On Jan 15,  the Hunga Tonga–Hunga Ha’apai volcano, a mostly submerged volcano located about 60km northwest of Tonga in the southwest Pacific, erupted. 

This created a cloud about 400km in diameter — about 10 times the size of Singapore — that then got dispersed by the wind. 

The eruption also produced powerful and destructive tsunamis, which travelled across the Pacific Ocean for thousands of kilometres and damaged submarine and coastal infrastructure worth millions of dollars.

While the Tongan eruption happened nearly 10,000 km from Singapore, it is a timely reminder that Southeast Asia is not immune from such natural forces of nature. 

A HIDDEN THREAT 

Southeast Asia is one of the most volcanically active regions on Earth. Our region hosts about 750 active and potentially active volcanoes inland. 

Some are capable of very large eruptions, such as the eruption of Krakatau off Java in 1883 and the eruption of Mount Pinatubo in the Philippines in 1991. 

The majority of the active inland volcanoes are well studied and monitored but there is a looming threat hidden under the sea.

The Smithsonian Institution’s Global Volcanism Program, which compiles information about eruptions of the last 10,000 years, reports only two potentially active submarine volcanoes in Southeast Asia. 

These two volcanoes, Ile des Cendres and Veteran, are located off the coasts of Vietnam. Maps of the seafloor also indicate submarine volcanoes in the South China Sea, the Andaman Sea and along the Indonesian subduction zone. 

But we do not know whether they have been active in recent times.  

We suspect that there are many more underwater enigmatic giants in areas we have not mapped yet.

We need to better understand these enigmatic giants to become more resilient against volcanic activity in Southeast Asia. 

But studying underwater volcanoes comes with many logistical challenges. 

First, oceans are too vast to focus on every underwater feature. And secondly, regional methods to map oceans’ floors, usually with satellites, do not provide enough resolution to image all submarine volcanoes.

ERUPTIVE POTENTIAL OF SUBMARINE VOLCANOES IN SOUTHEAST ASIA

Ile des Cendres and Veteran volcanoes are located on the margin of the Sunda shelf southeast of Vietnam, which is the southern part of the continental shelf of mainland Southeast Asia. 

These volcanoes sit where the water depth is mostly shallower than 100m. 

Because their summit is relatively shallow, they can generate powerful submarine explosions similar to the recent Tongan eruption, and can produce tsunamis travelling across the waters of the entire Southeast Asian region.

The South China Sea has about 80 mapped submarine volcanoes, and some of them are also shallow enough for violent eruptions to have a dramatic impact. 

The deeper submarine volcanoes can be dangerous too. They can produce large areas of floating volcanic rocks, called pumice rafts, and affect maritime traffic. 

This happened in 2012 during the submarine eruption at Havre volcano in the Kermadec Islands, in the vicinity of New Zealand. Deep volcanoes can also form large gas bubbles which rise from the deep sea and can damage or sink boats. 

For example, the 1984 eruption from the MacDonald Seamount, a volcano in the middle of the Pacific Ocean, affected a research vessel. 

Such scenarios can also occur to the west of Singapore. 

While most submarine volcanoes in the Andaman Sea are in deep waters, some emerge to form small volcanic islands. 

An eruption from one of these islands or submarine volcanoes could lead to the failure of the flank of the volcano and trigger a tsunami. 

This is likely what happened at Barren Island in prehistoric times. 

A tsunami generated in this area and travelling to the south towards the Malacca Strait could impact the coasts of Sumatra in Indonesia, west Malaysia and Singapore.

Large submarine eruptions from Southeast Asia can also impact the region’s air traffic. Airplanes usually fly within 11km of the ground, and the volcanic ash from a small to medium submarine volcanic eruption can easily reach that altitude. 

Volcanic ash can damage airplanes engines and endanger the lives of people on board. Southeast Asia is not new to the disruption of air traffic caused by a volcanic eruption. 

For example, the relatively small eruption of Mount Agung in Bali, Indonesia in 2018 affected aviation in the region and as far away as Australia. 

The threat to aircraft might have been forgotten with fewer people travelling in the past two years, but one should not forget that airports and local economies could be largely affected in case of a submarine eruption in the region, and we must prepare for that.

A FOCUS ON SINGAPORE

Even though Singapore does not host any volcanoes, our island nation is not immune to volcanic hazards and consequent impacts. 

Located at the heart of Southeast Asia, it is vulnerable to volcanic hazards from Indonesia and the Philippines, as well as from a submarine eruption from the Sunda shelf, the Andaman Sea and the South China Sea. 

The 1991 Pinatubo eruption occurred more than 2,000 km away, but had blanketed Singapore in a thin layer of ash. This eruption acts as a strong reminder that Singaporean communities can still be affected by volcanic eruptions.

A submarine eruption in Southeast Asia could also have a large economic impact on Singapore, given that it is home to one of the densest arrays of submarine communication cables in the world, with about 20 cables covering over 200,000 km. 

These cables connect Singapore to other continents, and some extend as far as northern Europe. 

Damage to one or more of these cables due to an eruption could cause inconvenience to international finance, telecommunications and the internet for millions of users in the region for days or weeks.

Submarine landslides or lava flows from one of these volcanoes could also damage offshore oil platforms, eventually leading to regional environmental disasters. 

Pumice rafts could disrupt our dense maritime traffic while the formation of an eruption column in the atmosphere, besides affecting our air traffic and economy, could affect living conditions and air quality. 

People with respiratory diseases could also be negatively affected with their conditions exacerbated due to the air pollution.

These are just some of the scenarios that Singapore and its neighbours will need to prepare for if a submarine volcano in Southeast Asia were to erupt. 

We can only be better prepared if we know where the submarine volcanoes are, what they are capable of, and how many people and assets are exposed and vulnerable to them. 

Knowing the location of these volcanoes is a key starting point to assessing what they can do and how we can protect ourselves. 

Investing in studies focused on unveiling the seafloor of Southeast Asia and its volcanoes will increase people’s preparedness and improve governments’ resilience. 

 

ABOUT THE AUTHORS:

Andrea Verolino is a research fellow at Nanyang Technological University’s (NTU) Earth Observatory of Singapore (EOS). Benoit Taisne is a principal investigator at the EOS and an associate professor at NTU’s Asian School of the Environment. Lauriane Chardot is a volcanologist working as a science communicator at the EOS.