What are the three main ways that scientists predict volcananic eruptions?

when the volcano is showing unusual signs. an increase in gas emissions,an increase in seismic activity,and also the volcano will bulge at the sides,equipment is used for this. vulcanologists should visit the volcano on a daily scale to see if there has been any more change. also on a seismograph,there are two types of wave pattern which can detect that magma is rising. (short term) which are the lines closest together and a sharp,this indicates that the magma is rising in powerful sharp portions and breaks the rock on its way up the conduit. these waves are the most significant,usually this type of wave would happen just before the volcano erupts,but it is not guaranteed. the (long term) waves, which are the waves that are more spread out and are longer aren't as significant because this means that the magma is rising slowly while breaking rocks rarther than quickly and breaking rocks. (i hope this information was useful, i am a major in geography and vulcanology)