Volcanoes erupt when molten rock called magma rises to the surface. Magma is formed when the earth’s mantle melts. Another way an eruption happens is when water underneath the surface interacts with hot magma and creates steam, this can build up enough pressure to cause an explosion.

In the park, the most famous volcano is the Yellowstone Caldera, or supervolcano. Additionally, but less well-known, are numerous rhyolite domes and flows, and basaltic shields and cinder cones. This volcano is the source of the basalt at Sheepeater Cliff.

When lava has low viscosity, it can flow very easily over long distances. But most importantly, highly viscous lava is associated with explosive eruptions and dangerous pyroclastic flows. An example of a low viscosity (fast flowing) lava is basaltic lava.

Current Eruptions

The volcano erupted on the afternoon of January 12, 2020, 43 years after its previous eruption in 1977. According to PHIVOLCS director Dr. Furthermore, Solidum confirmed that there was a magmatic intrusion that was driving the volcano’s unrest.

How can we tell when a volcano will erupt?

• An increase in the frequency and intensity of felt earthquakes.
• Noticeable steaming or fumarolic activity and new or enlarged areas of hot ground.
• Subtle swelling of the ground surface.
• Small changes in heat flow.
• Changes in the composition or relative abundances of fumarolic gases.

These destructive volcanoes tend to shake or undergo tremor for hours or minutes before an eruption. But even before tremors, they also can undergo regular, repeated, slow oscillations in ground swelling and collapse, as well as gas release.

Between eruptions, visible changes of importance to the scientists would include marked increase or decrease of steaming from known vents; emergence of new steaming areas; development of new ground cracks or widening of old ones; unusual or inexplicable withering of plant life; changes in the color of mineral deposits …

Active volcanoes have a recent history of eruptions; they are likely to erupt again. Dormant volcanoes have not erupted for a very long time but may erupt at a future time. Extinct volcanoes are not expected to erupt in the future. Inside an active volcano is a chamber in which molten rock, called magma, collects.

In theory, there is no limit on the number of volcanoes that could erupt at once other than the number of active volcanoes themselves: while it is thus theoretically thinkable, that all 600 volcanoes (on land) known to have had eruptions during recorded history erupt at once, this is so unlikely that it can be excluded …