9.21: Reading- Signs of an Eruption
In 2005 USGS geologist Chris Newhall made a list of the six most important signs of an imminent volcanic eruption. They are as follows:
- Gas leaks — the release of gases (mostly H 2 O, CO 2 , and SO 2 ) from the magma into the atmosphere through cracks in the overlying rock
- Bit of a bulge — the deformation of part of the volcano, indicating that a magma chamber at depth is swelling or becoming more pressurized
- Getting shaky — many (hundreds to thousands) of small earthquakes, indicating that magma is on the move. The quakes may be the result of the magma forcing the surrounding rocks to crack, or a harmonic vibration that is evidence of magmatic fluids moving underground.
- Dropping fast — a sudden decrease in the rate of seismicity, which may indicate that magma has stalled, which could mean that something is about to give way
- Big bump — a pronounced bulge on the side of the volcano (like the one at Mt. St. Helens in 1980), which may indicate that magma has moved close to surface
- Blowing off steam — steam eruptions (a.k.a. phreatic eruptions ) that happen when magma near the surface heats groundwater to the boiling point. The water eventually explodes, sending fragments of the overlying rock far into the air.
Contributors and Attributions
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- 4.5 Monitoring Volcanoes and Predicting Eruptions. Authored by : Steven Earle. Provided by : BC Campus. Located at : https://opentextbc.ca/geology/chapter/4-5-monitoring-volcanoes-and-predicting-eruptions/ . Project : Physical Geology. License : CC BY: Attribution