Unlike many extreme weather events, such as hurricanes and severe snowstorms, geological phenomena such as earthquakes and volcanic eruptions are difficult to predict. In recent years, however, a number of tools have been developed to help scientists make correct judgments of the risk of these events. Modern methods of analysis that use real-time satellite data to continuously revise computer models have greatly improved scientists' understanding of geological activity. Additionally, scientists now use satellite data to measure slight changes in the landscape around volcanoes. Earth's crust can rise a millimeter at a time as it is pushed up by the pressure of the hot liquid rock, or magma, below. Though this cannot be perceived by visual observation on the ground, satellite cameras far above can determine whether a volcano's surface is rising, an indicator of a possible eruption.

Scientists are particularly concerned about caldera volcanoes. These are large formations created by ancient volcanoes that collapsed inward after erupting. Calderas sit above pools of magma than can erupt with little warning. Because the rich soil around such volcanoes tends to attract dense human settlement, eruptions can be especially deadly. Calderas are not cone-shaped like typical volcanoes, so the possibility of an eruption often simply does not occur to people. Moreover, their fairly flat shape poses an additional risk: unlike with cone-shaped volcanoes which generally erupt from the top of the cone, there is not way to tell from where on the surface of a caldera volcano the magma will escape, and it may even come out of multiple spots.

Campi Flegrei, west of the Italian city of Naples, is a caldera volcano that scientists are examining closely, as more than 700,000 people live within its "danger zone." In recent years, patterns of land rise there have been similar to those that occured before caldera eruptions in other parts of the world, indicating that the crust may be near the breaking point. The Italian government has raised alert levels but has hesitated to take further steps such as evacuating residents. Experts cannot say with certainty where Campi Flegrei will erupt soon, or likewise give any timeline for future eruption. Residents of the area, having experienced numerous false alarms, do not want to evacuate when an eruption is far from certain. Furthermore, property values have fallen when past warnings were issued, allowing real estate investors to buy land and bargain rates. This has made some residents suspicious of the motive behind the emergency warnings.