 | There are five tremors a day on average. Monitoring records from the US Geological Survey shows that all of the earthquakes have been relatively small, with the largest being a 3.5. Some geologists argue that when it comes to forecasting a volcano eruption, it's not the size of the seismic activity, but more the quantity. |  A spate of small earthquakes around a volcano usually signifies that magma and gasses beneath the surface are beginning to navigate their exit. |
 | Volcanism at Yellowstone is relatively recent, with calderas that were created during large eruptions that took place 2.1m, 1.3m, and 630,000 years ago. The calderas lie over a hotspot where light and hot magma (molten rock) from the mantle rises toward the surface. The hotspot appears to move, but it is much deeper than the terrain and remains stationary while the North American Plate moves over it.  |
