A caldera is what's left when a volcano's magma chamber empties and the ground collapses. They range from 1 km to over 100 km across, and they're the signature feature of the most powerful eruptions in Earth's history. Yellowstone, Toba, Krakatau — all calderas. We track 108 of them in our database of 1,740 volcanoes worldwide.
In Our Database
108
VEI 6+ Eruptions
20
Recorded Eruptions
779
Active Since 2000
22
What Is a Caldera?
A caldera is a large depression — typically circular or oval — that forms when the roof of a volcanic magma chamber collapses inward. The word comes from the Spanish caldera, meaning "cauldron," which is exactly what they look like from above: massive bowl-shaped depressions, often filled with lakes, that mark the scars of past eruptions.
Don't confuse them with craters. A crater is a relatively small vent (usually under 1 km across) blasted out by an eruption. A caldera is a collapse feature — the ground sinks rather than gets blown outward. That's why calderas can be enormous. Yellowstone's caldera is 72 km across. Toba's is 100 km long. You can drive through Yellowstone's caldera without knowing you're inside one — early geological surveys missed it entirely because it's too big to see from the ground.
Our database tracks 108 caldera volcanoes, making up about 6% of all volcanoes. They're disproportionately important, though. Calderas are responsible for every VEI 7+ eruption in the geological record — the events that bury entire continents in ash and alter global climate for years.
By VolcanoDB Research Team. Data: Smithsonian Global Volcanism Program, Kobe University (2026), University of Geneva (2026).
How Do Calderas Form?
The basic mechanism is straightforward: a magma chamber empties (usually through a massive eruption), and the rock above it can no longer support its own weight. The surface collapses downward along ring-shaped faults, creating a depression that can be hundreds of meters deep.
But the details vary enormously depending on the magma chemistry, chamber size, and eruption style. Volcanologists recognize three main types of caldera formation:
Three Types of Caldera Formation
1. Explosive Collapse (Krakatoan Type)
The most dramatic type. A massive explosive eruption rapidly empties the magma chamber, and the roof collapses in hours to days. Krakatau's 1883 eruption collapsed two-thirds of the island into the sea. The resulting caldera was 7 km across and 250m deep. This type typically involves silicic magma (andesite to rhyolite) and produces enormous pyroclastic flows.
2. Resurgent Caldera (Valles Type)
After initial collapse, fresh magma pushes the caldera floor back up, creating a resurgent dome. Yellowstone's caldera floor has risen over 70 cm since 2004 in some areas. Toba's Samosir Island is a resurgent block that's risen 450m above the lake surface. These calderas are the largest on Earth because they form above massive, long-lived magma systems.
3. Summit Collapse (Hawaiian Type)
On shield volcanoes, calderas form gradually as magma drains from the summit reservoir during flank eruptions. Kilauea's summit caldera dropped 500m during the 2018 eruption when magma shifted to the Lower East Rift Zone. These calderas are typically smaller (under 5 km) and can form repeatedly over a volcano's lifetime.
The tectonic setting matters too. 79 of our 108 calderas sit above subduction zones, where oceanic plates dive beneath continental crust, generating the silica-rich magma that drives explosive eruptions. Only 8 are in rift zones — a sharp contrast with shield volcanoes, which favor hotspots and rifts.
Caldera vs Crater — What's the Difference?
People mix these up constantly — partly because "Crater Lake" is actually a caldera. Here's the key distinction:
The confusion is understandable — both are depressions at the top of volcanoes, and older terminology used the words interchangeably. But the formation mechanisms are fundamentally different, and so are the scales. A crater is what a firecracker does to a sandcastle. A caldera is what happens when you pull the tablecloth out from under the dishes.
Calderas by the Numbers
Stats pulled directly from our database of 1,740 volcanoes:
108
caldera volcanoes (6% of all)
779
recorded eruptions
20
VEI 6+ eruptions (3 were VEI 7+)
1,418m
average elevation
Countries With the Most Caldera Volcanoes
Country
Count
% of Total
Japan
23
21%
Indonesia
14
13%
Russia
11
10%
Papua New Guinea
7
6%
United States
7
6%
New Zealand
6
6%
Ethiopia
5
5%
Ecuador
4
4%
Chile
4
4%
Italy
3
3%
Japan dominates with 23 calderas — a consequence of its position above four converging tectonic plates. The Japanese island arc produces silicic magma that drives explosive eruptions and caldera formation. Indonesia's 14 calderas include some of the most famous in history (Krakatau, Toba, Tambora). The US count includes Yellowstone, Long Valley, and Crater Lake — all in the western states where the Pacific and North American plates interact.
8 Famous Calderas
Each links to its full VolcanoDB profile with eruption timeline, monitoring data, and nearby tours.
The most studied caldera on the planet. Three supervolcanic eruptions created nested calderas spanning 72 x 55 km — you can drive across it without realizing you're inside one. The last eruption (640,000 years ago) ejected 1,000 km³ of material, blanketing most of North America in ash. Today it powers Old Faithful and 10,000+ hydrothermal features.
Its 1883 eruption killed over 36,000 people, generated 30m+ tsunamis, and was heard 4,800 km away in Australia. The eruption collapsed 2/3 of the island into the caldera. Then Anak Krakatau ("Child of Krakatau") emerged from the caldera floor in 1927, growing steadily until its own partial collapse triggered a deadly tsunami in December 2018.
The largest eruption of the last 2 million years. Roughly 74,000 years ago, Toba ejected an estimated 2,800 km³ of material — nearly 3x Yellowstone's biggest. The resulting caldera is 100 x 35 km and now contains Lake Toba, the largest volcanic lake on Earth. Some researchers argue the eruption triggered a genetic bottleneck in early humans, though this remains debated.
Half a million people live inside this caldera. Located in metropolitan Naples, Campi Flegrei has been in a slow-motion crisis since 2005 — the ground has risen over 1 meter from magma pressure. Its last eruption was in 1538, but a March 2026 study revealed a massive capped geothermal reservoir beneath Pozzuoli that's slowly building pressure. The question isn't if it erupts again, but when.
Site of the most destructive eruption of the past 10,000 years. The Akahoya eruption (~5,300 BCE) produced pyroclastic flows that crossed 100 km of open ocean, devastating prehistoric Jomon settlements across southern Japan. A March 2026 Kobe University study confirmed the caldera is recharging — new magma is being injected at 8.2 km³ per millennium, refilling the same system that fueled the original eruption.
The deepest lake in the United States at 594 meters. Formed when Mount Mazama collapsed during a VEI 7 eruption roughly 7,700 years ago, ejecting 50 km³ of magma. The lake has no inlet or outlet — it's filled entirely by rain and snowmelt, giving it some of the clearest water on Earth. Wizard Island, a cinder cone, later grew from the caldera floor.
The Minoan eruption around 1600 BCE destroyed the Bronze Age settlement of Akrotiri and may have contributed to the collapse of Minoan civilization. The eruption hollowed out the island, creating the crescent-shaped caldera that's now one of the most photographed destinations on Earth. The volcanic island of Nea Kameni in the center is still active — its last eruption was in 1950.
One of the largest calderas in the world at 25 x 18 km. Aso has erupted over 20 times in our records, and Nakadake crater remains one of Japan's most active vents. Roughly 50,000 people live and farm inside the caldera — it's so large it contains towns, rice paddies, and railway stations. Its four major caldera-forming eruptions spread ash across all of Japan.
Active Calderas in 2026
Calderas aren't just geological relics. Several are making headlines right now:
Kikai Caldera — Recharging With Fresh Magma
A March 2026 study from Kobe University, published in Communications Earth & Environment, confirmed that Kikai's magma reservoir is being refilled with new magma — not remnants from 7,300 years ago. Using seismic refraction surveys with ocean-bottom seismometers, researchers mapped a low-velocity anomaly at 2.5-6 km depth beneath the caldera floor. The recharge rate: approximately 8.2 km³ per millennium. For context, the original Akahoya eruption expelled roughly 150 km³ — meaning the system would need ~18,000 years to rebuild to that level.
Tuscany — 6,000 km³ Magma Reservoir Discovered
In April 2026, researchers from the University of Geneva and Italy's INGV used ambient noise tomography to reveal a previously unknown magma reservoir beneath Tuscany's Larderello geothermal field. At approximately 6,000 km³, the reservoir is comparable in volume to Yellowstone's magma system. The magma sits 8-15 km deep and currently poses no eruption threat — no historical eruption is associated with this system — but its discovery shows how much we still don't know about what lies beneath our feet.
Campi Flegrei — Ground Still Rising
The bradyseism crisis at Campi Flegrei continues into 2026. Ground uplift has exceeded 1 meter since 2005, driven by a capped geothermal reservoir beneath Pozzuoli that accumulates pressure as water and steam build up under a fibrous caprock layer. Over 500,000 people live inside the caldera. Italy's civil protection agency maintains a Yellow alert level, and scientists are studying whether controlled fluid withdrawal could relieve pressure.
Track all currently active volcanoes — including calderas — on our active volcanoes page.
Calderas and Supervolcanoes
Every supervolcano is defined by its caldera. A supervolcanic eruption (VEI 8) ejects over 1,000 km³ of material, and the only way to move that much magma is for the entire roof to collapse. Yellowstone has done this three times. Toba did it once, creating the largest caldera on any continent.
But not all calderas are supervolcanoes. Most calderas form from VEI 6-7 eruptions — devastating regionally but not globally. The 3 VEI 7+ eruptions in our caldera data represent the rare events that shaped continents. The 20 VEI 6+ events are more common but still separated by centuries.
Caldera vs Stratovolcano vs Shield Volcano
How calderas compare to other volcano types, with numbers from our database:
The key distinction: calderas aren't really a "type" of volcano in the same way stratovolcanoes and shield volcanoes are. They're a feature that can form on any large volcano when its magma chamber collapses. Stratovolcanoes develop calderas (Crater Lake started as a stratovolcano called Mount Mazama). Shield volcanoes have summit calderas (Kilauea, Mauna Loa). The Smithsonian GVP classifies a volcano as a "Caldera" when the collapse feature is the dominant landform — when the original cone is gone and the basin is what's left.
For the complete breakdown of all volcano types, see our types of volcanoes guide.
Caldera Hazards
Caldera-forming eruptions are the most dangerous volcanic events on Earth. Here's what makes them so destructive:
Pyroclastic Flows
Caldera collapses generate the largest pyroclastic flows on record. Kikai's Akahoya eruption sent flows across 100 km of ocean. Toba's deposits are found 3,000 km away. These incandescent clouds of gas and rock travel at 100-700 km/h — nothing survives in their path.
Tsunamis
When a caldera collapses into the sea — or when pyroclastic flows enter the ocean — the displacement generates massive tsunamis. Krakatau's 1883 collapse produced waves over 30m high that killed 36,000 people along the coasts of Java and Sumatra. Anak Krakatau's 2018 flank collapse sent a 5m tsunami without warning.
Climate Impact
VEI 7+ caldera eruptions inject sulfur aerosols into the stratosphere, reflecting sunlight and cooling global temperatures. Tambora's 1815 eruption caused the "Year Without a Summer" in 1816 — crop failures across Europe and North America. Toba may have caused a 6-10 year volcanic winter 74,000 years ago.
Explore All 108 Caldera Volcanoes
Browse eruption timelines, alert levels, and elevation data for every caldera in our database
The most recently active caldera volcanoes we track. Click any volcano to see its full profile with eruption timeline, elevation data, and nearby tours.
A caldera is a large volcanic depression — typically 1 to 100 km wide — formed when the ground collapses into an emptied or partially emptied magma chamber. Unlike craters, which are carved out by explosions, calderas are created by collapse. They're the signature landform of the most powerful eruptions on Earth (VEI 7-8). Our database tracks 108 caldera volcanoes worldwide.
What is the difference between a caldera and a crater?
Size and formation mechanism. A crater is typically less than 1 km across and forms by explosive excavation — the eruption blasts out a hole. A caldera is 1 to 100+ km across and forms by gravitational collapse — the roof of a magma chamber caves in after the magma erupts or drains away. Craters are usually at the top of a volcano; calderas can swallow the entire volcano. Crater Lake in Oregon is actually a caldera, despite its name.
Is Yellowstone a caldera?
Yes. Yellowstone is actually three nested calderas from three separate supervolcanic eruptions: 2.1 million years ago, 1.3 million years ago, and 640,000 years ago. The most recent caldera is 72 x 55 km — large enough that early surveyors didn't recognize it as a volcanic feature. Today it's monitored continuously by the Yellowstone Volcano Observatory, and the magma chamber is estimated to contain about 10% melt.
What is the largest caldera on Earth?
The Apolaki Caldera in the Philippine Rise (Benham Rise), discovered in 2019, measures approximately 150 km in diameter, making it the largest known caldera on Earth. Among calderas on land, Toba in Sumatra is the largest at 100 x 35 km. It was created roughly 74,000 years ago by the biggest eruption of the past 2 million years. Yellowstone's caldera is the next largest at 72 x 55 km.
Can a caldera erupt again?
Yes — and many do. Krakatau's caldera has spawned Anak Krakatau, which erupted as recently as 2021. Kikai Caldera in Japan last erupted in 2025 and scientists confirmed in March 2026 that its magma system is recharging at 8.2 km³ per millennium. 22 caldera volcanoes in our database have erupted since 2000. However, caldera-forming eruptions (VEI 7+) are extremely rare — the last one was Tambora in 1815.