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The Yellowstone Volcano Observatory (YVO) is aptly named – the consortium of 8 organizations collaborates to study and monitor the active geologic processes and hazards of the Yellowstone Plateau. However, that's not all we do.
The U.S. Geological Survey Volcano Hazards Program, one of the consortium members, is responsible for monitoring all potentially active volcanoes in the country. It just so happens that nearly a dozen of these volcanic centers are within the Yellowstone Volcano Observatory's area of responsibility – and only one of them is Yellowstone! So, what are these other YVO volcanoes?
The volcanoes of the American Southwest include over forty volcanic fields containing about 1400 single volcanoes (vents) that have erupted over the course of the past 2.5 million years. Most of these single volcanoes are monogenetic, meaning that they only produced one eruptive episode that may have lasted for days to years. Outside of Yellowstone, the USGS arm of YVO is responsible for monitoring volcanoes in Utah, Colorado, New Mexico, and Arizona.
So, why are there these volcanoes spread throughout the American Southwest? All over the world, volcanoes generally occur adjacent to subduction zones, at hot-spots, and where the Earth's crust is thin. Yellowstone is a hot-spot volcano situated above an upwelling plume of hot rock within the mantle. An age progression of volcanic centers to the southwest of Yellowstone marks the 16 million years of systematic movement of the North American tectonic plate over the stationary mantle plume. The southwestern U.S. volcanoes aren't adjacent to a subduction zone, nor are they situated above a mantle plume. Instead, they occur in areas where the continental crust is thin due to the tectonic processes of rifting and extension.
Rifting and extension cause the crust to fracture and thin, providing space for the mantle to rise upward. As mantle material moves to shallower depths, it depressurizes and melts and then ascends towards the surface. Upon reaching the surface, magma can erupt as lava flows and cinder cones—for example, Sunset Crater, Arizona; Dotsero, Colorado; and the Carrizozo lava flow, New Mexico. Magma may also stall beneath the surface, melt surrounding rock, and accumulate in large reservoirs that can erupt very violently, as was the case over one million years ago at Valles caldera, New Mexico.
The locations of volcanic fields and individual volcanoes are dictated by zones of weak crust and areas of pre-existing magma storage. Future eruptions will not necessarily occur from the location of a previous vent. This is the nature of monogenetic volcanic fields—eruption sites open for a single episode of activity, and subsequent eruptions can occur anywhere within the field. This is the inherent volcanic hazard in the southwestern USA—new eruptions can originate at unknown locations within broad areas of widely varying land use patterns.
Even though volcanic eruptions are comparatively rare in the American Southwest, the States of Arizona, Colorado, New Mexico, and Utah were host to numerous volcanic eruptions in the past 10,000 years and will experience volcanic activity in the future. This is why YVO is investing in monitoring for potential signs of volcanic unrest in these states. For more information on the volcanoes of the Four Corners region, check out the links below.