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Caldera Chronicles

Caldera Chronicles is a weekly article written by U.S. Geological Survey Yellowstone Volcano Observatory scientists and colleagues.

June 18, 2018 Article Link

YVO – not just Yellowstone! Meet the volcanoes of the American Southwest!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Wendy Stovall, Geologist with the U.S. Geological Survey and Deputy Scientist-in-Charge of the Yellowstone Volcano Observatory.

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 a 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?

Sunset Crater is the youngest cinder cone of the San Francisco Volcanic Field, which hosts 600 cinder cones and associated lava flows.  (Click image to view full size.)
Sunset Crater is the youngest cinder cone of the San Francisco Volcanic Field, which hosts 600 cinder cones and associated lava flows.
Eruptions between 1064 and 1067 AD produced three lava flows that covered 8 km2 (3 mi2) and a field of scoria and spatter that covers 2300 km2 (890 mi2). Archeological evidence shows that there were communities of people living in the area who were impacted by the eruption.

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.

The northern end of San Francisco Volcanic Field several cinder cones surround SP Crater (250 m, 820 ft high) – a monogenetic cinder cone and associated 7-km- (4.3-mi-) long lava flow. (Click image to view full size.)
The northern end of San Francisco Volcanic Field several cinder cones surround SP Crater (250 m, 820 ft high) – a monogenetic cinder cone and associated 7-km- (4.3-mi-) long lava flow.
The San Francisco Volcanic Field is an area of young volcanoes in Northern Arizona's Colorado Plateau that covers 4,700 square kilometers (1,800 square miles).

Utah
Colorado
Arizona
New Mexico