"Volcanic activity" refers to the natural process occurring within a volcano where hot molten rock, ash, and gases are released from the Earth's surface, often resulting in eruptions or the formation of new geological features. Full definition
A drop of volcanic activity in the early 20th century may have had a warming effect. (skepticalscience.com)
I have heard it said that periods of severe volcanic activity in the geological past increased global temperatures by emitting substantial volumes of greenhouse gases. (newclimatemodel.com)
They're typically formed from by volcanic activity and can reach 1,000 metres high. (businessinsider.com)