Volcanologists obviously want to keep people safe from volcanic eruptions. However, they are typically very hesitant to evacuate people too early even though they know there may still be a chance the volcano could erupt violently. Why don't volcanologists "play it safe" and just evacuate everybody at the first signs of activity?
An increase in the frequency and intensity of felt earthquakes. Noticeable steaming or fumarolic activity and new or enlarged areas of hot ground. Subtle swelling of the ground surface.
Because Volcanoligist don't always have the funds to evacuate constantly, also much of there funds go to learning about the signs of volcanoes and therefore planes and other supplies are low.
