Volcano Watch: Eruption? Intrusion? What’s the difference?

  • USGS graphic Time-series plots of earthquake hourly counts in Kilauea summit region (top) and tilt at the Sandhill station located southwest of Kilauea’s caldera (bottom). These plots show the increase in activity associated with the recent south caldera intrusion at the summit of Kilauea. The increase in the earthquake counts correlates to the influx of magma pressurizing the volcano. Increasing tilt indicates accumulation of magma. These USGS time-series plots show data from Aug. 22-31.

We know that when a volcano erupts, molten red rock makes it to the surface, while during an intrusion it doesn’t. The difference between the two processes, if we depend on seismicity (earth shaking) or deformation (changes in ground surface) instrumentation, is not obvious. The events during the start of either are identical. But we can’t be certain that an intrusion will lead to an eruption.