A central volcano is the main eruption point of a volcanic system — the place where magma collects before migrating outward along fissure swarms. Iceland's ~30 volcanic systems each have one, and they're responsible for some of the most consequential eruptions in recorded history. We track 44 Icelandic volcanoes in our database.
Iceland Volcanoes
44
Recorded Eruptions
300
Volcanic Systems
~30
Active Since 2010
6
What Is a Central Volcano?
A central volcano is the primary eruption center of a volcanic system — a distinct geologic concept that's poorly explained across the internet. Search for it and you'll find one-sentence definitions and Wikipedia stubs. Here's what it actually means.
Every volcanic system has plumbing. Magma rises from the mantle into a shallow reservoir (typically 2-10 km deep). From that reservoir, it can erupt in two ways: straight up through the central volcano, or laterally along fissure swarms — belts of fractures that radiate outward, typically aligned with the rift zone. The central volcano is where the plumbing converges. It's the focal point.
This concept matters most in Iceland, where it was developed by Icelandic volcanologists in the 1960s-70s to describe the island's ~30 volcanic systems. Each system has: (1) a central volcano (which may be a stratovolcano, a caldera, or a shield volcano), and (2) a fissure swarm that can extend 30-200 km from the center.
By VolcanoDB Research Team. Data: Smithsonian Global Volcanism Program, Icelandic Meteorological Office, University of Iceland Institute of Earth Sciences.
How Do Central Volcanoes Work?
Think of it like a river system. The central volcano is the lake where water (magma) collects. The fissure swarms are the river channels that carry it outward. Sometimes the lake overflows (eruption at the central volcano). Sometimes water finds a path through the river channels (fissure eruption kilometers away).
Central Volcano Anatomy
Magma Reservoir
Sits 2-10 km beneath the central volcano. In Iceland, these reservoirs are typically 2-5 km³ in volume. Krafla's reservoir was accidentally pierced at 2.1 km depth in 2009 — confirming the magma was exactly where geophysicists predicted.
Central Edifice
The visible volcano above the reservoir. Can take many forms: a glacier-covered stratovolcano (Katla, Hekla), a caldera (Krafla, Askja, Grímsvötn), or a broad shield (Theistareykir). The form depends on eruption frequency, magma composition, and whether it sits under a glacier.
Fissure Swarm
A belt of fractures, grabens, and volcanic fissures extending 30-200 km from the central volcano. Aligned with Iceland's rift zone direction (roughly NE-SW). When magma pressure exceeds what the central volcano can vent, it migrates laterally along these swarms. The 2014 Holuhraun eruption traveled 45 km from Bárðarbunga along its swarm.
This is why Icelandic eruptions can seem confusing — an eruption attributed to one volcanic system can occur tens of kilometers from its central volcano. The 1783 Laki eruption is officially part of the Grímsvötn system, even though the fissure is 50 km southwest of Grímsvötn's caldera. The magma came from Grímsvötn's reservoir and traveled along the fissure swarm.
Iceland's Central Volcanoes
Iceland sits on the Mid-Atlantic Ridge — one of the only places on Earth where a divergent plate boundary rises above sea level. The island has approximately 30 volcanic systems, arranged along the rift zones that run through the center and south of the country.
Here are the 10 most significant systems:
Volcanic System
Central Type
Fissure Swarm
Eruptions
Last
Grímsvötn
Caldera
120 km
20+
2011
Bárðarbunga
Stratovolcano
190 km
20+
2014
Krafla
Caldera
90 km
20+
1984
Katla
Fissure vent(s)
80 km
20+
1918
Hekla
Stratovolcano
40 km
20+
2000
Reykjanes
Crater rows
70 km
20+
2025
Askja
Stratovolcano
200 km
14+
1961
Hengill
Crater rows
50 km
13+
~100 CE
Vestmannaeyjar
Fissure vent(s)
30 km
10+
1973
Öræfajökull
Stratovolcano
25 km
2+
1727
Notice the range of fissure swarm lengths: Askja's extends 200 km, while Vestmannaeyjar's is just 30 km. Longer fissure swarms don't necessarily mean more dangerous systems — Katla has an 80-km swarm but is considered far more hazardous than Askja (200 km) because it sits under a glacier and produces jökulhlaups.
8 Notable Central Volcanoes
Each links to its full VolcanoDB profile with eruption timeline, monitoring data, and seismic activity.
The poster child for central volcano research. Krafla's famous "Krafla Fires" (1975-1984) produced nine eruptions along its 90-km fissure swarm, while the central caldera (10 km wide) acted as the magma distribution hub. Now it's the site of the Krafla Magma Testbed (KMT) — the world's first attempt to deliberately drill into a known magma body. In 2009, the Iceland Deep Drilling Project accidentally hit molten rock at 2.1 km depth here, producing superheated 450°C steam that generated 36 MW of power from a single well.
Iceland's most feared volcano. Katla's central volcano sits beneath Mýrdalsjökull glacier, and its eruptions trigger catastrophic glacial floods (jökulhlaups) that can discharge 100,000-300,000 m³/s — rivaling the Amazon River's flow rate. Its fissure swarm extends 80 km to the northeast. Katla has erupted ~20 times since 930 CE, roughly every 50 years. The last eruption was in 1918 — 108 years ago — making it statistically overdue.
Medieval Icelanders called it the "Gateway to Hell." Hekla is unusual for a central volcano: it erupts along a ridge rather than from a single vent, producing fissures that open across its entire 5-km summit ridge. Its eruptions have been getting shorter but more frequent — the last five occurred in 1970, 1980, 1981, 1991, and 2000. Warning time before a Hekla eruption is notoriously short: as little as 30-80 minutes between first seismic signal and eruption.
Grímsvötn Volcanic System · Fissure swarm: ~120 km
Iceland's most active volcanic system, with a central caldera mostly hidden beneath the Vatnajökull ice cap. Its 120-km fissure swarm is the longest in Iceland, stretching southwest to the Laki fissure that produced the devastating 1783-84 eruption — one of the most significant volcanic events in recorded history. The Laki eruption killed 20% of Iceland's population and caused a famine-inducing haze across Europe.
Bárðarbunga Volcanic System · Fissure swarm: ~190 km
Home to Iceland's largest known volcanic system by fissure swarm length (~190 km). Its 2014-2015 Holuhraun eruption was the biggest Icelandic eruption in 230 years — producing 1.6 km³ of lava over six months from a fissure 45 km northeast of the central volcano. The eruption demonstrated exactly how central volcano plumbing works: magma migrated laterally from beneath Bárðarbunga's caldera along the fissure swarm before breaking the surface.
Contains the deepest lake in Iceland — Öskjuvatn (220m) — which formed when the caldera floor collapsed during the VEI 5 eruption of 1875. That eruption's ash fell on Scandinavia and caused a wave of Icelandic emigration to North America. Askja's 200-km fissure swarm is one of the longest in Iceland. NASA astronauts trained in Askja's caldera in the 1960s because the landscape resembles the lunar surface.
Eyjafjallajökull Volcanic System · Fissure swarm: ~30 km
Relatively small as Icelandic central volcanoes go, but globally famous for its 2010 eruption that closed European airspace for six days. The eruption was VEI 4 — moderate by Icelandic standards — but the interaction between magma and glacial ice produced extremely fine ash. Its fissure swarm is connected to Katla's system, and historically, Eyjafjallajökull eruptions have preceded Katla eruptions (though not this time, so far).
Reykjanes Volcanic System(s) · Fissure swarm: ~70 km
The Reykjanes Peninsula hosts multiple overlapping volcanic systems that have erupted eight times since 2021 — the most intense eruption sequence Iceland has seen in centuries. The Sundhnúkur fissure system reactivated in December 2023, sending lava toward the evacuated town of Grindavík. This isn't a single central volcano but rather a series of fissure systems along the Mid-Atlantic Ridge's on-land extension.
Central Volcanoes Outside Iceland
The "central volcano + fissure swarm" model was developed for Iceland, but the concept applies anywhere volcanic systems have a focal eruption point connected to radiating fractures.
Taupo Volcanic Zone, New Zealand
New Zealand's TVZ has a comparable structure — central volcanic complexes (Taupo, Rotorua, Okataina) connected to fault-controlled rift basins. The TVZ is a back-arc rift, not a mid-ocean ridge, but the principle is the same: a central magma focus with radiating fracture systems.
East African Rift
The East African Rift hosts volcanic systems that share characteristics with Iceland's central volcano model. Erta Ale in the Afar Depression acts as a central focus for its rift segment, while fissure eruptions extend along the rift axis.
Galápagos Islands
Each Galápagos shield volcano (Fernandina, Wolf, Sierra Negra) acts as a central volcano for its part of the archipelago, with circumferential and radial fissure systems. The 2018 Sierra Negra eruption demonstrated lateral magma migration similar to Icelandic fissure-fed eruptions.
Krafla Magma Testbed: Drilling Into a Central Volcano
The most ambitious volcano science project of the decade is happening at Krafla. The Krafla Magma Testbed (KMT) aims to drill directly into the known magma body beneath this central volcano's caldera. The concept was validated in 2009 when the Iceland Deep Drilling Project accidentally hit magma at 2.1 km — the first time anyone had drilled into molten rock.
The KMT project, backed by an international consortium, plans to create a permanent borehole into the margin of the magma chamber. If successful, it would enable direct measurement of magma properties — temperature, pressure, composition, gas content — that we've only estimated from the surface. It could revolutionize eruption forecasting for central volcanoes worldwide.
Central Volcano vs Other Volcano Types
"Central volcano" is a classification by function, not by form. Here's how it compares to the shape-based classifications:
The key insight: a central volcano can BE a stratovolcano (Hekla), a caldera (Krafla), a shield volcano (Theistareykir), or even a fissure system (Reykjanes). The term describes where the volcano sits in the plumbing hierarchy, not what it looks like. For the full breakdown of shape-based classifications, see our types of volcanoes guide.
Iceland's Volcanoes by Type
The 44 Icelandic volcanoes in our database break down into these physical forms:
Iceland is the best place on Earth to see central volcano systems up close. You can hike into Askja's caldera, drive the Ring Road past Hekla and Katla, visit the Reykjanes eruption sites, and walk between tectonic plates at Þingvellir.
Check our volcano tours page for guided volcano experiences in Iceland, or explore individual profiles like Krafla, Hekla, and Askja for specific tour availability.
Explore All 44 Iceland Volcanoes
Browse eruption timelines, alert levels, and tectonic data for every Icelandic volcano in our database
What is the difference between a central volcano and a stratovolcano?
A central volcano is defined by its role in a volcanic system — it's the main eruption focus connected to radiating fissure swarms. A stratovolcano is defined by its shape and composition — a steep cone built from alternating layers of lava and ash. The two categories overlap: many central volcanoes ARE stratovolcanoes (like Hekla and Askja), but others are calderas (Krafla, Grímsvötn) or fissure systems (Reykjanes). "Central volcano" describes a volcano's plumbing system; "stratovolcano" describes its physical form.
How many central volcanoes are in Iceland?
Iceland has approximately 30-33 volcanic systems, most with a clearly defined central volcano. Our database tracks 44 Icelandic volcanoes, which include central volcanoes, associated fissure vents, and secondary centers. The most active systems — Grímsvötn, Bárðarbunga, Krafla, Katla, and Hekla — have each produced 20 or more recorded eruptions.
Are central volcanoes dangerous?
Yes, particularly in Iceland where many central volcanoes sit beneath glaciers. When magma erupts under ice, it produces catastrophic glacial floods (jökulhlaups) that can discharge 100,000+ m³/s. Katla's jökulhlaups have historically destroyed farms, bridges, and coastal areas. Ash from Icelandic eruptions has disrupted European air traffic (Eyjafjallajökull, 2010) and caused continent-wide famine (Laki, 1783). The short warning time before eruptions — as little as 30 minutes for Hekla — makes them especially hazardous.
What is a fissure swarm and how does it relate to a central volcano?
A fissure swarm is a belt of fractures, faults, and volcanic fissures that radiates outward from a central volcano, typically aligned with the rift zone direction. Think of it as the underground plumbing: magma collects in the reservoir beneath the central volcano, then migrates laterally along the fissure swarm. The 2014 Holuhraun eruption demonstrated this perfectly — magma traveled 45 km northeast from Bárðarbunga's central caldera along its fissure swarm before erupting. Fissure swarms in Iceland range from 30 km (Vestmannaeyjar) to 200 km (Askja).