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Global Volcanic Activity Monitor
The activity listed above is drawn from the Smithsonian Institution and US Geological Survey's Weekly Volcanic Activity Report, the authoritative summary of currently active and erupting volcanoes worldwide. It is compiled and vetted by staff at the Global Volcanism Program and updated every Wednesday. Importantly, it is not a list of every rumbling volcano on Earth — it is a curated weekly summary of the systems showing notable activity that meets the program's reporting criteria, typically averaging around sixteen volcanoes. Because the report is preliminary and reflects a specific week, the picture changes as new eruptions begin and others quieten. For the complete detail on any volcano listed, follow the link through to its full report.
Volcanoes are, in essence, openings in the Earth's crust through which molten rock, gas and ash escape from the hot interior below. The molten rock, called magma while underground and lava once it reaches the surface, rises because it is less dense than the solid rock around it, and because it carries dissolved gases that expand as it nears the surface and the pressure drops. That gas is the key to how violent an eruption becomes. In runny, low-gas magma the gas escapes gently, producing the relatively calm effusive eruptions that send rivers of lava flowing, as often seen in Hawaii and Iceland. In thick, sticky, gas-rich magma the gas cannot escape easily and builds enormous pressure until it is released explosively, blasting out ash, rock and gas in the dangerous explosive eruptions associated with volcanoes like Mount St. Helens or Vesuvius. The character of a volcano's eruptions is therefore largely set by the chemistry and gas content of its magma.
Predicting eruptions is difficult, but volcanoes usually give warning signs that monitoring scientists watch closely. Rising magma fractures rock as it forces its way upward, producing distinctive patterns of small earthquakes, so a swarm of seismic activity beneath a volcano is one of the most important warning signs. The ground itself deforms, swelling and tilting as magma accumulates beneath it, and this can now be measured with great precision from satellites and ground instruments. The gases released change too, with rising sulphur dioxide emissions often signalling that fresh magma is approaching the surface. Increases in heat, changes to hot springs and fumaroles, and other subtle shifts add to the picture. No single sign is a guarantee, which is why observatories combine many streams of data to assess whether a volcano is moving toward eruption. The result is expressed in alert levels that guide authorities and the public.
The scale most often used to describe the size of an explosive eruption is the Volcanic Explosivity Index, or VEI, which runs from zero to eight. It is based chiefly on the volume of material an eruption ejects, and like several natural-hazard scales it is logarithmic, meaning each step up represents roughly a tenfold increase in erupted volume. Gentle effusive eruptions sit at the bottom of the scale, while the largest eruptions in geological history, the caldera-forming super-eruptions, sit at the top and are fortunately extremely rare. Most eruptions reported in any given week are modest in these terms, even when they are locally significant and disruptive.
Volcanoes are not scattered randomly across the planet; they cluster along the boundaries between the great tectonic plates that make up the Earth's surface. By far the most active zone is the Pacific Ring of Fire, the horseshoe of intense volcanic and earthquake activity that traces the edges of the Pacific Ocean through the Andes, Central America, the western United States, Alaska, Japan, the Philippines, Indonesia and New Zealand. Here oceanic plates plunge beneath others at subduction zones, generating the wet, gas-rich magmas that feed explosive volcanoes. Other volcanoes rise where plates pull apart, as along the mid-ocean ridges and in Iceland, or over isolated "hot spots" in the mantle far from any plate boundary, of which Hawaii is the classic example. Understanding this geography explains why the same regions appear again and again in the weekly reports.
Volcanic eruptions affect people far beyond their immediate surroundings. Ash clouds are a serious hazard to aviation, capable of shutting down airspace across whole regions, as the 2010 Icelandic eruption famously demonstrated. Large eruptions can influence the climate, as sulphur injected high into the atmosphere reflects sunlight and can cool the planet slightly for a year or two. Locally, eruptions threaten lives and property through lava flows, ash fall, fast-moving flows of hot gas and debris, and mudflows, while also, over the long term, creating some of the most fertile soils and dramatic landscapes on Earth. Monitoring and reporting volcanic activity, as the weekly report above does, is part of how the world manages these risks.