1.The most important volcano in North America is Mount Saint Helens, located in Skamania County, Washington, in the Pacific Northwest region of the US, at 96 miles (154 km) south of the city of Seattle and 53 miles (85 km) northeast of Portland, Oregon. This active volcano is located in the Cascade Range and is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire that includes over 160 active volcanoes. St Helens is the fourth volcanic peak in the Cascade Range.