It’s the quiet ones you have to watch out for.

Contrary to popular belief, it’s not the big-name volcanoes like Yellowstone and Mount Etna in Sicily that pose the greatest threat. A UK volcanologist argued that the biggest danger could come from hidden volcanoes that appear dormant and are barely monitored.

“Often overlooked, these ‘hidden’ volcanoes erupt more often than most people realize,” wrote Mike Cassidy, a professor of geography and environmental science at the University of Birmingham, in a recent piece for the Conversation. “In regions like the Pacific, South America and Indonesia, an eruption from a volcano with no recorded history occurs every seven to ten years.”

He claimed that these eruptions don’t just affect the surrounding communities, but can also cause a butterfly effect that’s felt across the world. These collateral effects include drastic temperature changes and monsoon disruptions that impact agriculture across large swathes of land, resulting in famine, disease and major social upheaval.

Cassidy cited the case of the Hayli Gubbi volcano in Ethiopia, which erupted for the first time in its nearly 12,000-year existence on Sunday.

The blast sent massive plumes of ash shooting into the air and coated the neighboring village of Afdera in dust with volcanic debris reaching as far as Yemen and India. Thankfully, no casualties were reported.

This eruption wasn’t an outlier, either.

In 1982, unmonitored Mexican volcano El Chichón blew its stack after lying dormant for centuries, causing smoldering avalanches of rock, ash and gas that flattened the last swaths of jungle.

It also clogged rivers, destroyed buildings, and triggered ash clouds that fell as far as Guatemala.

A staggering 2,000 people died and 20,000 were displaced during the disaster.

And the effects weren’t just felt in the West.

The sulfur from the eruption formed reflective particles in the upper atmosphere that cooled the Northern hemisphere and shifted the African monsoon southwards, causing an extreme drought and contributing to the Ethiopian (and East African) famine of 1983-85 that killed at least 1 million people. 

“Few scientists, even within my field of Earth science, realize that a remote, little-known volcano played a part in this tragedy,” Cassidy lamented.

Despite the literal mountains of evidence, fewer than half of active volcanoes are monitored, while the lion’s share of scientific research is centered around the big names.

“There are more published studies on one volcano (Mount Etna) than on all the 160 volcanoes of Indonesia, Philippines and Vanuatu combined,” declared Cassidy.

Meanwhile, despite the attention toward the Yellowstone supervolcano — one of Earth’s largest volcanic systems, with the capacity to wreak havoc on an entire continent — scientists say that this apocalyptic caldera will likely not erupt within our lifetime.

“There will be eruptions, but it will probably be thousands of years before we can expect an eruption,” Erik Klemetti Gonzalez, an earth and planetary sciences professor at Denison University in Ohio.

Why are we turning a blind eye to these sleeper magma-spouters? Cassidy chalked the phenomenon up to human bias, claiming that people tend to assume that a volcano that has “not erupted for generations” will remain quiet in the future.

So, while well-known volcanoes such as Mt. Etna — which erupted in June — receive tons of coverage, these stealth lava-shooters barely move the needle.

This is problematic given that “three-quarters of large eruptions (like El Chichón and bigger) come from volcanoes that have been quiet for at least 100 years,” Cassidy observed.

To help make volcano monitoring less like a game of tectonic roulette, the volcanologist recommends shifting attention toward Latin America, Southeast Asia, Africa and the Pacific, where millions of people live near volcanoes that have barely any record of activity.

“This is where the greatest risks lie, and where even modest investments in monitoring, early warning and community preparedness could save the most lives,” Cassidy declared.