Malacca Strait: How one volcano could trigger world chaos

Disruption of key trade routes is a well-established problem, due to crime or human error. Piracy has long bedevilled the area, but the strait, cooperatively policed by Indonesia, Malaysia, Singapore, and Thailand, is generally under control. Still, it is not uncommon for ships to collide here: 10 American sailors died as a result of the USS John McCain running into a Liberian-flagged tanker in 2017. But at 1.7 miles (2.7 km) at its narrowest, the strait is not slender enough to be blocked by an errant container ship in the way that the Suez Canal was by the 400m (1,312ft) Ever Given in 2021. 

The greatest menaces to the Malacca Strait, which separates the Malay Peninsula from the Indonesian island of Sumatra, lie in the natural world. Of the many intriguing maps of activity in the region, the most arresting is the one that collates the world’s active volcanoes and recent earthquakes. Along the coast of Sumatra and the more southerly part of Java, following the course of the Sunda Trench, is a band of earthquake activity, and several volcanoes.

On Java, two volcanoes, Semeru and Merapi, have recently erupted. In the Sunda Strait, which separates Java from Sumatra, is Krakatoa, and further west is Tambora, whose eruption in 1815 caused crop failure as far afield as in Europe and the eastern United States.

The Tambora eruption was magnitude VEI7 in the Volcanic Explosivity Index (VEI), on a logarithmic scale going up to VEI8. An event like 1815 might occur once or twice per millennium. But an eruption need not be of quite so high a magnitude to cause severe problems at a global choke point.

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In 2018, researchers at the University of Cambridge’s Centre for Risk Studies envisaged the effects of scenarios including a VEI6 eruption at Marapi. The eruption, they suggested, might produce ash clouds and fine tephra – fragments of rock ejected into the air – that waft across the Malacca Strait towards Singapore and Malaysia. The resultant damage to local infrastructure and supply chains, with aviation particularly badly affected, would combine with a global temperature drop of 1C to wipe an estimated $2.51tn (£2tn/€2.3tn) off global GDP over a five-year period. That figure dwarfs the estimated $5bn (£4bn/€4.6bn) that the VEI4 eruption of Eyjafjallajökull, in Iceland, wiped from the global economy.

Marapi’s last VEI4 eruption was 2010. A VEI6 eruption at Marapi is lower-probability: its return period, which is the estimated average time between eruptions, is 750 years. Yet the stakes are high enough to merit taking the prospect seriously, says Lara Mani, a volcanologist at the University of Cambridge’s Centre for the Study of Existential Risk. And Marapi is one of several active volcanoes in the region. VEI4, VEI5 and VEI6 eruptions, says Mani, “can still really disrupt the strait. And the thing is, when a volcano starts, it doesn’t tell you when it’s going to stop.”