Volcano Observatory Scenario
WHEN WOULD YOU CALL RED ALERT?
Staff at volcano observatories are constantly monitoring activity / changes in activity at volcanoes. They have to process a lot of data and decide whether what their instruments are recording represents "baseline" or "elevated" activity.
Deviations from the "baseline" indicate changes in the sub-surface system beneath the volcano - referred to as "unrest", sometimes this is because an eruption is imminent. Observatory scientists have to think carefully about when to communicate changes ocurring at the volcano to the public and governments.
When an eruption is already happening, scientists have to continue to monitor the volcano to look for any signs of a change in eruption style, which happens often. An eruption may start off effusively (erupting lava flows or domes) and then transition to explosive (ash clouds and pyroclastic density currents). A change like this means a drastic change in the hazard posed to communities nearby. The opposite can also happen, and knowing when an eruption of any type might stop is also important as people want to know when it is safe to return to their normal lives.
An effusive eruption could continue for weeks or months before turning explosive...or it may just stop without an explosion, this causes a lot of uncertainty amongst decision-makers and the public about what is the safest course of action.
Take a look at the scenario below - based on real data from an eruption - and think about when you would communicate "YELLOW ALERT - unrest" vs "RED ALERT - dangerous eruption imminent" to the public. If you call a RED ALERT authorities will evacuate, but if this happens > 10 days before a dangerous eruption, people are likely to drift back...
The timeline showed what happed during the 2020-21 eruption of La Soufrière St Vincent.
Observations made by scientists during and after the eruption, via instruments, satelites and on-the-ground studies were used to reconstruct the explosive sequence and link it to the material that was left on the ground afterwards. Doing this is vital as it helps us to figure out what caused the eruption styles we saw.