Why does the study of volcanoes around the ring of fire start in alaska?

The volcanoes are studied around ring of fire because 70% of volcanoes in US are found in that region.

The cause of "ring of fire" is the subduction of tectonic plates in northern portion.  

Ring of fire is areas in Pacific Ocean where the volcanic eruption and earthquake frequently occur. The volcanic eruption and earthquake occur mainly due to the plate movements.

The plate that carry ocean is denser than that of continental plates and the collision of such plate creates earthquake and volcanic eruption.