More than 100 eruptions have occurred in the past 20 million years with a broad range of eruptive styles. These volcanic processes have created a range of different volcanic landforms, including stratovolcanoes, shield volcanoes, lava domes and cinder cones, along with a few isolated examples of rarer volcanic forms such as tuyas. Large persistent volcanoes of the Northern Cordilleran Volcanic Province can remain dormant for hundreds or thousands of years between eruptions and therefore the greatest risk caused by volcanic activity is not always readily apparent. Volcanics older than 14 million years are mainly found in the northern portion of the volcanic province while volcanics ranging from nine to four million years old exist only in the middle of the volcanic province. At least three types of volcanic zones are present in the Northern Cordilleran Volcanic Province, including large persistent lava plateaus like those found at the Mount Edziza volcanic complex, polygenetic volcanoes such as Hoodoo Mountain and monogenetic volcanoes like the basaltic cinder cones found throughout the volcanic province. When Northern Cordilleran volcanoes do erupt, pyroclastic flows, lava flows and landslides can devastate areas away and mudflows of volcanic ash and debris can inundate valleys downstream. Falling ash from explosive eruptions can disrupt human activities hundreds of kilometres downwind, and drifting clouds of fine volcanic ash can cause severe damage to jet aircraft even hundreds of kilometres away. Volcanic deposits in the Northern Cordilleran Volcanic Province include lava flows, welded and unwelded pyroclastic deposits, hydroclastic deposits and other ice-contact volcanic deposits. The variety of different volcanic deposits is partly due to changes in eruption characteristics from mainly subaerial eruptions to broadly subglacial eruptions throughout the history of the Northern Cordilleran Volcanic Province.