 However, it is known volcanoes in the U.S. states of Alaska, Washington, Oregon and California have been more active in historic times than those within Canada.Therefore, volcanoes in the United States are monitored with caution and attention by the United States Geological Survey.Growing awareness of volcanism, especially the threat from volcanoes in the United States, has led to a number of changes in the way Canadians are dealing with volcanic hazards.