When Quiet Undersea Volcanoes Turn Disruptive¶
Source: When Quiet Undersea Volcanoes Turn Disruptive \ Date Published: 2026-05-26 \ Author/Org: Evan Howell / Quanta Magazine \ Time to read: 12 min
TL;DR¶
Conventional wisdom held that mid-ocean ridge volcanoes erupt quietly because deep-ocean pressure suppresses gas expansion. But Expedition M201 (June 2024) led by Jonas Preine found that at shallow depths of around 300 metres, this rule breaks down: seawater contacting lava flashes to steam, powering explosions capable of breaching the surface and forming new islands — much like Surtsey did in 1963.
Core Discovery & Context¶
The Assumption: Mid-ocean ridges — Earth's largest volcanic system — are assumed to erupt quietly, as the crushing pressure of the deep ocean suppresses gases. Most of the Mid-Atlantic Ridge lies at least 2,500 metres below sea level.
The Discovery: Expedition M201 (June 2024, aboard the ship Meteor) led by Jonas Preine found evidence that this rule breaks down at shallow depths (~300 metres), leading to violent, island-forming eruptions.
"We just don't know nearly as much about them." — Isobel Yeo, National Oceanography Center
Key Findings¶
The Depth Threshold¶
- ~300 metres: The transition point where the Mid-Atlantic Ridge shifts from quiet to explosive
- Mechanism: Water pressure is low enough for seawater contacting lava to flash to steam, powering explosions that can breach the surface
- Observed features: Smooth, steep-sided, flat-topped mounds with widespread debris — unlike the usual jagged terrain
"The key parameter here is depth." — Ross Parnell-Turner, Scripps Institution of Oceanography
The Erosive Cap¶
North Atlantic storm waves erode the tops of these volcanoes to a uniform depth of ~40 metres below sea level, explaining their flat appearance.
"It looks like someone dumped a truckful of volcanic sand over everything." — Robert Sohn, Woods Hole Oceanographic Institution
Volcanoes vs. Glaciers: The Great Debate¶
Alternative theory: The features could be tuyas (table mountains) from the last ice age (~20,000 years ago), where magma melted through a thick glacial cap.
Pro-volcano evidence: Volcanic material sits on top of abandoned glacial rubble, meaning eruptions happened after the glaciers retreated.
Preine's nuanced view: Retreating glaciers may have released crustal pressure, indirectly fueling a spike in volcanic activity along the ridge.
Historical Precedent: Surtsey¶
| Property | Detail |
|---|---|
| Emergence | November 14, 1963 — without warning |
| Final height | 171 metres above sea level over 3 years |
| Namesake | Surtur, the Icelandic fire god |
| Pattern | One of 14 documented eruptions on the northern Reykjanes Ridge in 1,000 years |
Current Activity in Iceland¶
A massive magma chamber has been swelling under the Reykjanes Peninsula since ~2020. Grindavík (~3,700 residents) was evacuated in 2023, many permanently. Pressure is building again. An earthquake swarm occurred on the Reykjanes Ridge in early 2026.
"We are really in the middle of a very remarkable event right now." — Páll Einarsson, Univ. of Iceland
Preine states the "chances are not low" for another island like Surtsey to form.
Global Implications¶
Shallow stretches of mid-ocean ridges across the globe cross the same ~300-metre depth threshold, including: - The Azores - The Galápagos - The Red Sea
This suggests that explosive mid-ocean ridge volcanism is a global phenomenon, periodically capable of building islands that briefly rise above the surface before waves grind them away.
Key Takeaways¶
- Mid-ocean ridge volcanoes at depths shallower than ~300m can erupt explosively, forming new islands
- Expedition M201 found evidence that these features exist along the Reykjanes Ridge, challenging the prevailing quiet-eruption paradigm
- Current magma chamber swelling in Iceland and a 2026 earthquake swarm suggest the region may be primed for another Surtsey-like event