What would indicate pressure in a volcano that is is about to erupt?

Answer 1

There are several things to look for in a volcano that is showing major signs of unrest, however it should be noted that no amount of unrest is a sure fire indicator of an eruption. As fast as unrest starts in a volcano it can just as easily cease. Some of the major indicators however that one would look at are seismic information, deformation information, visual observation, gas discharge levels, as well as satellite thermal imaging. All of these different aspects can give greater understandings of what is going on inside a volcano since unfortunately we do not have the ability to actually look inside of them yet.

Here is a breakdown of each category:

1. Seismicity - Regular seismic readings at volcanoes that are monitored closely will reveal a normal trend of activity for earthquakes in that volcanoes region. Things that would be a sign of unrest or impending activity are if there is a sharp increase in number of seismic events, or if they turn to a harmonic tremor or long period event. These two types of events are often times very specifically alligned with the movement of magma within a volcanic system.
2. Deformation - As pressure builds often times stellites as well as GPS units (If they are installed for monitoring on the volcano) will begin to shift. The building pressure will slightly change the shape of the mountain, although it is very rare for these effects to be visible to the naked eye there are rare cases where it has happened.
3. Visual Observation - Often times visual observations of impending activity are the last ones to show before an eruptiont akes place. Sensors and monitoring equipment are much more likely to detect the subtle differences within a volcano than standard observation will, however visual observation can also detect things sometimes that sensors otherwise cannot.
4. Gas Discharge - Taking measurements of gas readings of a volcano are important. Measuring the volcanic gas emission levels will often times hint if magma is approaching the surface, as the emission levels will jump the closer the magma gets to the surface.
5. Satellite Thermal Imaging - Although not available everywhere in the world, it is often used on certain volcanoes to see if they can detect thermal anomolies on the surface. This has proven helpful in monitoring specific types of volcanoes for the appearance of a lava dome or plug at the summit. Thermal imaging is also very useful when the volcano cannot be monitored visually either due to remoteness, or due to severe weather.