Ring of Fire
Not usually. Earthquakes associated with eruptions rarely exceed magnitude 5, and these moderate earthquakes are not big enough to destroy the kinds of buildings, houses, and roads that were demolished in the movie.
There is no evidence that a catastrophic eruption at Yellowstone is imminent, and such events are unlikely to occur in the next few centuries. Scientists have also found no indication of an imminent smaller eruption of lava.
Metropolitan Portland, Oregon, like Auckland, New Zealand, includes most of a Plio-Pleistocene volcanic field.
Ground deformation (swelling, subsidence, or cracking) is measured with a variety of techniques, including Electronic Distance Meters (EDM), the Global Positioning System (GPS), precise leveling surveys, strainmeters, and tiltmeters.
Lahars are commonly initiated by: 1) large landslides of water-saturated debris, 2) heavy rainfall eroding volcanic deposits, 3) sudden melting of snow and ice near a volcanic vent
Instruments to measure sulfur dioxide and carbon dioxide can be mounted in aircraft to determine the quantity of gas being emitted on a daily basis. Such instruments can also be used in a ground-based mode.
Lahars can be of any size. They may be as small as several centimeters wide and deep, flowing less than one meter per second.
The Hawaiian shield volcanoes are the largest mountains on Earth.