Lava

Metropolitan Portland, Oregon, like Auckland, New Zealand, includes most of a Plio-Pleistocene volcanic field.
The Hawaiian shield volcanoes are the largest mountains on Earth.
Eruptions in the Cascades have occurred at an average rate of 1-2 per century during the last 4000 years, and future eruptions are certain.
The Alaska Peninsula and the Aleutian Islands have about 80 major volcanic centers that consist of one or more volcanoes. 
Alaskan volcanoes have produced one or two eruptions per year since 1900.
During the past 10,000 years, about 60 giant debris flows from Mount Rainier have filled river valleys to a
Mount Shasta (California) has erupted, on the average, at least once per 800 years during the last 10,000 years, and about once per 600 years during the last 4,500 years.
Eruptions of Mount Rainier usually produce much less volcanic ash than do eruptions at
Igneous rocks (from the Greek word for fire) form from when hot, molten rock (magma) crystallizes and solidifies.
Volcanoes that produced exceedingly voluminous pyroclastic eruptions and formed large calderas in the past 2 million years would include Yellowstone, Long Valley in eastern California, Toba in Indonesia, and Taupo in New Zealand.