Andesitic volcanism is most common along subduction zones where an oceanic and a continental plate are colliding. Some continental material gets dragged down with the subducted oceanic plate. These less dense minerals melt and rise to the surface as andesitic lava. The Cascade Range of the Pacific Northwest is a fine example of an andesitic volcanic mountain range. Mt. St. Helens erupted in 1980, most recent eruption in lower 48 states.
Andesitic lava holds lots of gas, so eruptions are very explosive.
Much of this cools and congeals in the atmosphere and rains down as volcanic ash, or tephra . Sunset Crater in Arizona is a nice example of a cinder cone. Like Mt. Fujiyama or Mt. Kilomanjaro. 2. since andesitic lava is viscous, material does not flow very far from the vent. Forms a steep sided, cone-shaped mountain.