The ground shakes. Then it shakes again. You’re thinking earthquake, obviously—except this time there’s a mountain involved, and it’s not exactly staying put.
When the Earth Decides to Throw a Tantrum in Two Different Ways
Here’s the thing about volcanoes and earthquakes: they’re like feuding siblings who share the same bedroom. They’re constantly bumping into each other, stealing each other’s thunder, and occasionally teaming up to cause absolute chaos. Scientists spent decades trying to untangle this mess, and turns out, the connection runs deeper than anyone imagined.
Take Mount St. Helens in 1980.
Before that catastrophic eruption on May 18th—the one that blasted 1,300 feet off the summit and killed 57 people—the region experienced thousands of earthquakes. Not tiny tremors either. We’re talking magnitude 5.1 shakers that had geologists scrambling. The quakes were basically the mountain’s way of announcing: “I’m about to do something spectacularly destructive.”
The Magma Highway That Nobody Can See But Everyone Feels
Magma doesn’t politely ask for permission when it wants to rise through the Earth’s crust. It shoves. It cracks rock. It creates pathways by brute force, and every single one of those fractures generates seismic waves. The technical term is “volcano-tectonic earthquakes,” which sounds fancy but really just means “earthquakes caused by angry molten rock trying to escape.” These quakes cluster around volcanic conduits and can occur at depths ranging from surface level down to 20 kilometers.
Wait—maybe it works the other way too?
Absolutely. The 1975 Kalapana earthquake in Hawaii—magnitude 7.7—triggered eruptions at Kilauea volcano within hours. The quake essentially squeezed the magma chamber like a toothpaste tube, forcing lava to the surface through pre-existing weaknesses. It’s geology’s version of cause and effect, except both things can be the cause, which makes studying this relationship delightfully complicated.
That Time Iceland Got Both at Once and Scientists Lost Their Minds
Iceland sits on the Mid-Atlantic Ridge, which is basically a giant crack in the Earth’s crust where tectonic plates are slowly divorcing. In 2014, the Bárðarbunga volcanic system erupted after a swarm of earthquakes—around 1,600 tremors in just 48 hours—signaled that magma was on the move. The lava flow, called Holuhraun, lasted six months and produced 1.6 cubic kilometers of lava. That’s enough to cover Manhattan in a layer 300 meters deep, if you’re looking for a cheerfully terrifying comparison.
The earthquakes weren’t just a warning sign; they were part of the eruption itself. As magma drained from the chamber beneath Bárðarbunga, the caldera collapsed, generating more quakes. It was a feedback loop of geological violence that scientists monitored in real-time, using everything from GPS stations to seismometers to aerial drones.
The Subduction Zone Surprise That Changed Everything We Thought We Knew
For years, researchers assumed volcanic activity and seismic activity in subduction zones—where one tectonic plate dives beneath another—were separate phenomena that just happened to occur in the same neighborhood. Then came Chile in 2011. The magnitude 8.8 Maule earthquake in 2010 was followed by increased volcanic activity at several Chilean volcanoes, including Puyehue-Cordón Caulle, which erupted in June 2011 after being dormant since 1960.
Turns out, massive earthquakes can alter stress patterns in the crust over huge distances, essentialy uncorking volcanoes that were already primed to erupt. The Maule quake changed pressure conditions up to 500 kilometers away, affecting at least four volcanic systems. It’s like shaking a champagne bottle—the pressure was already building, but the shake triggers the release.
When Scientists Start Arguing About Which Came First and Why It Matters
The chicken-or-egg debate in volcanology goes something like this: did tectonic stress cause the magma to move, or did moving magma cause tectonic stress? The answer, frustratingly, is yes. Both. Sometimes simultaneously. The 2018 Kilauea eruption in Hawaii’s Lower East Rift Zone involved magnitude 6.9 earthquakes that occurred as magma forced its way through underground channels, destabilizing the volcano’s entire flank. Over 700 structures were destroyed, not by lava directly, but by ground deformation and related seismic activity.
This matters because prediction depends on understanding causation. If earthquakes precede eruptions consistently, they’re useful warning signs. If eruptions trigger earthquakes, that’s a different hazard model entirely. And if both happen together in some chaotic geological dance? Well, that’s where we are now—trying to model systems that refuse to follow simple rules.
Modern monitoring stations track both seismic activity and ground deformation, using satellite radar interferometry to measure changes as small as millimeters. When Ecuador’s Cotopaxi volcano showed increased earthquake activity in 2015—jumping from a baseline of 50-60 quakes per day to over 500—scientists knew something was brewing. The volcano didn’t fully erupt, but the seismic data revealed magma movement at depths between 2-12 kilometers, providing invaluable information about what happens inside these geological powder kegs.
The connection between volcanoes and earthquakes isn’t just academic curiosity—it’s a matter of survival for the 800 million people worldwide who live within potential volcanic hazard zones.
