Volcanic activity, explained
Magma Watch puts 70 closely watched volcanoes on one map, coloured by their current alert level and sized by their explosivity record, so you can see at a glance which ones are restless. It is a curated selection, not a complete list of the world’s volcanoes.
Where does the volcanic activity data come from?
The map and list are built from a snapshot of 70 well-known volcanoes embedded in the page and based on the Smithsonian Global Volcanism Program (GVP): position, type, VEI, magma type, last eruption year, population nearby, and a default alert level and aviation colour code. Every 5 minutes the page asks two live sources for newer alert levels: the USGS Volcano Hazards Program volcanic activity notices, which cover US volcanoes such as those in Alaska, Hawaii and the Cascades, and GeoNet’s volcanic alert levels for New Zealand. Volcanoes elsewhere keep the levels from the snapshot. The status line shows which sources answered; if neither did, it says “GVP static”. The GVP itself is not queried live, but clicking a triangle opens that volcano’s page on the GVP website.
What is the Volcanic Explosivity Index (VEI)?
The VEI is a logarithmic scale from 0 to 8 developed in 1982 by Chris Newhall and Steve Self to compare volcanic eruptions. From VEI 2 upward, each step represents roughly a tenfold increase in erupted volume. Key reference points: VEI 0–1 (effusive, continuous like Kīlauea) → VEI 2 (Stromboli-type, common) → VEI 4 (Eyjafjallajökull 2010, disrupted EU airspace for 6 days) → VEI 5 (Mount St. Helens 1980) → VEI 6 (Pinatubo 1991, lowered global temps by 0.5°C) → VEI 7 (Tambora 1815, an estimated 71,000 deaths, Year Without a Summer) → VEI 8 (Toba about 74,000 years ago; whether it caused a human population bottleneck is still debated). Most current eruptions are VEI 1–3.
What do the alert levels mean?
The USGS uses a dual notification system. The ground-based alert level runs from Normal (background, non-eruptive) → Advisory (elevated unrest above background) → Watch (heightened unrest, eruption may occur) → Warning (eruption is occurring or imminent). Simultaneously, an aviation color code runs Green → Yellow → Orange → Red. Red means an eruption is producing significant ash cloud that poses a hazard to aviation. The distinction matters: a volcano can be at Warning level but not Red if the eruption is effusive (lava flows only) without producing significant ash. Volcanic ash is catastrophic for jet engines, which is why aviation authorities monitor this separately.
On this map a volcano at Warning or aviation Red is drawn as erupting (red-orange with a pulsing ring), and New Zealand’s GeoNet levels 0–5 are translated onto the same four steps. The On Alert tile counts volcanoes at Watch or Warning; Aviation Red / Orange counts the elevated aviation colour codes.
How many volcanoes are actively erupting right now?
There is no single number: it depends on how “eruption” is defined. The Smithsonian GVP keeps a list of current eruptions and publishes a weekly volcanic activity report with the USGS. Some volcanoes, like Stromboli (Italy), Yasur (Vanuatu) and Erta Ale (Ethiopia), have been active almost continuously for decades or longer, while others such as Merapi (Indonesia), Etna (Italy) and Popocatépetl (Mexico) have frequent episodes. On this page the Currently Erupting tile counts volcanoes in its 70-volcano dataset that are at Warning or aviation Red and either have a live USGS notice or erupted this year (or last year, during January to March). It is a count for this dataset, not a worldwide total.
Why do triangles appear on the map instead of circles?
The triangle (▲) is the usual map symbol for a volcano. On this map a triangle’s size follows the VEI stored for that volcano in the dataset, so bigger triangles mean a more explosive record, and its colour follows the current alert level. A pulsing ring marks every volcano at Warning or aviation Red. Hover a triangle for its details and click it to open its Smithsonian GVP page. Compare with the companion app Tectonic Pulse, which uses circles scaled by earthquake magnitude.
Which regions have the most active volcanoes?
Volcanic activity is concentrated along the same plate boundaries as earthquakes. The Pacific Ring of Fire hosts most of the world’s active volcanoes, and Indonesia has more historically active volcanoes than any other country. Alaska’s Aleutian arc, Kamchatka, Japan, the Philippines and the Central American arc (Guatemala to Costa Rica) are consistently active. In Europe, Italy is the most closely watched: Etna and Stromboli in Sicily, Vesuvius and Campi Flegrei around Naples. Iceland sits where the Mid-Atlantic Ridge crosses a hotspot, and the East African Rift (Nyiragongo, Erta Ale, Ol Doinyo Lengai) is another major zone. Hawaii is a hotspot far from any plate boundary: the Pacific Plate moves over a mantle plume, building the island chain. The region buttons on this page use the region stored for each volcano; Antarctica’s Erebus is listed under Asia.
What is a magma type and why does it matter?
Magma composition largely decides how an eruption behaves. Basaltic magma (low silica, about 45–52%) is runny, so gas escapes easily and eruptions are usually effusive, with lava flows and fountains, like Kīlauea. Andesitic (about 52–63% silica) and dacitic magma (about 63–68%) are more viscous and typical of subduction-zone stratovolcanoes; Mount St. Helens erupts dacite. Rhyolitic magma (above about 68% silica) is the most viscous and traps gas, which can drive violently explosive eruptions such as Toba. Composition also affects whether a volcano produces lava flows, pyroclastic flows (fast, hot avalanches of gas and rock), lahars (volcanic mudflows) or large ash plumes. The map tooltip shows the magma type stored for each volcano. Calderas typically form when a magma chamber empties in a large eruption and the ground above collapses.
Which third-party services does the page call?
Your browser requests public data from the USGS Volcano Hazards Program API and the GeoNet API (New Zealand); both only return public alert information, and the page sends no personal data with these requests. The photos in the slideshow are served from this site. No account or install is needed.
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