The question of how many dormant volcanoes exist in the world is complex because providing a single, precise number is impossible. This difficulty stems from the lack of a universal scientific definition for “dormant” and the geographical challenge of classifying every volcanic feature on Earth. The total number is constantly being revised as new research refines our understanding of volcanic activity and history.
Defining Volcanic States
Volcanologists categorize volcanoes into three states: active, dormant, and extinct, though the boundaries are often fluid. An active volcano is defined as one that has erupted within the last 10,000 years, corresponding to the current geological epoch, the Holocene. This definition is used by organizations like the Smithsonian Institution’s Global Volcanism Program (GVP) to catalogue known features.
The most ambiguous classification is “dormant,” describing a volcano that is not currently erupting but is expected to erupt again. A dormant volcano has not erupted within the 10,000-year window but possesses an active magmatic system beneath it. A volcano considered “quiescent” is still active, while a truly dormant one has been silent for a much longer period.
An extinct volcano is one that scientists believe is highly unlikely to erupt ever again because its magma source has been depleted or the volcanic system has moved away from its heat source. However, this classification is not absolute, as some volcanoes previously thought to be extinct have shown signs of reawakening. The classification of a volcano is therefore an assessment of its probability of eruption rather than a fixed state.
The Estimated Global Count
The most widely cited figures for known volcanoes come from the GVP, which focuses on features active during the Holocene era. Based on their data, approximately 1,222 volcanoes have shown confirmed activity within the past 12,000 years. This figure represents potentially active volcanoes, including those currently erupting and those considered dormant in the short-term sense.
The total number of potentially active volcanoes worldwide is estimated to be about 1,350, excluding the continuous volcanic ridges on the ocean floor. Of this group, only about 500 have had eruptions confirmed in historical times. This leaves a large number of land-based volcanoes technically classified as dormant, having not erupted in millennia but still possessing a magma system capable of future activity.
A much larger and more uncertain number exists beyond the active and potentially active terrestrial volcanoes. Some estimates suggest tens of thousands of individual volcanic features globally when including extinct and unclassified structures. The volume of volcanic activity on Earth means the count of truly dormant features, with potential for future eruption, is far greater than the number of currently recognized active volcanoes.
Why Pinning Down the Number is Difficult
One of the greatest challenges in counting dormant volcanoes is the overwhelming presence of submarine volcanoes. The majority of Earth’s volcanic activity occurs underwater along the mid-ocean ridges and other divergent plate boundaries. Most of these deep-sea features remain unmapped and unclassified, making it impossible to include them in any definitive global count.
On land, the difficulty lies in distinguishing between a long-dormant volcano and one that is truly extinct. For very old volcanic structures, the cone and surrounding features may be heavily eroded, obscuring the evidence of past activity. Without extensive geological dating, determining if a volcano’s magma plumbing is permanently sealed or simply quiet can be nearly impossible.
The lack of a uniform definition also contributes to the problem, as different scientific bodies may apply different time cutoffs to classify a feature as dormant or extinct. A volcano considered extinct by one group because it is outside the 10,000-year Holocene window might be deemed dormant by another if geophysical evidence suggests a deep magma reservoir. This subjective classification ensures the total number remains an estimate rather than a fixed quantity.
Monitoring Dormant Volcanoes
Despite the uncertainty in the total number, scientists dedicate significant resources to monitoring known dormant volcanoes that pose a risk to human populations. Monitoring is carried out continuously to detect subtle changes that may signal the reawakening of the system. This work focuses on recognizing precursory signals that indicate magma is moving closer to the surface.
One primary technique is seismology, which involves using networks of seismometers to detect small earthquakes and ground vibrations caused by magma fracturing the surrounding rock. Changes in ground shape, known as deformation, are also tracked using Global Positioning System (GPS) stations and satellite radar technology called Interferometric Synthetic Aperture Radar (InSAR). A measurable bulge or tilt on the volcano’s flank can indicate rising pressure from below.
Geochemical analysis of gas emissions is another important tool, as an increase in gases like sulfur dioxide or carbon dioxide can precede an eruption. By combining data from these different methods, scientists can assess the internal state and issue timely warnings. The ongoing monitoring effort shifts the focus from knowing the exact number to mitigating the risk from the volcanoes most likely to reawaken.