Sunset crater, San Francisco volcanic field

November 26, 2018

Boulder, Colo., USA: The San Francisco Volcanic Field is a 4,700 square kilometers (1,800 square miles) area in the southern boundary of the Colorado Plateau. The field contains more than 600 scoria cones active in the past six million years. The Sunset Crater is the youngest of these scoria cones, and was active about 1000 years ago.

This eruption heavily affected prehistoric inhabitants over a wide area, forcing migration and dramatically altering settlement, subsistence, economic, and ritual. However, despite these and several additional archaeological studies, only a few have focused on the physical characteristics of the eruption.

The eruption developed in three distinct phases: an initial fissure phase, followed by a highly explosive phase, and a final low explosive waning phase. The first phase was characterized by the opening of a 10-km-long fissure, which produced spatter mounds (Gyp Crater), a lava flow effused from the southwest end of the fissure (Vent 512 flow), and a 0.01 cubic kilometer dense rock equivalent (DRE) of pyroclastic fall deposit (Unit 1).

During the second highly explosive phase, the activity migrated to the northwest to evolve into a single-vent eruption, which formed the main scoria cone. The central vent activity was initially characterized by variable eruptive styles, which started the process of cone building, deposited a second pyroclastic layer (Unit 2; 0.01 square kilometers DRE), and started the effusion of the two main lava flows (Bonito and Kana'a).

Following the initiation of effusive activity, the eruption increased in explosivity to produce three sub-Plinian units from the central vent (Units 3, 4 and 5), which emitted more than 0.22 cubic kilometers DRE of basalt, with associated eruption columns >20 km high. A final waning phase produced several units, commonly discontinuous and reworked (< 0.01 cubic kilometer DRE cumulative volume).

Sunset Crater volcano represents an interesting case of monogenetic volcanism in that its activity was characterized by highly explosive eruptive phases up to sub-Plinian in scale and intermittent episodes of lava effusion that heavily affected pre-historic communities in the area. The comparatively large volume of pyroclasts, the high eruptive columns and high mass eruption rates make Sunset Crater the most explosive monogenetic eruption studied to date.

Explosive basaltic volcanism like this should be considered when assessing volcanic hazards in continental settings, such as in the western United States.

Subplinian monogenetic basaltic eruption of Sunset Crater, Arizona, USA

GSA Bulletin,, Authors: Fabrizio Alfano, Michael H. Ort, Laura Pioli, Stephen Self, Sarah L. Hanson, Kurt Roggensack, Chelsea M. Allison, Robert Amos, Amanda B. Clarke Contact: Fabrizio Alfano,

GSA BULLETIN articles published ahead of print are online at Representatives of the media may obtain complimentary copies of articles by contacting Kea Giles. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to The Geological Society of America Bulletin in articles published. Non-media requests for articles may be directed to GSA Sales and Service,

Geological Society of America

Related Eruption Articles from Brightsurf:

Large volcanic eruption caused the largest mass extinction
Researchers in Japan, the US and China say they have found more concrete evidence of the volcanic cause of the largest mass extinction of life.

Researchers model source of eruption on Jupiter's moon Europa
A new model shows how brine on Jupiter's moon Europa can migrate within the icy shell to form pockets of salty water that erupt to the surface when freezing.

Using a volcano's eruption 'memory' to forecast dangerous follow-on explosions
Stromboli, the 'lighthouse of the Mediterranean', is known for its low-energy but persistent explosive eruptions, behaviour that is known scientifically as Strombolian activity.

Continuous infrared winds discovered during the eruption of a stellar mass black hole
A team of researchers from the Instituto de Astrofísica de Canarias (IAC) has detected for the first time the constant infrared emission from winds produced during the eruption of a black hole in an X-ray binary.

New studies reveal inside of central energy release region in solar eruption
Prof. LIN Jun from the Yunnan Observatories of Chinese Academy of Sciences, collaborating with Prof.

Philippine volcanic eruption could prompt El Niño warming next winter
Climatological models suggest that gases from an erupting Philippine volcano could have significant impact on the global climate if more explosive eruptions occur.

Study suggests rainfall triggered 2018 Kīlauea eruption
In May 2018 Kīlauea volcano on the island of Hawaii erupted, touching off months of intense activity.

Beacon in space: BRITE Constellation observes complete nova eruption for the first time
Satellite images from the BRITE mission with the participation of researchers from TU Graz and the Universities of Innsbruck and Vienna document for the first time the complete development of a nova - from eruption to maximum brightness and burn out.

Tree rings could pin down Thera volcano eruption date
Research led by the University of Arizona Laboratory of Tree-Ring Research has anchored a long sequence of tree rings, providing context for the civilizations that existed throughout the Bronze and Iron Ages, including the eruption of Thera.

Pre-eruption seismograms recovered for 1980 Mount St. Helens event
Nearly 40 years ago, analog data tapes faithfully recorded intense seismic activity in the two months before the historic eruption of Mount St.

Read More: Eruption News and Eruption Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to