What are signs that indicate that a volcano will erupt?

Question

What are signs that indicate that a volcano will erupt?

Answer 1

Earthquakes

Expansion of the mound

Answer 2

Small EQs and tremors (maybe big ones)

Changes in the shape of the volcano

Release of steam and other gases from cracks and the mouth of the volcano

Increased amounts of heat emitting from the volcano

Answer 3

Sometimes neither of the  two answers above will answer to your question. Mount St. Helens in Washington State erupted with almost no warning except of a pressure raise inside its huge magma chamber far below underneath the volcano.

And since the area of Mt. St Helens is located inside the "Ring Of Fire" around the Pacific Ocean, small and even large earthquakes occur there on a regular base, without indicating that a major volcano is about to erupt.

But commonly it is true, that earthquakes and changes in the shape of a vocano indicates a near-future eruption.

Answer 4

I think that I have to agree with Lady Geologist on this one. Mt. St. Helen's had all of those symptoms. The USGS just didn't make the connections. The Geologists studying the mountain at the time, didn't understand what they do today. In the last almost 30 years, a lot has been learned about how volcanoes behave. However we still can not predict the moment of eruption only know that is possible and imminent.  Consider the surprise that Kilauea recently gave when the vent in the crater opened up. That was pretty much un expected. In fact it had been almost a hundred years since the last eruption in the crater.