Warning signs commonly precede an eruption. Scientists continually monitor volcanoes for signs of steam eruptions, rising magma, earthquakes, a change in ground formation and temperature and chemistry changes of the ground and springs.
The U.S. Geological Survey (USGS) Volcano Hazards Program uses an alert-notification system to indicate the level of potential danger for volcanoes. Color-coded triangular signs are posted along with hazard details.
Green with an "N" indicates inactivity and a normal alert level. Yellow with an "A" is an advisory alert which indicates some signs of unrest. Orange with the image of an eye dictates a watch alert with increased signs of potential eruption or a present eruption with limited danger. Red with an exclamation point is a warning level meaning a dangerous eruption is imminent.
These color codes are also used to alert the aviation industry of volcanic activity that may affect a pilot's visibility or flight time.
Unfortunately, warnings signs may be present for weeks, months or years without any activity, according to the USGS. Pinpointing the accuracy of an eruption is difficult.
