global risks and decide what to do next. This will be important for national preparedness of governments as well as businesses, who rely on (and are relied upon by) countries like Tonga as part of their global supply chains. WTW and the Willis Research Network work closely with academic and industry partners to identify insurance needs and offer solutions that improve our view of risk and increase resilience, with volcanic hazards being key issues on the agenda.

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